FR2560398A2 - Anaglyph assembly - Google Patents

Abstract

The anaglyph assembly consists on the one hand of a pair of anaglyphic images, left and right in two colours, and, on the other, of anaglyphic spectacles whose "right" and "left" eyepieces form a pair of optical filters of two colours appropriate to those of the images. One of the filtering eyepieces is formed by a "dichroic" interference filter and other is formed by a transparent chemically coloured medium such as a so-called "gelatin" piece.

Description

ENSFMBLE AMAGL YPHE
An anaglyph unit has been described in the main patent implementing principles different from those known hitherto which are essentially based on the conventional trichromy.
However, this has drawbacks which were mentioned in the main patent and among which is the presence of "ghosts" when observing, with ad hoc eye filters, tereoscopic images printed with cyan ink
The main patent describes means which, notannent, pern'ette: it to remedy this drawback.

It should be remembered that the imperfection of the known technique leads to adopting for printing images a cyan ink as pale as possible in the hope of reducing the effect of these "ghost" images.
This effect is mainly due to the properties of cyan inks which, instead of completely absorbing red and totally reflecting blue and green as they should theoretically do, reflect a little red and absorb a little blue and even more of green.

The eye looking at this image printed in cyan ink through a cyan filter sees this gray ink (gray-cyan) by the presence of red, by lack of green and also by lack of blue. While he sees the white background of the paper in cyan because this cyan filter absorbs the red reflected by the paper (white - red = cyan) but this cyan is perceived more clearly because the white paper reflects better than the cyan ink blue and even more virtue D1ou, by contrast, the perception of a gray-cyan "ghost" of the image that the eye fitted with the cyan filter should not see, which image stands out against the lighter background
We have already tried to improve these effects, but without contradicting the theory of classical trichromy.

 Thus, the document WO-A-80O1209 is known, the object of which is to hold better visual comfort, while sufficiently respecting the conventional trichromy, when constituting anaglyphic oculers.

To obtain this result, a low transmission of the complementary spectral region is tolerated for each of the eyepieces implementing the tricnromy. For example, (Figure 10) the cyan eyepiece 102 transmits a little red (in the order of 10X) and the red eyepiece 103 transmits a little green, the color contained in cyan. Likewise
(Figure flf, the green eyepiece 104 transmits a little blue and a little red, and the magenta eyepiece 106 transmits substantially lO of green.

 These spectral modifications being made in the framework of the three-color process, the admissible proportion of tolerable complementary light is necessarily very low: 5% to 15% (page 4, lines 22, 23) and practice shows that one cannot validly go above 10%.

 The object of the present invention is, quite differently, to obtain the perception of the relief by combinations of spectral intervals different from those of the conventional three-color process.

 The proportion of light fixed for one of the eyepieces in a spectral region prohibited in conventional three-color is then on the contrary imposed by considerations foreign to this conventional three-color. Therefore, the determination of the proportions of light according to the principle of the invention leads to setting values generally of the order of 20 to 25% and in any case greater than 15X. According to certain variants, this proportion of light deemed incompatible with classic tri-color can be up to 100%. The latter case amounts to shifting the spectral limits imposed on the filters by the conventional three-color process.

 We also know the document US-A-4,134,644 which describes an anaglyph set situated within the framework of the conventional three-color process and using complementary ocular filters, in this case a green filter and a red-blue filter (magenta ).

 The essential originality consists in splitting the classic green filter into two filters and A '(figure 2), the first green-blue whose maximum transmission is located at 515 gauges and the second green-yellow whose maximum transmission is located at 540 nanometers. It is thus expected that the interocular opposition and the perception of "ghosts" would be eliminated.

 But this only improves the implementation of additional filters in accordance with what is required by the conventional three-color process.

 However, a spectral overlap is also used between the eye filter B and one of the green filters, A (figure 2) but the transmission in the common part (A and B), in figure 2 is between 0 and 10% .

 Between A'and B there is also an overlap with a transmission of between 0 and 5% approximately. This transmission could not be greater in the context of three-color printing.

 On the contrary, as has already been clarified in the main patent, the present invention transgresses this limitation because it is deliberately outside the principle of conventional three-color printing.

 In addition, this addendum brings improvements to the provisions of the main patent.

 To this end, the invention of the present additive relates to an anaglyph assembly according to claim 1 of the main patent, characterized in that one of the filtering eyepieces is constituted by an interference filter called "dichroic" and the other by a chemically colored transparent support, such as a piece called "gelatin".

According to other features of the invention
- the filtering eyepiece consisting of a chemically colored transparent support is red, the other filtering eyepiece being constituted by a dichroic filter of appropriate color.

 - the eyepiece filters perform a hexachromy, the extent of the visible spectrum being divided into six regions, substantially from 400 to 450 nanometers, from 450 to 500 nanometers, from 500 to 550 nanometers, from 550 to 600 nanometers, from 600 to 650 nanometers, from 650 to 700 nanometers, one of the filters transmitting only from 400 to 450 nanometers, from 500 to 550 nanometers and from 600 to 650 nanometers, the other filter transmitting only from 450 to 500 nanometers, from 550 to 600 nanometers and from 650 to 700 nanometers, and the inks and pigments intended for printing stereoscopic images being suitable according to substantially the same hexachromic spectral sharing.

 - the images forming a stereoscopic pair are obtained by printing dots of appropriate additive primary colors which do not overlap each other when they do not belong to the same stereoscopic image, the shadows and the shades tapered being obtained by an additional printing in black strictly limited to the common parts of the two stereoscopic images.

 - At least one of the superimposed images forming a stereoscopic pair is printed using fluorescent ink (s).

 - one of the stereoscopic images being printed in cyan and Other in red, the negative image of 11 cyan image is printed either in light red or in light magenta whose density has a maximum value of approximately 25%.

 The subject of the invention is also a method for printing two anaglyphic images according to claim 1 of the main patent with an optimal offset, characterized in that to determine this offset, one of these two images is first applied on a first support, then we apply the second image on a second transparent support, then we place the second support on the first, then we observe all of these two supports by means of appropriate anaglyphic eyepieces and we move the supports one with respect to the other until obtaining an offset that is deemed optimal, then a definitive location of the position of the second image relative to the first is carried out, then then this second is applied image on the first support, then we finally proceed to photogravure and printing of known type.

 The invention also relates to a method for obtaining two anaglyphic images its claim% of the main patent in the case where at least one of the colors has a rattan component whose spectral range is incompatible with three colors , characterized in that stereoscopic shots are taken either in black and white through preferably dichrolic filters ensuring the desired spectral selection, or in color according to the Lippmann interference method with said dichroic filters.

then 3 from the images thus selected. we carry out all appropriate operations such as projection, photcgravore and printing.

The invention will be better understood from the detailed description below made with reference to the accompanying drawing. Of course, the description and the drawing are only given by way of indicative example and not imitative. On the drawing:
Figures to to 17 show the theoretical spectral curves of examples of pairs of filters according to the invention.

 FIGS. 18 to 23 show the theoretical spectral curves of pairs of filters in accordance with the invention which are particularly suitable for remedying the most common defects of cvon dyes used in printing.

 FIG. 24 represents the spectral curve of a gelatin filter in accordance with the invention remarkable for its effectiveness in suppressing the "ghosts" originating from the cyan dyes.

 FIG. 25 represents the spectral curve of a filter analogous to the previous one but of the so-called “dichroïgue” interference type.

 FIG. 26 represents the spectral curve of a cyan type filter, the upper transmission limit of which is shifted towards shorter wavelengths than those of conventional cyan filters.

 FIG. 27 represents the spectral curve of a filter combining the characteristics of the curves represented in FIGS. 25 and 26.

 FIG. 28 represents the spectral curve of a filter which can advantageously be coupled to the filter of FIGS. 24 to 27.

 FIG. 29 represents the spectral curve of a filter derived from the previous one and having remarkable transparency up to approximately 600 nanometers.

FIG. 30 shows a couple of films which implements a division of the visible spectrum into six parts thus constituting a hexachromy
FIG. 31 represents a variant of the pair of filters in FIG. 30.

FIGS. Ra 17 represent examples of pairs of anaglyphic eyepieces according to the invention and which supplement the examples of the main patent. Their own characteristics are evident and explicit in the figures where the transmissions of each of the filters are clearly indicated.
In FIGS. 18 to 23, couples of filters are represented which respond to the problem, already mentioned, posed by the usual defects of the cyan dyes commonly used to constitute one of the anaglyphic images. One of these defects consists in that the cyan dyes absorb a little blue radiation between 400 and 4o nanometers, and more green radiation between 510 and 570 manometers approximately, hence the perception of a gray-cyan "ghost" through a cyan type eyepiece, wedme it has been said more high.

 To remedy this drawback, the invention provides, according to a variant, to deliberately weaken the transmission of radiation between 400 and 460 nm approximately and / or between 510 and 570 nm, for the cyan type filter constituting one of the eye filters.

 According to another variant, the invention remedies this drawback and eliminates the perception of ghosts by providing for compensating the contrast between the ghost and its environment by lowering the luminance of the latter.

 In other words, the negative image of the image printed in cyan is overprinted in light red or light magenta. The maximum density of this light red or this light magenta is at most around 25X for a cyan ghost itself of maximum density and is proportionate in the other cases.

 As. as we know, we use three "typons", that is to say three raster positives, to print in cyan, magenta and yellow respectively. We can therefore achieve the overprint by incorporating an additional screening in the magenta print.

 Furthermore, in accordance with the present invention, the limits between these spectral regions do not systematically coincide with those of the three-color process. This is how we must understand the diagrams represented in FIGS. 18 to 23, where the limits between the spectral regions can be moved according to any combination borrowed from the variants represented in FIGS. 9 to 84 of the main patent and 1 to 17 of this addendum.

 FIGS. 18 to 23 represent the thermal diagrams of pairs of eyepieces of which the cyan type filter exhibits a marked weakening of the transmission coefficients in the regions from 400 to 480 nm and / or from 510 to nm. fln.

 FIG. 24 represents the transmission curve of an eye filter according to the invention, in: chemically colored "gelatin", this filter being intended to be coupled with a filter of primary red type. The curve has a peak at around 500 nrn, corresponding to a maximum of the transmission coefficient, of a value of 0.6.

 On the longer wavelength side, the transmission coefficient T decreases by around 520 nin until it vanishes around 580; 590 nm whereas for a conventional cyan type filter, it would only decrease from around 570 nm On the side of the shorter wavelengths, while for a conventional cyan type filter we would maintain the transmission at high values up to 400 nm (dotted curve), for the present filter according to the invention, the value of the transmission coefficient is deliberately weakened. Here, this weakening is progressive from the maximum value 0.6 for 500 nm to a value close to zero for 400 nm, thus absorbing a lot of blue.

 The advantage of characterizing the transmission curve of this filter in this way is that it almost eliminates the "ghosts", as much thanks to the weakening in the blue as the weakening in the green, according to what has been explained above.

 FIG. 25 represents the transmission curve of a dichroic eye filter, that is to say an interference filter produced by means of thin layers. The transmission coefficient T is maintained at a high maximum (0.9) of approximately 500 Mi up to approximately 560 to 580 nm, the coefficient 0.5 corresponding to approximately 570 to 590 nm. On the shorter wavelength side, the value of the transmission coefficient is deliberately lowered progressively to a very low value at 400 nm. The suppression of cyan ghosts is here obtained by the weakening in blue.

 The advantage of such a filter compared to the previous one is its great transparency in the wavelengths which it is desired to transmit, hence great visual comfort. In addition, extending the maximum transmission to longer wavelengths not only increases visual comfort, but also has the advantage of much better color perception in the case of polychrome anaglyphs.

 FIG. 26 represents a variant for which the transmission curve of the filter, for example dichrofque is maintained at maximum up to 400 nm, but goes down again from 520 to 560 nm on the side of the longer wavelengths, the transmission of a coefficient 0.5 lying at about 530 to 570 nm. Three curves are indicated for this descending part. Another variant is shown in dotted lines, in which the transmission curve goes down between 450 and 400 nm.

The desired effect is produced by a weakening in the green and, in the very last variant, by a slight weakening in the blue.

 FIG. 27 represents a variant for which the transmission curve has a maximum of approximately 470 to 530 nm. The transmission coefficients are deliberately weakened in both blue and green, which corresponds to the case of many cyan inks. The choice between these variants must be made experimentally according to the particular characteristics of the inks used.

the fionre 28 represents the transmission curve of an ocular filter intended to be cauplé with that represented in one of the figures 24, 25, 26, 27. It is a filter of the type known as primary red in the sense of the classic three-color process In this region of the spectrum, the filters in gelatin chemically colored or in glass or plastic tinted in the mass, exhibit transmission curves very close to those of the dichrolic filters. These gelatin filters are much less expensive than dichrofic filters. It is advantageous to couple according to the invention a dichrolic filter of the type shown in one of FIGS. 24, 25, 26s 27 with a gelatin filter of a type as shown in Figures 28 or 29 below commented. According to intention, two optimal transmission curves are shown in Figures 28 and 29
In FIG. 28, the maximum transmission coefficient (around 0.8) of approximately 700 nm to 640 nm has a value of 0.5 between approximately 610 and 620 nm, and a value of 0.10 for approximately 590 nm .

 In FIG. 29, the transmission coefficient, maximum (around 0.9) from 700 nm to 640 nm, and still being equal to 0.8 for 620 nm, has a value of 0.5 for approximately 600 na and a value of 0 , 10 for approximately 590 nm. This filter has great transparency in the region of primary red up to CO on approximately. It represents an optimal compromise between the rigor of the spectral selection required for the perception of the relief without annoying ghost (red, this times) and the desire for the greatest clarity of the perceived image and the best vision of colors in the case of polychrome anaglyphs.

 These red gelatins, generally very thin and fragile, can be mounted between two glasses. By coupling such an eyepiece with one of the eyepieces described with reference to FIGS. 24, 25, 26, 27, a pair of optimal anaglyphic glasses is produced.

 The names that appear above in parentheses are those that have been used conventionally since Newton.

 Jointly, the image intended for the left eye is produced in a color comprising, in its spectral composition, none of the wavelengths comprised respectively between 400 and 450 nm, 500 and 550 nm, 600 and 650 nm. The image intended for the right eye is produced in a color comprising, in its spectral composition, none of the wavelengths between 450 and 500 nm, 550 and 600 nm, 650 and 700 nm respectively.

These images therefore stand out. with left / right and right-left inversion, at the same flexachromy as that of the eye filters
In practice, these spectral limits are not strict, because one is obliged to take into account the constraints imposed by the characteristics of the dyes or of the treatments making it possible to produce the filters. It is noted that, respectively, each of the filters and the corresponding image are transparent for wavelength intervals belonging to spectral regions incompatible with the conventional three-color process.

 Indeed, according to the latter, one third of the visible spectrum is opposed to all of the other two thirds. While here, we find for the same eye filter components belonging to each of the three thirds. One eyepiece is transparent for three sixths of the spectrum and the other eyepiece for the other three sixths. This results in a rigorous balance between the two eyes thanks to the distribution of the visible spectrum into two equal parts each consisting of three sixths.

 We thus grant the sharing of the spectrum in three parts with the need to respect the binocular vision (3 X 2 = 6) to perceive the relief, which is called here the hexachromy. All the inconveniences resulting from the sharing of the spectrum between the two eyes at a rate of 1/3 - 2/3 disappear.

 FIG. 31 represents a pair of eyepieces of the same type as that shown in FIG. 1, but where the filters have a low transparency (from Ifordre from 10 to 15 X) for the wavelengths completely obscured in the example shown in FIG. 30. It is also possible to slightly shift the hexachromic spectral cutting limits while holding account of the light efficiency curves and of the considerations developed at the beginning of this description.

According to the present invention, an anaglyphic image is obtained in additive synthesis, by juxtaposing point by point the two right and left images, each of them being respectively filtered through complementary filters in the sense of the conventional three-color process.
(for example, in cyan and red) and printed using additive primary color inks (blue, green, red), so that these respective elements never overlap when they do not belong not to the same stereoscopic image Each of these images is thus made up of points, that is to say of separate elements contributing in large numbers to constitute an image at a distance.

A composite image is thus obtained presenting itself according to a pointillism which merges visually at a distance in an additive synthesis giving the perception of the relief and the colors.

It still remains to add to this composite image gray and black which cannot be obtained by an additive synthesis. It is imperative to add black only in the parts of the images seen simultaneously by the two eyes. If we added them in zones of shift to be seen by one or the other of the eyes exclusively, we would destroy the relief and we would introduce a gray ghost. In order to correctly carry out this addition, it is necessary first to obtain a black and white positive of the parts common to the left and right images. We first produce a monochrome anaglyphic image and we re-photograph it making sure that the ddcao lage fringes in cyan and red appear white in this photograph
Or, we go through a direct color print of a slide in paper positive, known as "Cibachrome". We then draw from the latter a artwork for printing in light black. The artwork intended for this black printing must be produced using a light screen.

 Such anaylyphic images are achievable in typography.

in offset or rotogravure, provided that great care is taken.

They can be made more easily for large format prints such as posters '' posters '' intended to be observed from a fairly large distance. In this case, the disjoint elements of the pointillist composite image can have fairly large dimensions, which simplifies the location.

 The polychrome anaglyphs by pointillist additive synthesis according to the invention are particularly well suited to the implementation of the previously described hexachromy. The selection of the left and right images having been operated for example respectively through appropriate filters, these images are printed in pointillism according to the same selection, one of the images for example having to be seen purple, green, orange, the other image to be seen blue, yellow, red, these colors corresponding to the spectral intervals from 400 to 450, 500 to 550, 600 to 650 nm, and from 450 to 500. 550 to 600, 650 to 700 nm. All this by small juxtaposed elements those intended for the right eye not encroaching on those intended for the left eye. The exact rendering of all the colors and the visual comfort obtained are very superior to those of all the other anaglyphic processes.

For the selection of the two left and right images, it is
free to use any known process for superimposing
additionally three filterings through band filters
bandwidths 400-450, 500-550, 600-650 nm for one of the images and at
through 450-500, 550-600, 650-700 nm bandwidth filters
for the other image.

 A correct hexachromy initially requires a selection of the colors of the subject which one wishes to reproduce according to the six spectral bandwidths characterizing hexadromy Or. The photographic emulsions in existing colors are trichromes and are therefore not able to make a selection with the inside each of the three-color bandwidths, as required by the hexachromy. In order to make this selection, the invention provides two main means by using existing photographic emulsions, to the exclusion of three-color emulsions.

 According to the first means, the subject is photographed directly in black and white in six shots obtained respectively through six dichroic filters each corresponding respectively to one of the six bandwidths of the hexachromy, then one proceeds to all projection operations, from photogravure, appropriate printing using the same filters.

according to the second means, we go through the intermediary of at least one photogr-.ple on an interference plate of the Lippmann type, then we proceed to the selection operations, after which we use the stereoscopic images obtained: projection, photogravure and printing etc. It is possible to take at least one photograph on an interference plate of the Lippmann type through the dichroic filters specific to the dubachromy. then proceed to all appropriate selection, projectlon, photogravure and printing operations, which avoids selection after shooting
The same requirement exists for correctly implementing the division of the visible spectrum into two equal parts for example and, in general, in all cases where the sharing of the spectrum does not correspond to the conventional three-color process. all these cases, it is impossible to make a correct selection using existing photographic emulsions which are trichromes. We then operate as it just said, taking as many black and white shots through as many dichroic liters as necessary the non-trichrome spectral sharing chosen

Anaglyphs, both monochrome and polychrome, are subject to a loss of luminance caused mainly by the colored filters through which we look at them. To remedy this drawback, the invention provides that the anaglyphic images are printed using inks or fluorescent or luminescent pigments as there are for other uses such as panels and tracksuits.
Linos to be seen better especially at night when they are lit. In this way, the reflectance is significantly increased and the color saturation improved. For example, pure and bright yellows are obtained.

One of the difficulties encountered when carrying out
anaglyphic impressions is that it is very difficult to determine the horizontal shift that should be given to the two
left and right images for optimal results. On this shift, zero for certain points homologous to the images and maximum for certain others, depend the more or less correct, more or less accentuated perception, of the relief, the visual comfort or on the contrary eyestrain.

 However, as long as iron has not obtained an anaglyphic impression, one cannot appreciate these various effects of the offset of the two superimposed images. In order to control the operations before the actual printing on paper, a printing simulation is generally used by means of powder dyes according to the process known under the name of "Cromalin". acts of anaglyphs. we are led to try a certain number of shifts before having a sufficient idea of the best shift to adopt. and again 4n is not sure that it is really the best.

 To overcome this difficulty, the invention provides for applying one of the two images to a first support and the other image to a second transparent support. Then, place the second transparent support, over the first in order to be able to observe the two images at the same time and, this, with eyepieces with appropriate anaglyphic filters. We then move the supports relative to each other, by example by sliding the transparent support on the first support kept fixed, so as to vary their relative positions until the operator considers having found the best offset, This depends on the subject and the taste of the operator .

or constraints imposed by external necessities. When the operator has made his choice, he makes a precise location of the relative positions of the two supports, using for this means well known to those skilled in the art. The second image is applied to the first support and a document is obtained from which the known photogravure and printing operations are carried out.

Claims (5)

CLAIMS j Anaglyph assembly according to claim 1 of the main patent, characterized in that one of the filtering eyepieces is constituted by n so-called "dichroic" interference filter and the other by a chemically colored transparent support, such as a so-called "part" gelatin  1- Anaglyph assembly according to claim 1, characterized in that the filtering eyepiece constituted by a transparent chemigupment colored support is of red color, the other filtering eyepiece being constituted by a dichroic filter of appropriate color.  3 Anaglyph assembly according to claim 1, characterized in that the filters of the eyepieces achieve a hexachromy, the extent of the visible spentre being divided into six regions, substantially from 400 to 450 nanometers, from 450 3,500 nonometers, from 500 to 560 nanometers . from 550 to 600 nanometers, from 600 to 650 nanometers, from 650 to 700 nanometers, one of the filters transmitting only from 400 to 450 nanometers. from 500 to 550 nanometers and from 600 to 650 nanometers, the other filter transmitting only from 450 to 500 nanometers, from 550 to 600 nanometers and from 650 to 700 nanometers, and the inks and pigments intended for printing stereoscopic images being appropriately according to substantially the same hexachromic spectral division.  4 Anaglyph assembly according to claim @, characterized in that the images forming a stereoscopic couple are obtained by printing suitable additive primary color dots which do not overlap each other when they do not belong to the same stereoscopic image, the shadows and the shades turned down being obtained by an additional print in black strictly limited to the common parts of the two stereoscopic images.  5- An anaglyph assembly according to claim 1, characterized in that at least one of the superimposed images forming a stereoscopic couple is printed by means of fluorescent ink (s).  6- Anaglyph assembly according to claim 1 characterized in that one of the stereoscopic images being printed in cyan and the other in red, the negative image of the cyan image is printed either in light red or in light magenta whose density has a maximum value of about 25X.  7- A method for printing two anaglyphic images according to claim 1 of the main patent with an optimal offset. characterized in that to determine this offset, we first apply one of these two images on a first support, then we apply the second image on a second transparent support, then we place the second support on the first, then we observe all of these two supports by means of appropriate anaglyphic eyepieces and the supports are moved relative to each other until an offset is deemed optimal, then a definitive location of the position of the second image with respect to the first, then then this second image is applied to the first support, then one finally proceeds to photogravure and printing operations of known type.  8- ProcedA for obtaining two anaglyphic images according to claim 1 of the main patent in the case where at least one of the colors has at least one component whose spectral range is incompatible with the three-color process, characterized in that l 'stereoscopic shots are taken either in black and white through preferably dichroic filters ensuring the desired spectral selection, or in color according to Lippmann's interference method with said dichroic filters, then from the images thus selected, we proceed for all appropriate operations such as projection, photoengraving and printing