US2384665A - Photographic tone correction mask - Google Patents

Description

Sept. 11, 1945. F. c. WILLlAhEf-i ET AL 2,384,665

I PHOTOGRAPHIC TONE CORRECTION MASK Filed Aug. 3.5, 1942 Frank/m C. MY/iams h/es/qy [HansonJn Howardfi 0h INVENTORS A TTOR NE Y5 Patented Sept. 11, 1945 PHOTOGRAPHIC TQNE CORRECTION MASK Franklin 0. Williams, Wesley T. Hanson, Jr., and Howard F. Ott, Rochester, N. Y., assignors to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey Application August 15, 1942, Serial No. 454,944

11 Claims.

This invention relates to a process in photogr'aphy, and more particularly to a process in subtractive color photography whereby there is formed a tone correction mask which when placed in registry with a color. transparency efiects an improved tone reproduction curve for the transparency.

In duplicating or printing transparencies, especially those obtained by the reversal processes of subtractive color photography, by a reversal process, the low contrast in the highlight regions of the original is exaggerated by being printed onto a similar material which gives low contrast in' the highlight regions. The contrast inthe highlight regions of the duplicate or printis, therefore, lower than it was in the original. Also, in printing from multicolored originals which consist in whole or in part of dyes, the fact that the light absorption of the dyes extends to the whole spectrum rather than being confined to one part of the spectrum makes it impossible to obtain printed records of the individual dyes simply by restricting thecolor of the printing light. Since in most three-color photographic processes the three dyes are not equally bad in this respect, the final result of printing such a film is to introduce unequal parts of all three records in each image which is made, regardless of the color of light used in printing or the sensitivity of the photographic materials used.

In order to compensate for the deficiencies of the dyes used in such processes, negative color correction masks are prepared by exposing a suitand-white and color photography for improving tone reproduction during printing from blackand-white or colored images having improper tone reproduction characteristics.

Another object of the present invention, and

, the preferred embodiment thereof, is .to provide able sensitive emulsion layer through the multi bar 3, 1941, and elsewhere.

In the present invention we describe a method of preparing a color correction mask which not only corrects for the deficiencies of the subtractive dyes of the color process, but also has tone I; reproduction characteristics such that when a print is made from the combination of the mask P with the original transparency of which the mask is a record, large improvement in the final tone reproduction of the transparency is achieved in the print or duplicate.

One object of the present invention is to proa tone and color correction mask of use in color photography for improving the tone reproduction and color during printing from colored images.

In general, the objects of our invention are accomplished by-forming in a photographic emulsion layer an image of opposite sign to a transparency having improper tone reproduction characteristics, of which it is a record, the characteristic curve of the image being such that when the image is combined with the transparency an improvement in tone reproduction is achieved.

In the figure of the accompanying drawing are shown by means of graphical representation, the characteristic curves of the various photographic elements employed in our invention.

In the figure of the accompanying drawing,

curve M represents the characteristic curve of an image obtained by low intensity exposure through a color transparency having a tone reproduction curve such as curve 1. Curve M1 represents the characteristic curve of an image obtained by exposure through'the transparency and the image having the characteristic curves labeled T and M.

Curve T1 represents the corrected reproduction curve of the transparency obtained when in printing, the image having curve M1 is used as a mask for the transparency having curve T.

Our invention will now be described with particular reference to the accompanying drawing.

In a typical case to which our invention is particularly applicable, there is at hand a color transparency having a reproduction curve such as curve T of the drawing. In the normal process of reproducing this transparency, as for instance, onto a multicolor film by means of the reversal process of color photography employing color-forming development, therewould be obtained a. print in the toe region of which the low contrast of the toe of the curve'T would be exag erated. This is true whether or not the usual color correction mask is employed in the printing process. ,However, if in the manner of our invention another characteristic be imparted to water, about 125 F cc.. 500 p-Methylamino-phenol sulfate grams 1.0 Sodium sulfite, desiccated do 75.0 Hydroquinone do 9.0 Sodium carbonate, desiccated do 25.0 Potassium bromide do 5.0 Cold water to 1iter 1.0

Following development the film is fixed, washed and dried. The resulting mask has substantially the same characteristics as shown in curve M of the drawing. For use with most color transparencies a gamma of'the range of the order of 1 to 4 is satisfactory for this image.

The mask is then combined with the original color transparencyand'a' print of the combination is made with red light onto a low contrast panchromatic negative emulsion. For this exposure a tri-color red filter may be used, such as Wratten No. 25 filter, depending upon the type of color correction desired. The exposed emulsion layer may be a part of the photographic stripping film described in Nadeau U. S. Patent 2,266,435, granted December 16, 1941. The emulsion of this film, in case the exposure is with red light, may be of low contrast and highly red sensitive. The exposure given is sufilcient to record all of the detail in the color transparency. Thereafter, the exposed film is developed for about eight minutes at 70 F. to a gamma of approximately 0.5 in a developing solution of the following composition:

Water, about 125 F cc' 750 p-Methylamino-phenol sulfate grams 2.0 Sodium sulfite, desiccated do 100.0 Hydroquinone do 5.0 Borax, granular 1 do 2.0 Water to "liter" 1.0

The film is then fixed, washedand dried in the usual manner. The mask thus obtained has substantially the characteristics shown by curve M1 of the drawing, wherein the image corresponding to the straight-line portion of the curve is of low gamma having density variations of opposite sign to the density variations of transparency having curve T, and the shoulder or high density region is a positive with respect to the transparency T. Since the mask is a positive in the shoulder region it may be said to have no density variations of opposite sign to the density variations of the transparency in that region. Generally, a gamma of the range of the order of 0.3 to 0.6 is satisfactory for the mask, and the ratio of gammas of this mask to the gamma of the above high gamma image is, therefore, of the order of 1/0.6 to 4/03. The higher the ratio selected the greater the correction imparted to the transparency.

In order to print color and tone corrected prints from the original transparency, the first prepared mask is removed from the transparency and the second mask placed in registry with the transparency, as, for instance, by laminating the mask to the transparency, prints being made on a suitoverall decrease in contrast in the reproduction curve, but in the low density region corresponding to the highlights of the transparency. the contrast has been raised so that constant contrast is obtained throughout the length of the characteristic curve. Of course, since the exposing light for the exposure of the final mask is preferably selected so as to compensate for the errors in absorption of the dyes used in the process, color correction is also effected. The choice of wave length of exposing light depends upon whether or what correction is desired but generally a light of longer wave length than blue is satisfactory, such as red, green, yellow, especially substantially monochromatic yellow light, chosen according to the principles laid down in the prior U. S. Patent 2,294,981 above cited.

As above mentioned the mask of the invention having characteristics substantially as shown by curve M1, in order to compensate for low con-. trast in the highlight portion of a transparency, must have littleor no gradation in the shoulder region, and may actually be a positive in the shoulder region in respect to the transparency. In curve M1 the mask is shown as having decreasing density, i. e., positive density gradient, in the shoulder region to compensate for the low contrast in the toe of the transparency curve T.

We contemplate as within our invention tone and color correction masks of the general characteristic described, wherein the straight line portion of the characteristic curve is negative to a transparency of which it is a record, and in which in the shoulder region there is little or no gradation of opposite sign to the transparency, but including density variations of the same sign in that region. Therefore, herein and in the appended claims, where we state that the mask has in the shoulder region no appreciable density variations of opposite sign to the density variations of the transparency, we mean it to be understood that this includes in the shoulder region: (1) small density variations of opposite sign to the transparency but of an order less than normally obtained with photographic emulsions, (2) no density gradation in the portion of the shoulder masking the toe of the transparency, and, (3) density varying in the same direction as the density variations of the transparency.

Another use for which the mask of our invention is especially adapted is in projecting or viewing of color transparencies. That is, in reversal processes of color photography where colored images are formed by means of color-forming development, images are obtained commonly having high contrast and the usual low contrast in the shoulder and toe regions. (See curve T.) A mask prepared as described is especially suitable forcombining with such a transparency when it is desired to obtain the best image for viewing or projecting.

As is apparent, our-invention is not limited to use in processes of color photography; however, our preferred embodiment resides therein. That is, in processes of black-and-white photography As shown by curve T1 of the when printing from transparencies having improper tone reproduction characteristics, as for instance, from a black-and-white image having lower gamma in the toe and shoulder regions of the characteristic curve than in the straightiine portion, a tone correction mask may be prepared which when used in printing in combination with the image of which it is a record of opposite sign, gives an improvement in tone reproduction. In the past, practically the only method of improving tone reproduction in blackand-white photography has been to print an original transparency onto a material giving an im-' age of different contrast, thereby altering the overall contrast in the print but obtaining some compensation for errors in tone of the original.

In addition, our invention may be used in conjunction with printing from a colored negative transparency, as for example, prepared from photographic elements designed as described in Jelley and Vittum U. S. Patent 2,322,027, granted June 15, 1943, Mannes et a1. U. 5. Patents 2,304,939 and 2,304,940, granted December 15, 1942, that is, in conjunction with color films which aiter'original exposure are immediately developed to subtractively colored dye images. In this case, the final mask is a negative record of the color negative but, of course, is a positive in respect to the final positive color print. In fact, our invention is applicable to the improvement of tone reproduction in any process of photography wherein the image of which the mask is a record has tone reproduction errors of the order described.

Also apparent, is the fact that the masks of our invention may be designed so as to correct not only for tone reproduction errors of the transparency being printed, but also to correct for tone reproduction errors introduced by the duplieatin process. This is accomplished by giving the mask a shoulder gamma compensating for tone errors of both the toe of the transparency and any toe introduced in the duplicating process.

Our invention having thus been described we would have it understood that the disclosure herein is by way of example, and that we consider as included in our invention all modifications and equivalents falling within the scope of the appended claims.

What we claim is:

1. In a process of printing a color transparency in natural colors the method of forming a photographic tone and color correction mask which comprises giving a light-sensitive emulsion layer a low energy exposure with white light through a color transparency, forming in the exposed layer a silver image of opposite sign to said color transparency, exposing a second light-sensitive emulsion layer through a combination of said color transparency and the image in said firstmentioned layer, and forming a silver image in said last-mentioned exposed layer of gamma lower than the gamma of said other image.

2. In a process of printing a color transparency in natural colors the method of forming a photographic tone and color correction mask which comprises giving a light-sensitive emulsion layer a low energy exposure with white light through a a color transparency, forming in said exposed layer a silver image of opposite sign to said color transparency, exposing a second light-sensitive emulsion layer through said color transparency and the image in said first-mentioned layer, and forming a silver image in said lastmentioned exposed layer, said last-mentioned image being of gamma lower than the gamma of said other image and being of opposite sign to said transparency in the straight line portion of its characteristic curve and of the same sign as said color transparency in the shoulder portion or its char-'- acteristic curve.

3. In a process of printing a color transparency in natural colors the method of forming a photographic tone and color correction mask which comprises giving a light-sensitive emulsion layer a low energy exposure with white light'through a positive color transparency, forming in the exposed layer a silver image of opposite sign to said color transparency, exposing a second lightsenstive emulsion layer through said color transcomprises giving a light-sensitive emulsion layer a low energy exposure with white light through a positive color transparency so as to record only the toe densities of said transparency, forming in the exposed layer a silver image of opposite sign to said color transparency, exposing a second light-sensitive emulsion layer through a combination of said color transparency and the image in said first-mentioned layer, and forming a silver image in said last-mentioned exposed layer, said last-mentioned image being of gamma lower than the gamma of said other image andbeing of opposite sign to said transparency in the straight line portion of its characteristic curve and of the same sign as said transparency in the shoulder portion of its characteristic curve.

5. In a process of printing a color transparency in natural colors the method of forming a photographic tone and color correction mask which comprises giving a light-sensitive emulsion layer a low energy exposure with white light through a positive color transparency, forming in the exposed layer a silver image of opposite sign to said transparency, exposing a second light-sensitive emulsion layer through said color transparency and the image in said last-mentioned layer with light of wave length which will correct for the inaccuracies in absorption of the dyes used in the process, and forming a silver image in said lastmentioned exposed layer, said last-mentioned image being of gamma lower than the gamma of said other image and being of opposite sign to said color transparency in the straight line portion of its characteristic curve and of the same sign as said transparency'in the shoulder portion of its characteristic curve.

6. In a process of printing a color transparency in natural colors the method of forming a tone and color correction mask which comprises giving a light-sensitive emulsion layer a low energy exposure with white light through a positive color transparency, developing in the exposed layer a silver image of opposite sign to said color transparency and having a gamma of 1 to 4, exposing a second light-sensitive emulsion layer through said transparency and the image in said last-mentioned layer with red light, developing a sliver image in said last-mentioned exposed layer, said last-mentioned image being of oppoa gamma of 0.3 to 0.6 in the straight line portion of its characteristic curve and of the same si n as said color transparency in the shoulder portion of its characteristic curve.

'I. In a process of printing a color transparency in natural colors the method of forming a tone and color correction mask which comprises giving a light-sensitive emulsion layer a low energy exposure with white light through a positive color transparency sufllclent to expose only those densities less than about 0.6 in the transparency, developing in the exposed layer a silver image of opposite sign to said color transparency and having a gamma of 1 to 4, exposing a second light-sensitive emulsion layer through a combination of said color transparency and the image in said last-mentioned layer with yellow light, developing a silver image in said last-mentioned exposed layer, said last-mentioned image in the straight line portion of its characteristic curve being of, opposite sign to said color transparency and having a gamma of 0.3 to 0.6 and of the same sign as said color transparency in the shoulder portion of its characteristic curve.

8. In a process of printing a color transparency in natural colors, the method of forming a photographic tone and color correction mask which comprises giving a light-sensitive emulsion layer a low energy exposure with white light through a negative color transparency, forming in the exposed layer a silver image of opposite sign to said transparency, exposing a second light-sensitive emulsion layer through a combinationof said transparency and the image in said firstmentioned layer, and forming a silver image in said last-mentioned exposed layer of gamma lower than the gamma of said other image.

9. In a process of printing a color transparency in natural colors, the method of forming a photographic tone and color correction mask which comprises giving a light-sensitive emulsion layer a low energy exposure with white light througha negative color transparency, forming in the exposed layer a silver image of opposite sign to said transparency, exposing a second light sensitive emulsion layer through said transparency and the image in said first-mentioned layer, and forming a silver image in said last-mentioned exposed layer, said last-mentioned image in the straight line portion of its characteristic curve being of gamma lower than the gamma of said other image and being of opposite sign to said color transparency in the straight line portion of its characteristic curve, and of the same sign as saidcolor transparency in the shoulder portion of its characteristic curve.

10. In a process of printing a color transparency in natural colors, the method of forming a photographic tone and color correction mask which comprises giving a light-sensitive emulsion layer a low energy exposure with white light through a negative color transparency sufiicient to expose only those densities less than about 0.6 in the transparency, forming in the exposed layer a silver image of opposite sign to said color transparency, exposing a second light-sensitive emulsion layer through said color transparency and the image in said first-mentioned layer, with light of wave lengths which will correct for the inaccuracies in absorption of the dyes used in the process, and forming a silver image in said last-mentioned layer, said last-mentioned image in the straight line portion of its characteristic curve being of gamma lower than the gamma of said other image and being of opposite sign to said color transparency in the straight line portion of its characteristic curve, and of the same sign as said color transparency in the shoulder portion of its characteristic curve.

11. In a process of printing a color transparency in natural colors, the method of forming a photographic tone and color correction mask which comprises giving a light-sensitive emulsion layer a low energy exposure with white light through a negative color transparency suflicient to expose only those densities less than about 0.6 in the transparency, forming in the exposed layer a silver image of opposite sign to saidcolor transparency and having a gamma of 1 to 4, exposing a second light-sensitive emulsion layer through said color transparency and the image in said first-mentioned layer with yellow light, and forming a silver image in said last-mentioned layer, said last-mentionedimage in the straight line portion of its characteristic curve being of opposite sign tosaid color transparency and having a gamma of 0.3 to 0.6 and of the same sign as said color transparency in the shoulder portion of its characteristic curve.

FRANKLIN C. WILLIAMS. WESLEY T. HANSON, JR. HOWARD F. 0T1.

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