US3663220A

US3663220A - Material and a process for the production of color corrected reproductions

Info

Publication number: US3663220A
Application number: US29283A
Authority: US
Inventors: Ehrhard Hellmig; Erich Reckziegel
Original assignee: Agfa Gevaert AG
Current assignee: Agfa Gevaert AG
Priority date: 1969-04-29
Filing date: 1970-04-16
Publication date: 1972-05-16
Anticipated expiration: 1989-05-16
Also published as: DE1921739A1; BE749704A; FR2040412A1; GB1314441A

Abstract

A process for the production of color duplicates from a multicolored original by a photographic color reversal process comprising the steps of producing a black and white masking image from the color original, registering the black and white masking image with the original, exposing a multilayered color photographic duplicating material through the combination of the color original and the black and white masking image, the said duplicating material comprising a red sensitive silver halide emulsion layer with a color coupler for the production of the cyan partial image, a green sensitive silver halide emulsion layer containing a color coupler for the production of the magenta partial image and a blue sensitive silver halide emulsion layer with a color coupler for the production of the yellow partial image and color reversal processing the exposed material to produce a color duplicate in true colors.

Description

United States atent Hellmig et al.

[ 51 May 16, 1972 [72] Inventors: Ehrhard Hellmig; Erich Reckziegel, both of Leverkusen, Germany Agfa-Gevaert Aktiengesellschaft, Leverkusen, Germany [22] Filed: Apr. 16, 1970 [21] Appl.No.: 29,283

[73] Assignee:

[51] Int. Cl. G030 7/18, G03c 5/50 [58] Field of Search ..96/6, 5, 23

[56] References Cited OTHER PUBLICATIONS Evans, Ralph E., W. T. Hanson Jr. and W. Lyle Brewer; Principles of Color Photography, 1953, John Wiley & Sons, lnc. pp. 389- 403, 545, 575- 576, 585, 590- 597 and 606 Primary Examiner-N0rman G. Torchin Assistant ExaminerAlfonso T. Suro Pico Attorney-Connolly and Hutz [57] ABSTRACT A process for the production of color duplicates from a multicolored original by a photographic color reversal process comprising the steps of producing a black and white masking image from the color original, registering the black and white masking image with the original, exposing a multilayered color photographic duplicating material through the combination of the color original and the black and white masking image, the said duplicating material comprising a red sensitive silver halide emulsion layer with a color coupler for the production of the cyan partial image, a green sensitive silver halide emulsion layer containing a color coupler for the production of the magenta partial image and a blue sensitive silver halide emulsion layer with a color coupler for the production of the yellow partial image and color reversal processing the exposed material to produce a color duplicate in true colors.

6 Claims, N0 Drawings MATERIAL AND A PROCESS FOR THE PRODUCTION OF COLOR CORRECTED REPRODUCTIONS The present invention relates to a process for the production of color corrected reproductions, in particular color duplicates, and to photographic materials for performing the process.

There is an increasing demand in practice for the production from a transparent color original of so-called duplicates which are completely identical to the original in all important image qualities and particularly the colors.

The method generally applied for this purposes is the color reversal process in which a contact copy, or an enlargement of the original, is copied on to a special multilayered color photo graphic material suitable for photographic reversal processing. This reversal copying material is available both on transparent supports, (reversal copying film), and on opaque supports, (reversal copying paper). In this method, one positive color image is'produced directly from another positive color image without making an intermediate color negative image. All such so-called direct positive processes, e.g. the silver dye bleaching process which directly produce a color copy, in principle give the same result and will hereinafter be referred to by the term color reversal process.

Since color reversal diapositives generally have a high density range, and the available reversal copying material also has a gamma, sometimes called contrast or gradation, value (the symbol for which is the Greek letter 7) beyond the nominally required value of 1.00, the original diapositive is, in these cases, provided with a black and white mask of negative gradation consisting of a silver image, before the copy is produced on the reversal copying film. This mask reduces the density range of the original image and is, therefore, also known as contrast reducing mask which means that this mask reduces the gradation of the grey tone values, and hence also the density range of the original between white and black". Since such masks also affect the colors to an extent which cannot be controlled, the colors obtained in the color copy are more liable to change and are variable in character if the color original, or the reversal copying material or even the gradation of the mask or the color of the light to which the mask is exposed, are changed.

It is among the objects of the present invention to overcome these disadvantages and to provide a process for the production of duplicates in true colors by means of a black and white mask. We now have found a process for the production of color copies from a multicolored original by a photographic color reversal process, using an uncolored mask obtained from the color original which mask is registered with the original for copying, and in which process a. at least one of the image dyes for the partial image produced by colorforming development in the copyforming material has equal side absorptions in the spectral ranges of the main absorptions of the dyes for the other two partial images, and

b. the photographic material for the production of the uncolored mask consists of one or more silver halide emulsion layers, each of which is associated in such a manner with the copy-forming material containing the image dye with equal side absorption, that the spectral sensitivity of the emulsion layer is complementary to the main density of the particular image dye and its gamma value is numerically equal, but opposite in sign, to the side absorption of this image dye, based on the grey equivalent color density The present invention relates both to the properties of the photographic material for the production of the reversal color copy and to the properties of the black and white mask or the photographic material for the production of the mask, which properties are related to each other in a particular way characterized by the invention. The reversal copying material contains a blue sensitive silver halide emulsion layer with a color coupler which yields upon color-forming development the dye for the yellow partial image, a green sensitive silver halide emulsion layer with a color coupler capable of reacting with the oxidation product of a color-forming developer to form a magenta dye, and a red sensitive silver halide emulsion layer with a color coupler which yields upon color-forming development the dye for the cyan partial image.

According to the present invention, the reversal copying material is characterized in that at least one of the dyes for the partial images produced upon color-forming development must have equally high side absorptions in the spectral range of the main absorptions of the dyes for the other two partial images. Side absorptions or subsidiary densities as distinct from main absorptions are to be understood as meaning the absorption of the particular dye in the two thirds of the spectrum in which the dye should be completely transparent if copies in true colors are to be produced. Thus, for example, for the magenta dye the side absorptions lie in the blue and red third of the visible spectrum, i.e. in the wavelength regions of from 400 to 500 millimicrons and from 600 to 700 millimicrons; the main absorption lies in the green third of the spectrum (from 500 to 600 millimicrons). The most complete effect is, of course, obtained in the process of the present invention when the dyes of all three partial images satisfy the conditions relating to the side absorptions, but the side absorptions need only be equal for each individual dye image and may have different magnitudes for the three dye images. The means for meeting this condition are known. The lower of the two side absorptions is increased by adding a suitable quantity of a dye component which has its main density there. This method has, however, certain disadvantages. Since the quantity of dye component added is very small compared with the quantity of dye component which has to be corrected, the unequal behavior in the coupling kinetic of the two components results in that the desired equality of the two side absorptions is not maintained for the whole density range of the main absorption of the dye. In practice densities of from 0 to about 2.5 occur which necessarily leads to a falsification of color in the color copy. Moreover, the addition of such small quantities of dye component is very critical, and minor deviations in quantity produce a comparatively pronounced effect.

These disadvantages can be obviated by mixing suitable quantities of two or more dye components which have the same main absorption (e.g. two or more cyan color couplers), but have different side absorptions to make the side absorptions substantially equal. In the case of a cyan partial image in which the side absorptions are required to be equal, a cyan color coupler component Cyan l is used, the side absorption of which in the green third of the spectrum is higher than in the blue third of the spectrum, and a cyan color coupler Cyan II is used in which the reverse holds true with respect to the side absorption, and these two couplers are mixed in such quantities that equally high side absorptions are obtained in the two side thirds of the spectrum. The following numerical example shows that this object can in fact be achieved.

Side Absorption in the blue in the green Cyanl bl=0.l5 gl=0.29 Cyan ll bl] 0.25 gll 0.18

lf 0, and c are the required concentrations of Cyan l and Cyan ll which when mixed provide the same side absorptions, the following equation must hold true:

Side absorption in the blue third of the spectrum 0,0 l 5 0,,0-25 0,029 c,,-0- l 8 side absorption in the green third of the spectrum whence c,/c,, l /2.

This means that Cyan I should be mixed with Cyan II in the ratio of 1:2.

In the following it is assumed that each of the three image dyes yellow, magenta and cyan of the copy-forming reversal film meets the first condition of this invention, namely equal side absorptions. The side absorptions are equal to a, b and c for the yellow, magenta and cyan dye of the copy-forming material if it has just been exposed and processed in such a way that it shows a neutral color (grey) of density 1.00 (standardized adjustment). It should be noted that the side absorptions are here not based on the main density of the particular image dye but on the grey density which can be subtractively mixed with the given three image dyes (grey equivalent color density). In other words, the values for a, b and c are numerically equal to the absolute values for the side absorptions of yellow, magenta and cyan image dye when these colors are adjusted to grey of density 1.

According to the present invention, the condition for the black and white masking film associated with this copy-forming material is as follows: Each image dye with equal side absorption must have associated with it a mask layer having a gradation or gamma value equal to that of the side absorption of the image dye, and with a spectral sensitivity complementary to the image dye. Under the above condition, therefore, the masking films consist of three light sensitive silver halide emulsion layers, one of which is only blue sensitive and must be developed to the gamma value yb, the second is only green sensitive and must be developed to the gamma value 7 3, and the third is only red sensitive and must be developed to the gamma value yr, and the gamma values b, 7g and yr are numerically equal to the side absorptions a, b and c referred to above. Moreover, the sensitivity of these three layers measured at the threshold must be equal if the mask film is exposed to unfiltered light, (so-called white light). Accurate adjustment to the source of light is, however, not necessary in the case of white light since the gamma values of the three individual layers are very flat and at the most equal to a few tenths. The total gradation y of the masking films is a b c. This, only in the rarest cases, exceeds a value of 0.50 and it is particularly advantageous to choose image dyes with the lowest available side absorptions as will be shown later.

The density curves of the masking film need not ascend in a completely straight line. On the contrary, as is well known it is advantageous to let the density cdlves flatten off in the socalled upper part (shoulder), because the reproduction of the light portions in the color duplicate is then better than if the ascent of the curve is completely rectilinear. If desired, the reproduction of light can be improved by a light mask combined in a known manner with the mask according to the invention.

in practice, the invention can be simplified in various ways without impairing its essential effect.

Since the yellow dye only has very slight side absorptions which, even in conventional masking processes, are regarded as negligible and may, therefore, be put equal to (a O), the masking film need only consist of two layers, namely the green sensitive silver halide emulsion layer of gradation b and the red sensitive silver halide emulsion layer of gradation c. A material of this type has been disclosed e.g. in U.S. Pat. No. 3,485,627 in which the exact composition and other features (arrangement of layers, lack of definition, built-in filter layer) have also been described. The composition of this two-layered masking film can be still further simplified by providing only one light sensitive layer of gradation b c which is only green and red sensitive, and the sensitivity ratio for green and red actinic light corresponds to the gradation ratio b and c of the corresponding two-layered material. A material of this type has been described, for example, in US. Pat. No. 3,291,602. It has been found in practice that this material, which has been simplified to a single light sensitive layer, enables almost the same satisfactory color reproduction to be obtained in the reversal copy as with the two-layered masking film. The use of black and white masks in the production of color images in combination with dye images, which have equal side absorptions, is already known but the present invention differs fundamentally from such known processes.

ln this known process multicolored intermediate images are interposed between the original and the reproduction, for example a color negative is taken from the original and serves as an original for the production of the copy. in the known process, this intermediate image contains image dyes with equal side absorptions which only have black and white masks of the corresponding gradation associated with them. Although this process eliminates the side absorptions of the image dye of the intermediate image, and hence its effect on the color reproduction in the copy, it does not eliminate the errors due to the dye images of the copyforming material. In the prior art process, there is no association between the image dyes of the copy-forming material and the black and white partial masks, and, therefore, no optimum color reproduction is achieved.

The present invention is basically distinguished over the foregoing prior art since in the process of the present invention the partial masks are determined by the image dyes of the copy-forming film. However, the masks are produced from the original image (original diapositive) and, in contrast to the prior art, not from an intermediate image (since there is none), nor from the image which contains the image dyes with the pairwise equal side absorptions (since in the present invention this is the reversal copying material and, therefore, not an image). Completely unexpected and unpredictable advantages arise from these fundamental differences. Because of the association of the properties of the reversal copy-forming photographic material with those of the masking film, a copying system consisting of these two materials and the instructions for use can be brought on to the market without having to take into consideration the originals, i.e. the optical properties of the image dye of these originals. The origin and optical properties of these originals are of no significance, and instead of transparencies reflection copies can even be used as originals and reproduced or duplicated equally successfully by this system. Another advantage is that the entire system can be rendered more economical and mechanized in that both the mask, since it has to be developed to a predetermined gradation, and the reversal copy-forming material can be processed in automatic apparatus according to a prescribed process.

in addition to the above mentioned conditions for associating the masking with the reversal copy-forming film according to the present invention, there now enters a third condition for obtaining a gradation in the duplicate equal to that of the original image. Since the gradation or gamma value of the original image is lowered by the masking, the gradation of the reverse copying film (7p) must accordingly be steeper than 1.00. In other words, if y (equal to a b c) is the total gradation of the mask, l-y is the gradation of the original which is provided with the mask according to the present invention, then the gradation 7;; of the reversal copy-forming material must be 'yp= 1/1-7 or -yp (-y-y 1.00.

The greater the gamma value of the mask, i.e. the higher the side absorptions of the image dyes of the reverse copying film, therefore, the higher must be the gamma value of the reversal copy-forming material.

This condition, of course, only applies if the reproduction is to be of the same type as the original, i.e. if a color diapositive is to be produced as a duplicate of an original color diapositive or if a reflection copy duplicate is to be produced from a reflection copy original, but the condition does not apply if the reproduction is required to have a different type of density range from the original, e.g. if a color diapositive is to be produced as a copy of a reflection copy or the converse. If the gradation, or what amounts to the same the density range of the copy, is to differ from that of the original by the factor v, then the above equations assume the following form:

lf a reflection copy is to be produced from a color diapositive by the process according to the present invention, then v is a number between 0 and l (proper fraction); in the reverse case, it is a number greater than 1. The copy-forming material must, therefore, have a gradation altered (reduced or increased) by this factor.

EXAMPLE 1 Copy-forming material and 0.78 g. of the cyan coupler of the following formula (see German Pat. 1,137,311):

The first mentioned coupler has a side absorption, based on the main density in the red spectral region, of 4 percent in the blue and of 22 percent in the green region, and the second coupler mentioned has a side absorption of 15 percent in the blue region and percent in the green region.

2. A protective gelatine layer containing 1.5 g of gelatine per square meter.

3. A green sensitive silver bromide gelatine emulsion layer which contains 2.8 g of gelatine, 2.0 g of silver bromide and 0.95 g and 0.15 g, respectively, of the two magenta couplers of the following formulas per square meter:

(S00 German Offcnlcgirngschrift 1,622,922)

N (S00 German Pat. 1,070,030)

Based on the green main density, these have a side absorption of 26 and 7 percent, respectively, in the blue region and of and 12 percent, respectively, in the red spectral region.

4. A yellow filter layer which contains 1.5 g of gelatine and 0.3 g of colloidally distributed silver per square meter.

5. A blue sensitive silver bromide gelatine emulsion layer containing 4.5 g of gelatine, 3 g of silver bromide and 1.5 g of the yellow coupler of the following formula:

ls zr (Soc (lol'nutn Pat. 900,781)

per square meter.

6. A protective gelatine layer containing 1.5 g of gelatine per square meter is arranged uppermost.

The copy-forming material has a gradation of 1.33 measured between the densities 0.7 and 2.0 after it has been processed. The side absorptions of the image dyes are 13 percent both for magenta and for cyan. For yellow, they are regarded as negligible.

Masking material Calculation of the mask gradations:

The side absorptions of the image dyes in the copy-forming material are 0.13 for magenta and 0.13 for cyan, based on the main density in each case.

From this it is calculated that a colorless copy can be obtained from these image dyes composed of 0.76 X yellow, 0.88 X magenta and 0.88 X cyan, which can be expressed in the following matrix scheme:

Yellow Magenta Cyan O.76 0.12 0.12 total 1.00 0.00 0.88 0.12 total 1.00 0.00 0.12 0.88 total 1.00

The side absorptions a, b, c based on the side absorption 1.00 can be read off directly from this as a 0.0, b 0.12 and c 0.12.

Composition of the masking material An lsopan fine grain color emulsion (see BIOS Final Report, No. 1355, page 35) diluted 1 1 by the addition of a 3 percent aqueous gelatine solution is cast on a transparent polyester support based on polyethylene terephthalate of thickness 0.15 mm to produce a film 3.5 p. in thickness. In addition to the usual additives (hardeners, wetting agents) 40 mg of the red sensitizer Rr 1953 (see FIAT Final Report, 943, pg. 53) and 4 g of Acilanorange GX (Color Index No. 16230) in aqueous solution are added to the emulsion per kilogram of original emulsion.

A second layer of the above dilute lsopan fine grain color emulsion to which the green sensitizer Rr 340 (see FIAT Final Report, 943, pg. 46) and the same quantity of Acilanorange have been added before dilution is cast on this emulsion layer, again in a thickness of 3.5 pt. The quantity of sensitizer is such that these emulsions have the same sensitivity when they are exposed as a combination of layers through the antihalation layer (see below), and then developed for 2% minutes in the developer described below. A hardened gelatine layer 1 n in thickness is then cast on the uppermost emulsion layer for protection against mechanical damage. A 3 ,u. thick colored, clear, hardened antihalation layer containing one each of the known yellow, red and green dyes which can be bleached in photographic baths is applied on gelatine to the other side of the support. The color density of this layer is 1.5 behind a blue filter (Agfa-Gevaert Repro color separation filter 4); 0.3 behind a green filter (Agfa-Gevaert Repro color separation filter 5) and 0.3 behind a red filter (Agfa-Gevaert Repro color separation filter 622).

Preparation of the mask The above described masked film is brought, with the colored antihalation layer, into contact with the transparent multicolored original which has to be masked and is exposed through this layer with unfiltered light. It was then treated for 2% minutes in the following developer:

p-methylaminophenolsulfate 7.5 g. Sodium sulfite 40.0 g. Hydroquinone 3.5 g. Soda (sicc) 30.0 g. Potassium bromide 3.0 g.

Made up to 1 liter with water Preparation of the copy BLACK WHITE DEVELOPER Development temperature 20C. Development time 10 minutes.

Sodium polyphosphate 2 g p-methylaminophenol 3 g Sodium sulfite 50 g Hydroquinone 6 g Sodium carbonate sicc. 40 g Potassium thiocyanate 2.5 g Potassium bromide 2 g. Potassium iodide 6 mg. Made up to 1 liter with water Acid stop bath 2 minutes Water 1000 ml. Glacial acetic acid 8.6 ml.

The film is then washed for 10 minutes and uniformly exposed for 2 seconds. Color development Development time 15 minutes at 20C.

Sodium hexametaphosphate Sodium sulfite N ,N-diethylphenylene diamin sulfate Potassium bromide Made up with water to 1 liter.

(DUNN m se Acid stop bath as above, washing for 10 minutes. Bleaching with the following bath:

Potassium ferricyanide Potassium phosphate prim. Sodium phosphate sicc. Made up with water to l liter.

100 g. 60 g. 40 g.

Minutes washing and fixing with a bath of the following composition:

Sodium polyphosphate l g. Borax l5 g. Sodium sulfite sicc. g Sodium thiosulfate 200 g Made up with water to 1 liter.

The film is then again washed for 10 minutes.

A duplicate identical in color and gradation to the original is obtained.

Similar results are obtained when the following coupler combination is used in the red sensitive layer of the copyforming material instead of the above cyan coupler:

0.35 g per square meter of the cyan coupler (see US. Pat. No. 2,313,586)

square meter of the cyan coupler (see German Offenlegungsschrift 1,522,402 ofAug. 14, 1969) having 14 percent side absorption in the blue and l 1 percent in the green spectral region. The same applies to the following coupler combination in the red sensitive layer.

0.6 g of a color coupler of the following formula (Sec German Auslogcsuhrift 1,038,588)

having 5% side absorption in the blue and 3S; ii the green region of the spectrum mixed with 0.9 g. o

the following coupler (sou Swiss Pni'. 222,821).

l ii i1 I C0-NIl- CH CH -N\ (IO-CH1;

l SOIIII having 22 percent side absorption in the blue and 17 percent in the green spectral region.

The color coupler combination of the green sensitive layer may also be replaced e.g. by the following: 0.85 g per square meter of a coupler of the following formula (see Journal of Photographic Science, Vol. 16, pg. 5, 1968) which has a side absorption of 33 percent in the blue spectral region and of 20 percent in the red region, mixed with 0.25 g of the magenta coupler which has a side absorption of 7 percent in the blue spectral region and 12 percent in the red spectral region.

What we claim is:

l. A process for the production of a color copy from a multicolored original by a photographic color reversal process comprising the steps of producing a black and white contrastreducing mask from the color original, registering the black and white mask with the original, exposing therewith a mul tilayered color photographic duplicating material comprising a red sensitive silver halide emulsion layer containing a color coupler for the production of a cyan partial image, a green sensitive silver halide emulsion layer containing a color coupler for the production of a magenta partial image and a blue sensitive silver halide emulsion layer containing a color coupler for the production of a yellow partial image, and color reversal processing the exposed material to produce a color copy in true colors, wherein a. at least the cyan or magenta partial image has equal side absorption in the two thirds of the spectrum outside the main absorption of the image dye, and

b. the photographic material for the production of the black and white mask comprises a silver halide emulsion having a spectral sensitivity complementary to the main absorption of the image dye in the emulsion of the copy-forming material in which the dye image has equal side absorption, and a gradation numerically equal, but negative in sign, to said side absorption based on the grey equivalent color density 1.

2. The process of claim 1, wherein the photographic material for the production of the black and white mask contains a mixture of two silver halide emulsions in form of a single silver halide emulsion layer, wherein the spectral sensitivity of one of these emulsions is complementary to the main absorption of one dye image and the spectral sensitivity of the other of these emulsions is complementary to the main absorption of another dye image of the copy-forming material which is to be corrected and the sensitivity ratio of the two emulsions corresponds to the gradation ratio of the side densities.

3. The process of claim 1, wherein the magenta partial image and the cyan partial image each have equal side absorptions.

4. The process of claim 1, wherein the gradation of the copy-forming material (7 is related to the gradation of the mask (7) as 'y (1'y l.

5. The process of claim 1, wherein at least one of the silver halide emulsions forming the cyan or magenta partial image contains a mixture of color couplers, each coupler of a mixture providing essentially the same main absorptions but unequal side absorptions, and the color couplers are mixed in such a ratio that the sum of the side absorption provided by the color coupler mixture is substantially equal in the two thirds of the spectrum outside the main absorption.

6. A copy-forming material for performing the process of claim 1, comprising a red sensitive silver halide emulsion layer which contains at least one color coupler for the cyan partial image, a green sensitive silver halide emulsion layer which contains at least one color coupler for the magenta partial image, and a blue sensitive silver halide emulsion layer which contains at least one color coupler for the yellow partial image, wherein in at least one of the layers there is a mixture of color couplers each coupler in the mixture providing unequal side absorptions but these inequalities substantially compensating each other in the mixture so that the image dye produced upon color reversal processing has equal side densities.

Claims

2. The process of claim 1, wherein the photographic material for the production of the black and white mask contains a mixture of two silver halide emulsions in form of a single silver halide emulsion layer, wherein the spectral sensitivity of one of these emulsions is complementary to the main absorption of one dye image and the spectral sensitivity of the other of these emulsions is complementary to the main absorption of another dye image of the copy-forming material which is to be corrected and the sensitivity ratio of the two emulsions corresponds to the gradation ratio of the side densities.
3. The process of claim 1, wherein the magenta partial image and the cyan partial image each have equal side absorptions.
4. The process of claim 1, wherein the gradation of the copy-forming material ( gamma D) is related to the gradation of the mask ( gamma M) as gamma D(1- gamma M) 1.
5. The process of claim 1, wherein at least one of the silver halide emulsions forming the cyan or magenta partial image contains a mixture of color couplers, each coupler of a mixture providing essentially the same main absorptions but unequal side absorptions, and the color couplers are mixed in such a ratio that the sum of the side absorption provided by the color coupler mixture is substantially equal in the two thirds of the spectrum outside the main absorption.
6. A copy-forming material for performing the process of claim 1, comprising a red sensitive silver halide emulsion layer which contains at least one color coupler for the cyan partial image, a green sensitive silver halide emulsion layer which contains at least one color coupler for the magenta partial image, and a blue sensitive silver halide emulsion layer which contains at least one color Coupler for the yellow partial image, wherein in at least one of the layers there is a mixture of color couplers each coupler in the mixture providing unequal side absorptions but these inequalities substantially compensating each other in the mixture so that the image dye produced upon color reversal processing has equal side densities.