US2221025A - Color correction process and product - Google Patents

Description

Nov. 12, 1940.

D. L. M wADAM EI'AL COLOR CORRECTION PROCESS AND PRODUCT Filed April 10, 1937 2 Sh'eets-Shget 1 500 [L/L WAVELENGTH 0F EXPOSIAG LIGHT.

600 Ill/L WAVELENGTH OF EXPOSING LIGH'B JILL/11"" fii gz s fl BY W- @JMM . David ATTORNEYS.

Nov. 12, 1940.

D. L. M ADAM ETAL COLOR CORRECTION PROCESS AND PRODUCT Filed April 10, 1937 1 4. 1 11 g 42 Bum-GREEN mwrm 4 12 mm SENSIIIVE (1i) Il- RED ssusmvs (A) Y I, among) 1. 1O

yawn Pmursk MAGENTA PRINTER YELLOW mm?- (A) 2 Sheets-Sheet 2 ENTA PNITIVE IMAGE LLOW NEGATIVE IMAGE INVENTQRS;

. ATTORNEYS.

Patented Nov.12,

UNITED STATES.

PATENT orrlcr.

2.23.025 ooLon connsc'rronrnocsss AND rnonoc'r I David L'MacAdam and J. Stand, Rochester,

N. .Y., minors to Eastman Kodak Company,

Rochester,

N. Y., a corporation or New Jersey Application April '10, 1937, Serial No. 136,168 2 Claims. (Cl. 95-2) This invention relates to photographic repro-v duction of color and particularly to methods and materials useful in the graphic arts for reproduction of colored objects and natural-colored scenes.

At the present time it is impossible to obtain theoretically correct color reproduction in printing processes as employed in the graphic arts and in the reproduction of colored objects and natural colpred scenes by photographic methods. This defect in present reproduction methods is due to the limitations of the materials employed.

' of hand retouching in an attempt to render the results more nearlyrepresentative oi the original subject. The more recent method involves the use otcorrecting positive masks to print a corrected image oivarious oi the color separation images taken through red, green, and blue filters.

The hand retouching method of color correction is obviously a cumbersome and expensive procedure and, therefore, has been supplanted to a large extent by the masking method. Masking methods now in use, as will be readily understood, involve a subtraction of photographic densities in order to arrive at a corrected color separation image. Theoretical investigations indicate that more satisfactory corrections over wider ranges of color would he'obtained if transmissions were subtracted instead of densities. A

method for accomplishing this result will bev pointed out in the iollog description of our invention.

It is, therefore, an object of the present invention to provide a method for producingtheoretically correct color separation images of colored objects. A furtherobiect is to provide a method for color correction involving subtraction of transmissions of photographic images. A still iurtherobject is to provide a novel photographic material for use in the graphic arts to produce corrected photomechanical printing plates. Other objects will appear from the following description. of our invention.

These objects are accomplished by recording the color separation images of the obiect photographed on a multi-layer material having dii ferentially sensitized layers, one of which records a negative image in a special type of, emulsion and another of which records a correcting positive image in the usual type of emulsion. A

corrected positive color-separation image is printed from these combined images onto a single layer of the special emulsion and may then be used for the production of colored prints or photo-mechanical printing plates. The images obtained in this way overcome the deficiency of the recording materials but do not overcome the deficiencies due to defects in the pigments, inks or dyes used to print the final reproduction.

In the accompanying drawings, Figs. 1, 2 and 3 represent spectral sensitivity curves theoretically desired for the recording material designed to trecord thered component of a colored ob ec Fig. 4 is a sectional view of the sensitive element used to record the red components of the object and Fig. 4A is asectional view of this film after exposure and development, according to the present invention. j,

Fig. 5 is a sectional view of the sensitive ma terial used to record the blue components otthe object.

Fig. 6 is a sectional view of the sensitive ma terial used to record the green component of the object.

Fig. 7 is a diagram indicating the relation oi the exposure of the special material used to record the primary components oi the color object, to the transmission of the image formed in it, and l v Fig. 8 is a diagram indicating the relation of the exposure to the density of the image formed in this material.

On the basis or available dyes, inks or pigments used in color reproduction or printing processes, the theoretical sensitivity of a sensitivelayer which would produce a fully corrected color separation image, may be calculated. The pigments ordinarily used for color reproduction according to the subtractive process are blue-green, magenta and yellow. These are often referred to as the blue, redf and yellow pigments or inks. A theoretical spectral sensitivity curve for the blue-green printing plate, that is, the plate which prints the blue-green inkor pigments, is represented'in Fig. 3 of the drawings. As shown in the shaded portion of Fig. 3

this curve includes a portion which extends below the base line. This energy in the spectral region should decrease the densities which are produced-by energy in the spectral regions where tit the curve is above the base line. The spectral region for which the curve lies below the axis is called the region of "negative sensitivity.

Since it is impossible to obtain a negative,

sensitivity with any known photographic materials, some means must be devised to secure the eflect of negative sensitivity. One method of securing this effect is .by a photo-electrichas a transmission which decreases linearly as.

the-exposure of the image increases, the theoretical conditions can be satisfied. Such linear transmission is characterized in theterms of the more familiar H and D system by a characteristic curve which has a long toe portion with the part of the curve which rises rapidly to high densities being symmetrical with the toe -when the curve is bisected by a line at 45 to the exposure axis. A sensitive material ofthis type has been used to record sound photographically and is described for example in the 'Journal of the Society of Motion Picture Engineers vol. .17, 1931, page 1'72. The image in this material is processed to a negative.

When making use of the special material describedabove; the effect of negative sensitivity is obtained by recording the negative image on a special material of the toe emulsion" type and having the sensitivity indicated in Fig. 1, and by recording the positive correcting image on an ordinary emulsion having the eilective sensitivity indicated in Fig. 2. I

The use of two separate recording layers in this way, however, involves the necessity of registration of the separate images when printing the corrected image. We have devised a method and material in which the difilculty of securing proper registration is not encountered. The separate images are recorded in two superposed emulsion layers on the same support and are processed to negative and positive images, respectively, and are colored in such a way that they maybe printed separately or simultaneously to form a corrected color-separation image.

The material which we propose to use for this purpose will now be described by reference to Figs. 441A, 5 and 6 of the .accompanying drawings. As shown in Fig. 4 a support-layer It! is coated with a layer of a red-sensitive emulsion II and a green-sensitive emulsion l2. The emulsion H is of the toe emulsion" type described above and the emulsion I2 is of the ordinary type in which for the straight line portion of the H and D curve D= (log the;

i where n is the photographic density, E, is the exposure, i is the inertia, and'y is a constant resensitive layers ii and I2 and permits only red and green light to pass to these sensitive layers- Both images are then processed to negative ima es and the image in layer l I is then reversed to form tions of colors are conceivable. These colored images may be formed by any suitable method. They may be formed, for example, by developingboth layers in a color-forming developer, 'such as one of the developers described in Marines and Godowsky U. S. Patent No. 2,059,884, granted November 3, 1936, and the image in the upper layer bleached differentially. reversed and processed to the second color. It is also possible to develop both images initially in an ordinary deveioper and then color. them by any suitable method. These images constitute the blue-green printing element when used to print a corrected image.

In a similar manner the yellow printer element comprises ablue-sensitive layer It and a. greensensitive layer l6 carried by support l0, asshown in Fig; 5. A yellow filter layer ll is located be"-' tween the sensitive layers I5 and I6. This eleyellow negative image in layer l5 and a magenta positive image in layer IS. The filter dye of layer I! is removed in this process.

The magenta printer element is shown in Fig. "6

in which the support carries emulsion layers l8 and i9 having an interposed yellow filter layer 20. This element is exposed from the emulsion side to the object to be recorded and the green component of the object is recorded in layer i8 I and the red and blue components in layer i9. This element is then processed as in the case of the other printer elements to a yellow negative image in ayer I8 anda magenta positive image in layer i9, e filter dye 20 being removed in the processing. In the case oi the magenta printer it is also possible to make the layer I9 sensitive only to red or blue, in case it is desired to correct by thesubtraction of one or the other of these color components.

In order to obtained a corrected positive image for mob of the color separation components of the original object, the three printer elements areprinted separately onto an emulsion of the toe emulsion type described above. The printing ing light should be a mixture of the blue and green wave length bands. The use oi light exe hibiting single spectral lines appears to afford optimum conditions for this printing in order to obtain sharp absorption for both images. One

. method of obtaining such spectral lines is to pass the light from a mercury are through an ultraviolet absorber, such as a Wratten 2-A filter and thereby use the two very narrow regions of the spectrum in which practically all of theenergy oi this light source is concentrated. These bands are at approximately 435 mu and550 mu and are, therefore, suitable for independent printing of magenta and yellow images. If necessary, the yellow lines in-the mercury spectrum may be removed by a didymium filter.

By printing in this way the yellow image in the emulsion layer adjacent to the support will be printed by the blue band of light without appreciable interference from the magenta image and the magenta image in the outer emulsion layer will be printed by the green light without interference from the yellow image. This is, in effect, a double exposure method as'contrastedwith ordinary masking methods in which all componentsof the printing light are modified by both the negative and masking images.

The printing material should have the same contrast for blue and green printing bands and as stated above must also give a transmission characteristic which decreases linearly as the exposure I increases.

The positive color separation images produced, in this way from each of the three negative images together with their correcting images are fully corrected and the process is more satisfactory than processes previously used for this purpose. 'The corrected positives produced in this print negatives on ordinary preparing photo-mechanical they may be used for the protransparencies as still photo- It is to be undermaterial for use in printing plates or duotion of color graphs or as motion pictures.

stood that our process is not limited to the graphic arts where printing from a press is involved, but that the same materials and process may he used for bettercolor re prints on paper or for the reproduction of color transparencies by various photographic processes.

We claim: I

1. An exposed and developed photographic element comprising a single transparent support having permanently attached thereto two superposed layers each containing a visible image representing one of the primary color components of a colored object, one of the images being a colored negative image the light of some narrow spectral region, decreases linearly with increase in exposure producing it, and the other image being a differently colored positive image, in which the logarithm of the transmission for light of a second narrow spectral region is directly proportional to the logarithm of the exposure producing it.

2. An exposed and developed photographicelement comprising a single transparent support having permanently attached thereto two superposed layers each containing a. visible image representing one of the primary color components of transmission of which, for

roduction in the making of a colored object, one of the images being a yellow negative image the transmission of which, for

light of a" definite portion of the blue spectral region, decreases linearly with'lncrease in exposure producing it, and'the other image being a magenta positive image in which the logarithm of the transmission for light of a definite portion of the green spectral region is directly proportional to the logarithm of the exposure producing it. DAVID L. MACADAM- CYRIL J. STAUD.

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