US1980941A - Color photography - Google Patents

Description

COLOR PHOTOGRAPHY Filed Nov. 12, 1927 /feJv Q Clear Gela/li? d y d. d

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a k a@ w@ d Patented Nov. 13, 1934 UNITED. STATES COLOR PHOTOGRAPHY Leopold D. Mannes and Leopold Godowsky, Jr.,

New York, N. Y.

Application November 12, 1927, Serial No. 232,735

4 Claims.

This application relates to improvements in color photography and has for its ultimate object the photographic reproduction in color of pictures of good definition and of substantially ac- 5 curate color'values, without the complication of l registering a plurality of separate iilms or pro- .ducing a plurality of separate images in a multilayer film.

A particular advantage of our improved process is that it does not require any unusual exactitude of formulae or time of exposure, or any treatment of exceptional delicacy, and color photographs of uniformly good quality may be produced if the work is carried out with no more care and attention than required for producing good black and white pictures.

Prior to the development of the process described in our prior Patent No. 1,516,824, granted November 25, 1924, photographic reproductions in color had been produced by superimposing separate pictures representing the different color values in the object photographed, the separate pictures being colored 'tp correspond with the color values for which they were sensitized. If the individual pictures are not taken by a single exposure through the same lens they are not capable of exact registry, and if produced at a single exposure the subsequent separation for individualcoloring requires such great care in execution as not to be capable of use on a commercial scale because of the prohibitive cost of carrying out the process.

Prior to our patented process it had also been proposed to use film having two separate emul-l sions on its opposite faces to produce the separate images representing the different color values in the object photographed, but this process is faulty in that gooddenition cannot be obtained and also involves such difliculty in its l0 execution as to preclude its commercial use-on any extended scale.

Qur patented pro'cess is an improvement upon the'above described processes in that the separate'images representing the different color L5 values in the scene are all recorded in a single emulsion on one side of the -film or other support, the emulsion being in layers differently sensitized to record the different color sensations. This process, however, as will be apparent from 0 our patent, involves careful vexecution both in the preparation of the film Iand in the developing and coloring of the images, and whereas pictures of good definition and substantially accurate color values are produced by this method, 5 the cost of carrying out the process is considera alllyt's greater than producing pictures in black and I Our present invention involves the use o1' a novel form of film wherein separate images corresponding to the separate color values in the scene photographed are produced in a single lay-` er of emulsion. It also involves novel steps in the process of treatment, and the resulting pictures have novel and unique characteristics, all of which novel features will be hereinafter more fully described and claimed. x

In carrying out our present invention we employ a photographic iilm or plate having an emulsion on one surface thereof composed of two or more dilerent emulsions each sensitized to record a particular color value, mixed together and spread in a uniform homogeneous layer on the lm or plate. The picture is taken at a single y exposure and the :tilm is then so treated as to produce a colored, positive picture wherein the image is made up of differently colored particles uniformly distributed throughout the whole emulsion, whereby the pictures viewed by either transmitted or reflected light present the appearance of a single picture with its different portions colored in various colors made up by combining the two or more basic colors, as the case may be, in varying proportions representing the originalv colors in the scene photographed.

Our improved process is particularly applicable to the now widely used amateur motion picture processes wherein the iilm originally exposed in the camera is-developed into a positive for use in the projector. In the practice of our process the film is exposed in the camera in exactly the 4saine manner as an ordinary lm and when processed according to our present invention, produces a positive film in substantially natural colors adapted for projection in an ordinary projecting machine without the use of color filters, gratings, prisms, or other adjuncts diilicult of operation.

Our improved process is nevertheless adaptable for the reproduction of duplicates in the form of films for projection and also paper prints. This is accomplished by printing or projecting through the originally exposed developed and colored film upon .a illm or other support carrying a similar emulsion, and thereafter developing and coloring the print in substantially the same manner employed in developing and coloring the originally exposed iilm.

In the accompanying drawing we have diagrammatically illustrated the successive changes which take place in the emulsion on the iilm as the successive steps y'oil our process (as a two- --color process) are carriedout from the exposure ofthe film to the completed picture, the process, however, being adapted to three-color work by slight modification as fully explained in the following speciflcation.

Fig. 1 is a diagrammatic view showing a multicolor object to be photographed;-

Fig. 2 illustrates diagrammatically a section of the film before exposure according to the key which appears in the drawing above Fig. 1;

Fig. 3 is a similar view illustrating the nlm after exposure in photographing the object shown in Fig. 1;

Figs. 4-8 inclusive indicate diagrammatically in accordance with the key the successive steps followed in the process of producing the picture; and

Fig. 9 is a similar diagrammatic view illustrating the completed picture.

In said drawing, the small circles are supposed to represent separate particles of the emulsion on the film which have been separately sensitized to record different color values, and the nature of such particles at the particular state in the process, that is, whether unexposed, exposed, developed, xed, colored, etc., is indicated by the shading of the particle according to the -key which also appears on the drawing, the 30 drawing beingl self-explanatory as far asvpossible. f

As stated above, our improved process may be carried out with the photographic emulsion applied to film, glass, paper or other support. Thisemulsion for two-color work, which is the specific process described in the present application, consists of the usual single homogeneous layer of gelatin through which are uniformly distributed the grains of silver halide which may be of any desired speed within the usual commercial ranges. To all external appearances the emulsion is the same as an ordinary photographic emulsion for producing black and white pictures, and in fact our emulsion may be used for ordinary black and white pictures if the usual developing process be followed instead of the color process herein described.

Our improved emulsion differs from the ordinary photographic emulsion only in that it is composed oftwo batches, one of which has been sensitized to one of the two colors which are to be used to color the resulting picture, while the other batch has been similarly sensitized to the other color. In accordance with the particular process herein described, the emulsion to be used is divided into two substantially equal parts, and

one of the `parts is made sensitive to orange-red light 'by the application of some such dye-sensitizer aspinacyanol or napthacyanol, and the other part is sensitized to green light by the use of a dye-sensitizer such as pinailavol. After the emulsion is sensitized by the addition of the dye, excess dye is removed by washing, so that the 65', emulsions when mixed will allow each separate silver halide grain to retain its own color sensitivity unimpaired by contact or juxtaposition with a grain which has been sensitized to the opposite color. p

After each of the two parts of the batch has been separately color-sensitized and washed as, described, they are mixed together and stirred sufficiently to insure aI uniform mixture of the two separate parts throughout the batch and then spread on the film or other support in a layer Silver nitrate which need be no thicker than the ordinary emulsion layer for black and white work.

The emulsion may be prepared as above described with no further treatment, but in order to get effective color separation with the emulsion just described it is desirable that the exposure be made through a yellow filter in order to remove most of the blue-violet rays, for the reason that the dye sensitizers which make the mixed particles of the two batches of emulsion sensitive to orange-red and blue-green, respectively, do not equally affect the normal sensitization of the silver salt to the blue-violet rays. By employing a yellow filter effective color separation can be obtained,l but the resulting picture is not in all respects a faithful reproduction' of the natural colors because of the loss of the blueviolet component. To avoid the use of the yellow filter and the resulting loss of the blue-violet f rays we preferably desensitize for the blue-violet rays the batch of emulsion which has been redsensitized before mixing with the other batch.

This desensitizing step is preferably carried out by soaking the emulsion at about 20 C. for ten minutes in a solution consisting of Indian yellow in water, to which some silver nitrate is added,

the ingredients being in the following proportions:

Distilled water l 10 ounces Indian yellow 100 grains 2 grains After soaking as described, the emulsion is washed halide grains in the emulsion and thereby produce A a more complete desensitization than' can be otherwise obtained* *Indian yellow is a natural pigment obtained from India and sold under that name. Its chemical c0nstitu tion is generally understood to be principally a mixture of the euxanthates of calcium and magnesium. What other ingredients or impurities it contains are not definitely established, nor is it known whether the desensitizlng effect is. due to the above-mentioned substances or to other ingredients.

y To maintain equality of the photo-chemical characteristics of the red-sensitized portion of the emulsion andthe green-sensitized portion it is preferable to similarly treat the green-sensitized part with a solution of silver 'nitrate and water, but this step is of course not necessary and the balance may obviously be obtained by other expedients. 1

1 The plate or film coated with the emulsion thus described is exposed in an ordinary camera'for an interval depending upon the speed of the silver salt forming the emulsion, the treatment above described adding but little to the time of exposure that an untreated emulsion of the same original speed would require.

In the example depicted in the drawing we have assumed that the object photographed consists of a color card having four areas, namely, white,

orange-red, blue-green and black, as shown in y Fig. 1. The entire surface of the film is covered with a uniform layer of emulsion made up of particles, half of ywhich are red-sensitized and half 0f which areblue-green sensitized, and in 15g Throughout the several views of the drawing the red-sensitized particle is vrepresented by the upper circles and the green-sensitized particle by the lower circles. These particles are indicated in Fig. 2 as unexposed by the dotted line shading. as indicated in the key.

Fig. 3 shows the nlm after exposure. In the portion of the nlm where the image of the white end of the color card forming the subject will appear, the particles of both the green-sensitized and the red-sensitized emulsion will be exposed (i. e. anected by the light) as the white light contains both elements. In the portion of the nlm where the image of the orange-red area of the card will appear the orange-red sensitized particles will be exposed while the blue-green sensitized particles will not be exposed. In the portion of the nlm where the blue-green image will appear the blue-green particles will be exposed, thereby forming a latent image, while the other particles will be'substantially unaffected. In the portion of the film corresponding to the black section of the color card the particles of neither group will be affected. The exposed particles are indicated by the light horizontal shading.

The next step in the process is to develop the nlm. Any suitable developer may be used for this purpose, preferably a soft working" developer, to give detail and harmonious color rendering.

It is also desirable that a developer be selected which produces a minimum of relief effect in the gelatin. To this end caustic alkalies should not be used. Sodium carbonate is preferable as an alkali, and as little as possible should be used. Metol and glycin are suitable as developing agents, as are also acid amidol developers. As will be later explained, it is essential that development at this stage be carried out completely, that is, that none of the latent images be left undeveloped. I

In the following description, for the sake of brevity we will refer to the four sections of the nlm upon which the sections of the color card will be depicted, as the white, red, green and black sections, respectively. Fig. 4 shows the results of the developing step. In the white section of the nlm both the green-sensitive and red-sensitive particles have been developed into a silver image. In the red section a silver image has been produced in the red-sensitive particles only. The

other particles remain in their original condition. In the portion of the nlm corresponding to the green section .of the 'color card the silver image is composed of the green-sensitive particles only,

the other particles remaining red-sensitive asA before. In the black section of the nlm the particles of lboth groups remain of course unaffected. e y

The next step in the process is to expose the developed nlm to a uniform red light. By this step all of the red-sensitive particles not exposed and developed out in the original exposure and nrst development are exposed. The result of this step is illustrated in Fig. 5. As here shown, the white section remains unchanged, and the orangered section remains unchanged, the red light having no effect on either the developed silver image or the green-sensitive particles which are still iny their original condition. In the portion of the nlm corresponding to the blue-green section of the color card the particles forming the silver image remain unaifected by the exposure,

but the previously'unan'ectedfred-sensitive grains are converted into a latent image. Also, in the black section of the nlm the red-sensitive grains are converted into a latent image.

Afterexposure to red light, as above described, the nlm is treated with a color-forming developer, that is, one which forms a colored insoluble pre- 'cipitate in the gelatin in situ with the silver image simultaneously formed. A color-forming developer Aproducing a blue-green color is employed. A suitable agent is dimethyl-paraphenylene-diamine-hydrochloride with alpha-naphthol, or indoxyl, or paraphenylene-diaminedrochloride with trichlornaphthol. After this development the emulsion is well washed.

The en'ect of this step is to develop and simultaneously color blue-green the latent images formed in the blue-green and black sections of the nlm by the exposure to red light as above described. Fig. 6 shows the condition of the nlm after this step. In the white section both the orange-red sensitivev and blue-green sensitive emulsions contain metallic silver images. In the orange-red section the orange-red sensitive particles have been converted into a silver image, while the blue-green sensitive particles remain unexposed. In the blue-green section of the nlm the orange-red sensitive particles have been converted into a silver image and also colored bluegreen while the blue-green sensitive particles -constitute a developed but uncolored silver imnlm to white or blue-green light to thereby form latent images in the remaining unexposed particles, namely the blue-green sensitive particles in the sections of the nlm in which the orangered and black portions respectively of the color card are depicted. The result of this step is illustrated in Fig. 7.

The nlm is then developed with an orange-.red color forming developer, such as thio-indoxyl, or paranitrobenzylcyanide with dimethyl-paraphenylene-diamine. The nlm is then well washed to remove the excess. Fig. 8 indicates the condition of the nlm at this stage. Both emulsions throughout now contain metallic silver images. In addition the blue-green sensitive emulsion in the orange-red section contains an orange-red image; the orange-red sensitive emulsion in the blue-green section contains a blue-green image, and in the black section both emulsions contain color images corresponding to the `color for which the other emulsion was originally sensitized.

The nnal step in the process is to .dissolve out all the silver images. Any suitable solvent such as potassium ferri-cyanide with hypo may be used for this purpose. Fig. 9 shows the result of this step. The white section of the nlm is transparent. The orange-red section contains a positive orange-red dye image formed in the normally blue-green sensitive portion vof the emulsion. Similarly the blue-green section contains a positive blue-green dye image, While the black section contains both an orange-red and a blue-green image and is therefore opaque.

The resulting picture is a true positive of the object photographed in natural colors so far as such colors can be reproduced by any two-color process. Let* us consider the orange-red section of the color cardvas not strictly orange-red but of a shade predominantly orange-red and slightly blue-green. On exposure and development bothemulsions will contain silverimages but the image in the blue-green sensitive emulsion will be of an intensity corresponding to the proportion of blue-green in the color on the color card. Likewise the extent to which the :blue-green sensitive emulsion is unexposed corresponds to the proportion of orange-red color in the color on the card. Hence when this portion of the emulsion is completely exposed by exposure to white light (Fig. 7) and subsequently developed with the orange-red color forming developer the resultant orange-red image will be of an intensity corresponding with the conversion effected by the second exposure only. In other words the images which are reproduced in'color are not the images produced by the original exposure, but the images produced by the subsequent exposures to red light and white. These images are in intensity the complements of the objects in .the scene photo#- graphed and must thereforebe colored respectively with the opposite color.

The above described process is also applicable to three-color work by utilizing an emulsion made up of three batches instead of two, the particles of each batch being sensitized to record one of the three colors. For example, one batch may be made red-sensitive by using a dye-sensitizer such as pinacyanol, the second batch may be, rendered green-sensitive by the use of a dye-sensitizer such as erythrosin and the third batch rendered bluesensitive by means of a dye-sensitizer such as auramine.

In carrying out this three-color process the above described procedure is followed through the step of exposure to red light illustrated in Fig. 5. After this exposure the film is subjected to the action of a color-forming developer such as trichlornaphthol with dimethyl-paraphenylenediamine, which provides a green color suitable for the green component of a three-color picture. The lm is then exposed to green light and after 'exposure is developed with a red color-forming developer such asthio-indoxyl. 'After this step the film is again exposed, this time to a bluewhite light to convert the blue-sensitive particles which still remain unaffected by the previous exposures to red and green light, respectively. The image thus produced is developed with a color-forming developer consisting, for example, of alpha-chlorethylacetoacetate with diethyl-v paraphenylene diamine, which produces a suitable yellow for the third component.

After this step the silver is dissolved out in the same manner as above described, producing a transparent colored positive similar to. the picture produced by the two-color process but with g the more faithful reproduction of the colors in the scene photographed which results from using three colors.

v Instead of using color-forming developers as above described, the steps of developing and coloring may be separately performed. In the process as so modied the steps as illustrated in Figs. 2 to 5 inclusive will be carried out as above described, but instead of immediately developing the images produced by the red light exposure, the developed silver Aimages formed by the first development are completely-dissolved out. Any well known formula may be used for this purpose, such as potassium bichromate and sulphuric acid or cuprr. chloride andA ammonia. This step does 3 not destroythe. still unexposed green sensitive.

particles nor the undeveloped but exposed redsensitive particles.' This treatment does, however, destroy the' color sensitivity of the undeveloped particles, that is to say, it reduces the emulsion back to normal silver haloid grains sensitive to white light. After this step no image will be visible in "the emulsion. The particles forming the silver image will be transparent and the remaining particles will correspond with the ordinary exposed but undeveloped film. Before proceeding with theprocess lthe "bleaching solution used for dissolving out the silver must be thoroughly washed out. l

The next step in the process is to'again subject the illm to .the action vof development. 'I'he exposed particles in the section of film correspending to the blue-green portion of the color card and the black. portion .are converted into a silver image. The-other particles remain unchanged. Particles of both kinds exposed to the white light reflected from the white section of the color card are transparent. In the orangeremaining particles-remain unexposed, but their sensitivity to green' light has been destroyed. In the green section of the film the red-sensitive particles formY a silver image .and the original. green-sensitive particles have been dissolved out. In the black section the red-,sensitive particles form a silver image and the green-sensitive particles remain unexposed, but .no longer greensensitive.

'I'he next step in the process, lis to subject the fllm to a blue-green toningv bath to thereby tone the silver images o f the second development step to a blue-green color. Any of the well known iron toning formul may be used for this purpose, for example, the silver image may be bleached with potassium ferri-cyanide and thereafter toned with a solution of ferrous chloride.

The particles thus affected are4 the original red-sensitive particles in the portion-of the lm corresponding to the blue-green and black sections of the color card.

After this toning step the lm is thoroughly washed to remove any surplus of the toning solution. 'I'he filmV is then exposed to a white light, to thereby produce latent images in the remaining light-sensitive particles, that is, the original green-sensitive particles in the portions of the fllm which depict the orange-red color sensation in the scene photographed and the original greensensitive particles vin those portions of the lm corresponding to the black sections of the color card or other. subject photographed.

'Ihe illm is then subjected to the action of 'the developer to develop the latent images formed by this exposure. For this purpose a non-alkaline developer must be ,used such, for example, as diamidophenol, generally known as amidol. The use of an alkali developer for this development would permanently destroy the blue-green image produced by the toning bath. The amidol developer temporarily bleaches this image, but by thoroughly washing the film after the development is complete, the color is restored. y

The final step of the processconsists in tonn the silver image produced by the last development step to the desiredorange-red color. Any well known solution may be used for this purpose, such, for example, as uranium ferrocyan" nide, or the image may be colored with a basic.` aniline-dye in conjunction .with a mordant such.

as copper ferro-cyanide, etc. After this step the nlm is thoroughly washed and then dried to form a positive transparent picture of the scene photographed with the color values in the scene reproduced as accurately as possible with two colors only.

This modified process involves more steps than the rst described process. ferred process differences of' image texture and internal contrasts are minimized. On the other hand the colors produced by color-forming developers are regarded by some as not so nearly complementary as colors which may be obtained with metallic toning solutions or dyes such as may be used in the last described process.

The film produced as above described may itself be used with a projector and the process is thus particularly adapted for so-called amateur motion pictures Where reproductions of the film are not usually required. 'Ihe colored positive may, however, be used in making reproductions by means of ordinary printing methods using white light, in the usual manner and printing on a lm of substantially the identical character as the lm used for the original picture, and thereafter subjecting it to the identical process above described.

It will of course be understood that the invention is not limited to the use of the particular color sensitizing solutions, developers, colorformers or toning solutions specified above. These may obviously be widely varied. The entire nlm is saturated with the developer or other solution used, the particles which are not to be affected by the particular solution being in a virtually insoluble dye in situ the silver of both negative and positive images being removed as the final step.

2. The method of producing a direct positive photograph which comprises exposing a sensi-l tive emulsion layer to a light image, developing said layer in an ordinary photographic developer Without fixing it, reversing the developed image by exposure to light, developing in a color-forming developer, and finally removing the silver from negative and positive images.

3. In a photographic reversal process, the step of developing the reversed image in a colorforming developer.

4, In a photographic reversal process comprising exposure to an image, development in an ordinary photographic developer, vre-exposure to light, and` re-development, the step of developing the reversed image in a color-forming developer.

LEOPOLD D. MANNES. LEOPOLD GODOWSKY, JR.

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