BE894967A - SILVER BROMOIODIDE PHOTOGRAPHIC PRODUCTS - Google Patents

Description

       

  Bromoiodide photographic products

  
silver.

  
The present invention relates to a photographic product comprising a support and at least one photosensitive emulsion layer formed by a dispersion medium and tabular silver bromoiodide grains.

  
A. Grains of silver bromoiodide.

  
The radiation-sensitive emulsions used in photography are formed from a dispersion medium, usually gelatin, containing microcrystals
(known as grains) of photosensitive silver halide. Emulsions other than silver bromoiodide have little use for photographic products intended for taking pictures. The name silver bromoiodide does not designate silver bromide crystals on the one hand and silver iodide crystals on the other hand, but crystals which contain both bromide and iodide.

   Usually, in photography, the silver bromoiodide grains are formed of a crystalline network of silver bromide in which the silver iodide can be incorporated up to its solubility limit in silver bromide, that is, up to about 40 mole% iodide, depending on the grain formation temperature. Unless otherwise indicated, all the halide percentages are given relative to the silver present in the emulsion, the grain, or the region of the grain considered; for example, a grain of silver bromoiodide containing 40 mole% iodide also contains 60 mole% bromide.

   The iodide concentrations in silver bromoiodide emulsions represent a practical compromise between on the one hand the advantages provided by iodide, such as better latent image formation, better natural sensitivity, and better adsorption. additives, and secondly the drawbacks inherent in high iodide concentrations, such as inhibition of development and resistance to chemical sensitization.

  
Duffin, in Photography Emulsion Chemistry, Focal Press, 1966, p.18, writes:

  
"An important factor to consider in the case of iodobromide emulsions, is the place of iodide, which can be mainly in the center of the grain, be distributed throughout the grain, or be mainly on the external surface of the grain. iodide is determined by the conditions of preparation, and obviously exerts an influence on the physical and chemical properties of the crystal ".

  
Silver iodide is much less soluble than silver bromide; therefore in a single-jet precipitation where both bromide and iodide are initially fully present in the reactor, and where the silver salt is added to the reactor to form the bromoiodide grains of silver, silver iodide tends to precipitate first and to concentrate in the center of the grains. In a double rush

  
jet, where iodide and bromide are added together in the reactor, along with the silver salt, it is possible to distribute the silver iodide throughout the grain. By continuing the addition of iodide while stopping or decreasing the addition of bromide, it is possible

  
forming on the grains a shell of silver iodide or silver bromoiodide having a higher iodide content. Methods for obtaining selective localization of silver iodide in grains are described in U.S. patents. 3,206,313, 3,317,322, 3,505,068,

  
4,210,450, and to British patents 1,027,146 and

  
1,477,901.

  
Different grain patterns, regular and irregular, have been observed in photographic silver halide emulsions. Regular grains are often cubic or octahedral in shape. The grain edges can be rounded due to ripening effects and, in the presence of strong ripening agents such as ammonia, the grains can even be spherical or have the form of thick, almost spherical tablets, as described for example in United States patent 3,894,871 and by Zelikman and Levi in "Making and Coating Photography Emulsions", Focal Press, 1964, pp. 221-223.

   We have frequently observed in variable proportions rod-shaped or tabular-shaped grains associated with grains of other shape, especially when the pAg (i.e. the negative logarithm of the silver ion concentration) of the emulsions were modified during precipitation, as is the case, for example, in simple jet precipitation processes.

  
The tabular silver bromide grains have been the subject of numerous studies, but the grains thus studied were often large grains without photographic utility. What, in the present description, is understood by tabular grain is a grain delimited by two parallel or practically parallel crystalline faces which each have a significantly larger surface

  
larger than any other side of the crystal constituting the grain. The shape index, i.e. the ratio of the diameter to the thickness of a tabular grain, is therefore clearly greater than 1: 1. Tabular-grain silver bromide emulsions of high shape index have been described by De Cugnac and Chateau in "Evolution of the Morphology of Silver Bromide Crystals During Physical Ripening", Science et Industries Photographiques, vol. 33, No. 2 (1962), pp. 121-125.

  
From 1937 until around the 1950s, the Eastman Kodak Company sold a film for radiography called "Duplitized" and whose reference was "No Screen X-ray Code 5133". This product included on each side of a film support a sulfur-sensitized silver bromide emulsion. Since the emulsions were intended for direct exposure to X-rays, they were not spectrally sensitized. The grains were tabular and had an average shape index of 5: 1 to 7: 1 and these tabular grains represented more than 50% of the projected surface, while the grains

  
  <EMI ID = 1.1>

  
projected. By repeating these emulsions several times, we note that in the emulsion where the shape index is the highest, the tabular grains have a diameter

  
  <EMI ID = 2.1>

  
average aspect ratio of 7: 1. Other reproductions of these emulsions have produced thicker, smaller diameter grains which have a lower average shape index.

  
Tabular grain emulsions of silver bromoiodide have been described in the prior art, but none of these emulsions actually have a high average shape index. The question of tabular grains of silver bromoiodide is discussed by Duffin, Photographic Emulsion Chemistry, Focal Press,
1966, pp. 66-72 and by Trivelli and Smith, in "The Effect of Silver Iodide Upon The Structure of BromoIodide Precipitation Séries", in The Photographie Journal, vol. LXXX, July 1940, pp. 285-288. According to Trivelli and Smith, a marked decrease in grain size and shape index is observed as iodide is introduced. Gutoff, in "Nucleation

  
and Growth Rates During the Precipitation of Silver Halide Photography Emulsions ", (Photographic Sciences and Engineering, vol. 14, No. 4, July-August 1970, pp. 248-
257, describes the preparation of bromide and silver bromoiodide emulsions by a single jet process using a continuous precipitation apparatus.

  
Methods for preparing emulsions consisting mainly of silver halides in the form of tabular grains have recently been described in publications. U.S. Patent 4,063,951 describes the formation of tabular-shaped silver halide crystals bounded by cubic faces (100) and whose shape index (calculated relative to edge length) is between 1.5 and 7: 1. The tabular grains have a square or rectangular shape characteristic of the crystal faces (100).

   US Patent 4,067,739 describes the preparation of silver halide emulsions consisting mainly of twin crystals of the octahedral type; these crystals are formed by first preparing crystalline seed seeds which are then grown by Ostwald maturation in the presence of a silver halide solvent and the growth of the grains is completed without renucleation or maturation of Ostwald by controlling the

  
pBr (negative logarithm of bromide ion concentration). U.S. Patents 4,150,994,

  
4,184,877 and 4,184,878, as well as the English patent

  
1,570,581 and German patent application publications 2,905,655 and 2,921,077 relate to the formation of octal tabular twin silver halide grains of octahedral shape from seed crystals with at least iodide content 90% by mole. In several of these references, the increase in covering power is mentioned and it is indicated that the emulsions obtained are useful for black and white and color films. According to United States patent 4,063,951, the upper limit of the shape index of these tabular grains is 7: 1; but, according to the very low shape indices obtained in the examples (2: 1), this upper limit of 7: 1 appears to be overestimated.

   It is clear, as the reproduction of the examples and the examination of the published photomicrographs shows, that the grain shape indices obtained according to the other references cited above are also less than 7: 1. Japanese patent application
142,329, published November 6, 1980, apparently incorporates the same elements as those of U.S. Patent 4,150,994, although not limited to the use of crystalline iodide seed seeds d 'silver.

  
B. Speed, granularity and awareness.

  
Silver halide photography uses as indicated, radiation-sensitive silver halide grains. During the photographic exposure, latent image centers are formed by absorption of only a small number of quanta of radiation which make a whole grain selectively developable. It is this property that precisely gives silver halide photography its exceptional speed, compared to many other imaging means.

  
Continuous research continued for more than a century has improved the sensitivity of emulsions to silver halides. Various types of chemical sensitization have thus been developed, for example by means of noble metals such as gold, by chalcogens such as sulfur and / or selenium and by reduction sensitization. These sensitizations, used alone or in combination, make it possible to improve the sensitivity of the emulsions to silver halides. When pushing chemical awareness beyond

  
at an optimal level, relatively low gains in speed are obtained, which are also accompanied by a sharp drop in image discrimination (maximum density minus minimum density). This decrease results from an increase in the haze (minimum density). Optimal chemical awareness therefore consists in finding the best compromise between speed, image discrimination and minimum density, for a specific photographic application.

  
In general, when the silver halide emulsions are sensitized chemically, the sensitivity extension obtained beyond the spectral region of natural sensitivity is completely negligible. To sensitize the silver halide emulsions over the entire visible spectrum and even beyond, spectral sensitizers are used which are generally methine dyes. The sensitivity of the emulsion is extended from the region of natural sensitivity, as a function of the concentration of spectral sensitizing dye and this until reaching an optimum beyond which, in general, this sensitivity then decreases rapidly (conf. Mees, Theory of the Photography Process, Macmillan, 1942, pp. 1067-1069).

  
In the range of dimensions of the silver halide grains of common photographic products, the maximum speed that can be achieved for optimal sensitization increases linearly with increasing grain size. We can consider that the number of quanta that a grain must absorb to become developable is independent of its size. However, the density that a given number of grains forms during development is directly related to the size of these grains. If the objective is to produce a maximum density of 2 for example, fewer grains with an average diameter of 0.4 µm are needed than grains with an average diameter of 0.2 µm to obtain this density . In total, less radiation was necessary to make a smaller number of grains developable.

  
Unfortunately, the density produced is concentrated on a smaller number of sites and the point density variations are greater.

  
Whoever examines the image draws a perception which is called the grain of the image. The objective measurement of these same variations constitutes granularity. Although quantitative measurements of granularity could have been made in different ways, the most common measurement is that known as RMS (root mean square) granularity which can be defined as the standard deviation of density through a micro opening. (from 24 to 48 / µm). Once the maximum acceptable granularity has been determined for a given emulsion, the maximum speed that can be obtained with this emulsion is also determined.

  
From the above, we can see that the problem is not generally to achieve maximum speed in the absolute sense, but rather to reach maximum speed with optimal awareness, everything

  
by obtaining the granularity requested for the practical case considered. The real improvements, as regards the sensitivity of the emulsions, are those which make it possible to improve the speed without sacrificing the granularity,

  
or to reduce the granularity without sacrificing speed, or which make it possible to improve both the speed and

  
granularity. The usual vocabulary of technology

  
summarized this definition of the improvement of the sensitivity in the expression: improvement of the relation speed / granularity of an emulsion.

  
FIG. 1 schematically represents a graph of the variation of the speed as a function of the granularity for five emulsions with silver halides 1, 2, 3, 4 and 5 of the same composition which each differ in grain size, while being otherwise sensitized, lying down and treated identically. The emulsions have respectively a maximum speed and a different granularity, but

  
there exists between these emulsions a pre-visible linear relationship, as shown by line A representing the variation of the speed as a function of the granularity.

  
All emulsions whose representative points can be aligned on line A have the same speed / granularity relationship. Emulsions whose sensitivity is really improved have a representative point located above the line A. For example, emulsions 6 and 7 whose representative point is located on the speed / granularity curve B have a better speed / granularity relationship than that of any of emulsions 1 to 5. Emulsion 6 has a higher speed than that of emulsion 1, but its granularity is not greater. The speed of emulsion 6 is identical to that of emulsion 2, but with a very lower granularity.

   The emulsion 7 has a speed greater than that of the emulsion 2, but its granularity is less than that of the emulsion 3 which, itself, has a speed less than that of the emulsion 7. The emulsion 8 , the representative point of which is located below line A has the worst speed / granularity relationship in FIG. 1. The emulsion 8 has in fact the highest photographic speed of all the emulsions represented,

  
but this speed can only be achieved at the cost of a disproportionate increase in granularity.

  
Given the importance of the speed / granularity relationship in photography, significant efforts have been made to be able to determine this relationship quantitatively in all cases. Comparing with precision, the speed / granularity relationships of a series of emulsions which differ by a single characteristic, for example the size of the silver halide grains, is normally an easy problem. We have often compared the speed / granularity relationships of photographic products whose characteristic curves are similar.

  
However, quantitative comparisons of speed / granularity relationships of photographic products have not generally been carried out since such comparisons are subjective in nature and become more pronounced as the other photographic characteristics become different. In addition, comparisons of speed / granularity relationships between photographic products forming analog images, for example, products for black photography

  
and white, and products that form color images involve many considerations other than those related to sensitivity. Indeed, the substances responsible for the density formation

  
and therefore responsible for the granularity, are of very different origin and nature. For granularity measurements in silver and color imaging systems, see: "Understanding Graininess and Granularity", Kodak Publication No. F-20, Revised 11-79, that available from Eastman Kodak Company, Rochester, New York 14650; Zwick, "Quantitative Studies of Factors Affecting Granularity", Photographic Science and Engineering, Vol. 9, N [deg.] 3, May-June 1965; Ericson and Marchant, "RMS Granularity of Monodisperse Photography Emulsions", Photography Science and Engineering, Vol. 16, N [deg.] 4, July-August 1972, pp. 253-257; and Trabka "A RandomSphere Model Dye Clouds", Photography Science and Engineering, Vol. 21, N [deg.] 4, July-August 1977, pp. 183-192.

  
U.S. Patent 3,320,069 describes a silver bromoiodide emulsion with an iodide content of between 1 and 10 mol% and which has a very exceptional speed / granularity relationship for the formation of 'argentic images (i.e. black and white images). The emulsion is sensitized

  
  <EMI ID = 3.1> with sulfur, selenium or tellurium. It is applied in a layer on a support at a rate of 33 to 110 mg of silver per square decimeter, then it is exposed in an intensity scale sensitometer and treated at 20 [deg.] C in the developer Kodak DK-50 (developer with N-methyl-paminophenol and hydroquinone sulfate) for 5 minutes. Under these conditions, the emulsion provides a logarithm of rapidity from 280 to 400. On the other hand, the index calculated by subtracting the value of the granularity from the logarithm of rapidity, is between 180 and 200.

  
Preferably, gold is used in combination with the sensitizer belonging to the sulfur group and the precipitation of the silver halides is carried out in the presence of thiocyanate. However, if desired, this thiocyanate can be added to the silver halide at any time before washing. The use of thiocyanate during precipitation and sensitization of silver halides is described in U.S. Patents 2,221,805, 2,222,264 and

  
2,642,361. Emulsions of United States Patent 3,320,069 also provide exceptional speed / granularity relationships for color photography, although the granularity values for dye images are not available.

  
In a small number of cases, studies have been made of the highest photographic speeds that can be achieved at higher levels of granularity than those normally used. In "The Relationship Between Speed and Grain Size", The Journal of Photography Science, vol. 17, 1969, pp. 116-125, Farnell reports on work concerning the speed in the blue of bromoiodide and silver bromide emulsions in the absence of spectral sensitization. When the projected area of the grains exceeds approximately

  
  <EMI ID = 4.1> Farnell observes that the speed does not increase any more when the grain size increases, as one would normally expect if one retains the hypothesis that the number of absorbed quanta necessary to obtain a developable grain is independent of the size of this grain; in fact, a decrease in speed as the grain size increases is indicated.

  
Farnell attributes the decrease in sensitivity of large grains to the fact that their diameter is large compared to

  
to the average scattering distance of the electrons formed photochemically, and necessary to produce the latent image sites, which is limited. More light quanta must be absorbed by a large grain than by a small one in order to form a developable latent image site.

  
Another author, Tani, in "Factors Influencing Photography Sensitivity", Journal Soc. Photogr.

  
  <EMI ID = 5.1>

  
formulates the same conclusions as Farnell and continues the discussion concerning the reduction in sensitivity of large silver halide grains by relating it to other causes linked to the presence of dyes used for spectral sensitization. According to Tani, the sensitivity of a spectrally sensitized emulsion also depends on (1) the relative quantum efficiency of spectral sensitization, (2) desensitization due to dyes and (3) the absorption of light caused by dyes. . Tani observes that the parameter (1) is very close to unity and is therefore not likely in practice to be further improved. Tani further indicates that the absorption

  
of light by grains covered by dye molecules is proportional to the volume of the grain when the grain is exposed to blue light and proportional to the surface of the grain when the grain is exposed

  
1 in light of the blue minus. Thus, the importance of the increase in sensitivity in the blue minus is generally lower than the increase in sensitivity in the blue when the grain size of the emulsion increases. If we try to increase absorption

  
of light simply by increasing the amount of dye covering the grain, this does not necessarily lead to an increase in sensitivity due to the desensitization caused by the dye as the amount of the latter increases. The desensitization is attributed more to a less good formation of the latent image than to a reduction in the formation of the electrons generated by photochemical way. Tani suggests that one possibility, to improve the speed / granularity relationship of large silver halide grains, would be to prepare core and shell emulsions in order to avoid desensitization.

   (The internal doping of silver halide grains in order to allow the use of quantities of dyes which would otherwise cause a desensitizing effect, is described in US Patent 3,979,213). C. Sharpness.

  
Granularity, because of its relationship with

  
speed is often a point on which the discussion of image quality focuses; however, the issue of image clarity can be considered independently. Some factors that influence image clarity, such as lateral scattering caused by image-forming products during processing, are related to image-forming products and treatments more than the silver halide grains themselves. However, since they scatter light, the silver halide grains also have a direct influence on the sharpness at the time of the photographic exposure. We know, for example, that with silver halide grains

  
  <EMI ID = 6.1>

  
diffusion of visible light is maximum.

  
The decrease in sharpness of an image caused by light scattering generally increases as the thickness of the silver halide emulsion layer increases. The explanation of this phenomenon illustrated by the diagram in fig. 2, is as follows. If a light photon 1 is deflected at a point 2 by a grain of halo-

  
  <EMI ID = 7.1>

  
direction of its original path and if this photon is then absorbed by a second grain of silver halide, in

  
a point 3, after having crossed an emulsion layer thickness t, the photon recording of the photon undergoes a lateral displacement x. If, after

  
  <EMI ID = 8.1>

  
is absorbed at a point 4, the photon recording of the photon undergoes this time a lateral displacement 2x.

  
It is therefore understood that the greater the displacement due to the thickness of the silver halide grains in a photographic product, the greater the risk of a reduction in image clarity by scattering of light. Of course, Figure 2 is a block diagram showing the phenomenon in a very simple case; in

  
in practice, a photon undergoing the reflection of several grains successively before being actually absorbed, it is necessary to use statistical methods to predict what may be its final point of absorption.

  
In the case of products for color photography, containing at least three layers of superimposed silver halide emulsion, the risk of loss of image clarity is increased since the silver halide grains are distributed over the minus three layer thicknesses. In some cases, the displacement resulting from this thickness is further increased by the presence of additional elements, that is to say, substances which contribute to increasing the thickness of the layers. emulsion themselves, for example when

  
  <EMI ID = 9.1>

  
rees to the emulsion layers, ie additional layers interposed between the silver halide emulsion layers, which also contribute to increasing the deviation due to the thickness; such additional layers are, for example, the separate layers adjacent to the emulsion layers containing the substances for consuming the oxidized developer or the dye image-forming substances. In addition, in color photography products, there are at least three superimposed elements each containing at least one layer of silver halide emulsion. This characteristic constitutes an important cause of loss of image clarity by scattering of light.

  
Diffusion phenomena caused by the different layers of superimposed emulsions being added to each other, the emulsion layers furthest from the source of exposure may exhibit decreases.

  
particularly important sharpness.

  
U.S. Patent 3,402,046 describes a means for obtaining clear, crisp images in the green-sensitive emulsion layer of a product for color photography. In such a product,

  
the emulsion layer sensitive to green is placed under the emulsion layer sensitive to blue and this respective arrangement of the two layers is responsible for a loss of sharpness in the layer sensitive to green. According to United States patent 3,402,046, it is proposed to reduce the scattering of light by using, in the upper emulsion layer sensitive to blue,

  
7 silver halide grains with an average diameter of at least 0.7 µm and preferably between

  
  <EMI ID = 10.1>

  
of 0.6, uni indicated above.

  
D. Separation of the velocities in the blue and the blue minus.

  
The natural sensitivity of silver bromoiodide emulsions in the blue part of the spectrum is sufficient to allow these emulsions to record blue light without the aid of spectral sensitization in blue. When these emulsions are used to record exposures to green and / or red light (blue minus), they are spectrally sensitized accordingly. Regarding black and white photography and monochromatic photography
(chromogenic), the resulting orthochromatic or panchromatic sensitization is advantageous.

  
With regard to color photography, advantage is taken advantage of the natural sensitivity of silver bromoiodide for emulsions used to record blue light. However, when these silver halides are used in the emulsion layers intended to record the light of the green parts

  
and red in the spectrum, the natural sensitivity in blue becomes a drawback. Indeed, in these emulsion layers, the simultaneous responses to blue light and green light, or to blue light and red light, will alter the tint of the color image that we are trying to reproduce .

  
In the design of products for color photography using silver bromoiodide emulsions, the issue of color alteration can be analyzed in two different ways. The first way consists in considering the difference between the speed in the blue of the emulsion layers registering the green or the red and the respective rapidities in the green or the red of these same emulsion layers.

  
The second way to approach the problem is to consider the difference between the speed in blue of each emulsion layer recording blue and the speed in blue of the corresponding emulsion layers recording green or red. In general, to obtain a product intended for color photography, capable of recording exactly color images by exposure to daylight (i.e.
5500 [deg.] K), it is necessary to provide a difference of approximately 1.0 log E between the speed in the blue of each emulsion layer recording the blue and the speed in the blue of the corresponding emulsion layers recording the green or red.

   It is known that such speed differences cannot be achieved with silver bromoiodide emulsions, unless they are used in combination with one or more known means for reducing spoilage.

  
colours. And even in this case, we are not always able to obtain a product in which the velocities are separated by a deviation from a full log E. However, even when such a speed difference could be achieved,

  
a further increase in the separation between the velocities in blue and the blue minus will correlatively allow a reduction in the recording of blue by the layers having to record the blue minus.

  
By far the most common means of reducing the effects of exposure to blue of silver bromoiodide emulsion layers spectrally sensitized for red and green, i.e.

  
decreasing their speed in the blue, consists

  
having emulsion layers behind a yellow filtering layer, that is to say a blue absorbing layer. Yellow filter dyes or yellow colloidal silver are generally used interchangeably for this purpose. In a typical multi-layered product for color photography, all emulsion layers are

  
  <EMI ID = 11.1>

  
silver. The emulsion layers intended to record the green and the red are placed behind a yellow filter, while the emulsion layer or the emulsion layers intended to record the blue light are placed in front of the filter layer.

  
Such an arrangement has a number of drawbacks which are well known. If the exposure to blue light of the emulsion layers recording green and red is reduced to a tolerable level, the use of the yellow filter imposes an order in the arrangement of the layers which is not ideal. The emulsion layers recording green and red receive light which has already passed through both the blue sensitive emulsion layer and the yellow filter. This light has undergone a certain diffusion and, consequently, the sharpness of the image is affected.

   Since the emulsion layer recording blue provides by far the recording which contributes the least to the visual impression, the fact that this layer is arranged so as to be closest to the source of exposure does not constitute for image clarity, a factor as favorable as that which could be obtained by placing in the same place the emulsion layers sensitive to red or green. In addition, the yellow filter is itself imperfect and actually absorbs a small part of the green light in the spectrum, which

  
which results in a loss of speed in the green. The substance used to constitute the yellow filter, in particular if this substance is yellow colloidal silver, increases the cost of the products and makes it necessary to replace treatment solutions more frequently, in particular the bleaching and bleaching-fixing solutions.

  
separate in a photographic product the

  
or the emulsion layers sensitive to blue and the emulsion layers sensitive to red or green by inserting a yellow filter, has the additional disadvantage of causing a reduction in the speed of the emulsion layer sensitive to blue. This is due to the fact that the yellow filter layer absorbs the blue light which passes through the blue-sensitive emulsion layer (s) while in the absence of the yellow filter layer, this blue light would be reflected and would reinforce the exposure. One way to increase the speed is to move the yellow filter layer so that it is not placed immediately under the blue-sensitive emulsion layer.

   Such a means is described in English patent 1,560,963; however, this patent received that the improvement of the speed in blue is actually obtained, but at the cost of an imbalance in the reproduction of colors in the emulsion layers sensitized to green and red which are arranged on the filter layer yellow.

  
Various ways have been suggested to eliminate the use of yellow filters; each proposed solution has its own drawbacks. US Patent 2,344,084 proposes to have a layer of silver chloride or silver chlorobromide spectrally sensitized for green or red in the position closest to the source of exposure, being since the natural sensitivity of these silver halides in blue is negligible. Since the natural sensitivity of silver bromide in blue is high, it is not used in the emulsion layer closest to the source of exposure, but forms an underlying emulsion layer intended to record the blue light.

  
According to the patents of United States of America 2,388,859 and 2,456,954, it is proposed to eliminate the contamination due to blue light in the emulsion layers recording green and red by giving these layers a sensitivity. respectively 50 times and
10 times weaker than that of the emulsion layer registering blue. On these emulsion layers, there is the yellow filter layer, so as to adjust the sensitivities of the emulsion layers recording blue, green and red for the blue, green and red lights respectively and to increase the separation of the velocities in the blue and the blue minus of the emulsion layers recording the blue minus.

  
This means allows the emulsion layers to be applied in any order, but its disadvantage is that it requires the presence of a yellow filter; it also has other drawbacks. In order to obtain, without the use of a yellow filter, differences in sensitivity between the layers recording the blue and the blue minus, according to the teachings of the patents of the United States of America 2 388 859 and 2 456 954, grains are used. larger silver bromoiodide in the blue recording emulsion layer.

   But if we try to obtain the desired differences in sensitivity, only by playing on the differences in grain size, we are led to use emulsion layers sensitive to blue with excessive grain and / or layers of emulsion recording the blue minus whose grain size is too small and which are consequently relatively rapid. To overcome this difficulty, it is known that one can increase the proportion of iodide in the grains of the layer registering blue; this way you can increase the sensitivity in blue without increasing the grain size. But again, if the goal is to obtain emulsion layers

  
  <EMI ID = 12.1> recording the blue minus, which have a photographic speed exceeding a very average level, obtaining an emulsion layer recording the blue, whose speed would be at least ten times greater, is not possible by maintaining an acceptable grain level, even by increasing the percentage of iodide in the emulsion layer recording blue.

  
Yellow filters, although they are used to decrease the proportion of blue light reaching the underlying emulsion layers, do not in any way eliminate the transmission of blue light. Thus, even in the case where yellow filters are used, we can hope for further improvements by better separation of the sensitivities in the blue and the blue minus of the silver bromoiodide emulsion layers intended to record the blue minus. of the spectrum.

  
The present invention relates to a photographic product consisting of a support, and at least one emulsion layer sensitive to radiation formed by a dispersion medium and tabular grains of silver bromoiodide, these products a / have a better separation between the velocities in the part of the spectrum to which the silver bromoiodide grains are naturally sensitive and in the part of the spectrum for which the silver bromoiodide grains have been spectrally sensitized, b / have a better speed relationship / granularity and c / have increased sharpness.

  
The photographic product according to the invention, having the above properties, is characterized in that at least half of the total projected surface of the silver bromoiodide grains consists of

  
tabular grains having two opposite parallel main faces, a thickness of less than 0.5 μm,

  
  <EMI ID = 13.1> being defined as the diameter of a circle whose surface is equal to the projected surface of the grain), and an average shape index, defined as the ratio of the diameter of the grain to its thickness, greater than 8 : 1; in addition, these tabular grains of silver bromoiodide comprise at least one central region, lying between the two main faces, containing a lower proportion of iodide than in at least one peripheral region also lying between the two main faces.

  
The present invention offers unique and completely unexpected advantages. If we compare photographic products according to the invention to photographic products containing conventional emulsions with silver bromoiodide, or emulsions with tabular grains of low shape index described previously, we find that we obtain much better speed / granularity, for example, the photographic speed is higher for a comparable granularity, or the granularity is reduced for a comparable speed. In addition, the emulsions of the invention are superior, with regard to these same photographic properties, to core and shell emulsions, with comparable surface concentrations of iodide, but consisting of non-tabular grains.

   The emulsions according to the invention are particularly advantageous when they are spectrally sensitized and used to produce color images; unexpectedly, these emulsions provide increased dye yields when used with color developers

  
and dye-forming couplers.

  
The photographic products according to the invention using emulsions with tabular grains of high shape index increase the clarity of the layers of underlying emulsions when these emulsions are arranged to receive light without significant diffusion. The emulsions according to the invention are particularly effective at

  
this regard when arranged so as to be in the layers closest to the source of exposure. If the emulsions according to the invention are sensitized spectrally outside the blue part of the spectrum, there is a large separation between the sensitivity in the blue region of the spectrum and the sensitivity in the region of the spectrum to which they have been spectrally sensitized. The silver bromoiodide emulsions with tabular grains sensitized in the blue minus are much less sensitive to blue light than in the blue minus light, and they do not require any protective filter to give acceptable records of the blue minus when expose them with neutral light, for example daylight at 5500 [deg.] K.

   The increases in blue sensitivity obtained by using spectral blue sensitizers with the silver bromoiodide emulsions of the present invention are very large when compared with the natural speed of these emulsions in blue.

  
The comparison of radiographic products formed from photographic products according to the invention, with similar radiographic products containing conventional emulsions, shows that the exposure through the support is reduced thanks to the emulsions according to the invention. It is also possible to obtain a level of exposure through the support comparable to that of conventional products with the emulsions of the invention, but with a lower silver content.

  
The emulsions of the invention can also be used in products for image transfer photography. Photographic products are thus obtained by image transfer which may have a better speed / silver ratio.
(amount of silver halogen per unit area), faster access to a visible transferred image and stronger contrast of the transferred image for a shorter development time.

  
FIGS. 1, 12 and 13 are graphs representing the variation of the speed as a function of the granularity,

  
Figures 2 and 4 are relative diagrams

  
to the diffusion of light,

  
Figures 3 and 6 are reproductions of photomicrographs of silver bromoiodide emulsions

  
with tabular grains of high shape index, according to the invention, FIG. 5 is a graph representing the variation of the iodide content as a function of the number of moles of precipitated silver bromoiodide,

  
Figures 7 to 11 are reproductions of photomicrographs of tabular grains of high shape index, according to the invention.

  
The term "high shape index" applied to the silver bromoiodide emulsions of the invention means that the silver bromoiodide grains whose thickness

  
  <EMI ID = 14.1>

  
with a diameter of at least 0.6 µm, have an average shape index greater than 8: 1 and represent at least
50% of the total projected surface of the silver halide grains. Tabular grains which individually meet the criteria for diameter and thickness indicated above are hereinafter referred to as "tabular grains with a high shape index". (This expression is applied in the same way to emulsions and to grains of different halide compositions).

  
The advantages obtained with the tabular grain emulsions thus defined are attributable to the unique location of iodide inside the grains. Tabular grains of high shape index are characterized by two opposite main parallel faces and by a central region between the two main faces containing a lower proportion of iodide than in at least one peripheral region of the same grain, also between the two main faces. In a preferred form, the peripheral region is an annular region surrounding the central region.

  
The central region usually forms the first part of the grain precipitated. However, the central region can be introduced during precipitation;

  
for example, in some cases, the central region may itself surround a previously precipitated region, having a higher iodide content.

  
The central region can be formed essentially of silver bromide or silver bromoiodide; preferably its iodide content is less than 5 mol% (optimally, less than 3 mol%), and lower by at least 1 mol% than that of the lateral region. The iodide content in the peripheral region can reach the saturation limit of silver iodide in the crystal lattice of silver bromide at the precipitation temperature, that is to say about 40% by mole

  
  <EMI ID = 15.1>

  
peripheral preferably contains from 6 to 20 mol% of iodide.

  
The central region forms part of the tabular grain, the size of which can vary depending on a certain number of factors such as the thicknesses and shape indices of the grains, the iodide concentrations in the lateral region, the nature of the developer, the additives and the final photographic use. The importance of the central part of the tabular grains is conventionally evaluated. Depending on a number of factors, including those listed above, the central region may constitute from 1 to 99% by mass of the tabular grains of high shape index.

  
In many applications, for example those in which the thicknesses and shape indices of the grains have the preferred values, the iodide content varies progressively and the lateral region is annular, the central region constitutes from 2 to 50% and, so optimal, from 4 to 15%, of tabular grains with a high shape index. On the contrary, when the variation in iodide concentration between the central and lateral regions is sudden, the central region preferably constitutes from 97 to 75% of the tabular grains.

  
We can get the specific location

  
iodide simply by increasing the proportion of iodide present during the growth of tabular grains. It is known that, during the growth of tabular grains, the silver halide deposits predominantly, if not entirely, on the edges of the grains. By properly selecting the precipitation conditions, the thickness of the tabular grains increases little, if at all, after the initial nucleation. By abruptly changing the iodide concentration present during the precipitation of the grains, it is possible to produce a sudden increase in the iodide concentration in one or more peripheral regions towards the edges of the grain relative to the central region.

  
In some cases, these peripheral regions appear crenellated. It is also possible to gradually increase the iodide concentration so as to obtain

  
a continuous variation from the central region to an annular region. It is also possible, although

  
it is not usually advantageous to lower the iodide concentration in the outermost part of the tabular grains.

  
The limitation of the central region by the opposite main faces of the tabular grains is

  
an important feature of the invention. The iodide content need not be uniform in the central region. For example, the iodide content may be higher, and usually is actually higher in the vicinity of the main faces of the tabular grains. Thus, by concentration of iodide in the central region or in the peripheral region of a tabular grain, we mean the average concentration in these regions. The central and peripheral regions can have the same surface iodide concentration on the main faces, but it is advantageous that the difference in iodide concentration between the central region and the peripheral region is that indicated.

  
  <EMI ID = 16.1>

  
preferably from a depth of 0.025 µm in the thickness of the grain, these distances being measured perpendicular to the main faces. In other words, in the central region, the thickness of the surface area where the iodide concentration can be that of the peripheral region does not exceed 0.035 µm and

  
  <EMI ID = 17.1>

  
The silver tabular grains of high shape index according to the present invention are

  
  <EMI ID = 18.1>

  
diameter is at least 0.6 µm and the average shape index of which is greater than 12: 1 and preferably 20: 1. You can get very high average shape indices
(100: 1 and even 200: 1 or more). Preferably, the silver halide grains which have the characteristics of diameter and thickness indicated above represent at least 70% and preferably at least 90% of the total projected surface of the silver halide grains.

  
The thinner the tabular grains representing a given percentage of the projected surface, the higher the average shape index of the emulsion.

  
In general, the average thickness of the tabular grains is

  
  <EMI ID = 19.1>

  
although in principle even thinner tabular grains can be used. For certain particular applications, for example, for use in photographic films by image transfer, it may be desirable to use thicker tabular grains

  
  <EMI ID = 20.1>

  
However, to obtain high shape indices without excessively increasing the grain diameter, it is normally considered that the average thickness of the tabular grains

  
  <EMI ID = 21.1>

  
The grain characteristics of the silver halide emulsions indicated above can be readily demonstrated by methods well known in the art. As indicated, the expression "shape index" designates the ratio of the diameter of the grain to the thickness of this grain. The term "diameter" itself is defined as the diameter of a circle having an area equal to the projected area of the grain as it appears on a photomicrograph or on an electron micrograph of the emulsion sample. From the bridged shadows of an electron micrograph of an emulsion, it is possible to determine the thickness and diameter of each grain and to identify those of the tabular grains whose thickness is

  
  <EMI ID = 22.1>

  
data, the shape index of each of these tabular grains can be calculated and the shape indices of all the tabular grains of the sample whose thickness is less than 0.5 μm and preferably 0.3, µm and the diameter is greater than 0.6 µm can be used to average which is the average shape index. According to this definition, the average shape index is the average of the shape indices of each grain. In practice, it is generally simpler to obtain an average thickness and an average diameter of the tabular grains having a thickness of less than 0.5 µm, and preferably less than 0.3 µm and a diameter of at least less

  
  <EMI ID = 23.1>

  
then the ratio of these two means. Whatever the evaluation method chosen, and taking into account the tolerances of the particle size measurements, the values obtained for the average shape index do not differ significantly.

  
One can add up the projected areas of tabular silver halide grains which satisfy the thickness and diameter conditions, and then, separately, add up the areas of other silver halide grains in the photomicrography; from these two respective sums, one can obtain the percentage of the total projected surface occupied by the tabular grains of silver halides whose thickness and diameter satisfy the conditions expressed above.

  
For the above assessments, a reference tabular grain was chosen; this grain has a thickness of less than 0.5 µm and preferably less than

  
  <EMI ID = 24.1>

  
thin tabular grains with thicker tabular grains whose photographic characteristics are unknown

  
  <EMI ID = 25.1>

  
as a reference since for smaller diameters it is not always possible to distinguish the grains which are tabular from those which are not.

  
The term "projected area" is used in the same sense as the terms "projective area" or "projection area", commonly used in the art (see for example James & Higgins, Fundamentals of Photography Theory, Morgan & Morgan New York, p. 15).

  
FIG. 3 represents a typical photomicrograph of an emulsion according to the present invention which has been chosen to illustrate the various grains which may be present. The grain 101 constitutes an example of a tabular grain whose thickness and diameter meet the conditions expressed above. It is clear that the vast majority of the grains present on the photograph of the figure

  
3 are tabular grains whose thickness and diameter meet these conditions. The average shape index of these grains is 16: 1. But, in this photomicrography, we also note the presence of a small number of grains whose thickness and diameter do not meet the above conditions. Grain 103, for example, is an example of a grain that is not tabular.

  
  <EMI ID = 26.1>

  
is an example of a fine grain that does not meet the diameter requirements. Depending on the conditions of preparation of the emulsion, which will be examined in more detail below, secondary populations of non-tabular grains, fine grains or thick tabular grains may be present alongside the grains having the desired characteristics. It is also possible that other non-tabular grains, for example in the form of sticks, are also present. We generally seek to obtain a maximum of tabular grains satisfying the relative conditions

  
thickness and diameter; however, the presence

  
of these secondary populations of grains does not leave an emulsion outside the scope of the present invention

  
from the moment when this emulsion has a high shape index as defined above.

  
High form index silver bromoiodide emulsions can be prepared by controlling the introduction of iodide as follows. A dispersion medium is introduced into a conventional reactor for the precipitation of silver halides, equipped with an appropriate stirring device. In general, the dispersion medium thus initially introduced into the reactor represents at least about 10% and preferably 20

  
to 80% of the total mass of the dispersion medium which will be present in the silver bromoiodide emulsion at the end of the precipitation. The dispersion medium can be removed from the reactor by ultrafiltration during the precipitation of the silver bromoiodide grains, according to the indications of Belgian patent 886,645 and French patent 2,471,620; the volume of dispersion medium present at the start in the reactor can therefore be equal to or even slightly greater than the volume of the silver bromoiodide emulsion which will be in the reactor at the end of the precipitation of the grains.

   Preferably, the dispersion medium introduced at the start consists of water or of a dispersion of peptizer in water, optionally containing other substances, for example one or more agents for maturing silver halides and / or metal dopants, described in more detail below. When a peptizing agent is present at the start, its concentration represents at least 10% and preferably at least 20% of the total peptizing agent present at the end of the precipitation of silver bromoiodide. An additional quantity of the dispersion medium is added to the reactor with the silver salt and the halides and optionally by means of a separate jet. Usually, the proportion of dispersing medium is adjusted, in particular in order to increase the proportion of peptizing agent, once the addition of the salts is complete.

  
  <EMI ID = 27.1> A small part, generally less than 10%

  
by mass of the bromide used to form grains of silver bromoiodide, is present at the start in the reactor to adjust the concentration of bromide ions at the beginning of the precipitation of the silver bromoiodide. In addition, at the start of precipitation, the dispersion medium contained in the reactor should in principle not contain iodide ions; in fact, the presence of iodide ions before the introduction of silver salt and bromide promotes the formation of thick grains which are not tabular.

   When in the present description, it is indicated that the reactor does not in principle contain iodide ions, this means, with regard to the ingredients present in the reactor, that if the iodide ions are present in the reactor, their concentration relative to the ions bromide is insufficient to cause precipitation of a distinct phase of silver iodide. This is why, in practice, it is preferred to maintain the iodide concentration in the reactor below 0.5 mol% relative to

  
the total amount of halides present in the reactor before the introduction of the silver salt. If the pBr of the dispersion medium is initially too high, the tabular grains of silver bromoiodide produced will be comparatively thick and therefore have a low shape index. Care is therefore taken to maintain the initial pBr of the reactor at an equal or lower value

  
1.6 and preferably less than 1.5. On the other hand, if the pBr is too low, this promotes the formation of silver bromoiodide grains which are not tabular; this is why it is necessary to maintain the pBr equal to or greater than 0.6 and preferably greater than 1.1. We recall that

  
the pBr is the negative logarithm of the bromide ion concentration and that the pH, the pi, the pAg are defined in the same way respectively for the concentrations

  
hydrogen, iodide and silver ions.

  
During precipitation, the silver salts, bromide and iodide are added to the reactor according to well known techniques. In general, a solution of a soluble silver salt, for example a solution of silver nitrate, is introduced into the reactor, together with solutions of bromide and iodide. Bromide and iodide are also introduced in the form of an aqueous solution of one or more ammonium or alkali metal salts, for example sodium or potassium, or alkaline earth metal salts, for example magnesium salts or calcium. The silver salt, at least initially, is introduced into the reactor by a separate jet from that of the iodide. The iodide and bromide can be added to the reactor separately or as a mixture.

  
When a silver salt is introduced into the reactor, the nucleation phase of the grain formation process is started. We form a population of germs capable of constituting precipitation sites for silver bromide and silver iodide as and

  
as the addition of the silver salt, bromide and iodide continues. The precipitation of bromide and silver iodide on existing germs constitutes the growth phase of grain formation. The shape index of the tabular grains formed according to the present invention is less influenced by the concentration of iodide and bromide during the growth phase than during the nucleation phase. That’s why during

  
during the growth phase, it is possible to increase the latitude for fixing the pBr so as to have, during the introduction of the salts, a pBr of between approximately 0.6 and 2.2 and preferably between 0.8 and 1.6 . This latter interval is particularly preferred when the rate of formation of the germs continues appreciably during the introduction of the salts, as is the case in the preparation of emulsions with high polydispersity.

  
If the pBr rises above 2.2 during the growth of the tabular grains, this leads to the formation of thicker grains, but there is in many cases a tolerance which makes it possible still to obtain shape indices greater than 8 : 1.

  
A variant for the introduction of the silver salts, bromide and iodide consists in introducing these salts at the start or in the growth phase, in the form of fine grains of silver halides in suspension in a dispersion. The diameter of the grains is such that their maturation of Ostwald on larger seeds is possible as soon as they are introduced into the reactor, if such seeds are present. The maximum useful grain diameter depends on the specific conditions prevailing in the reactor, for example the temperature and the presence of a solubilizing or maturing agent.

   It is thus possible to introduce grains of silver bromide, silver iodide and / or silver bromoiodide; since the bromide and / or iodide preferentially precipitates over chloride, it is also possible to use grains of silver chlorobromide and silver chlorobromoiodide; these silver halide grains are preferably very small, that is to say that their

  
  <EMI ID = 28.1>

  
Subject to the iodide concentration and the pBr conditions set out above, the concentration and the flow rate of the jets of silver, bromide and iodide salts can be produced in suitable conventional forms. The silver salts and the halides are preferably introduced at a concentration of between 0.1 and 5 moles per liter, although wider intervals can be envisaged ranging from 0.01 mole per liter to saturation. The preferred precipitation techniques are those which allow obtaining the most rapid precipitation times.

  
  <EMI ID = 29.1> short by increasing the amounts of silver and halide salts introduced during precipitation. This increase can be obtained by increasing either the flow rate or the concentration of the salt jets. We prefer to increase the flow rate of the jets, but by keeping it below a threshold from which the formation of new germs would be favored, that is to say from which there would be a renucleation, according to the indications given to patents of the United States of America 3,672,900,

  
3,650,757, 4,242,445, as well as in the publication of the German patent application 2,107,118, in the European patent application 80102242 and by Wey in Photography Science and Engineering, Vol. 21 N [deg.] 1, January / February
1977 p. 14 et seq. By avoiding the formation of additional germs in the growth stage, relatively monodisperse populations of tabular silver halide grains can be obtained. Emulsions with coefficients of variation of less than about 30% can be prepared. Remember that the coefficient of variation is the standard deviation of the diameter

  
of grain multiplied by a hundred and divided by the average grain diameter. If deliberately promoting renucleation during the growth phase, it is of course possible to form polydispersed emulsions whose coefficient of variation is significantly higher.

  
The preparation of tabular grain silver bromoiodide emulsions with high form index has

  
has been described with reference to a process providing emulsions which are neutral or non-ammoniacal; But

  
the present invention is not limited to this particular process. Another method is an improvement on that described in US patent 4,150,994, as well as in the publications of the German applications.

  
2,985,655 and 2,921,077. In a preferred form, the concentration of silver iodide in the reactor is lowered to 0.05 mole per liter and the maximum diameter of the grains of silver iodide initially

  
  <EMI ID = 30.1>

  
The location and concentration of the iodide that is desired in the tabular grains of silver bromoiodide according to the invention can be obtained by regulating the introduction of the iodide. To obtain a limited iodide concentration in the central region, the initial introduction of iodide can be delayed or limited until the central region of the grain is formed. Since silver iodide is much less soluble than other silver halides, there is much less iodide in solution during precipitation, even if the rates of addition of bromide and iodide are equal; almost all the iodide introduced precipitates immediately, while the halide ion in solution is mainly bromide. In other words, iodide is incorporated into the growing part of the grain as it is added to the reactor. However,

  
however, some iodide migration may occur within the grain. It is found, for example, that the proportion of iodide present in the central region is slightly higher than that which can normally be expected from the concentration of bromide and iodide introduced simultaneously during the formation of the central region of the grains. This migration of iodide inside the grain is compensated for by minor adjustments within the technician's reach.

  
By adjusting the proportion of iodide in the halides that are introduced during precipitation, it is possible to increase, gradually or suddenly, the iodide content in the peripheral regions of the tabular grains. Alternatively, it is proposed to stop the addition of iodide, or bromide and iodide, to the reactor, before the end of the addition of the silver salt, so that the salt of silver reacts with bromide ions in solution, resulting in the formation of a shell of silver bromide on the tabular grains of silver bromoiodide.

  
Modifiers may be present during precipitation of the tabular grains, either initially in the reactor, or added along with one or more of the salts, according to conventional methods. These modifiers can be compounds of copper, thallium, lead, bismuth, cadmium, zinc, medium chalcogen (i.e., sulfur, selenium and tellurium), gold and noble metals of group VIII, according to the indications given to the patents of the United States of America 1 195 432, 1 951 933,

  
2,448,060, 2,628,167, 2,950,972, 3,488,709, 3,737,313,

  
3,772,031, 4,269,927 and in the journal Research Disclosure, volume 134, June 1975 publication 13452. The journal Research Disclosure and the title which preceded it Product Licensing Index, are published by Industrial Opportunities Limited; Homewell, Havant; Hampshire, P09 1EF; United Kingdom. Tabular grain emulsions can be sensitized by reduction inside the grains during precipitation, as described by Moisar et al; Journal of Photography Science, volume
25, 1977 pages 19 to 27.

  
The silver salts and the halides can be added to the reactor by means of surface or sub-surface supply tubes, by gravity feed or by means of devices which allow the rate of addition to be regulated. as well as the pH, pBr and / or pAg of the contents of the reactor, as indicated in the patents of the United States of America

  
3,821,002 and 3,032,304 and by Claes in Photographische

  
  <EMI ID = 31.1>

  
obtain a rapid distribution of the reagents in the

  
7 reactor, it is possible to use specially adapted mixing devices such as those described in the patents of the United States of America 2 996 287, 3 342 605, 3 415 650, 3 785 777, 4 147 551 and 4 171 224, British patent application 2,022,431A, to German patent applications

  
2,555,364 and 2,556,885 and in Research Disclosure, volume 166, February 1978, publication 16662.

  
To precipitate tabular grain emulsions, a dispersing medium is initially present in the reactor. Advantageously, the dispersing medium is formed of an aqueous suspension of peptizer. The concentration of peptizer can be between 0.2 and about 10% by mass relative to the total mass of the constituents of the emulsion in the reactor. It is common to keep the peptizing concentration in the reactor below about 6% of the total mass, before and during the formation of the silver halide, and to later adjust the concentration to higher values. by emulsion vehicle (the

  
vehicle term including binder and peptizer), by additional vehicle additions, to obtain optimal coating characteristics. The initially formed emulsion may contain approximately 5 to 50 g

  
of peptizer per mole of silver halide, preferably about 10 to 30 g per mole of silver halide. An additional vehicle can be added later to bring the concentration up to 1000 g / mole of silver halide. Advantageously, in the finished emulsion, there are more than 50 g of vehicle per mole of silver halide. Once coated and dried in

  
a photographic product, the vehicle forms approximately

  
30 to 70% by mass of the emulsion layer.

  
Vehicles can be chosen from the substances usually used in silver halide emulsions for this purpose. The preferred peptizers are hydrophilic colloids which can be used alone or in combination with hydrophobic substances. Suitable hydrophilic vehicles include substances such as proteins, protein derivatives, cellulose derivatives, for example cellulose esters, gelatin, for example gelatin treated with an alkaline agent (skin or bone gelatin). or gelatin treated with an acid agent (pigskin gelatin), gelatin derivatives, for example acetylated gelatin and phthalylated gelatin. These and other vehicles are described in Research Disclosure, vol. December 176, 1978, publication 17643, section IX.

  
The vehicle, in particular hydrophilic colloids, as well as useful hydrophobic substances combined with them, can be used not only in the emulsion layers of the photographic product elements of the invention, but also in other layers, such as overlays, interlayers and layers placed below the emulsion layers.

  
The preparation of the silver bromoiodide emulsions according to the invention can comprise a step of maturation of the grains. Solvents of known silver halides are used to promote maturation, such as for example an excess of bromide ion in the reactor. It is known, for example, that the bromide solution introduced into the reactor can itself promote maturation. It is also possible to use other maturing agents, which can be entirely incorporated into the dispersing medium in the reactor before the addition of silver salt and halide, or which can be introduced into the reactor at the same time as a or more of the silver salts, halides

  
or peptizer. According to another embodiment, the curing agent can be introduced independently during the addition of the halide and the silver salt.

  
Advantageous ripening agents are those which contain sulfur. Thiocyanates can be used in the form of alkali metal salts, usually sodium and potassium, and ammonium thiocyanates. Conventional amounts of thiocyanate can be used, but the advantageous concentrations are generally between about 0.1 and 20 g of thiocyanate per mole of silver halide. The use of thiocyanate as a ripening agent is described in US Patents 2,222,264, 2,448,534 and 3,320,069. Thioethers, such as those described in US Patents, can also be used conventionally. United States of America 3,271,157, 3,574,628 and 3,737,313.

  
Tabular grain emulsions of index

  
of high form are preferably washed to remove the soluble salts, by known techniques such as decantation, filtration and / or by setting in jelly and filtration, as described in Research Disclosure, vol. 176, December 1978; publication 17643, section II. It is particularly advantageous according to the present invention to complete the maturation of the tabular grains by washing after the end of precipitation, to avoid increasing their thickness, reducing their shape index and / or excessive increase in their diameter. Emulsions with or without a sensitizer can be dried and stored before use.

  
Once the tabular grain emulsions of high shape index have been formed, they can be surrounded by a shell to obtain an emulsion at heart

  
and shell, by methods well known in the photographic art. Any silver salt photographically useful for the formation of a shell can be used on tabular grain emulsions with an index of

  
  <EMI ID = 32.1> high form prepared by the present process. Techniques for forming silver salt shells are described in U.S. Patents 3,367,778,

  
3,206,313, 3,317,322, 3,917,485 and 4,150,994. Conventional shell formation techniques do not favor the formation of tabular grains with a high shape index, the average shape index of the emulsion decreases

  
as the hull grows. If the conditions in the reactor are favorable for the formation of tabular grains during the precipitation of the shell, the growth of the shell occurs preferentially on the outer edges of the grains so that the shape index does not decrease. Tabular grain emulsions with a high shape index and comprising a core and a shell are particularly useful for forming internal latent images,

  
and can be used to obtain negative or positive-direct effect products.

  
The methods for preparing tabular grains described above make it possible to obtain emulsions in which the tabular grains meeting the criteria of thickness and diameter necessary to obtain a high shape index, represent at least
50% of the total projected area of the total population of silver halide grains; but additional benefits can be obtained by increasing the proportion of tabular grains. It is advantageous that at least 70% (and optimally at least 90%) of the total projected surface are represented by tabular silver halide grains meeting the criteria of thickness and diameter.

   Although the presence of small amounts of non-tabular grains is fully compatible with most photographic applications, the proportion of tabular grains can be increased to obtain the full benefits of the grains

  
7 dishes. Larger, tabular silver halide grains can be mechanically separated from smaller, non-tabular grains in a mixed grain population using conventional separation means, such as a centrifuge or hydrocyclone. Separation by hydrocyclone is illustrated in US Patent 3,326,641.

  
It is generally more practical to prepare emulsions of silver bromoiodide with tabular grains of high shape index according to the invention in which practically all the grains, and particularly those which meet the criteria of diameter and thickness indicated above. above, comprise a central region, and at least one peripheral region having a higher iodide content. One can then mix such an emulsion once prepared with another silver halide emulsion with tabular grains of high shape index, such as a silver bromoiodide emulsion having a practically uniform iodide concentration, or in which iodide is concentrated in the vicinity of the central grain region.

   The mixed emulsions obtained generally have an improved photographic response, in direct relation to the proportion of silver bromoiodide present in the form of tabular grains according to the invention, the iodide concentration of which is lower in the central region than in the regions peripheral devices. The emulsions defined according to the present invention may contain only the quantity of tabular grains of silver bromoiodide of high form index having a higher iodide content in at least one peripheral region than in

  
the central region, sufficient to produce an improvement in the photographic response, but it is advantageous that at least 50%, and optimally, at least 90%, by mass, of the tabular grains of silver bromoiodide of index of high form, have a central region containing a lower proportion of iodide than the peripheral regions.

  
The tabular-grain silver halide emulsions of high form index, according to the present invention, are chemically sensitized. They can be chemically sensitized with active gelatin, as indicated by T.H. James, The Theory of the Photography Process 4th Ed., Macmillan, 1977, pp. 67-76; chemical sensitization can also be carried out with sulfur, selenium, tellurium, gold, platinum, palladium, iridium, osmium, rhodium, rhenium, or phosphorus sensitizers or with combinations of these different sensitizers and a pAg of for example between 5 and 10 and a pH of between 5 and 8, and at a temperature between

  
  <EMI ID = 33.1>

  
Research Disclosure, Vol. 120 - April 1974 - $ 12008, Research Disclosure, Vol. 134 - June 1975 - $ 13,452, to patents in the United States of America 1,623,499, 1,673,522,

  
2,399,083, 2,642,361, 3,297,447, 3,297,446; English Patent 1,315,755; U.S. Patents 3,772,031, 3,761,267, 3,857,711, 3,565,633, 3,901,714 and 3,904,415 and the British Patent 1,396,696; chemical sensitization is optionally carried out in the presence of thiocyanates, as described in US Patent 2,642,361, in the presence of sulfur-containing compounds such as those described in

  
  <EMI ID = 34.1>

  
and 4,054,457. Emulsions can be chemically sensitized in the presence of chemical sensitization modifiers, that is, compounds known for their ability to suppress haze and increase speed under these conditions; such compounds are for example azaindènes, azapyridazines, azapyrimides, benzothiazolium salts and sensitizers having one or more heterocyclic rings.

  
Examples of modifiers are given in U.S. Patents 2,131,038, 3,411,914, 3,554,757, 3,565,631, 3,901,814 as well as Canadian Patent 778,723 and by Duff in in Photography Emulsion Chemistry, Focal Press (1966), New York, pp. 138-143. In addition to the various chemical sensitizations defined above, or as an alternative to these sensitizations, the emulsions can also be sensitized by reduction, for example with hydrogen, as described in the United States patents. '' America 3 891 446 and

  
3,984,249, or by subjecting them to conditions combining a low pAg, for example less than 5 and / or

  
at a high pH, for example above 8 or by means

  
different reducing agents such as stannous chloride, thiourea dioxide, polyamines and borane amines, as described in the patents of the United States of America 2 983 609, 2 518 698, 2 739 060,

  
2,743,182, 2,743,183, 3,026,203, 3,361,564, as well as in Research Disclosure, vol. August 136, 1975, $ 13654.

  
One can carry out a chemical sensitization on the surface or a chemical sensitization in an area located immediately under the surface, as described in the patents of the United States of America 3 917 485 and 3 966 476.

  
In addition to chemical sensitization, the high form index tabular grain emulsions of the present invention are also spectrally sensitized. With tabular grain emulsions of index

  
high form according to the invention and with other emulsions also mentioned in the present description, it is intended to use spectral sensitizing dyes which exhibit maximum absorption in blue and blue minus, that is to say in the red and in the green of the visible spectrum. In addition, for certain specific uses, spectral sensitizing dyes can be used which improve the spectral response in the region of the spectrum situated beyond the visible part. One can for example use spectral sensitizers absorbing in the infrared region.

  
Silver halide emulsions can be sensitized spectrally with dyes belonging to various classes, in particular cyanines, merocyanines, cyanines and merocyanines (tri-, tetra-, or polynuclear complexes), oxonols, hemioxonols, dyes styrylics, merostyrylics and streptocyanines.

  
Cyanine-type spectral sensitizers include two basic heterocyclic rings linked by a methine bond; these heterocyclic nuclei are derived for example from

  
quaternary salts of quinolinium, pyridinium, isoquinolinium, 3H-indolium, benz [e] indolium, oxazolium, oxazo-

  
  <EMI ID = 35.1>

  
nazolinium, imidazolium, imidazolinium, benzoxazolium, benzothiazolium, benzoselenazolium, benzimidazolium, naphtoxazolium, naphtothiazolium, naphtoselenazolium, dihydronaphtothiazolium, pyrylium and imidazopyrazinium.

  
The spectral sensitizing dyes of the merocyanine type comprise, linked by a methine bond, a nucleus of basic character of the type found in the formula of cyanines and an acid nucleus derived for example from barbituric acid, acid 2 -thiobarbiturate, rhodanin, hydantoin,

  
  <EMI ID = 36.1>

  
zoline-5-one, 2-isoxazoline-5-one, indan -1,3-dione, cyclohexane-1,3-dione, 1,3-dioxane-4,6-dione, pyrazolin- 3,5-dione, pentane-2,4-dione, alkylsulfonyl acetonitrile, malononitrile, isoquinolin-4-

  
7 one and chroman-2,4-dione.

  
One or more spectral sensitizing dyes can be used. Dyes are known with sensitization maxima for wavelengths distributed over the entire extent of the visible spectrum and providing spectral sensitivity curves of very different shape. The choice and relative proportions of dyes depends on the region of the spectrum to which the grains are to be sensitized and on the shape of the spectral sensitivity curve which it is desired to obtain.

  
Dyes with partially overlapping spectral sensitivity curves often provide, when used in combination, a curve such that the sensitivity at each wavelength in the overlap region is approximately the sum of the sensitivities of each dyes. Thus, it is possible to use combinations of dyes having different maxima, to obtain a spectral sensitivity curve have a maximum located between the sensitization maxima of each of the dyes.

  
Certain combinations of spectral sensitizing dyes produce an oversensitizing effect, that is to say provide in a region of the spectrum, a spectral sensitization greater than that resulting from the use of one of the dyes alone at any concentration, or resulting from the addition of several dyes. Oversensitization can be achieved with selected combinations of spectral sensitizing dyes and other additives such as stabilizers, anti-stars, development accelerators or inhibitors, coating aids, optical brighteners and anti-static agents. Mechanisms for explaining oversensitization and compounds for achieving it, are described by Gilman in "Review of the Mechanisms of

  
7 Supersensitization ", Photography Science and Engineering Vol. 18, 1974, pp. 418-430.

  
Spectral sensitizing dyes can also exert other actions on emulsions.

  
These dyes can also play the role of anti-veil, stabilizers, development accelerators or inhibitors, halogen acceptors or electron acceptors, as described in the patents of the United States of America 2 131,038 and 3,930,860.

  
Among the spectral sensitizers useful for sensitizing silver bromoiodide emulsions, mention may be made of those described in Research Disclosure, Vol. 176, December 1978, publication 17643, section III.

  
For the spectral sensitization of grains of non-tabular silver halides or of weak shape index, the conventional amounts of dyes can be used. To take full advantage of the advantages offered by the present invention, it is preferable to adsorb an optimal quantity of sensitizing dyes on the surface of the tabular grains of high shape index. By optimum quantity is meant the quantity sufficient to reach at least 60% of the maximum photographic speed which it is possible to achieve with these grains under the conditions provided for the exposure. The amount of dye to be used depends on the nature of the dye or the combination of dyes chosen, or on the size and shape index of the grains.

   It is known in the photographic technique that optimal spectral sensitization can be obtained with organic dyes when these dyes are used in an amount which makes it possible to produce a single layer.

  
on about 25% or more of the total available area of the surface-sensitive silver halide grain, as described for example by West in "The Adsorption of Sensitizing Dyes in Photography

  
  <EMI ID = 37.1> Emulsions ", Journal of Phys. Chem., Vol. 56, p. 1065,

  
1952; by Spence et al. in "Desensitization of Sensitizing Dyes", Journal of Physical and Colloid Chemistry. flight. 56 n [deg.] 6, June 1948, pp. 1090-1103; and by Gilman et al. in U.S. Patent 3,979,213.

  
The optimum amounts and concentrations of dyes can be determined by the methods indicated by

  
Mees, in Theory of the Photography Process pp. 1067-

  
1069, already cited.

  
To record exposure to blue light

  
in the emulsion layers, we are generally satisfied

  
to use the natural sensitivity in the blue of silver bromoiodide, but appreciable advantages can be obtained by using spectral sensitizers,

  
for blue. When planning to exhibit emulsions

  
of the present invention in the region of their natural sensitivity, sensitivity gains can be obtained

  
increasing the thickness of the tabular grains. By

  
example, it is advantageous to increase the thickness of the

  
grains in the case of photographic products for

  
image transfer. According to a preferred embodiment

  
of the invention, the emulsions consist of silver bromoiodide sensitized for blue, the

  
tabular grains are less than 0.5 µm thick,

  
  <EMI ID = 38.1>

  
form greater than 8: 1, preferably greater than 12: 1

  
and these grains represent at least 50% of the total projected surface of the silver halide grains present in the emulsion; this percentage is preferably equal to 70% and, according to an optimal embodiment, at least 90%.

  
Spectral sensitization can be carried out at any stage of the preparation of the emulsion which has been recognized to be useful for this purpose. Usually, spectral sensitization is carried out after the end of the sensitization.

  
1 chemical tion. However, spectral sensitization can be carried out, either at the same time as chemical sensitization, or entirely before chemical sensitization, and even it can be started before the precipitation of the silver halide grains, according to the indications given to patents of the United States of America 3,628,960 and 4,225,666. The patent of the United States of America 4,225,666 specifically provides for introducing the spectral sensitizing dye into the emulsion in stages, so that 'a part of

  
this dye is present before chemical sensitization, while another part is introduced after chemical sensitization. Unlike what is stated in the patent of the United States of America

  
4,225,666, it is possible according to the present invention to add the spectral sensitizer after 80% of the silver halide has been precipitated. Sensitization can be improved by adjusting pAg, including through cyclic variations, during chemical sensitization and / or spectral sensitization. A specific example of pAg adjustment is given in Research Disclosure, volume 181, May 1979 publication 18155.

  
Silver bromoiodide emulsions with tabular grains of high shape index, chemically and spectrally sensitized, have a better speed / granularity relationship than that obtained up to now with silver bromoiodide emulsions containing low tabular grains shape index and / or having the best known speed / granularity relationships. The best results are obtained by using spectral sensitizing dyes in the blue minus.

  
According to an advantageous embodiment, the spectral sensitizers are incorporated into the emulsions of the invention before chemical sensitization.

  
Similar results have also been obtained in some cases by introducing other adsorbable substances, such as curing modifiers, into the emulsions before chemical sensitization.

  
Independently of the prior incorporation of adsorbable substances, it is advantageous to use thiocyanates during chemical sensitization at concentrations of between approximately 0.002 and 2 mol% relative to silver, as described in the United States patent. United States of America 2,642,361 already cited. Other curing agents can be used during chemical sensitization.

  
A third means which can be used alone or in combination with only one or two of the means indicated above, consists in adjusting the concentration of silver and / or silver halide present, immediately before or during chemical sensitization. Soluble silver salts can be introduced, such as silver acetate, silver trifluoroacetate and silver nitrate, as well as salts which can precipitate on the surface of the grains, such as silver thiocyanate. , Silver phosphate, silver carbonate, etc. Fine silver halide grains can be introduced
(i.e. bromide, iodide and / or silver chloride) capable of undergoing Ostwald maturation on the surfaces of the tabular grains. For example, a Lippmann emulsion can be introduced during chemical sensitization.

   Chemical sensitization of spectrally sensitized high index tabular grain emulsion can be carried out at one or more sites distinct from the tabular grains. It is believed that the preferential adsorption of spectral sensitizing dyes on the crystallographic surfaces forming the main faces of the tabular grains allows chemical sensitization to occur selectively on crystallographic surfaces different from these grains.

  
Advantageous chemical sensitizations for obtaining the best speed / granularity relationships are sensitization to gold and sulfur, sensitization to gold and selenium, and sensitization to gold, sulfur and selenium. In an advantageous embodiment of the invention, the silver bromoicdide emulsions with tabular grains of high shape index contain chalcogen, such as sulfur and / or selenium, which may not be detectable, and gold which is detectable. Emulsions also usually contain detectable amounts of thiocyanate, although the concentration of thiocyanate in the final emulsion can be greatly reduced by known washing techniques.

   In the various embodiments indicated above, the surface of the tabular grains of silver bromoiodide may comprise another silver salt such as a silver thiocyanate, or another different silver halide (e.g. silver chloride or silver bromide), although this other silver salt may be present in undetectable quantities.

  
Although it is not necessary to obtain all their advantages, the emulsions defined according to the invention are preferably sensitized chemically and spectrally in an optimal manner, in accordance with current manufacturing practices. This means that their speed represents at least 60% of the maximum of the logarithm of the speed that can be expected from grains in the spectral region of sensitization and under expected conditions of use and treatment. The logarithm of speed is defined as being equal to
100 (1-log E), where E is measured in lux. second at a density of 0.1 above the veil.

   Once the silver halide grains of a product have been characterized, it is possible to estimate, from other analyzes carried out on the product and from the evaluation of its performance, whether a layer d The emulsion of this product was sensitized chemically and spectrally in an optimal way, by comparison with other comparable commercial products. To obtain the advantages of clarity presented by the products according to the invention, it is immaterial whether the silver halide emulsions have been sensitized chemically or spectrally in an effective or ineffective manner.

  
Once tabular grain emulsions of high shape index have been produced by precipitation methods, washed and sensitized as described above, the preparation can be completed by incorporating additives conventional photographic images, and they can be used in photographic applications requiring the production of a silver image, for example conventional black and white photography.

  
The photographic products according to the invention intended to form silver images can be tanned sufficiently to avoid having to use additional tanning agents during processing. This makes it possible to increase the covering power, in comparison with

  
photographic products tanned and similarly treated but containing non-tabular grain emulsions. In particular, it is possible to tan the tabular grain emulsion layers of high shape index and the other hydrophilic colloid layers of a black and white photographic product sufficiently

  
to reduce swelling of the diapers to less than 200%. The percentage of swelling (a) is determined by making

  
  <EMI ID = 39.1>

  
days at a relative humidity of 50%, (b) by measuring the thickness of the layer, (c) by immersing the photographic product in distilled water at 21 [deg.] C for 3 minutes and (d) by measuring the change in layer thickness. It is in particular preferable to tan the photographic products intended to form silver images since the addition of tanning agents in the processing solutions is not necessary, but the emulsions used according to the present invention can be subjected to tanning. of different strength commonly used. It is also specifically planned to incorporate the tanning agents in the processing solutions, as described for example in Research Disclosure vol. 184, August 1979, publication 18431, Paragraph K, concerning in particular the treatment of radiographic products.

  
Usually useful tanning agents or pre-tanning agents are described in Research Disclosure, Volume 176, December 1978, item 17643, Section X.

  
We can prevent the instability which increases the minimum density in the negative type emulsion layers, that is to say the haze, or which increases the minimum density or decreases the maximum density in the positive emulsion layers. direct, incorporating stabilizing agents, anti-stars, agents inhibiting the effects of mechanical stresses, agents stabilizing the latent image and similar additives in the emulsion and the adjacent layers before coating, as described in Research Disclosure ,volume
176, December 1978, item 17643, Section VI. Most effective anti-stars in emulsions can also be used in developers, and can be classified into a few general categories, like this

  
was offered by C.E.K. Mees, in The Theory of the Photography Process, 2nd edition, MacMillan, 1954, pages 677 to 680.

  
When using aldehyde type tanners,

  
  <EMI ID = 40.1> we can protect emulsion layers with conventional anti-stars.

  
In addition to sensitizers, tanning agents, anti-stars and stabilizers, various other conventional photographic additives can be added. The choice of additives depends on the exact nature of the photographic application and is within the reach of the technician. Various useful additives are described in Research Disclosure, volume 176, December 19 78, publication 17643. Optical brightening agents can be introduced, as described in publication 17643 in paragraph V- They can be used in emulsion layers or in the separate layers of the photographic products according to the invention, absorbent and diffusing substances, described in paragraph VIII. Coating aids described in section XI, and plasticizers and lubricants described in section XII can be added. We can add

  
antistatic layers described in paragraph XIII. Methods of introducing the additives are described in paragraph XIV. Matting agents described in paragraph XVI can be incorporated. It is possible, if desired, to incorporate developers and development modifiers described in paragraphs XX and XXI. When

  
the photographic products according to the invention must be used for radiographic applications, the emulsion and the other layers of the radiographic product can take all the forms described in Research Disclosure publication 18431, cited above. Emulsion layers described here as well as the other conventional silver halide emulsion layers, interlayers,

  
overcoats and substratum, if the product according to the invention contains them, can be applied and dried as described in Research Disclosure, Volume 176, December 1978, publication 17643, paragraph XV.

  
According to a common practice in the art, provision is made to mix the tabular grain emulsions with a high shape index of the present invention either with another such as those described above, or with a conventional emulsion, in order to obtain specific characteristics. For example, it is known to mix emulsions to adjust the characteristic curve of a photographic product for a specific purpose. The mixture can be used to increase or decrease the maximum densities obtained by exposure and treatment, to decrease or increase the minimum density, and to adjust the shape of the characteristic curve between the foot and the shoulder.

   The emulsions used according to the invention can be mixed with conventional silver halide emulsions such as those described in Research Disclosure volume 176, December.
1979, publication 17643, paragraph I, particularly

  
in subparagraph F of paragraph I.

  
When a relatively fine grain silver chloride emulsion is mixed with the emulsions

  
of the present invention, or that this silver chloride emulsion is introduced into an adjacent layer,

  
an additional increase in contrast and / or sensitivity is obtained, that is to say that the relationship between speed and granularity of the emulsion is improved, as described in US Patents 3,140,179 and 3,152,907.

  
In the simplest form, the photographic products according to the invention are formed from a

  
single layer of emulsion containing an emulsion of silver halides with flat grains of high shape index

  
and a photographic support. Of course, they can comprise more than one layer of silver halide emulsion as well as an overlay, a substratum and interlayers. Instead of mixing the emulsions as indicated above, it is generally possible to obtain

  
the same result by applying the emulsions to be mixed in the form of separate layers. The application of separate layers to obtain the latitude of exposure is well known in the art and has been described by Zelikman and Levi, "Making and Coating Photography Emulsions", Focal Press, 1964, pages 234-238 and the patent of United States of America 3,662,228 and British Patent 923,045. It is furthermore well known that photographic speed can be increased when fast emulsions and slow emulsions are applied in separate layers,

  
instead of mixing them. Usually, the fast emulsion layer is applied closer to the source of exposure radiation than the slow emulsion layer. This means can be extended to at least three superimposed layers of emulsion. Such layer arrangements are provided in the production of the products according to the invention.

  
The layers of the photographic products can be applied on various supports. Typical photographic supports include polymer films, wood fiber, for example paper, metal plates and sheets, glass and ceramic supports, provided with one or more substrates to improve adhesive, antistatic, dimensional properties , abrasive, antihalo, hardness and

  
friction, and / or other surface properties of the support. These supports are well known in the art. See for example Research Disclosure volume 176, December 1978, publication 17643, Section XVII.

  
The emulsion layer or layers are generally applied in the form of continuous layers on supports having opposite planar main surfaces, but this is not always the case. The emulsion layers can be applied as segments of laterally spaced layers on the surface of a flat support.

  
When the emulsion layer or layers are segmented, a microcellular support is preferably used. Such supports are described in PCT patent application W080 / 01614 published on August 7, 1980 and in the corresponding Belgian patent 881,513 as well as in the United States patent of 4,307,165. The width of the microcells can

  
  <EMI ID = 41.1>

  
for ordinary black and white photography applications, especially when the photographic image needs to be enlarged.

  
The photographic products according to the invention can be exhibited photographically in any usual manner. See in particular Research Disclosure publication 17643, cited above, paragraph XVIII. The present invention is particularly advantageous when the photographic exposure is carried out with electromagnetic radiation belonging to the region of the spectrum in which the included spectral sensitizers have absorption maxima. When photographic products are intended to record blue, green, red or infrared exposures, spectral sensitizers absorbing in the blue, green, red or infrared parts of the spectrum are present.

   For the formation of black and white images, it is advantageous that the photographic products are sensitized orthochromatically or panchromatically, in order to extend the sensitivity throughout the visible spectrum. The radiant energy used for the exposure can be non-coherent or coherent, that is to say in phase, for example produced by lasers.

   Within the useful response limits determined by conventional sensitometric techniques, photographic exposures under conditions of ambient temperature and / or pressure, high or reduced, low or high intensity exposures, continuous or intermittent exposures can be used , exposure times ranging from about a minute to relatively short durations of the order of a millisecond or microsecond, exposures by solarization, as described by TH James, The Theory of the Photography Process, 4th edition, MacMillan, 1977, Chapters 4, 6,
17, 18 and 23.

  
After exposure, the photosensitive silver halide contained in photographic products can be treated in a conventional manner to form a visible image, by bringing this silver halide into contact with an aqueous alkaline medium in the presence of a contained developer. in the middle or in the product.

  
Once the silver image has formed in the photographic product, it is common practice to fix the undeveloped silver halide. The tabular grain emulsions with a high shape index of the invention are particularly advantageous in that they allow fixing to be carried out more quickly, which makes it possible to obtain shorter treatment times.

  
The photographic products and techniques described above for producing silver images can be readily adapted to the production of color images, through the use of colorants. Probably the simplest way to obtain a projectable color image is to incorporate a conventional dye in the support of a photographic product, and to form a silver image as described above. In the areas where the silver image is formed, the product can no longer transmit light, and in the remaining areas, Light is transmitted with a color corresponding to the color of the support. One can easily form a colored image this way. The same results can also be obtained by using in conjunction with a product containing a transparent support, a layer or a separate product containing a color filter.

  
Dye images can be formed in silver halide photographic products by selective destruction or formation of dye. Developers containing dye image formers can be used such as the couplers described in Research Disclosure, volume 176, December 1978, publication 17643, section XIX paragraph D. The developer contains a chromogenic developer (for example an aromatic primary amine) which is capable, in its oxidized form, of reacting with the coupler to form the dye.

  
It is also possible, in a conventional manner, to incorporate the dye-forming couplers in photographic products. They can be incorporated in various quantities to obtain different photographic results. For example, it is possible to limit the concentration of coupler with respect to the silver content to values lower than those normally used in emulsion layers of intermediate or faster sensitivity.

  
In general, colorless non-diffusible dye-forming couplers are chosen which are capable of forming primary subtractive colors, that is to say yellow, magenta and blue-green. Dye-forming couplers having different reaction rates in separate layers or in a single layer can be used to achieve the desired results in specific photographic applications.

  
Dye-forming couplers can liberate at the time of coupling groups with photographic effects such as inhibitors or development accelerators, bleaching accelerators, developers, solvents of silver halides, toning modifiers, tanning agents, veiling agents, anti-stars, competing couplers, chemical or spectral sensitizers and desensitizers. Couplers releasing a development inhibitor (DIR) are well known in the art. Dye-forming couplers and non-dye-forming compounds are also known which, by coupling, release various photographic effect groups. It is also possible to use DIR compounds which do not form a dye by reaction with oxidized chromogenic developers.

   It is also possible to use DIR compounds which cut through oxidation. Relatively light-insensitive silver halide emulsions, such as Lipmann emulsions, as interlayers, and overlays, have been used to prevent or control the migration of development inhibitor groups.

  
In photographic products, color chromogenic couplers such as those used to form full-face masks for negative color images can be incorporated, and / or competing couplers. Photographic products may also contain conventional stabilizers for the dye image. All that has just been described is described in Research Disclosure, volume 176, December 1978, publication 17643, Section VII.

  
Dye images can be formed or enhanced by methods which involve associating with

  
a color-forming reducing agent, an oxidizing agent in the form of an inert complex of a transition metal and / or a peroxide.

  
Color images can be produced in the photographic products according to the invention by selective destruction of dyes or dye precursors, for example by bleaching processes

  
of silver dyes.

  
To form color images in silver halide photographic products, the developed silver is usually removed by bleaching.

  
The bleaching can be improved by incorporating a bleaching accelerator or a bleaching accelerator precursor into the treatment solution or into a layer of the product. In some cases, the amount of silver formed by development is small compared to

  
to the amount of dye produced, particularly in processes including enhancement of the dye image, as described above, and the bleaching of silver can be suppressed without significant visual effect. In other applications, the silver image is kept and a dye image is produced to increase or supplement the density provided by the silver image. When it is desired to enhance the silver image with a dye, it is usually preferred to form a neutral dye or a combination of dyes which together produce a neutral image.

  
The present invention can be used to obtain color images. In general, any product for color photography of conventional type containing at least one emulsion layer of silver halides, can be improved simply by adding to this emulsion layer (or by replacing it with) , a tabular grain emulsion layer of high shape index, in accordance with the present invention. The present invention thus finds application in color photography, either by additive or subtractive three-color synthesis.

  
With regard to the formation of color images by additive synthesis, an application of the invention consists in using the networks of elementary filters, blue, green and red in combination with a photographic product in accordance with the present invention and capable of providing a silver image. Through this network of additive primary filters, a photographic product is photographically exposed comprising a panchromatic sensitized layer and consisting of an emulsion according to the present invention, that is to say

  
with tabular grains of high shape index. After the processing and development of a silver image, the examination of this silver image through the network

  
of filters allows you to observe a color image. The best way to use these images is to examine them by projection. So both the photographic product and the filter network have the same transparent support

  
in common.

  
By applying the invention to the product for color photography by subtractive synthesis of dyes, other particular advantages can be obtained. This type of photographic product includes a support

  
and generally a set of three superimposed layers of silver halide emulsions for separately recording blue, green and red, providing dye images of yellow, magenta and blue-green respectively.

  
According to a preferred embodiment, an emulsion of silver bromoiodide with tabular grains of high shape index, sensitized by the blue minus, in accordance with the indications given above, forms

  
minus one of the layers for recording green light or red light in a set of three emulsion layers for recording blue,

  
green and red of a product for color photography; in addition, this tabular grain emulsion is arranged to receive, during the exposure of the

  
  <EMI ID = 42.1>

  
blue light in addition to the light that the emulsion is intended to record. The relationship between blue light and the light of the blue minus that the layer receives,

  
  <EMI ID = 43.1>

  
4log E = log AND log EB

  
log AND representing the logarithm of the exposure to green light or red light depending on what the tabular grain emulsion records and

  
  <EMI ID = 44.1>

  
sition in blue light that these tabular grains also receive. (In each case, E is expressed in Ix.s. unless otherwise indicated).

  
In practice, according to the present invention,

  
  <EMI ID = 45.1>

  
at 0.3, still makes it possible to obtain an acceptable reproduction of a polychrome subject. This is a surprising fact if we consider the high proportion of grains of the emulsion according to the invention which has a diameter greater than 0.7 μm. With an emulsion of comparable silver halides, but not tabular or made up of grains with a lower shape index, the color rendering is more disturbed and is generally unacceptable.

  
According to a specific and preferred embodiment, a product according to the invention comprises a set of three emulsions recording blue, green and red of which at least those recording blue minus are silver bromoiodide emulsions in accordance with the present invention. The emulsion layer recording the blue of this set of three emulsions can also advantageously be an emulsion with tabular grains of high shape index according to the present invention. According to a preferred embodiment, the tabular grains present in each of the emulsion layers of this: set of three elements have a thickness of less than 0.3 / μm, an average diameter at least equal to 1.0 / μm and of preferably at least 2.0 µm.

   According to yet a preferred form of the present invention, the products for color photography have an ISO sensitivity index at least equal to
180.

  
The products for color photography according to the present invention do not need a yellow filter layer placed between the exposure source

  
and emulsion layers sensitive to green and / or red to protect these layers from exposure to blue light. However, such a yellow filter layer may be present and in this case, its density may be reduced to a value lower than that of any other yellow filter layer which has been used until now to protect the sensitive emulsion layers. green and red in photographic products intended to be exposed to daylight. According to a preferred embodiment, there are no emulsion layers registering blue between the emulsion layers registering green and / or red and the radiation source used for the exposure. That is why,

  
the photographic product does not contain in practice

  
of blue-absorbing substances between the green-sensitive and red-sensitive emulsion layers and the incident radiation from the exposure.

  
Although only one of the green or red registering silver bromoiodide emulsion layers is made up of tabular grains of high shape index, the product for color photography contains at least three emulsions separate to record blue, green and red respectively. The other emulsions, that is to say the emulsions other than those consisting of grains with a high shape index, can be conventional emulsions of any shape. Different types of conventional emulsions are described in Research Disclosure, publication 17643 cited above, $ I. According to a preferred embodiment of the present invention, all the emulsion layers contain grains of silver bromoiodide.

  
In particular, at least one emulsion layer recording green and at least one emulsion layer recording red consist of tabular grains of high shape index, in accordance with the present invention.

  
If the product comprises more than one emulsion layer to record the green and / or the red, the preferred embodiment consists in that at least the fastest emulsion layer contains the tabular grains of index of high form, as indicated above. Of course, all the emulsion layers recording the blue, green and red of a photographic product can advantageously consist of tabular grains such as those described above, although this is not necessary for the

  
implementation of the present invention.

  
The present invention applies perfectly to products for color photography as described above in which the speed and the contrast of the emulsion layers recording blue, green and red can be very variable. Since the silver bromoiodide emulsion layers with tabular grains of high shape index, spectrally sensitized in green or red, have a relatively low speed in blue, it is possible to arrange these layers of emulsion recording green and / or red at any place in a product for color photography, without taking into account the remaining emulsion layers and without taking the usual precautions to prevent exposure of these emulsion layers in blue light.

  
The present invention applies in particular to products for color photography intended for the reproduction of colors by exposure to daylight. Photographic products of this type are characterized in that they provide recordings of blue, green and red exposures, the contrasts of which are more or less harmonized and the speed of which presents limited variations when exposed to a source of 5500 [ deg.] K (daylight).

  
The expression "roughly harmonized contrast" means that the contrast of the blue, green and red records differ by less than 20% and preferably by less than
10% compared to the value of the contrast of the recording in blue. Limited variations in speed of recording in blue, green and red can be expressed as a variation

  
  <EMI ID = 46.1>

  
speed is the biggest difference between the speed of green or red recording and the speed of blue recording.

  
The measurements of contrast and logarithm of rapidity necessary for establishing these relationships in a photographic product according to the invention can be determined by exposing this photographic product.

  
  <EMI ID = 47.1>

  
spectrally non-selective density scale (neutral density), for example a carbon control object, then

  
in processing the photographic product preferably under the conditions corresponding to those of the use for which it is intended. The densities in blue, green and red are measured by transmitting blue light at a wavelength of 435.8 nm, green light at a wavelength of 546.1 nm and the red light at a wavelength of 643.8 nm, like this

  
is described in the American standard PH2.1-1952 published by the American National Standards Institute (ANSI), 1430 Broadway, New York, N.Y. 10018; the characteristic curves in blue, green and red of the photographic product are thus obtained. If the photographic product has a reflective support rather than a transparent support, density measurements are carried out by reflection. From the characteristic blue, green and red curves, speed and contrast can be determined by well-known methods. The particular techniques for measuring speed and contrast are of no specific interest from the moment when each of the blue, green and red records are the subject of identical measurements in order to allow comparisons.

   Many standard sensitometric measurement techniques for color photographic products for different applications have been published by ANSI. These are for example the American Standard PH2.21-1979, PH2.47-1979 and PH2.27-1979.

  
The products for color photography according to the present invention allow the reproduction of colors when exposed to daylight.

  
and they provide particular advantages over conventional products having these characteristics. In the photographic products according to the invention, the speed in the blue of the bromine emulsion layers

  
  <EMI ID = 48.1>

  
in green and red, is limited and this limited speed can be used to separate the speed in blue of the emulsion layer recording blue and the speed in blue of emulsion layers recording blue minus. Depending on the application considered, the use of tabular grains in the emulsion layers recording green and red may in itself provide sufficient separation of the responses in blue from the emulsion layers recording blue and blue minus.

  
For certain applications, it may be desirable to further increase the separation between the speed in blue of the layers recording the blue and the speed in the blue of the emulsion layers recording the blue minus; for this, use is made of conventional separation techniques which thus add to the separation possibilities obtained using the tabular grains with a high shape index according to the present invention.

   For example, in a photographic product, the fastest emulsion layer recording green can be placed in the position closest to the radiation source and the emulsion layer recording blue fastest in position the farthest from the source of exposure; in this case, the difference in speed in the blue of the emulsions recording blue and green, although being equal to 1.0 log E when these emulsions are applied in separate layers and exposed separately, can be effectively reduced by the layering;

   indeed, the emulsion layer registering the green receives all the blue light during the exposure, but this layer registering the green and the other layers which are above it can absorb or reflect part of the blue light before it does not reach the emulsion layer registering blue. In such a case, increasing the proportion of iodide in the blue-recording emulsion layer can help to increase the separation of the velocities in the blue from the blue-recording layers and the blue minus which is already obtained using the tabular grains.

   When an emulsion layer recording blue is placed closer to the radiation source used for exposure than the emulsion layer recording blue minus, a yellow filter layer of limited density can be used between the layers emulsion recording blue and blue minus to increase the separation between blue and blue minus. However, it is never necessary to use any of these conventional techniques for separating velocities from the way they are used in the prior art to obtain a deviation of 1 log E or something similar for the separation of speed in blue. However, this remains possible if one wishes an exceptional separation of the velocities in the blue and in the blue minus, for a determined application.

  
Thus, the present invention achieves the objectives which, in color photography, condition the exact reproduction of colors in balanced lighting conditions, while allowing a wider choice in the production of the photographic product, compared to previous possibilities.

  
Products for color photography are often described so as to highlight the different elements of color forming layers that compose them. Most often, these products contain three of these superimposed elements, each containing at least one layer of silver halide emulsion capable of recording an exposure corresponding to a distinct third of the spectrum and at the same time producing the dye image. complementary primary subtractive. In this way, the elements recording blue, green and red respectively provide yellow, magenta and cyan dye images. The dye-forming substances need not be in the dye-forming elements; they can be supplied entirely from processing solutions.

   When the dye-forming substances are incorporated into the photographic products, they can be placed in an emulsion layer or in a layer intended to collect an oxidized developer or an oxidized electron transfer agent coming from an emulsion layer adjacent to the same dye-forming element.

  
In order to prevent the migration of oxidized developers or oxidized electron transfer agents between two dye-forming elements and thus avoid the resulting color alteration, it is common practice to use substances which react with these oxidation products. Such substances can be incorporated into the emulsion layers themselves, according to the indications of United States patent 2,937,086, and / or into interlayers between each dye-forming element, according to the indications of the United States patent. United States of America 2,336,327.

  
Each dye-forming element may contain only one layer, but most often it contains 2, 3 or more, having different photographic speeds. When the order of the layers does not allow this set of emulsion layers of different speeds to be arranged in a single element, it is common to produce a photographic product with several (usually 2 or 3) recording elements.

  
blue, green and / or red.

  
According to the present invention, at least one emulsion layer recording green or red containing tabular grains of silver bromoiodide according to the invention, is arranged in the photographic product so as to receive a higher proportion of blue light during the exhibition. This higher proportion of blue light reaching the emulsion layer

  
with tabular grains of high shape index is the consequence of a lower absorption of blue light by the superimposed yellow filter or else results simply from the elimination of this yellow filter. The higher proportion of blue light reaching the tabular emulsion layer may also result from a new arrangement of the dye-forming element which is closer to the source of exposure. For example, elements recording red and green and containing tabular grain emulsions of high shape index recording green and red, may be arranged closer to the source of exposure relative to the element recording the blue.

  
The products for color photography according to the present invention can have any shape compatible with the conditions defined above. Any of the six structures presented in "Spectral Studies of the Photography Process" (table
27-a, p. 211), Focal Press, New York, can be used. In order to provide a simple example, it is possible during the preparation of a conventional silver halide product for color photography, to

  
add one or more layers of emulsion with tabular grains of high shape index, sensitized to the blue minus and arranged so as to receive the exposure with the other layers of emulsion. However, in most cases, it is preferable to replace one or more layers of conventional emulsions recording the minus

  
blue by corresponding layers made up of tabular grains with a high shape index, possibly by modifying the order of the layers.

  
To illustrate the invention, a number of preferred structures are shown below.

  

  <EMI ID = 49.1>
 

  

  <EMI ID = 50.1>
 

  

  <EMI ID = 51.1>
 

  

  <EMI ID = 52.1>


  
B, V and R respectively designate elements recording blue, green and red of any conventional type.

  
T, in prefix, means that the emulsion layer or layers contain tabular grains of high shape index.

  
F, in prefix, means that the layer has a higher speed than that of at least one other element which, in the structure registers light in the same part of the spectrum.

  
L, in prefix, means that the emulsion layer is slower, i.e. has a lower speed than that of at least one other element of the structure recording light in the same part of the spectrum .

  
I, denotes an interlayer containing a substance to react with the oxidation products, but practically without a yellow filter.

  
Each fast or slow element may have a different photographic speed than that of another element of the structure which records light in the same third of the spectrum, due to its arrangement in the structure, its inherent properties or the association of these two factors.

  
  <EMI ID = 53.1>

  
felt the place of support. In general, the support is the most distant from the source of exposure, that is to say that in the diagrams it would be under the emulsion layers. If the support is colorless and transmits non-scattered light, that is to say if it is transparent, it can be placed between the exposure source and the layers. More generally, the support may be disposed between the exposure source and any color forming layer recording radiation for which the support is transparent.

  
In structure I, we see that there is no yellow filter. However, in accordance with practice, in products which contain a yellow filter, the blue-forming color forming element is arranged closest to the source of exposure. In its simplest form, each element of this product consists of a single layer of silver halide emulsion. In the variants, each color forming element may contain 2 or 3 or more different layers of silver halide emulsion.

   In the case of sets of 3 layers of emulsion, we compare the layers which in each element have the strongest speed, we preferably harmonize the contrasts and in this case, the photographic speeds of the layers recording the green and the red differ from the speed of the blue recording layer by a difference of less than 0.3 log E. When, in each element, there are 2 or 3 layers of emulsion of different speed or more, there are also preferably 2 or 3 sets of three or more emulsion layers in structure I, the contrast of which is thus fixed and the speeds of which exhibit this relationship. The absence of a yellow filter below the element recording the blue increases the photographic speed of this element.

  
The absence of a yellow filter in the interlayers is not absolutely necessary in the case of structure I. It is possible to have between the elements recording the blue and the green a yellow filter, at the rate of a quantity lower than the normal normal , without departing from the scope of the present invention. In addition the interlayer separating the elements recording the green and the red can in the same way also contain a yellow filter at a rate of a quantity which can go up to that used in a conventional way. When using such amounts of yellow filter, it is not necessary to limit the composition of the red recording element to the tabular grains of silver bromoiodide, as noted above, but it is possible to use any conventional grain shape consistent with the required considerations of contrast and speed.

  
  <EMI ID = 54.1>

  
We will not return to the common aspects of structures II to IX. The explanations which follow relate only to the aspects specific to each of the structures. In structure II, blue, green and

  
red are each recorded by two separate elements instead of incorporating the slow and fast emulsion layers recording blue, red or green respectively in the same elements. It is only necessary that the emulsion layers of the fastest elements consist of tabular grains of silver bromoiodide according to the invention. The slowest elements registering green and red, because of their slower speed, and the presence of the neck. che recording the faster blue above it, have adequate protection against exposure to blue light, without the need to use a yellow filter.

   The use of silver bromoiodide emulsions with tabular grains of high shape index in the emulsion layers of low speed elements registering green and red is not excluded. If one places the fastest element recording red on the slowest element recording green, one can increase the speed according to the indications of the patent of the United States of America 4,184,876 as well as to the publications German application 2 704 797, 2 622 923, 2 622 924 and 2 704 826.

  
Structure III present with structure

  
  <EMI ID = 55.1>

  
The element recording blue is furthest from the source of exposure. As a result, the green recording element is closest to the exposure source and the red recording element is closer to the exposure source than in the conventional case. This arrangement is very advantageous for obtaining images in color of great clarity and of which

  
7 the color quality is excellent. Since the element recording green, which contributes the most to the visual impression of the color image, being the closest to the source of exposure, it can provide an image of great clarity, since it does not there is no interposed layer to diffuse the light. The element recording the red, which comes second for the contribution to the visual impression of a color image, receives a light which has passed through only the element recording the green and which consequently has not been diffused by an element recording blue. Of course, the element recording the blue undergoes, by comparison with the structure I, a loss of sharpness, but this disadvantage is not significant

  
compared to the advantages resulting from the arrangement of the elements recording the green and the red, since the contribution of the element recording the blue to the visual impression of the color image is by far the least important.

  
Structure IV derives from structure III; it includes distinct, fast and slow elements for registering red, made up of tabular grain emulsions with a high shape index.

  
The structure V differs from the structure IV by the presence of an additional element recording the blue, arranged on the elements of low speed recording the green, the red and the blue. The fastest blue recorder includes a silver index bromoiodide emulsion with tabular grains of high shape index. In this case, the fastest blue recording element helps absorb blue light and

  
consequently to attenuate the transmission of the blue light on the elements registering the green and the red of weaker speed. A structural modification consists in not using an emulsion with tabular grains of high index in the elements registering the green and the red, of slower speed.

  
Structure VI differs from structure IV in the presence of a tabular grain element recording blue, between the elements recording green and red and the source of exposure. As indicated above, the tabular grain element registering the blue may consist of one or more tabular grain layers registering the blue and when there are thus several layers of emulsion registering the blue , their speed may be different. To counterbalance the effects of the less favorable position occupied by the element registering the red, structure VI provides a second rapid element registering the red which is placed between the tabular grain element registering the blue and the source of exposure.

   Because of its favorable arrangement, this second rapid element registering the red is faster than the first rapid element registering the red, this insofar as these two elements consist of identical emulsions. Of course, this first and second rapid elements recording the red can be made up of identical or different emulsions, the relative speeds of which can be adjusted by known techniques. Instead of using two rapid elements recording red, the second rapid element recording red can be replaced by a second rapid element recording green.

  
Structure VII is identical to structure VI, except that it provides both a second rapid element recording red and a second rapid element recording green arranged between the exposure source and the tabular grain element recording blue . Structures VIII and IX are of the classic type where an interlayer with a yellow filter is placed under the layer recording the blue. However, in these structures, a silver halide emulsion with tabular grains of high shape index is used in the emulsion layers closest to the source of exposure. These tabular grain emulsions can be sensitized to record red light

  
or to record the green light, or can be sensitized in pairs to record the red and green lights respectively.

  
Many other interesting structures are also possible. The structures I to IX shown are only examples. In each of these structures, the position of the elements registering green and red can be exchanged: the position of the fastest elements registering red and green can be exchanged in the different structures and / or it can be the same for the slowest elements registering green and red.

  
In general, for color photography, the emulsions are arranged so as to form a set of superimposed layers containing substances forming dyes incorporated, for example couplers, but this is not essential.

  
Three chromogenic components each containing a silver halide emulsion recording light corresponding to a third of the spectrum and a coupler forming the complementary primary subtractive dye, can be arranged together in a single layer of a product for color photography. Examples of such products are given in U.S. Patents 2,698,794 and 2,843,489.

  
This is due to the relatively large separation between the sensitivities in the blue and the blue minus of the elements recording the green and the red and consisting of emulsions of silver bromoiodide with grains

  
  <EMI ID = 56.1> tabular, that we can reduce the quantity of yellow filter or even eliminate these yellow filters and / or arrange the layers according to new structures. To measure the relative response of elements recording green and red to blue light in a product for color photography, one technique is to expose a sample of such a product through a density scale with neutral light, c that is to say with a light having a color temperature of 5500 [deg.] K, then processing the sample. A second sample is then exposed in the same way, but by inserting a Wratten 98 filter which transmits light only between
400 and 490 nm; the product is then treated in the same way as above.

   Using the transmission densities in blue, green and red, determined according to the American standard PH2.1-1952 mentioned above, three characteristic curves can be drawn

  
  <EMI ID = 57.1>

  
the speed in blue of the element (s) recording blue and the speed in blue respectively of the element (s) recording green and red, can be determined from the following relationships:

  

  <EMI ID = 58.1>


  
in which

  
BW98 is the speed in blue of the element recording the blue exposed through a Wratten 98 filter;

  
  <EMI ID = 59.1>

  
registering red, exposed through the Wratten filter
98;

  
BN is the rapidity in blue of the element registering blue, exposed to neutral light;

  
VN is the speed in the green of the element registering the green exposed to neutral light and;

  
  <EMI ID = 60.1>

  
recording red, exposed to neutral light.

  
In the present description, it is accepted that the densities in blue, green and red are due only to the elements recording respectively blue, green and red, which amounts to neglecting the parasitic spectral absorptions of the dyes yellow, magenta and Blue green. In fact, the importance of these parasitic absorptions is rarely sufficient to have a practical effect on the results obtained in the applications mentioned.

  
The elements recording the blue of the products for color photography according to the invention have, in the absence of any yellow filter, a speed in the blue which is at least six times, preferably at least eight times, and according to the optimal embodiment at least ten times, the speed in the blue of the elements recording the green and / or the red consisting of emulsions with tabular grains of high shape index conforming to the indications above.

   By way of comparison, an example is given below showing that, in a conventional product for color photography, in the absence of a yellow filter, the speed in the blue of the element recording the blue is less than four times (0.55 log E) the speed in the blue of the elements registering green by comparison with the factor 10 (0.95 log E) indicated above for a comparable product in accordance with the invention. This comparison illustrates the advantage with regard to the decrease in speed in the blue of the elements registering the green, when silver bromoiodide emulsions consisting of tabular grains with a high shape index are used.

  
The separation between the sensitivities in blue and in the blue minus of a product for color photography according to the invention can be measured in another way. This other measure consists in comparing the speed in the green of an element recording the green, or the speed in the red of an element recording the red, with the speed in the blue of these same elements. The exposure and treatment techniques described above are still used, with the difference that instead of exposure to neutral light, exposure to blue minus is used by intercalating

  
a Wratten 9 filter which transmits light only beyond 490 nm. We thus determine the differences

  
  <EMI ID = 61.1>

  

  <EMI ID = 62.1>


  
  <EMI ID = 63.1>

  
recording The green exposed through the Wratten 9 filter and,

  
RW9 is the speed in the red of the element recording the red exposed through the Wratten filter
9.

  
As before, the parasitic spectral absorption produced by the dyes, which is rarely significant, is neglected.

  
Elements recording red and green and containing tabular silver bromoiodide emulsions according to the above indications have velocities in blue and in the spectrum region where they are spectrally sensitized which are at least in a ratio 10 (1.0 log E) and preferably at least in a ratio 20 (1.3 log E). This expresses the difference between the speeds in blue and the speeds in blue minus. An example is given below in

  
7 which the speeds are in a ratio greater than

  
20 (1.35 log E), whereas in a conventional product for comparable color photography and containing no yellow filter, the velocities are in a ratio less than 10 (0.95 log E).

  
If we compare relations A and B and relations C and D for the same product, the results are not identical, even if the elements recording green and red are identical, except as regards the length of wave of their spectral awareness. Indeed, in most cases, the element recording the red receives a light which has already passed through the element recording the green. However, if we prepare a second product identical to the first, but in which we have exchanged the position of the elements recording the green and the red, we find that the element recording the red of the second product has practically identical values for relations B and D compared to the values of relations A and C for the elements registering the green of the first product.

   In other words, the choice of spectral sensitization in green as opposed to spectral sensitization in red has no determining effect on the quantitative values obtained with the above relationships. This is why it is customary not to distinguish speed in green and in red when compared to speed in blue, but to designate them generically under the name of speed in blue minus.

  
Tabular grain emulsions of index

  
of high form according to the invention are advantageous,

  
because, compared to non-tabular emulsions or with a lower shape index, they make it possible to reduce the scattering of light at large angles. As already indicated above in the comments relating to FIG. 2, it is well known that the sharpness of the image decreases when the thickness of an image increases.

  
or several layers of silver halide emulsions.

  
However, Figure 2 also shows that the lateral component of the diffusion (x and 2x) increases directly with

  
  <EMI ID = 64.1>

  
weak, the lateral displacement resulting from the diffusion remains weak and the sharpness of the image remains good.

  
The characteristic advantages which can be obtained with regard to sharpness, by using the tabular grains with a high shape index according to the invention, result from the reduction in scattering at large angles. We can give a quantitative demonstration of this. According to what is shown in FIG. 4, a sample of emulsion 1, in accordance with the present description, is applied to a transparent support 3 at the rate of 1.08 g of silver per square meter. Preferably, the emulsion and its support are immersed in a liquid
(not shown in the figure) having an appropriate refractive index to reduce the effects of Fresnel reflection on the surface of the support and of the emulsion. The emulsion layer is exposed in a direction perpendicular to the plane of the support by means of a collimated light source.

   From the source, the light follows a path materialized by the dotted line 7, forming an optical axis, which meets the emulsion at point A. The light which passes through the support and the emulsion can be detected at a constant distance of the emulsion on a hemispherical detection surface 9. At a point B which is at the intersection of the extension of the optical path and the detection surface,

  
a maximum light intensity is detected.

  
An arbitrary point C is chosen on the detection surface. The dotted line connecting A and C forms an angle 0 with a layer of the emulsion. In

  
  <EMI ID = 65.1> moving point C on the detection surface, the angle 0 can be varied from 0 to 90 [deg.]. By measuring the intensity of scattered light as a function of 0, it is possible, because of the symmetry of the scattering of light around the optical axis 7, to determine the cumulative light distribution as a function of 0. As regards concerning this distribution, one can consult DePalma and Gasper, "Determining the Optical Propoerties of Photography Emulsions by the Monte Carlo Method", Photography Science and Engineering, Vol. 16, N [deg.] 3, May-June 1971,

  
pp. 181-191.

  
After determining the cumulative light distribution as a function of 0 for values of 0

  
at 90 [deg.] in the case of emulsion 1 according to the invention, the same process is repeated in the case of a conventional emulsion consisting of grains whose average volume is the same and applied with the same silver grade on another part of the support 3. We compare the cumulative light distributions as a function of 0, in the case of the two emulsions, for values of 0 up to 70 [deg.] and in some cases up to 80 [ deg.] and more; this comparison shows that the quantity of scattered light is lower with the emulsions according to the invention. In figure 4, the angle 8 is complementary to the angle
0. Diffusion is therefore evaluated by reference to the angle

  
  <EMI ID = 66.1>

  
high form according to the invention, have less diffusion at large angles. Since the wide-angle scattering contributes significantly to reducing the sharpness of the image, the emulsions according to the invention make it possible in each case to increase this sharpness.

  
In the present description, the term "capture angle" designates the value of the angle 8 for which half of the light which reaches the detection surface is contained in a surface subtended by a cone formed by the rotation of the line AC around the polar axis of the angle 6 while the other half of the light which reaches the detection surface is in the remaining part of the surface.

  
The following theoretical considerations regarding the reduction of wide angle scattering cannot limit the present invention.

  
It is assumed that the main faces of a flat crystal, of high shape index, as well as the orientation of the grains in the layer are responsible for the

  
sharpness improvements. It has been observed that the tabular grains present in the silver halide emulsion layers are approximately aligned parallel to the planar surface of the support on which the layer is applied. Thus, the light, whose direction is perpendicular to the photographic product, has an incidence also perpendicular to one of the main faces of the crystals. The small thickness of the tabular grains, as well as their orientation in the layer, allows the emulsions according to the invention to be applied in thinner layers than conventional emulsions, which also contributes to improving the sharpness. However, the emulsion layers of a product according to the invention see their sharpness improved, even when their thickness is comparable to that of conventional emulsion layers.

  
According to a specific embodiment of the invention which is also preferred, the emulsion layers consist of tabular grains of high shape index whose minimum average diameter is at least

  
  <EMI ID = 67.1>

  
means of the grains, one can obtain at the same time a better speed and a better sharpness. Although the maximum average grain diameters may vary according to the granularity tolerable in a given application, the

  
  <EMI ID = 68.1> maximum average diameters of the grains with a high shape index of the emulsions according to the invention are in all

  
  <EMI ID = 69.1>

  
In addition to the advantages relating to the sharpness indicated above for the average diameters mentioned, it is possible with tabular grain emulsions of high shape index to avoid a certain number of drawbacks from which conventional emulsions consisting of grains having a diameter suffer. means of this order. First of all,

  
it is difficult to prepare conventional non-tabular emulsions whose grains have an average diameter greater than

  
  <EMI ID = 70.1>

  
the publication cited above, there is a decrease in the speed characteristics when the mean diameter

  
  <EMI ID = 71.1>

  
classical sions made up of grains of large average diameter, a greater volume of silver is present in each of the grains, in comparison with tabular grains of comparable diameter. Consequently, unless there are conventional emulsion layers with a higher silver content, which constitutes an undeniable practical disadvantage, the grain obtained with a conventional emulsion consisting of grains of large average diameter, is greater than the grain obtained. with emulsions according to the invention made up of grains the mean diameter of which is the same. On the other hand, if conventional coarse grain emulsions are used with or without an increase in the silver titer, this leads to the preparation of thicker layers to take account of the large thicknesses of these large diameter grains.

   However, the thickness of the tabular grains can remain very small even when the diameters exceed the values indicated to obtain the advantages as regards sharpness.

  
  <EMI ID = 72.1> These advantages of sharpness which can be obtained with tabular grains result in part from the shape of the grains regardless of their average diameter and this is why these grains make it possible to improve the sharpness

  
compared to conventional non-tabular grains.

  
Although it is possible to reduce the wide-angle scattering with monolayers of tabular grain emulsion with a high shape index according to the invention, this does not necessarily mean that the wide-angle scattering is reduced in the layers of a product for color photography. In certain assemblies of layers for color photography, the emulsions with tabular grains of high shape index according to the invention can indeed cause a deterioration in the sharpness of the underlying layers.

  
  <EMI ID = 73.1>

  
emulsion recording blue is located closest to the source of radiation used for exposure, while the underlying emulsion layer recording green consists of a tabular grain emulsion according to the invention. This emulsion layer registering green is itself above the emulsion layer registering red. If the blue-recording emulsion layer contains grains with an average diameter between 0.2 and 0.6 µm, as is generally the case for many non-tabular emulsions, maximum diffusion will be observed light passing through this layer before reaching the emulsion layers registering green and red.

   Unfortunately, if the light has already been scattered before reaching the high shape index tabular grain emulsion layer forming the green registering layer, the tabular grains can scatter the light passing through them more than a conventional emulsion. to reach the red registering layer. Consequently, the choice of emulsions and the arrangement of the layers entail in this particular case a significant deterioration in the sharpness of the emulsion layer registering the red, degradation which is greater than that which would be observed if this product did not include emulsion according to the invention.

  
In order to obtain the best advantages of the present invention with regard to sharpness, in an emulsion layer which is located under a tabular grain layer of high shape index according to the invention, it is desirable that this tabular grain layer is arranged in such a way that it receives practically non-scattered light, preferably light which is transmitted in a substantially specular manner. In other words, in the photographic products according to the present invention, improvements in sharpness are obtained in the emulsion layers arranged under the tabular grain emulsion layers only if these tabular grain emulsion layers are not themselves arranged under a layer whose turbidity causes a diffusion of light.

   For example, if an emulsion layer registering green, consisting of grains with a high shape index, according to the invention, is placed on an emulsion layer registering red and under a layer of Lippmann emulsion and / or a layer of emulsion recording blue with tabular grains of high shape index according to the invention, the sharpness of the layer registering red will be improved by the presence of the emulsion layers of tabular grains which are located above. If the angle of capture of the layer

  
or layers lying on the emulsion layer registering the green which comprises tabular grains. The index of high shape is less than about 10 [deg.], an improvement in the sharpness of the layer registering the red can be obtained. It is of course unimportant that the layer registering the red is itself a layer with tabular grains of high shape index according to the invention, at least as regards the effects of the layers above on the sharpness of the layer recording the red.

  
In a product for color photography containing several color forming elements arranged one above the other, it is preferable that at least the emulsion layer intended to be closest to the radiation source used for the exposure, either consisting of an emulsion with tabular grains of high shape index, in order to take advantage of the advantages procured by this invention as regards image clarity. According to a particularly preferred embodiment of the present invention, each emulsion layer which is arranged so as to be closest to a radiation source with respect to another emulsion layer, consists of an emulsion with tabular grains with a high form index. Layers II layouts

  
to VII described above constitute examples of products for color photography which according to the present invention make it possible to obtain a significant improvement in the sharpness of the underlying emulsion layers.

  
Products for color photography have been used to illustrate the advantages that high shape index tabular grain emulsions provide with regard to sharpness; but we can also improve the sharpness of multi-layer products for black and white photography, that is to say products forming silver images. In a common way, the emulsions are separated forming

  
black and white images in fast layers and in slow layers. If the tabular grain emulsions according to the present invention are used in the layers closest to the sources of exposure, the clarity of the underlying emulsion layers is improved.

  
The following examples illustrate the invention.

  
In each of the following examples, the contents of the reactor are vigorously stirred during the entire time in which the silver salts and the halides are introduced. Percentages are expressed by mass unless otherwise indicated. The term M expresses the molar concentration. All solutions are aqueous unless otherwise indicated.

  
EXAMPLE 1

  
An emulsion with tabular grains of silver bromoiodide having an average grain diameter of 1.7 μm (total average iodide content: 8.9 mol%) is prepared by double-jet precipitation at an accelerated rate.

  
At 4.5 liters of an aqueous gelatin solution (Solution A, 1.5% by mass of bone gelatin, 0.17 M in potassium bromide) at 55 [deg.] C and at pBr 0.77 , an aqueous solution of potassium bromide (Solution C, 2.15 M) and an aqueous solution of silver nitrate (Solution F, are added, by double jet and with stirring, with equal and constant flow rates for 2 min. 2.0M).
(1.36% of the total silver nitrate is consumed). Simultaneously, at the same rate, an aqueous solution of potassium bromide (Solution B, 2.15 M) is poured into solution C. The addition of solutions B and C is stopped after 2 minutes; the pBr is adjusted to 1.14 with the solution F at 55 [deg.] C. We pour simultaneously into the solution

  
C an aqueous solution (Solution D) 1.87 M in bromide

  
potassium and 0.24 M potassium iodide, at an accelerated flow rate (the flow rates are multiplied by 3.2 from the start to the end of the precipitation) for 21.4 min. At the same time, solution C and solution F are added to the reactor, by double jet, using the same accelerated flow rate. (83.7% of the total silver nitrate is consumed) and maintaining the pBr at 1.14. The addition of solutions D, C and F is stopped.

  
Aqueous solutions of potassium iodide (Solution E, 0.34 M) and silver nitrate (Solution G, 2.0 M) are then added by double jet at the same rate,

  
  <EMI ID = 74.1>

  
15.0% of total silver nitrate). 5.88 moles of silver nitrate are used to prepare this emulsion.

  
The emulsion is cooled to 35 [deg.] C, an aqueous solution of phthalylated gelatin (1.2 1 to 11.5%) is added
(see US patents 2,614,928 and 2,614,929), and the emulsion is washed twice by coagulation.

  
Figure 3 is an electron micrograph of a carbon replica of the emulsion prepared in this example, magnified 10,000 times. The average grain diameter is 1.7 µm and their average thickness is 0.1 µm. Tabular grains have an average shape index of
16: 1 and represent more than 80% of the total projected surface of the silver bromoiodide grains. FIG. 5 represents a graph giving, on the abscissa, the total number of moles of silver bromoiodide precipitated, and on the ordinate, the iodide content in mole%. Initially, iodide represents a very small percentage of the total halide.

   At the end of the precipitation, iodide represents 12 mol% of the total halide, and thus the concentration of iodide increases from a very low value in the central region to a much higher value in a annular region surrounding the central region. EXAMPLE 2

  
A tabular grain emulsion of silver bromoiodide having an average grain diameter of approximately 1.7 µm (total average iodide content:

  
7%. In mole), by double jet precipitation at an accelerated rate.

  
4.5 liters of an aqueous solution of bone gelatin (Solution A, 0.17 M potassium bromide,

  
  <EMI ID = 75.1>

  
by double jet with stirring, an aqueous solution of potassium bromide (Solution B, 2.33 M) and an aqueous solution of silver nitrate (SOlution D, 2.0 M), at the same flow rate, for 2 min ( consumes 1.58% of total silver nitrate). At the end of the two minutes, the addition of solution B is stopped, and solution D is added at constant rate for 10.7 minutes (8.43% of the total silver nitrate is consumed) until the pBr reaches 1.14 to 55 [deg.] C.

  
Solution C (KBr 1.94 M and KI 0.18 M) and solution D are added to the reactor by double jet at an accelerated rate (the rates are multiplied by 4.3 from the start to the end of the addition) in 22 min (88.4% of the total silver nitrate is consumed) at pBr 1.14. Solution E (AgN03 2.0 M) is then added at a constant rate until the pBr reaches 2.83 (1.61% of the total silver nitrate is consumed). 5.08 moles of silver nitrate are used to prepare this emulsion.

  
The emulsion is cooled to 35 ° C., 0.5 liter of an aqueous solution of phthalylated gelatin is added to it.
(25% by mass of gelatin) and washed twice by coagulation.

  
FIG. 6 represents an electron micrograph of a carbon replica of the emulsion prepared in this example, magnified 10,000 times. The average grain diameter is 1.7 µm and their average thickness is <EMI ID = 76.1>

  
average shape of about 28: 1 and represent more than 70% of the total projected surface of the silver bromoiodide grains.

  
EXAMPLE 3

  
An argen bromoiodide emulsion with tabular grains of high shape index, having a practically uniform iodide distribution in the grains, is prepared. This emulsion will be designated as control emulsion 1.

  
To prepare it, a procedure similar to that of Example 2 is used, but the iodide has been present in the reactor since the start of precipitation, and it is uniformly distributed in each grain of silver bromoiodide, at a average concentration of 9.0 mol%.

  
  <EMI ID = 77.1>

  
80% of the total projected surface of the silver bromoiodide grains.

  
The control emulsion 1 is chemically sensitized, for 15 min at 65 [deg.] C, with 100 mg of sodium thiocyanate per mole of silver, 7 mg of sodium thiosulfate pentahydrate per mole of silver, 3 mg of tetrachloroaurate potassium per mole of silver, and 30.4 mg of 3-methylbenzothiazolium iodide per mole of silver, and it is spectrally sensitized with 695 mg per mole of silver of the sodium salt of anhydro hydroxide -S-chloro-9-ethyl-

  
  <EMI ID = 78.1>

  
cyanine, hereafter called sensitizer A, and with 670 mg per mole of silver of the sodium salt of the hydroxide

  
  <EMI ID = 79.1>

  
oxazolocarbocyanine, hereinafter called sensitizer B.

  
A second control emulsion, designated control emulsion 2, of silver bromoiodide with tabular grains of high shape index, having an almost uniform iodide distribution in each grain, is prepared. The

  
  <EMI ID = 80.1>

  
control emulsion 1, except that the practically uniform concentration of iodide in the silver bromoiodide grains is 12 mol%. The average diameter of

  
  <EMI ID = 81.1> 0.12 / µm. The tabular grains have an average shape index of 27/1 and represent more than 80% of the total projected surface of the silver bromoiodide grains.

  
The control emulsion 2 is chemically and spectrally sensitized, in the same way as the control emulsion 1, except that the content of sodium thiosulfate pentahydrate is 18 mg / mole Ag, the content of potassium tetrachloroaurate is 10 mg / mole Ag, the iodide content of 3-methylbenzothiazolium is 15.2 mg / mole Ag, maturation takes place in 5 minutes instead of 15 minutes, at 65 [deg.] C;

  
the content of sensitizer A is 870 mg / mole Ag and the content of sensitizer B is 838 mg / mole Ag.

  
An emulsion useful in a photographic product in accordance with the invention, hereinafter referred to as Example 3, is prepared as in Example 1. The tabular silver bromoiodide grains of high shape index obtained have a surface iodide concentration of 12 mol% and an average iodide concentration of 8.9 mol%, reflecting the much lower iodide concentration in the central region than in the lateral annular region surrounding the central region. The average diameter of the grains is 2.1 μm and their average thickness

  
  <EMI ID = 82.1>

  
average shape of about 17/1 and represent more than 80%

  
of the total projected area of the grains. The emulsion is sensitized chemically and spectrally optimally, in a similar manner to the control emulsion 1, except that the concentration of sensitizer A is 870 mg / mole Ag, that of sensitizer B is 838 mg / mole d 'Ag, and the duration of chemical maturation is 5 min

  
at 65 [deg.] C. If the control emulsions 1 and 2 had been sensitized chemically and spectrally in an identical manner to the emulsion of Example 3, their sensitization would have been less than the optimal sensitization for the chemical and spectral sensitizers used, and their photographic properties (for example the relation speed / granularity) would have been altered.

  
If we compare the emulsion of Example 3 with the control emulsions 1 and 2, we can see that the control emulsion 1 has approximately the same percentage of iodide as the emulsion of Example 3, but uniformly distributed in all the grain. Control emulsion 2 has approximately the same surface iodide concentration as the emulsion of Example 3, but uniformly distributed throughout the grain. There is thus a direct comparison between a uniform distribution of iodide in the grains, on the one hand, and both the average concentration and the surface concentration of iodide in the grains according to the invention, on the other hand go. (The differences in detail in the chemical and spectral sensitization are not sufficient to explain the significant differences in photographic performance).

  
The emulsion of Example 3 and the controls 1 and 2 are applied separately on a triacetate support

  
  <EMI ID = 83.1>

  
2.5 g / m gelatin, to form a single layer magenta monochrome product. Each product also contains 0.75 g / m of the magenta coupler A. 1- (6-chloro-2,4-dimen-

  
  <EMI ID = 84.1>

  
pyrazolone, 3.2 g / mole Ag of potassium 5-sec-octadecylhydroquinone-2sulfonate, and 3.6 g / mole Ag of 4-hydroxy6-methyl-1,3,3a, 7-tetraazaindene. Products include

  
  <EMI ID = 85.1>

  
tanned with 0.46% by mass based on the total gelatin content of bis (vinyl-sulfonylmethyl) ether. Exposed for 1/100 s on a sensitometric scale of density 0 to 4.0 (plus a Wratten No. 9 filter and a neutral density filter 1.75) to a tungsten light source of 600 W and 3000 [deg .] K. Treated at 37.7 [deg.] C in a chromogenic developer of the type described in the journal British Journal of Photography Annual, 1979, pp 204-206;

  
  <EMI ID = 86.1>

  
different samples, to facilitate granularity comparisons.

  
The relative sensitivity in the green and the RMS granularity of each of the photographic products treated are determined. (We measure the RMS granularity by

  
the process described by H.C. Schmidt, Jr and J.H. Altman,

  
  <EMI ID = 87.1>

  
the granularity at a density of 0.60 above the veil.

  
The emulsions have practically a similar granularity, but the emulsion of Example 3 according to the invention has a higher speed. The speed / granularity relationship of the emulsion of the invention is therefore greater than that

  
witnesses. (The speed / granularity relationships of the witnesses are practically the same). Specifically, we consider that the speed / granularity relationship of the example

  
3 is from +15 to +20 logarithmic units of speed

  
higher than control 1 or control 2. The logarithm of the speed is equal to 100 (l-log E), log E being measured at a density of 0.6 above the veil. The emulsion of Example 3 has a higher speed

  
as control emulsions for a comparable granularity, but we can see from the discussion of

  
the speed and the granularity, that the emulsions as defined here may as well have a lower granularity for a comparable speed, or the combination of better speed and better granularity. In other words, it's not just

  
the speed, but the speed / granularity relationship, which is improved in the emulsions of the present invention.

  
It should be noted that the control emulsions do not represent the prior art, but were intended to demonstrate the importance of the distribution of iodide in the grains.

  
EXAMPLES 4 AND 5

  
Two silver bromoiodide emulsions with tabular grains of high shape index, as defined here, are prepared. The emulsion of Example 4 is precipitated so that the iodide concentration increases sharply during the growth of the grains. .

  
The emulsion of Example 5 is precipitated under conditions such that the iodide concentration gradually increases during the precipitation.

  
The emulsion of Example 4 is prepared as follows:

  
With 4.5 liters of an aqueous solution of gelatin of bone (Solution A, potassium bromide 0.17 M, 1.5% by mass of gelatin) at 55 [deg.] C and pBr 0.77, one add by double jet, with stirring, at the same rate, for 2 min, an aqueous solution of potassium bromide (Solution B1, 3.3 M) and an aqueous solution of silver nitrate

  
  <EMI ID = 88.1>

  
total money).

  
After 2 min, the addition of solution B-1 is stopped. The addition of solution C-1 is continued

  
at constant flow rate until the pBr reaches 1.14 at
55 [deg.] C. Aqueous solutions of potassium bromide (Solution B-2, 3.00 M) and potassium iodide are then added.

  
  <EMI ID = 89.1>

  
C-l) by triple jet, at pBr 1.14, and at accelerated flow

  
(the flow rate is multiplied by 10 from start to finish), until the solution C-1 is used up (about 34 min; 89.5% of the total silver nitrate is consumed).

  
An aqueous solution of silver nitrate (Solution C-2, 3.00 M) and solution B-3 are then added by double jet, at constant flow rate, until

  
the pBr reaches 2.83 to 55 [deg.] C (9.53% of the total silver nitrate is consumed). About 6.3 moles of silver nitrate are used to prepare this emulsion.

  
The emulsion is cooled to 35 ° C., 0.90 liters of an aqueous solution of phthalylated gelatin are added
(18.1% by mass of gelatin), and washed twice by coagulation.

  
The emulsion obtained has an average grain diameter of 2.4 µm, an average grain thickness of 0.09 µm, and an average shape index of 26.6: 1; the tabular grains represent more than 80% of the total projected surface of the silver bromoiodide grains.

  
The emulsion of Example 5 is prepared as follows:

  
A 6.0 liters of an aqueous solution of bone gelatin (Solution A, potassium bromide 0.17 M, 1.5% by mass of gelatin) at 55 [deg.] C and pBr, 0.77, an aqueous solution of potassium bromide (Solution B, 2.14 M) and an aqueous solution of silver nitrate (Solution F, 2.01 M) are added by double jet for 2 min. (0.96% of the total silver nitrate is consumed). Simultaneously, an aqueous solution of potassium bromide (Solution C, 2.35 M) is introduced into solution B, at the same flow rate.

  
After these two initial minutes, the addition of Solutions B and C is stopped. The addition of Solution F is continued until the pBr reaches 1.14 at
55 [deg.] C (about 16 min). (7.71% of the total silver nitrate is consumed). Solutions B and F are then added to the reactor, by double jet, at an accelerated flow rate (the flow rate is multiplied by 4.43 from start to finish) at pBr 1.14 and

  
at 55 [deg.] C until exhaustion of solution F. (We consume
80.6% of total silver nitrate). Simultaneously, an aqueous solution (solution D) of potassium bromide (1.89 M and potassium iodide (0.25 M) is added to solution B, at the same accelerated rate.

  
When solution F is exhausted, simultaneously added, at constant flow rate, to the reactor, <EMI ID = 90.1> aqueous solutions of potassium iodide (Solution E, 0.24 M) and silver nitrate (Solution G, 2.00 M)

  
  <EMI ID = 91.1>

  
(10.75% of the total silver nitrate is consumed).

  
The emulsion is cooled to 35 ° C., 1.5 liters of an aqueous solution of phthalylated gelatin are added thereto.
(13% by mass of gelatin) and washed twice by coagulation. A total of 8.34 moles of silver nitrates are used to prepare this emulsion.

  
The emulsion obtained has an average grain diameter of 2.1 / µm, an average grain thickness of

  
  <EMI ID = 92.1>

  
tabulars represent more than 80% of the total projected surface of the silver bromoiodide grains.

  
The iodide distribution in the emulsions obtained is examined under the electron microscope. The process used for this examination is that described by J.I. Goldstein and D.B. Williams, "X-Ray Analysis in the TEM / STEM", Scanning Electron Microscopy, 1977, vol. 1, III Research Institute, March 1977, p 651. The grains to be examined are placed on the grid of a microscope and cooled to the temperature of liquid nitrogen. One bombards with a focused beam of electrons, accelerated under a tension of 80 kV, a range of 0,2 / um, on each grain of which one examines the composition. The electron beam causes the emission of X-rays. By measuring the intensity and energy of the X-rays emitted, it is possible to determine the iodide / bromide ratio in the grain at the location of the electron bombardment.

   To serve as controls to determine the iodide concentration, we also examine tabular grains formed essentially of silver bromide, and non-tabular grains formed essentially of silver iodide.

  
  <EMI ID = 93.1>

  
below.

  
  <EMI ID = 94.1>

  

  <EMI ID = 95.1>


  
By looking at Table I, it can be seen that the emulsion of Example 4, in which the iodide concentration was suddenly increased during precipitation, has a very similar iodide concentration in the middle of the grain (range M) and in the edge of the grain (range E), this concentration being higher than in the center of the grain (range C). On the contrary, for the emulsion of Example 5, in which the percentage of iodide was progressively increased during precipitation, there is a progressive increase in the iodide content from the center of the grain (range C) to the edge grain (Range E). A single measurement in the middle of the grain (range M) allows this progressive increase to be observed, but a second measurement in the middle of the grain (range N) highlights it even better.

  
EXAMPLES 6 to 9 illustrating the speed / grain ratio

  
A series of emulsions of various shape indices are prepared as described below. The description of the physical characteristics of the emulsions is given in Table II below.

  
EXAMPLE 6

  
5.5 liters of 1.5% gelatin solution

  
  <EMI ID = 96.1>

  
with stirring and by double jet, solutions of potassium bromide 2.2 M and silver nitrate 2.0 M for 2 min, maintaining the pBr at 0.8 (0.56% of the

  
  <EMI ID = 97.1> total silver nitrate). The addition of the bromide solution is stopped, and the addition of the silver salt solution is continued for 3 min (5.52% of the total silver nitrate is consumed). The bromide and silver salt solutions are then added at the same time, keeping the pBr at 1.0, at an accelerated rate (2.2 times faster at the end than at the beginning), for 13 min. (34.8% of the total silver nitrate is consumed). The addition of the bromide solution is stopped, and the addition of the silver salt solution is continued for 1.7 min (6.44% of the total silver nitrate is consumed). 1.8 M potassium bromide and 0.24 M iodide solution are added by double jet

  
potassium, and the silver salt solution, for

  
15.5 min, at accelerated flow, (multiplied by 1.6 from the start

  
at the end), keeping the pBr at 1.6; 45.9% of the total silver nitrate is consumed. The addition of the two solutions is stopped, and maturation is carried out for 5 min with 1.5 g of sodium thiocyanate per mole of silver. We

  
  <EMI ID = 98.1>

  
potassium iodide and the silver salt solution, until the pBr reaches 2.9; 6.8% of the total silver nitrate is consumed.

  
We use about 11 moles of silver nitrate

  
  <EMI ID = 99.1>

  
a spectral green sensitizer, sodium salt

  
anhydro-5-chloro-9-ethyl-5'-phenyl-3'- hydroxide
(3-sulfobutyl) -3- (3-sulfopropyl) -oxacarbocyanine, per mole of silver, and after 20 min, the pAg is adjusted to 8.4. 3.5 mg of sodium thiosulfate pentahydrate per mole of silver and 1.5 mg of potassium tetrachloroaurate per mole of silver are added to the emulsion. Adjust the pAg to 8.1 with a potassium bromide solution and heat

  
  <EMI ID = 100.1>

  
7 EXAMPLE 7

  
At 5.5 liters of a 1.5% gelatin solution,

  
  <EMI ID = 101.1>

  
add, with stirring and by double jet, a 2.1 M solution of potassium bromide and a 2.0 M solution of silver nitrate, for 2 min, keeping the pBr at 0.8; 0.53% of the total silver nitrate is consumed. We stop

  
  <EMI ID = 102.1>

  
edition of the silver solution for 4.6 min, at a speed consuming 8.6% of the total silver nitrate. The bromide and silver salt solutions are then added at the same time, for 13.3 min, keeping the pBr at 1.2, at an accelerated rate (multiplied by 2.5 from start to finish); 43.6% of the total silver nitrate is consumed. The addition of the bromide solution is stopped, and the addition of the silver salt solution is continued for 1 min; 4.7% of the total silver nitrate is consumed.

  
A 2.0 M solution is added by double jet

  
in potassium bromide and 0.30 M in potassium iodide and the silver salt solution, for 13.3 min, at an accelerated rate (multiplied by 1.5 from start to finish) while maintaining the pBr at 1, 7 and consuming 35.9% of the total silver nitrate. 1.5 g of sodium thiocyanate per mole of silver are added to the emulsion and the emulsion is left for 25 min. A solution is added by double jet

  
0.35 M in potassium iodide and the silver salt solution, at constant equal flow rate, for approximately 5 min, until the pBr reaches 3.0; about 6.6% of the total silver nitrate is consumed. Approximately 11 moles of silver nitrate are used in total. Then a solution of 350 g of phthalylated gelatin in 1.2 liters of water is added, the emulsion is cooled to 30 [deg.] C, and washed with

  
the coagulation process of Example 6. The emulsion is then sensitized chemically and spectrally

  
optimally, in the same way as in Example 6.

  
 <1> (Phthalylated gelatin is described in U.S. Patents 2,614,928 and 2,614,929).

  
EXAMPLE 8

  
To 30.0 liters of a 0.8% gelatin solution containing 0.10 M potassium bromide, at 75 ° C., a 1.2 M solution of potassium bromide and a 1.2 M solution of silver nitrate, for 5 min, maintaining the pBr at 1.0; 2.1% of the total silver nitrate is consumed. 5 liters of a solution containing 17.6% of phthalylated gelatin are then added, and the emulsion is left for 1 min. The silver nitrate solution is then added to the emulsion until the pBr reaches 1.35; 5.24% of the total silver nitrate is consumed. A 1.06 M potassium bromide solution and 0.14 M potassium iodide solution and the silver salt solution are added by double jet, at an accelerated rate (multiplied by 2 from the beginning to the end); 92.7% of the total silver nitrate is consumed, and the pBr is maintained at 1.35.

   Approximately 20 moles of silver nitrate are used in total. The emulsion is cooled to 35 [deg.] C, washed by coagulation and chemically sensitized

  
and spectrally optimally in the same way as in Example 6.

  
EXAMPLE 9

  
4.5 liters of a 1.5% gelatin solution containing 0.17 M potassium bromide, at 55 [deg.] C and at

  
pH 5.6, a 1.8 M solution of potassium bromide and a solution are added, with stirring and by double jet.

  
2.0 M silver nitrate, at constant equal flow rates, for 1 min, at pBr 0.8; 0.7% of the total silver nitrate is consumed. The bromide solution, the silver salt solution and a 0.26 M solution of potassium iodide, at equal constant flow rates, are then added at the same time, for 7 min, while maintaining the pBr at 0.8 and consuming 4.8% of total silver nitrate. The triple jet is then continued for an additional period of 37 min, keeping the pBr at 0.8, at an accelerated rate (multiplied by 4 from start to finish); 94.5% of the total silver nitrate is consumed. A total of about 5 moles of

  
  <EMI ID = 103.1>

  
add 1 liter of water containing 200 g of phthalylated gelatin, and the emulsion is washed by coagulation. The emulsion is then sensitized chemically and spectrally optimally in the same manner as in Example 6.

  
Control 3. This emulsion is precipitated in the manner described in the US patent. 4,184,877.

  
At 17.5 liters of a 5% aqueous solution

  
  <EMI ID = 104.1>

  
jet, a 4.7 M solution of ammonium iodide and a 4.7 M solution of silver nitrate, at constant equal flow rates,

  
  <EMI ID = 105.1>

  
about 22% of the silver nitrate used for the preparation of seed seeds. The flow rate of the two solutions is then adjusted so as to consume, in 15 minutes, approximately 78% of the total silver nitrate used for the preparation of the seed grains. The addition of the ammonium iodide solution is then stopped, and the addition of the silver nitrate solution is continued until a pi of 5.0 is obtained. A total of approximately 56 moles of silver nitrate are used for the preparation of the seed emulsion. The emulsion is cooled

  
  <EMI ID = 106.1>

  
5% gelatin containing 4.1 moles of the silver iodide emulsion prepared above. A 4.7 M solution of ammonium bromide and a 4.7 M solution of silver nitrate are added by double jet, at constant equal flow rates, for 7.1 min, maintaining the pBr at 4.7; we consume

  
"7 40.2% of the total silver nitrate used for precipitation on the seed grains. The addition of the ammonium bromide solution alone is continued until the pBr reaches approximately 0.9 and we stop.

  
2.7 liters of an 11.7 M ammonium hydroxide solution are then added and the emulsion is left for

  
10 mins. The pH is adjusted to 5.0 with sulfuric acid, and the introduction in double jet of the solutions of ammonium bromide and silver nitrate is resumed for

  
14 min while maintaining the pBr at approximately 0.9, at a flow rate consuming 56.8% of the total silver nitrate. The pBr is then adjusted to 3.3 and the emulsion is cooled to 30 [deg.] C. A total of approximately 87 moles of silver nitrate are used. 900 g of phthalylated gelatin are added, and the emulsion is washed by coagulation.

  
The pAg of the emulsion is adjusted to 8.8 and 4.2 mg per mol of silver of sodium thiosulfate pentahydrate and 0.6 mg per mol of silver of potassium tetrachloroaurate are added. The maturation is then carried out by heating the emulsion at 80 [deg.] C for 16 min, cooling to 40 [deg.] C, adding 387 mg per mole of silver of a spectral sensitizer to green, the sodium salt

  
  <EMI ID = 107.1>

  
sulfobutyl) -3- (3-sulfopropyl) oxacarbocyanine, and the emulsion is left for 10 min. The chemical and spectral sensitizations are optimal for the sensitizers used.

  
Witness 4. This emulsion is of the type described in the US patent. 3,320,069.

  
A 42.0 liters of a 0.050 M solution of potassium bromide, 0.012 M potassium iodide and 0.051 M potassium thiocyanate, containing 1.25% of

  
  <EMI ID = 108.1>

  
by shaking, at equal rates, a solution 1.32 M in potassium bromide and 0.11 M in potassium iodide and a

  
¯7 1.43 M silver nitrate solution, for approximately

  
40 mins. 21 moles of silver nitrate are consumed. The emulsion is cooled to 35 [deg.] C and washed by coagulation according to the method described in the US patent. 2,614,928.

  
The pAg of the emulsion is adjusted to 8.1 and 5.0 mg per mol of silver of sodium thiosulfate pentahydrate and 2.0 mg per mol of silver of potassium tetrachloroaurate are added. Then heat the emulsion for maturation at 65 [deg.] C, cool it to 40 [deg.] C, add
464 mg per mole of silver of a green spectral sensitizer, the sodium salt of anhydrous hydroxide-5-

  
  <EMI ID = 109.1>

  
propyl) oxacarbocyanine, and the emulsion is left for
10 mins. The chemical and spectral sensitizations are optimal for the sensitizers used.

  
Witness 5. This emulsion is of the type described in the US patent. 3,320,069.

  
A 42.0 liters of a 0.050 M potassium bromide solution, 0.012 M potassium iodide, and 0.051 M potassium thiocyanate, containing 1.25% of

  
  <EMI ID = 110.1>

  
with stirring, and at equal flow rates, a 1.37 M solution of potassium bromide and 0.053 M potassium iodide, and a 1.43 M solution of silver nitrate, for approximately 40 min. 21 moles of silver nitrate are consumed. The emulsion is then cooled to 35 [deg.] C and washed

  
by coagulation in the same way as control 4.

  
The pAg of the emulsion is adjusted to 8.8 and 10 mg per mol of silver of sodium thiosulfate pentahydrate and 2.0 mg per mol of silver of potassium tetrachloroaurate are added. The emulsion is heated to 55 [deg.] C for

  
maturation, cooling to 40 ° C., 387 mg / mole Ag of a spectral sensitizer to green is added, the soium salt of 5-anhydro-5-chloro-9-ethyl hydroxide -

  
  <EMI ID = 111.1>

  
1 and the emulsion is left for 10 min. The chemical and spectral sensitizations are optimal for the sensitizers used.

TABLE II

  

  <EMI ID = 112.1>


  
* US Patent 3,320,069 does not give form indices. They were determined by repeating the examples and measuring the grains.

  
Emulsions 6 to 9 are emulsions with tabular grains of high shape index falling within the definition limits of the invention. Although some tabular grains with a diameter of less than 0.6 µm are included in the estimation of the average diameter of the tabular grains and the percentage of projected area, in these and other examples, unless their exclusion is specifically notified, it there are not enough grains of small diameter to significantly modify the figures indicated. To obtain a representative average shape index for the grains of the control emulsions, the average diameter of the grains is compared to their average thickness.

   Although it has not been measured, it can be estimated by visual observation, in each case, that the projected area which could be allocated to the few tabular grains which meet the criteria of the invention,

  
  <EMI ID = 113.1>

  
diameter of at least 0.6 / µm, represents a very small part, if any, of the total projected area of the total grain population of the control emulsions.

  
The chemically and spectrally sensitized emulsions are applied separately to a cellulose triacetate support, to form a single layer magenta product. Each product includes an emulsion with

  
  <EMI ID = 114.1>

  
2.14 g / m of gelatin to which a dispersion in a solvent of the formative coupler has previously been added

  
  <EMI ID = 115.1>

  
0.75 g of coupler per m, 3.2 g / mole Ag of potassium 5-secoctadecylhydroquinone-2-sulfonate, as an inhibitor of parasitic coloring, and 3.6 g / mole Ag of 4-hydroxy-6- methyl-1,3,3a, 7-tetraazaindene as an anti-veil. An overlay formed of gelatin is applied to

  
  <EMI ID = 116.1>

  
as a tanning agent at a rate of 1.75% relative to the total gelatin mass of all the layers.

  
The photographic products obtained are exposed for 1/100 s, on a sensitometric scale of density 0 to 3.0, a Wratten No. 9 filter and a neutral filter of density 1.2.6, to a tungsten light source of
600 W and 3000 [deg.] K. The products are treated at 37.7 [deg.] C by a chromogenic treatment method of the type described in the journal British Journal of Photography Annual, 1979, pp 204-
106. Development times vary to produce

  
3rd veil densities of approximately 0.10. The relative sensitivity to green and the RMS granularity are determined for each of the photographic products. (The RMS granularity is measured by the process described by H.C. Schmitt, Jr and J.H. Altman, Applied Optics, 9, pp. 871-874, April 1970).

  
The speed / granularity relationships of these layers are shown in FIG. 12, which is a graph giving, on the ordinate, the logarithm of the speed in the green, and on the abscissa, the RMS x 10 granularity.

  
Fig. 12 shows that silver bromoiodide emulsions with a high index of form which have been optimally chemically and spectrally sensitized have a much better speed / granularity relationship than that of silver bromoiodide emulsions whose index form is lower.

  
It should be noted that this experiment, carried out on layers of single-layer products in which all the silver halide emulsions have the same silver content and have a silver / current coupler ratio, constitutes the best way to illustrate the speed relationship. / granularity of a silver halide emulsion without introducing a disturbing interaction.

  
EXAMPLE 10

  
A product with incorporated couplers for color photography is prepared by applying the following layers in order on a cellulose triacetate film support:

  
Layer 1: Slow blue-green layer comprising an emulsion

  
silver bromoiodide, sensitized to red, gelatin, a blue-green image-forming coupler, a colored coupler and a DIR coupler.

  
Layer 2: Rapid blue-green layer comprising a sensitized silver bromoiodide emulsion

  
in the red faster than that of layer 1, gelatin, a blue-green image-forming coupler, a colored coupler and a coupler releasing a development inhibitor (DIR coupler).

  
Layer 3: Interlayer comprising gelatin and a

  
agent against the yellow veil, 2,5-di-secdodécylhydroquinone.

  
Layer 4: Slow magenta layer comprising an emulsion of

  
silver bromoiodide sensitized to green

  
(1.48 g of silver and 1.21 g of gelatin per square meter) 0.88 g per square meter of a magenta-forming coupler, 1- (2,4,6-trichlorophenyl) -3- [ 3- (2,4-diamylphenoxyacetamino) benzamido] -5-pyrazolone, 0.10 g per square meter of a colored coupler, 1- (2,4,6-trichlorophenyl) -3 - [&#65533; - (3-tert-butyl-4-hydroxyphenoxy) -

  
  <EMI ID = 117.1>

  
dino-4- (1-phenyl-5-tetrazolylthio) -5-pyrazolone and 0.09 g per square meter of potassium 5-sec-octadecylhydroquinone-2-sulfonate (agent against yellow veil).

  
Layer 5: Fast magenta layer comprising an emulsion

  
faster green-sensitized silver bromoiodide (1.23 g silver and 0.88 g gelatin per square meter), 0.12 g per square meter of a magenta coupler, 1- (2.4 , 6-trichloro-

  
  <EMI ID = 118.1>

  
benzamido] -5-pyrazolone, 0.03 g per square meter of a colored coupler, 1- (2,4,6-tri-

  
  <EMI ID = 119.1>

  
(3,4-dimethoxy) -phenylazo-5-pyrazolone and 0.05 g per square meter of potassium 5-sec-octadecylhydroquinone2-sulfonate.

  
Layer 6: Interlayer comprising gelatin and a

  
agent preventing yellow veil, 2,5-di-sec-

  
') dodecylhydroquinone.

  
Layer 7; Yellow filter layer comprising yellow colloidal silver and gelatin.

  
Layer 8: Slow yellow layer comprising an emulsion of

  
silver bromoiodide sensitized in blue, gelatin, a coupler forming yellow dye and an agent to prevent yellow veil, 5-sec-octadecylhydroquinone.

  
Layer 9: Rapid yellow layer comprising an emulsion of

  
silver bromoiodide sensitized in the faster blue, a coupler forming yellow and an agent preventing yellow veil, 5-secoctadécylhydroquinone.

  
Layer 10: UV absorbing layer comprising

  
gelatin and a compound for absorbing UV radiation, 3- (di-n-hexylamino) allylidenemalononitrile.

  
Layer 11: Protective overcoat comprising gelatin

  
and bis-vinylsulfonylmethylether.

  
In each image-forming layer, the silver halide emulsions consist of polydispersed grains, of low shape index, of the type described in United States patent 3,320,069. All emulsions are sensitized with optimally with sulfur and gold in the presence of thiocyanate and spectrally sensitized to the appropriate regions of the visible spectrum. The emulsion used in the fast magenta layer is an emulsion of silver bromoiodide with 12% iodide by mole, which is polydispersed (from 0.5 to 1.5, um) and whose shape index is low. (about 3: 1); this emulsion was prepared in a similar manner to emulsion # 4 described above.

  
We prepare a second product for color photography in the same way, except that in

  
the fast magenta layer, instead of the low form index emulsion, a silver bromoiodide emulsion of 8.4 mol% iodide consisting of tabular grains is used. The grains of this emulsion have an average size of approximately 2.5 μm, a thickness less than or equal to 0.12 μm, an average shape index greater than
20: 1 and their projected area measured according to the indications given above represents more than 75% of the total projected area. Shape index emulsions

  
  <EMI ID = 120.1>

  
spectral and chemical, according to the present invention.

  
Each photographic product is exposed for 1 / 50th of a second to the light of a tungsten source

  
  <EMI ID = 121.1>

  
a color developer of the type described in British Journal of Photography Annual, 1979 p. 204-206. The sensitometric results are presented in Table III below.

  

  <EMI ID = 122.1>


  

  <EMI ID = 123.1>


  

  <EMI ID = 124.1>
 

  
The results presented in Table III show that the tabular grains of the present invention make it possible to obtain an increase in sensitivity in the green with at the same time a very small increase in granularity.

  
EXAMPLES 11 and 12

  
Speed / granularity of products for black and white photography.

  
To illustrate the advantages of the invention with regard to black and white photography, five products are prepared from the emulsions chemically sensitized and spectrally prepared above (emulsions n [deg.] 6, 9, 3, 4 and 5), by applying each of these emulsions to a polyethylene terephthalate film support. Each product includes a silver halide emulsion at a rate per square meter, of 3.21 g of silver and 4.16 g of gelatin to which 3.6 g of 4-hydroxy-6-methyl- has been added before. 1,3,3a-7-tetraazaindene (anti-veil) per mole of silver. On each emulsion, an overlay is applied comprising 0.88 g of gelatin per square meter and

  
a tanning agent, bis (vinyl) sulfomethyl) ether at a rate of 1.75% relative to the total mass of gelatin.

  
Each photographic product is exposed for 1 / 100th of a second to a light source at

  
  <EMI ID = 125.1>

  
through a density scale from 0 to 3.0, associated with a Wratten n [deg.] 9 filter, and a neutral filter with a density

  
  <EMI ID = 126.1>

  
developer with hydroquinone and N-methyl-paminophenol sulfate (developer Kodak DK50), for 5 min with regard to emulsions with low shape index and for

  
  <EMI ID = 127.1>

  
maintain comparable corrected curves. The measurements of speed and granularity are plotted on the graph of FIG. 13 with on the abscissa the RMS granularity multiplied by ten and on the ordinate the logarithm of the speed in the green. The speed / granularity relationships of the control emulsions 3, 4 and 5 are lower than those of the emulsions 6 and 9 according to the present invention. EXAMPLES 13 and 14 illustrating the increased separation of the velocities between the regions of spectral sensitization and the regions of natural sensitivity.

  
Four products for color photography are hereinafter designated under the name of structures 1 to 4; except for the structural characteristics expressly identified below, the structure of these elements is the same.

  

  <EMI ID = 128.1>
 

  
SC is an overlay of gelatin;

  
FJ is a layer containing 0.69 g / m <2> of yellow colloidal silver serving as a yellow filter and the other abbreviations are identical to those already indicated for structures I to IX above. The elements recording blue (B), green (V) and red (R), the code of which does not include the letter T, consist of silver bromoiodide emulsions with low shape index, prepared according to the patent from the United States of America

  
3,320,069. The corresponding layers in the different structures have the same iodide content, unless otherwise specified.

  
The rapid emulsion with tabular grains sensitized in green (identified with the letter T in the diagrams above), is prepared as follows.

  
2.25 1 of a 1.5% by mass aqueous solution of bone gelatin containing potassium bromide (0.17 M,

  
  <EMI ID = 129.1>

  
simultaneously by double jet in two minutes and at constant flow rate, aqueous solutions of potassium bromide
(2.19 M, solution B-1) and silver nitrate (2.0 M, solution C-1) (0.61% of the silver nitrate was thus consumed).

  
After two minutes, the introduction is stopped.

  
  <EMI ID = 130.1>

  
thus consumed 2.44% of the silver nitrate). Then added to pBr 1.00. And at 80 [deg.] C, 0.4 1 of an aqueous solution of phthalylated gelatin (20% by weight of gelatin) containing potassium bromide (0.1 M, solution D).

  
By double jet, solutions B-1 and C-1 are then added in 24 minutes to the reactor using accelerated flow rates (multiplied by 4.0 between the start and

  
the end of the preparation). 44% of the total amount of silver nitrate was thus consumed. After 24 minutes, the jet of solution B-1 is stopped and the addition of C-1 is continued until a pBr of 1.80 is reached.

  
  <EMI ID = 131.1>

  
By double jet, the solution C-1 and a solution B-2 of potassium bromide are then added to the reactor.

  
  <EMI ID = 132.1>

  
achieves this addition in 12 minutes with accelerated flow rates (multiplied by 1.37 between the start and the end of the precipitation) by consuming 50.4% of the total silver nitrate.

  
By double jet, we then add solutions

  
  <EMI ID = 133.1>

  
2.16, which consumes 2.59% of the total silver nitrate.

  
A total of 6.57 moles of silver nitrate were used to prepare this emulsion.

  
The emulsion is cooled to 35 ° C., mixed with 0.30 liters of an aqueous solution of phthalylated gelatin (13.3% by mass of gelatin) and washed twice by coagulation.

  
The tabular silver bromoiodide grains obtained have an average diameter of 5.0 µm and an average thickness of about 0.1 µm. Tabular grains represent approximately 90% of the total projected grain area and have an average shape index of approximately 45: 1.

  
The fastest green-sensitive tabular grain emulsion is then spectrally and chemically sensitized optimally by the addition of
350 mg per mole of silver sodium hydroxide salt

  
  <EMI ID = 134.1>

  
800 mg / mol of silver of sodium thiocyanate, 6 mg / mol of silver of sodium thiosulfate pentahydrate and 3 mg / mol of silver of potassium tetrachloroaurate.

  
The rapid red-sensitive emulsion is an emulsion of silver bromoiodide with tabular grains prepared and sensitized in an optimal manner in a similar manner to that used for the emulsion of tabular silver bromoiodide sensitized for green described immediately above. above, with the only difference that is used as spectral sensitizers 144 mg per mole of silver anhydro hydroxide 5,6-dichloro-1-ethyl-3- (3-

  
  <EMI ID = 135.1>

  
thiacarbocyanine. Rapid emulsions sensitized to

  
  <EMI ID = 136.1>

  
in moles of iodide, while the fast emulsions with tabular grains sensitized to green and red of structures III and IV respectively contain 1.5% and 1.2% by mole of iodide.

  
Additional details regarding structures I to IV can be found in U.S. Patent 4,184,876.

  
  <EMI ID = 137.1>

  
identical neutral position by means of a source of 2850 [deg.] K with a power of 600 watts by inserting a filter for daylight 5 and a density scale from 0 to

  
4 with ranges of 0.20. We expose other samples

  
  <EMI ID = 138.1>

  
above, but also inserting a Wratten 98 filter so as to obtain the results of exposure to blue.

  
  <EMI ID = 139.1>

  
in the same way, but additionally inserting a Wratten 9 filter, so as to obtain the results of exposure to the blue minus. All the samples are treated in the same way for 3 min, 15 s at 38 [deg.] C by the method of processing the color negatives C-41 described in British Journal of Photography Annual, 1979, p. 204. The curves obtained for the different samples are compared after harmonization of the minimum density levels, that is to say by superimposing the parts of curves corresponding to the minimum densities. The results are collated in Table IV.

  

  <EMI ID = 140.1>


  

  <EMI ID = 141.1>
 

  
  <EMI ID = 142.1>

  
in the blue of the chromogenic element recording the blue and the logarithm of the rapidity in the blue of the chromogenic element recording the green; this difference is expressed by equation A above;

  

  <EMI ID = 143.1>


  
  <EMI ID = 144.1>

  
rapidity in blue of the chromogenic element registering blue and the logarithm of rapidity in blue of the chromogenic element registering red; this difference is expressed by equation B indicated above:

  

  <EMI ID = 145.1>


  
  <EMI ID = 146.1>

  
speed in the green of the chromogenic element recording the green and the logarithm of the speed in the blue of the element recording the green; this difference is expressed by equation C indicated above:

  

  <EMI ID = 147.1>


  
  <EMI ID = 148.1>

  
speed in the red of the chromogenic element recording the red and the logarithm of the speed in the blue of the chromogenic element recording the red, ex-

  
  <EMI ID = 149.1>

  
The comparison of structures II and III shows that the separation of the velocities is better with structure III which is produced with tabular grains in accordance with the present invention. In structure III, the separation of the velocities does not reach the value of structure I, but structure III does not use a yellow filter and consequently it does not entail the drawbacks already mentioned with regard to the use of these filters. Structure IV uses a yellow filter in a larger quantity than that required for the photographic products in accordance with the present invention, but it is found that in this structure IV a separation of the velocities greater than that of structure III could be obtained if desired , using even small yellow filter densities.

  
A monochrome product is prepared by applying to a film support the composition of the tabular grain emulsion layer sensitized for fast green described above, then by applying a protective gelatin overlay to this layer. The separation between the speed in blue and the speed in blue minus of this product is determined by means of the exposure and treatment techniques already described.

  
The quantitative expression of this separation is given

  
  <EMI ID = 150.1>

  
equal to 1.28 log E. These results show that an appropriate separation of the velocities in the blue at the blue minus can be carried out in accordance with the invention when a tabular emulsion layer of high shape index recording the minus blue is arranged so

  
to be the layer closest to the source of exposure and without benefiting from the protection of an overlay absorbing blue light.

  
EXAMPLES 15 to 19 concerning the improvement of the sharpness of the image in photographic products with several layers containing emulsions with tabular grains.

  
The following three examples show how image clarity is improved by using tabular grain emulsions with a high shape index. In these examples, the control products are produced with silver bromoiodide emulsions with low shape index of the type of those described in US Pat. No. 3,320,069. These emulsions with low shape index are designated in the following under the name of conventional emulsions and their physical characteristics are presented in Table V below.

  

  <EMI ID = 151.1>


  

  <EMI ID = 152.1>
 

  
Four silver bromoiodide emulsions with tabular grains (high shape index) are prepared by techniques similar to those described above in the examples relating to the improvement of the speed / granularity relationship. The physical characteristics of these emulsions are presented in Table VI.

  

  <EMI ID = 153.1>


  

  <EMI ID = 154.1>


  

  <EMI ID = 155.1>
 

  
The silver bromoiodide emulsions described above C1 to C6 and T1 to T4 are used to prepare a series of multilayer products. The variations are noted in the table of results. Although these emulsions are chemically and spectrally sensitized, such sensitization is not essential to obtain the results observed with regard to sharpness.

  
Basic structure A

  

  <EMI ID = 156.1>

EXPOSURE AND TREATMENT

  
The samples are exposed and developed as described below. Sharpness measurements are made by determining the modulation transfer functions. This process is known and described for example in Journal

  
  <EMI ID = 157.1>

  
The red light modulation transfer functions are obtained by exposing the products to several layers for 1 / 15th of a second at a modulation of 60% through a Wratten 29 filter and a neutral filter with a density of 0.7. The modulation transfer functions for green light are obtained in the same way, but using a Wratten 99 filter.

  
Products are treated for 3 minutes 4

  
at 38 [deg.] C using the C-41 process for color negative product, described in British Journal of Photography Annual
1979 p. 204. After treatment, from curves

  
Modulation transfer, measurements are made by cascade modulation transfer (CMT), at the magnification used for the 16 mm wide film.

RESULTS

  
The composition of the control samples and of the samples in accordance with the invention, as well as the stress values for the exposures in the red and in the green, are presented in Table VII.

  

  <EMI ID = 158.1>


  

  <EMI ID = 159.1>
 

  
Surprisingly, the results in Table VII show that the use of tabular grain emulsions in layers of a multi-layer product for color photography can cause a decrease in sharpness. If we consider the acutance in the red, we see that the sample

  
2 containing two layers with tabular grains is less clear (-1.0 CMT sharpness) than control 1 which only comprises conventional emulsions. Likewise, sample 3 with four tabular grain layers is less clear (-1.3, CMT unit) than sample 4 which contains only three tabular grain layers and is also less sharp (-0, 4 CMT unit) as sample 5 which contains two tabular grain layers. However, samples 6 and 7 show that with an appropriate arrangement of tabular grain emulsions (it is noted that the CMT height in the red of sample 6 is 1.3 units greater than that of sample 4) in the layers closest to the radiation source used for the exposure, very significant improvements are obtained compared to the control samples comprising only conventional emulsions.

   As shown in the table above, the acutance in the green of sample 6 is 6.3 CMT units greater than that of sample 1 and the acutance in green of sample 7 is greater 6.6 CMT units to that of sample 1.

  
Structure B

  
Overlay

  

  <EMI ID = 160.1>


  
The products of structure B are exposed and treated as above. The composition of the control samples and of the samples in accordance with the invention, as well as the CMT resistance values are presented in Table VIII.

  

  <EMI ID = 161.1>


  

  <EMI ID = 162.1>
 

  
The data in Table VIII show that the sharpness is improved when the tabular grain emulsions are arranged in the layers closest to the radiation source used for exposure; the sharpness is adversely affected when the tabular grain emulsions are arranged in intermediate layers which are themselves placed under light-scattering layers.

  
Structure C

Fast Magenta

  

  <EMI ID = 163.1>


  
Two monochrome products are prepared by applying compositions for fast and slow magenta layers to a support.

TABLE IX

  

  <EMI ID = 164.1>


  
The sharpness of the monochrome products is then measured according to the technique described above and the following results are obtained:

PAINTINGS

  

  <EMI ID = 165.1>


  
EXAMPLE 20 showing the decrease in the scattering of light at a wide angle by the use of tabular grains.

  
The quantitative detection method of angular light scattering described above with reference to FIG. 5 is used to specifically illustrate the reduction in wide angle scattering obtained by tabular grain emulsions of high shape index. according to the invention, by comparison with an emulsion with non-tabular grains of the same average volume. The emulsions according to the invention essentially consist of a dispersion medium and

  
  <EMI ID = 166.1>

  
and the average thickness of 0.23 µm, with an average shape index of 23.5: 1. Tabular grains represent more than 90% of the total projected surface of the grains present. The average grain volume is 5.61 µm. The grains of the non-tabular emulsion used as a control

  
  <EMI ID = 167.1>

  
spheres of the same volume, i.e. equivalent spheres, mean that the two emulsions have approximately the same grain diameter). For both emulsions, the total transmittance is 90% when immersed in a liquid with an appropriate refractive index. Each emulsion is applied to a transparent support at the rate of 1.08 g of silver per

  
square meter.

  
As shown more particularly in Table XI below, the percentage of total transmitted light received over the entire detection surface subtended by an angle 0 having up to a value of
84 [deg.], Is weaker with tabular grain emulsions with a high shape index than with the control emulsion with a similar average grain volume. The results of Table XI show that the capture angle for the two emulsions is less than about 6 [deg.]. Consequently, neither of these two emulsions can be considered as having diffusing characteristics resulting in real turbidity. When the angle 0 is 70 [deg.], The emulsion according to the invention has a diffusion

  
'j of the wide angle light which is only half that of the witness.

TABLE XI

PERCENTAGE OF LIGHT TRANSMITTED IN AN ANGLE 0

  

  <EMI ID = 168.1>


  
EXAMPLE 21 illustrating the spectral sensitization in the blue of the emulsion with tabular grains A.

  
A tabular silver bromoiodide emulsion containing 3% of iodide by mole is prepared as follows:

  
To 3.0 liters of a 1.5% gelatin solution, at a temperature of 60 [deg.] C, containing 0.17 M of bromide

  
of potassium, 4.34 M of potassium bromide in a 3% gelatin solution and a 4.0 M silver nitrate solution are added by double jet and with stirring; the addition is carried out in 2.5 min by keeping the pBr at 0.8 and consuming 4.8% of the total amount of silver used. The addition of the bromide solution is stopped and the addition of the silver nitrate solution is continued for 1.8 min until a pBr of 1.3 is reached, which consumes 4.3% of the money used. Then the silver nitrate solution is added simultaneously

  
and a 6% gelatin solution containing 4.0 M potassium bromide and 0.12 M potassium iodide;

  
this addition is carried out in 24.5 min with accelerated flow rates (by multiplying the flow rate by 2.0 between the

  
start and end of the operation) and maintaining the pBr at 1.3, which consumes 87.1% of the total money used.

  
The addition of the bromide solution is stopped and the addition of the silver nitrate solution is continued for 1.6 min with a flow rate consuming 3.8% of the total silver used and up to reach a pBr of 2.7.

  
The emulsion is then cooled to 35 [deg.] C,

  
added 279 g of phthalylated gelatin dissolved in 1 liter of distilled water and washed by coagulation. We

  
thus obtained a silver bromoiodide emulsion at

  
3 mol% of iodide, the grains of which have an average diameter of 1.0 μm and an average thickness of approximately 0.10 μm,

  
which gives a form index of 10: 1. These tabular grains represent more than 85% of the projected surface

  
of the total silver halide grains present in the emulsion layer.

  
We sensitize the emulsion chemically with

  
sodium thiocyanate, sodium thiosulfate and potassium tetrachloroaurate.

  
PRODUCT N [deg.] 1

  
A sample of this chemically sensitized emulsion is applied to a cellulose triacetate film support. The emulsion layer obtained c includes the tabular emulsion of silver bromoiodide for good reason,

  
per square meter, 1.8 g of silver and 2.9 g of gelatin

  
to which a dye-forming coupler has been added

  
  <EMI ID = 169.1>

  
2-octadecyl-5-sulfohydroquinone (1.69 g / mole of silver) and 4-hydroxy-6-methyl-1,3,3a, 7-tetraazaindene
(3.62 g / mole of silver).

  
  <EMI ID = 170.1>

  
A second sample of the tabular silver bromoiodide emulsion is spectrally sensitized to blue by the addition of 3 x 10-4 mole per mole of silver in the triethylamine salt of the hydroxide. <EMI ID = 171.1>

  
this spectrally sensitized emulsion is then applied in a layer, with the same magenta dye-forming coupler as in layer 1. Each product is exposed for l: 25th of a second through a density scale of 0 to 3.0, using a tungsten light source at 5400 [deg.] K, with a power of 500 W. It is treated for 3 min in a chromogenic developer of the type described in British Journal of Photography Annual,
1979 p. 204-206.

  
Product n [deg.] 2 has a photographic speed 0.42 log E higher than that of product 1, which shows the contribution of sensitization in blue to the increase in speed.

CLAIMS

  
1.- Photographic product comprising a support and at least one photosensitive emulsion layer formed by a dispersing medium and tabular grains of silver bromoiodide, characterized in that at least 50% of the total projected surface of the grains of silver bromoiodide consists of tabular grains having two opposite main parallel faces, a thickness

  
  <EMI ID = 172.1>

  
grain diameter being defined as the diameter of a circle whose surface is equal to the projected surface of the grain, and an average shape index, defined as the ratio of the diameter of the grain to its thickness, greater than 8: 1, at at least part of these tabular silver bromoiodide grains comprising a central region lying between the main faces, containing a lower proportion of iodide than at least one peripheral region also lying between the main faces.

  
2.- Photographic product conforming to the


    

Claims (1)

claim 1, characterized in that at least 50% of the total projected surface consists of tabular grains of silver bromoiodide whose thickness is less than 0.3 µm. 3.- Photographic product conforming to 1.a claims 1 or 2, characterized in that the tabular grains of silver bromoiodide have an index at least 12: 1 in average shape. 4.- Photographic product conforming to one claims 1 or 2, characterized in that the tabular grains of silver bromoiodide have an index at least 20: 1 in average shape. 5. Photographic product according to any one of claims 1 to 4 wherein the iodide contents in the central region and in the peripheral region differ by at least 1% by mole. 6. Photographic product according to any one of claims 1 to 5, characterized in that the central region contains from 0 to 5% by mole of iodide and the peripheral region contains up to 20% by mole of iodide . 7. Photographic product according to any one of claims 1 to 5, characterized in that the central region contains from 0 to 5 mole percent of iodide except in contiguous zones with main faces, contiguous zones including thickness is less than <EMI ID = 173.1> 8. Photographic product according to any one of claims 1 to 7, characterized in that the peripheral region is an annular region surrounding the central region, and the concentration of iodide in the tabular grains gradually increases from the central region towards the annular region. 9 .- Photographic product according to any one of claims 1 to 7, characterized in that the iodide present in the tabular grains of silver bromoiodide increases suddenly at the interface of the central region and the peripheral regions . 10.- Photographic product according to any one of claims 1 to 9, characterized in that the tabular grains of silver bromoiodide represent at least 70% of the total projected surface of the grains of silver bromoiodide. 11. Photographic product according to any one of claims 1 to 9, characterized in that the tabular grains of silver bromoiodide represent at least 90% of the total projected surface of the grains of silver bromoiodide. 12. Photographic product according to any one of claims 1 to 11, characterized in that the interior of the tabular bromoiodide grains &#65533; ^ Silver is doped. 13.- Photographic product according to claim 12, characterized in that the interior of the tabular grains of silver bromoiodide is doped with a metal from group VIII of the Periodic Table of the Elements. 14. Photographic product according to any one of claims 1 to 13, characterized in that the tabular grains of silver bromoiodide are chemically sensitized at the surface with a noble metal, a chalcogen, a sensitizer by reduction, or a combination of these sensitizers.  <EMI ID = 174.1> any of claims 1 to 14, characterized in that the tabular grains of silver bromoiodide are chemically sensitized in the presence of a ripening agent. 16.- Photographic product according to claim 15, characterized in that the maturing agent contains sulfur. 17. A photographic product according to any one of claims 1 to 16, characterized in that the tabular grains of silver bromoiodide are spectrally sensitized in the blue minus of the spectrum. 18.- photographic product according to any one of claims 1 to 17, characterized in that the peripheral region is an annular region surrounding the central region and containing at least 6 mole percent iodide. 19. Photographic product according to any one of claims 1 to 18, characterized in that a spectral sensitizer in the blue or in the blue minus is adsorbed on the surface of the silver bromoiodide grains. 20.- Photographic product according to any one of claims 1 to 19, characterized in that the tabular grains of silver bromoiodide are chemically sensitized optimally with gold in combination with at least one sulfur or selenium sensitizer, in the presence of a thiocyanate as maturation agent, and spectrally with a sensitizer , spectral having an absorption peak in the blue minus of the spectrum. 21. Photographic product according to any one of claims 1 to 20, characterized in that the tabular grains have an average shape index of between 20: 1 and 100: 1. 22. Photographic product according to any one of claims 1 to 21, characterized in that the grains are chemically sensitized in the presence of at least part of the spectral sensitizing dye. 23. Photographic product according to any one of claims 1 to 22, characterized in that an additional silver halide is present on the surface of the silver bromoiodide grains, in quan-  <EMI ID = 175.1> 24. Photographic product according to any one of claims 1 to 23, characterized in that the photosensitive emulsion layer formed by a dispersion medium and tabular grains of silver bromoiodide is placed to receive light transmitted without broadcasting. 25-- Photographic product according to any one of claims 1 to 24, characterized in that the tabular grains of silver bromoiodide have an average diameter of at least 2.a). 26.- Product according to any one of claims 1 to 25, for black and white photography, characterized in that the tabular grains of silver bromoiodide are, optimally, chemically and spectrally sensitized, orthochromatic or panchromatic way. 27.- Product according to claim 26 for black and white photography, characterized in that the emulsion layer containing the tabular grains of silver bromoiodide is above another layer of halide emulsion of silver forming images and is arranged to receive during exposure light which has not been diffused by a light transmitting layer placed above. 28.- Product according to claim 27 for black and white photography, characterized in that the emulsion layer containing the tabular grains of silver bromoiodide is the outermost layer of the photographic product. 29.- Product according to any one of claims 26 to 28 for black and white photography, characterized in that the silver bromoiodide grains are chemically sensitized with at least one sensitizer for gold, sulfur or selenium, in the presence of a thiocyanate as a ripening agent. 30.- Product formed of a support and emulsion layers to separately record the blue, the green and red, each consisting of a dispersing medium and silver bromoiodide grains, the emulsion layers recording green and red respectively containing spectral sensitizing dyes for green and for red, characterized in that at least one of the emulsion layers recording green and red contains tabular grains of silver bromoiodide sensitized chemically and spectrally according to any one of claims 1 to 25. 31.- Product according to claim 30, characterized in that one of the emulsion layers containing the tabular grains of silver bromoiodide is placed to receive the exposure radiation before the other emulsion layers of the product. 32.- Product according to claim 30, characterized in that one of the emulsion layers containing the tabular grains of silver bromoiodide is placed to receive light transmitted without diffusion, and located above at minus another emulsion layer of the photographic product. 33.- Product according to any one of claims 30 to 32, characterized in that the tabular grains of silver bromoiodide have a mean diameter  <EMI ID = 176.1> 34.- Product according to claim 30, characterized in that the recording emulsion layer blue is formed from tabular grains of chemically and spectrally sensitized silver bromoiodide as defined in any one of claims 1 and 3 to 25. 35.- Product according to any one of claims 30 to 34, characterized in that the tabular grains of silver bromoiodide are chemically sensitized at the surface with a gold sensitizer and at least one sulfur or selenium sensitizer. 36.- Product according to any one of claims 30 to 35, characterized in that at least one of the emulsion layers containing the tabular grains of silver bromoiodide is placed to receive, during the exposure of the product to a color temperature of 5500 * K, .blue light in addition to the light that the layer is intended to record, a log E for this emulsion layer being less than 0.6, where  <EMI ID = 177.1> log AND being the logarithm of the exposure to 'red or green light that this layer is intended to record, and log EB being the logarithm of the exposure to the blue light that this same emulsion layer receives at the same time. 37.- Product according to claim 36, characterized in that the -product contains an amount of yellow filter less than the usual amount or is free of yellow filter substance, between the radiation of incident exposure and at least one of the layers d emulsion containing tabular grains. 38.- Product according to claims 36 or 37, characterized in that at least one of the layers containing the tabular grains is placed to receive the exposure radiation before the emulsion layer recording the blue. 39.- Product according to claims 36 or 37, characterized in that one of the layers containing the tabular grains is placed to receive the exposure radiation before all the other layers of silver halide emulsions of the photographic product. 40.- Product according to any one of claims 30 to 39, characterized in that the silver bromoiodide tabular grains are present in the emulsion layer recording the green and / or the emulsion layer recording the red. 41.- Product according to any one of claims 30 to 40, formed of a support and elements of dye-forming layers separately recording blue, green and red, characterized by the following points: the elements of layers are chosen so that after exposure to color temperature  <EMI ID = 178.1> not selective, and treatment, they present, compared to their contrast and their speed in the blue, variations of contrast in the green and in the red less than 20%, and variations of speed in the green and in the red less than 0.3 log E, these variations in contrast and speed being determined by measuring the blue, green and red densities in accordance with the American standard PH2.1.1952, each of the elements comprises at least one emulsion layer formed of a dispersing medium and of silver bromoiodide grains, the silver bromoiodide grains from a set of three emulsion layers recording blue, green and red separately, are placed to receive exposure radiation before any other emulsion layer, and have an average diameter of at least 0.7, µm, the tabular grains of silver bromoiodide in the emulsion layers registering the green and the red of said set of three emulsions, have two opposite parallel main faces, with, lying between the main faces, a central region comprising less of 3 mol% of iodide and a peripheral region containing at least 6 mol% of iodide have a thickness of  <EMI ID = 179.1> ce of average shape of at least 12: 1, represent at least 70% of the total projected surface of the silver bromoiodide grains present in the same emulsion layer, and are chemically sensitized on the surface with gold and at least one sulfur or selenium sensitizer, the product is practically free of a yellow filter substance between the incident exposure radiation and the emulsion layers recording the green and red of the set of three layers. 42.- Product according to claim 41, characterized in that the dye-forming elements recording the green and the red of a set of three elements have a speed in the blue minus greater than at least ten times their speed in the blue . 43.- Product according to claim 41, characterized in that the elements of dye-forming layers recording the green and the red of a set of three elements have a speed in the blue minus at least twenty times greater than their speed in blue. 44.- Product according to claim 41, characterized in that the speed in the blue of the recording of the blue provided by the product, is at least six times greater than the speed in the blue of the recording of the blue minus provided by product. 45.- Product according to one of claims 41 or 42, characterized in that the speed in the blue of the recording of the blue provided by the product, is at least ten times greater than the speed in the blue of the recording of the blue minus provided by the product. 46.- Product according to one of claims 41 to 45, characterized in that the dye-forming layer elements recording the blue, green and red separately contain couplers forming dyes, yellow, magenta and blue respectively = vert_ 47.- Product according to one of claims 41 to 46, characterized in that the emulsion layer recording blue of a set of three elements contains a higher mole percentage of iodide than the emulsion layers recording green and red of a set of three elements. 48.- Product according to one of claims 36 to 47, formed of a support and elements of dye-forming layers recording blue, green and red separately, containing dye-formers respectively yellow, magenta and blue-green, and containing at least one layer d silver halide emulsion, characterized by the following: the elements are chosen so that after exposure of the product to a color temperature of 5500 [deg.] K through a spectrally non-selective and treated density scale, they present, in relation to their contrast and their rapidity in blue, variations in contrast in green and in red less than 20% and variations in speed in green and in red less than 0.3 log E, these variations in contrast and speed being determined by measuring the blue, green and red densities in accordance with American standard PH2.1.1952, a set of three emulsion layers recording blue, green and red separately is placed so as to receive the exposure radiation before any other emulsion layer, at least one of the emulsion layers recording the green and the red of said set is placed to receive the exposure radiation, transmitted practically without diffusion before at least one other emulsion layer, and to receive, during the exposure of the photographic product at a color temperature of 5500 [deg.] K, blue light in addition to the light that the layer is intended to record, Alog E for the said emulsion layer being less than 0.6, where  <EMI ID = 180.1> log AND being the logarithm of the exposure to red or green light that said emulsion layer is intended to record, and  <EMI ID = 181.1> the blue light which the said emulsion layer receives at the same time, and it contains silver bromoiodide grains having an average diameter of at least 1.0 µm, some of which are tabular silver bromoiodide grains that are chemically and spectrally sensitized, having opposite main parallel faces, with 1 between these main faces a central region containing less than 3 mole percent iodide and a peripheral region containing, at least 6 mole percent iodide, having a thickness of less than 0.3 µm, a  <EMI ID = 182.1> at least 12: 1, representing at least 70 percent of the total projected area of silver bromoiodide grains.