GB2043950A - Cooling Proofing by Light Exposure to Photographic Media - Google Patents

Abstract

Pre-press color proofing of a set of color separation films from which printing plates are to be made for color printing of a multi-color image on a paper or like printing base with a given set of printer's inks or the like, by: (a) preparing samples of the given inks or the like on the printing base or equivalent thereof; (b) determining the primary color component makeup of each sample in relation to a given illuminant source and from a color reference data base based on such illuminant source, determining a group of color filters and associated color filter exposure times appropriate to substantially reproduce each sample color on a selected photographic paper when the paper is exposed to the illuminant source through such filters for such exposure times; (c) exposing the undeveloped photographic paper to the light source in sequence through each color separation film and its associated group of color filters for the determined respective filter exposure times to substantially reproduce each separation film color image in the associated sample color on the photographic paper when developed, and (d) developing the exposed photographic paper to provide the pre- press color proof. s

Description

SPECIFICATION Color Proofing by Light Exposure to Photographic Media The present invention relates in general to the field of synthesizing colors on photographic media by the successive exposure thereof to an illuminant source through a group of up to three color filters for selected times for each desired color.More particularly, the method of the present invention relates to the art of preparing and using a color reference diagram or like data base to assist in determining the illumination exposure time needed for each of up to three color filters for each desired color, as disclosed in our Great Britain application Serial No, 14353/78, entitled Method of Obtaining a Target Color From a Light Source on Photographic Film or Paper, and then utilizing such exposure times to produce the target color on a color photosensitive photographic medium e.g. to produce a single sheet pre-press color proof from color separation negatives or the like.

Conventional prior practice with respect to color proofing in the printing trade essentially involves either actual press proofing (a procedure where actual test printing plates are made to literally color print the proof) or by use of primary color and black transparent overlays. For example, 3M Company markets, under the trademark "Color-Key", pre-press proofing materials involving presensitized ink pigment coatings, in either transparent or opaque colors, on transparent polyester base sheets. Each pigment coating is intended to be correlated with various process color printing inks. Each primary color and black "Color-Key" sheet is overlaid by its associated separation negative and after exposure and development, the four "Color-Key" sheets are overlaid in register to provide a "proof" or simulation of what the four-color work will look like when printed.Manifestly, such a pre-press proofing system, involving four overlaid sheets (which are glossy in character and which at best only indirectly match the colors of the proof with the actual colors of the printing inks to be used) falls well short of providing the user with a fully accurate proof in the sense of the colors, color registry and texture of the color work when press printed with inks on paper.

3M Company also markets a pre-press color proofing system under the trademark "Transfer Key", which is said to provide a complete four-color proof on a single sheet. In this system, factory precoated carrier sheets of color pigment, respectively bearing cyan, yellow, magenta and black pigment, are successively manipulated to laminate each pigment onto the base material by use of a proprietary laminator. Specifically, the cyan pigment is first laminated to the base material, which is then exposed to the cyan separation negative and the sheet then developed in a proprietary processor. The same exposure/development cycle is repeated with each color, producing the four-color proof. Pre-coated pigment carrier sheets are available only in certain colors, unless specially ordered.As manifest, such color proofing procedure, although providing a single sheet color proof, is of limited applicability and accuracy in that only certain laminating pigments are available, and is inherently rather slow in cycle time in that each pigment layer of the four-color proof must be separately and successively laminated, exposed and developed.

Another commercially available pre-press color proofing system is marketed by the duPont Company, under the trademark "Cromalin". In the Cromalin color proof system, dry pigment toners are factory "calibrated" to printing ink colors and each primary and black color reproduction is on a separate sheet of photopolymer film, the films after exposure and development being laminated together in registry to provide the color proof, The cycle time for this system is said to be "within an hour", rather than the hours or days required for press proofing.

Another known pre-press color proofing system which is commercially available in the Kodak Polytrans Colour Proofing Film System, such as described in "The Reproduction Color", by R. W. G.

Hunt, at page 546 (published by Fountain Press of Hertfordshire, England, Third Edition, 1975). In the Polytrans system screened color separation films are proofed by materials including films consisting of color-pigmented photopolymer matrices coated on a transparent film base. Exposure to blue or ultraviolet light hardens the photopolymer so that exposure thereof to the screened separations results in an image-wise pattern of the hardened polymer being obtained. Each exposed film is mounted on a suitable roller and rolled under heat and pressure onto a sheet of paper, the unhardened polymer transferring to the paper and taking the pigment with it. Four different colors of film are used and, by exposing each to the corresponding color separation positive, image-wise transfers can be obtained in each color.Each image is developed and transferred in succession, onto the paper, in register, with a color proof resulting after exposure of the transferred pigments to light. While the Polytrans system results in a color proof on a single sheet of paper, the color-pigmented photopolymer matrices used are necessarily precalibrated to printer's inks at the factory, and each color is separately and successively developed on the color proof. Registry of the respective color images on the paper can also prove to be a problem because the color images are applied to the paper by successive roller transfer.

In general, the present invention involves the method of obtaining the color proofing target colors from an illuminant source on a single sheet of photographic media or the like by preparing a color reference diagram or like data base characteristic of a given illuminant source (in the manner taught by our aforementioned Great Britain application 14353/78); using the color reference data base to aid in determining the exposure times to use with each of up to three color filters for each target color; exposing the photographic media through the color filters for their respective exposure times; and then developing the exposed photographic media to produce a pre-press color proof.

Another characteristic of the present invention is the providing of a relatively simple, inexpensive method of synthesizing color proofing target colors by sequentially exposing a photographic media to light of different colors which is extracted from an illuminant source by color filters and which is applied to selected portions of the photographic media, as by sequential exposure through a set of color separation films.

Further features of the present invention involve the development and use of a color reference data base for accurate color reproduction of color proofing target colors on photographic print media by use of an illuminant source and sets of color filters, which data include and interrelate (1) the chromaticity coordinates, dominant wavelength, and saturation percentages for each possible target color in relation to the given illuminant source, and (2) the chromaticity coordinates and filter percentage characteristic of each filter for each target color in relation to the illuminant source.

Optionally, the data can also include, or can in part be expressed in terms of target color densities, i.e.

the gray level and the proportionate levels of red, yellow and blue in each target color.

More specifically, embodiments of the present invention may be used to provide a method whereby pre-press color proofs may be rapidly, economically and accurately prepared on a single sheet of opaque photographic paper to show what the color reproduction will be like when printed using a given set of printer's inks and plates prepared from a given set of color separation films, the color proofing technique of the present invention offering the unique advantage of being able to directly utilize swatches of the actual printer's inks as target colors in the process and requiring only a single step of photographic media development rather than separate development steps for each color, as is characteristic of prior art pre-press proofing systems. The technique of the present invention realizes marked improvement in color proofing cycle time.The apparent capability of preferred examples of the present process in this respect is a cycle time of about fifteen minutes or even less, as compared with a cycle time of about an hour for previously known pre-press proofing processes, and as compared with a cycle time of at least several hours when using conventional press proofing techniques.

These and other features, advantages and characteristics of the method of the present invention will be apparent from the following detailed description of the preferred embodiments thereof in which reference is made to the accompanying figures.

Fig. 1 is a block diagram outlining typical application of the present invention to pre-press color proofing.

Fig. 2 is a block diagram outlining a typical color printing procedure including the production of a color proof from a given set of four-color separation films and a given set of printer's inks and printer's paper or the like, in accordance with the present invention.

The present invention is in some respects an application and improvement of the target color reproduction method disclosed in our aforementioned Great Britain application 14353/78, the disclosure of which is incorporated herein by reference. For discussion purposes, however, a brief overview of such target color reproduction method is set forth below, along with a discussion of some of the method's underlying principles.

Preliminarily, it may be assumed that every color visible to the human eye is composed entirely of red, green and/or blue components. Thus, it follows that any such color may be synthesized by the proper additive mixing of red, green and blue lights. However, the problem remains of how to determine what are the red, green and blue components of a given target color, and how to select and use color filters which will extract the proper amounts of red, green and blue light from a given illuminant source to reproduce that color on the particular photographic media being used.

Since, as has been explained, the color temperature of the illuminant source is a basic factor which must be considered, the starting point for a given target color reproduction is to determine the Kelvin temperature of the illuminant source which will be used to produce the target color. Having determined the color temperature of the illuminant source, it may then be located as by plotting thereof on a data base such as a CIE diagram working area.

Next, the target color data point is determined in the data base working area for the color to be achieved. This is done by comparing the target color to a color reference data base which was prepared with an illuminant source having the same color temperature and spectral distribution as the illuminant source being used to produce the target color. The location of the closest matching color on the data base, e.g. the coordinates of the matching color on the color reference diagram is taken to be that of the target color.

Then, a set of three filters is selected which can be used to produce the particular target color.

Filter triangle plots, or data base equivalent thereof, are then delineated and any set of three filters may be used which defines a filter triangle or equivalent coincident with the location of the target color. This is because, when considering photographic media, a set of three filters may be used to produce any color located within or on the filter triangle they define.

Once the red, green and blue components (x, y and z) of the target color and of each of the three color filters are known, a determination is made as to how much of each color filter is needed in order to produce the target color. This is done by determining what percentage of each color filter (i.e. what filter percentage) is needed to achieve a result such that the sums of their red, green and blue contributions equal, respectively, the red, green and blue components of the target color.

Each filter's exposure time is next determined by multiplying its respective saturation time by its respective filter percentage. Finally, the particular, positive photographic media being used is exposed sequentially to the illuminant source through each color filter for its respective exposure time. Upon developing the photographic media in accordance with the manufacturer's instructions, the target color is produced on the developed positive photographic media.

To further illustrate the significant feature of our earlier disclosed target color reproduction method, the following detailed example thereof is presented. A swatch of a bluish color was chosen to be the color for reproduction, i.e. as the target color.

A color reference data base in the form of a CIE diagram was produced according to the procedure set forth in our said Great Britain application 14353/78, with the same illuminant source as that of the illuminant source being used to prepare the target color (tungsten at 30500 K.). Then, the target color was compared to the color reference data base and it was noted that the x, y coordinates of the closest matching color thereon were x(red)=.21 1 and y(green)=.3425. Using these coordinates, a point for the target color was plotted on the working diagram. In connection with the working diagram it will be understood that such a diagram may be of the CIE type or may be any Cartesian coordinate system or equivalent data base, such as a computer program, having units which can be correlated with those used in a standard, CIE diagram.For example, a known data system involving programming a digital computer to determine CIE coordinates from spectro-photometric data is disclosed by J. E. McCarley et al in an article entitled "Digital System for Converting Spectrophotometric Data to CIE Coordinates, Dominant Wavelength and Excitation Purity, at 55 Journal Of The Optical Society of America, pp 355~360 (April, 1965). Other data systems known per se may also be used without departing from the scope of the present invention.

In the example being discussed, three color filters (Kodak Wratten Photomechanical filters 25 (red), 58 (green) and 47B (blue) were selected and located in the data base, either by use of the manufacturer's reference data, or by use of a spectrophotometer, or by direct comparison of the colored filters to the color reference diagram to find the coordinates of the closest matching color thereon, for example.

For the three filters selected, the following coordinates were supplied by the manufacturer: Filter x (red) y (greenJ z(hlue) 25 (red) .6850 .3147 .0003 58 (green) .2693 .6831 .0476 478 (blue) .1554 .0220 .8226 The saturation time for each color filter was determined for the particular, positive photographic paper being used (Kodak Ektachrome RC paper type 1993, manufactured by Eastman Kodak Company). In the example selected, the saturation times for the red, green and blue filters were found to be, respectively, 35.3 seconds, 37 seconds and 20.1 seconds.

After the saturation times have been determined for each filter, a final check on the accuracy of the result can be made by trial production of a gray at the plotted point for the illuminant source.

Whether a gray has been achieved may be checked, for example, by comparing the resulting color with a standard reference work such as the True Color Process Guide, published by Krug Litho Art Co., of Kansas City, Missouri, or by checking the sample on a reflective digital densitometer such as a GAM Model 1 26P, available from the Graphic Arts Manufacturing Company. If it is found that a gray has not been achieved, the dominant color(s) are observed and the exposure time(s) for the filter(s) are adjusted, as is known to those skilled in the art, until a gray is obtained.

Next, the filter percentages for the red, green and blue filters, in relation to the target color were found to be 0%, 48. 1%, 51.9%, respectively. These filter percentages (the proportionate filter exposures necessary to essentially reproduce the target color from the filter colors) can be obtained by interpolatively correlating the target color coordinates and the filter color coordinates. Thus, for example, the dominant filter 478 (blue) can be expected to provide the dominant target color component (z coordinate .4465) and will approximately do so at a filter percentage of 52% (.4465 .42775=01875 error).Similarly, the second significant color coordinate of the target color (y coordinate .3425) can be provided primarily by the filter 58 (green) which it will approximate at a filter percentage of 48%, taking into account the y component (green) contribution (.0114) of the 47B filter (blue) (.342 5--.01 14--.3279=.0032 error), with this filter 58 (green) also substantially providing the third target color component (x coordinate .2110) at the same filter percentage along with the x (red) component contribution (.0808) of the 47B filter (.21 10-.0808-.1 293=.0009 error), and making a z component (blue) contribution (.02285) reducing the blue error in the 47B and 58 filter contributions (.01 875-.02285=-.0041 error).Refinement of the interpolations results in the indicated respective filter percentages for the selected filters, in relation to the selected target color, of 0% for the 25 filter (red),48.1 for the 58 filter (green), and 51.9% for the 478 filter (blue).

By multiplying the red, green and blue filters' respective filter percentages by their respective saturation times, the desired exposure times for the respective filters were found to be 0 seconds, 17.8 seconds, and 10.4 seconds, respectively.

The undeveloped photographic paper is then exposed to the illuminant source through each of the up to three color filters for its respective exposure time. After the last exposure is made, the positive photographic media is developed in accordance with the manufacturer's instructions, with the result that the target color is obtained on the developed photographic paper.

A technique important to practical target color reproduction involves the determination of saturation time for a particular gray level, since this gives the base time for all colors on that level. This determination is made as follows: A trial exposure is made for a gray sample, using any combination of up to three filters, but the filter combination should be such as to produce a color balance of 1/3 each of cyan, magenta and yellow. The exposed sample, which involved negative print paper (Kodak 37 RC) as a further illustrative example, is then measured with a densitometer or like instrument (spectrophotometer or colorimeter) that identifies balance of cyan, magenta and yellow, i.e. the grayness of the sample. In the case where a densitometer is used for this measurement, four readouts are given by the instrument.As an example, the gray level of the sample may be 70 and the color densities may be cyan 65, magenta 72 and yellow 59. By adding these three densities, a total of 196 results. Since a color balance is desired, i.e. a relative density of of.33 .33 .33 of a density of 65 65 65, we note that the density balance in the selected example is 33% for cyan, 37% for magenta and 30% for yellow. In the instance of this example, these colors were obtained through the complementary filters Wratten 25, 58 and 47-B, for cyan, magenta and yellow. Subtracting the percent difference for each color, it is noted that cyan at 33% requires no correction, the magenta requires a reduction of -4% and yellow requires an increase of +3%.At this point a correction factoring system is employed to make a new exposure. In the correction system adopted in this examply, the correcting number (on a geometric progression scale) to reduce the magenta density by 4% is .9120. This number is then multiplied by the original exposure time, which gives a new time for the magenta exposure.

Correspondingly, yellow is 3% under so the correction factor in this instance would be 1.072 to give the new exposure time for yellow.

If it is preferred that the gray level be a different figure, say 66 by way of example, instead of 70, the correction figure to arrive at the preferred gray level is .942857, applicable to all exposure times.

Another sample is exposed, using the revised exposure times and the correction procedure is repeated if necessary until the desired gray balance and gray level are achieved. Once these exposure times are obtained it is next desirable to find the saturation time for that level for all colors. With the correct gray exposure time at hand, the three exposure times are divided by the correct "percentage of filter" amounts for gray, as determined from the chromaticity data base for the illuminant point, as earlier discussed.

Taking the "percentage of filter" amounts for the illuminant point, these figures are divided into the new times for gray and this determines the saturation times for this particular level of the chromaticity diagram for all colors. Using this time, any color can be achieved by multiplying its "percentage of filter" amount by the saturation time.

To illustrate this technique, and using the example initially discussed earlier, the following measurements and calculations occur; 1. Time used 10.1 sec. for the 25 filter (for cyan) 4.2 sec. for the 58 filter (for magenta) 2.4 sec. for the 47-B filter (for yellow) 2. Sample measured 70) 65 72 59 3. 65+72+59=196 65/196=33% 72/1 96=37% 59/197=30% 4. NEED 33% NEED 33% NEED 33% HAVE 33% HAVE 37% HAVE 30% 0 + 4% -3% 5.~6. .9120 1.072 x4.2 x2.4 10.1 3.8 2.6 NEW TIME 7. NEED .66 gray level HAVE .70 gray level .66/.70=.942857 10.1 3.8 2.6 x.942857 x.942857 x.942857 NEW NET TIMES for .66 gray 9.5 3.6 2.4 10.Assuming that these times for gray are correct, the following Saturation Times for the .66 level.

of the chromaticity diagram evolve, using the given photographic media used in the example: 9.5/.443458=21.4 sec.3.6/.379670=9.4 sec.

2.4A 176872=13.56 sec.

Any color can now be exposed for, using these times.

Thus, for the complement of a dominant wavelength of 410 at the 90% saturation level from the illuminant, can be computed by .083369 .003930 .912701 x21.4 x9.4 x13.45 1.8 .04 12.3 As will be evident, the determinations and operations of the exposure equipment can also be accomplished by computer, utilizing programming techniques known per se. In one prototype equipment at hand, an Apple II computer is used with a so-called x, y table to horizontally move the photographic media under a stationary mask opening through which the media is illuminated downwardly from a stationary illuminant source through selected filters. The computer also interfaces with exposure control mechanism, i.e. the light source and filters. In the prototype arrangement a computer is used with a color TV monitor.All necessary computations to provide the color reference data base for the light source and filters are programmed into the computer in a manner known per se.

The photographic media is moved on the x, y table under control of the computer so that the desired exposure point is directly in line with the mask opening and the light source. Filters are moved into line with the illuminant source sequentially and exposure times are also controlled by the computer to reproduce any desired target color in the manner characteristic of the present invention. Repeated exposure to develop an array of target colors can result in an entire data base working area being produced.

As earlier indicated, the present invention involves the application of the foregoing target color reproduction method to the field of color printing and specifically to the proofing, prior to the making of printing plates of the so-called color separation film negatives or positives from which the plates are to be made. Given a set of color separation films and a given set of printer's inks (e.g. yellow, magenta, cyan and black), the present invention provides, through use of photographic printing techniques, a simple and accurate way of determining what printed color reproductions will look like without actually having to prepare test printing plates.More specifically, the present invention provides a simple and straightforward pre-press color proofing technique whereby a given set of color separation films is "proofed" on photographic paper in a manner showing what the printed color reproduction will be like if printed with a given set of printer's inks, the color proof being "printed" by use of a light source and color filters rather than by use of the inks, with filtered light exposure times coordinated to the ink colors.

In making of color proofs from color separation films in a manner according to the present invention, each separation film (which is a black film base, positive or negative), may be considered simply as a mask controlling the areas or portions of the photographic print paper which are exposed to selected sets of filters for selected times simulating the color composition of the inks. By this technique, the "printing" of the photographic paper is accomplished by light in essentially the same manner as a printer would print with inks, i.e. with all colors "printed" on a single non-transparent sheet of paper, as distinguished from conventional color proofing techniques which commonly involve each primary color and black being developed on separate transparent sheets which are superimposed to simulate the final printed reproductions.

As a specific example of application of the present invention, it will be understood at the outset that color separation films, as made or available in the color printing field, are derived in a number of ways, such as through a camera process, conventional per se, which provides four color separation films, each of which in appearance is a black film base, positive or negative, but which constitutes respective records of the yellow content, the magenta content, the cyan content, and the black content of the original. Each such black base film is in effect a mask made of more or less microscopic dots or continuous tone which either partially pass (a negative film) or partially block (a positive film) light in the course of preparing the corresponding color printing plate to be used in the final printing process.

Each such "dot" or "tone" of the printing plate permits more or less of the corresponding ink to be applied to the paper on which the printed color reproduction is printed.

As diagrammatically illustrated in Fig. 1, to obtain a color proof of what the printed color reproduction will be, using a given set of inks and a given set of color separation films, the printer or color proofer, in utilizing the concepts of the present invention, first makes so-called "draw down" samples of the four inks on the paper or like base which is identical to or at least similar in color and texture to the paper or base on which the printing run is to be made. These are simply samples or "swatches" of the yellow, magenta, cyan and black inks which the printer has tentatively selected for the printing.Each ink swatch thus produced is then subjected to color analysis, as by comparison with a color reference data base developed and applied as taught by our aforementioned Great Britain Application 14353/78 to determine in each instance the red, green and blue components thereof, and up to three color filters are selected in each instance from which the color of each ink swatch, as a color proofing target color, can be reproduced from a given light source.As will be understood, with a given light source and with four swatches of a selected set of ink candidates (yellow, magenta, cyan and black), the analysis technique of the present invention provides the color proofer with information as to the identity of each of the up to three color filters to be used in the reproduction of each of the four target colors (the ink swatches), and the light source exposure times to be used with each of the color filters to reproduce each of the four target colors.

With this information at hand, a selected photographic print paper (such as Kodak Ektacolor RC 74 negative print paper, for example) is placed on pins in the exposure plane associated with the light source and filters (the pins matching pin holes in the separation films) the first (e.g. yellow) separation film is then placed on the unexposed photographic print paper, and the light source and first group of filters (e.g. the yellow group) are controlled to expose the photographic print paper and first (e.g.

yellow) separation film to the light source in sequence through the associated up to three filters for the determined illumination times to reproduce the first ink target color image on the photographic paper when the paper is developed. The first separation film is then removed from the print paper, the second separation film (e.g. magenta) is superimposed on the paper, and the exposure process is repeated using the second group of up to three filters (e.g. the magenta group) and the associated exposure times determined for the second (e.g. magenta) ink swatch.The second separation film is then removed from the photographic paper and the third (e.g. cyan) separation film superimposed thereon, with the exposure sequence again repeated using the up to three color filters of the third group of filters (e.g. the cyan group) and the associated exposure times determined from the target color analysis of the third (e.g. cyan) ink swatch. The third separation film is then removed from the photographic paper and the fourth separation film (e.g. black) superimposed thereon, with the exposure sequence again being repeated with the up to three color filters of the four group of filters (e.g. the black group) and the associated exposure times determined for the fourth (e.g. black) ink target color swatch.

The resulting photographic paper, thus exposed, is developed in the conventional manner, and the resulting developed print is an image-wise color proof on a single sheet of opaque paper, accurately showing the color proofer what the finished printed color material will look like when printed on the selected paper by use of the selected inks and printing plates prepared from the selected separation films, it being significant in this respect that the color proof is thus produced without test plates and without actual use (beyond the preparation of the original ink swatches) of the inks to be used on the paper to be used in the final color printing.

As a specific example of practice of the present invention, a set of color separation films was prepared from a graphic art overlay of a city tourist map and related text material. The separation films were produced by compositing various screen effects into four color separation negatives in a known manner. Specifically, various color effects were developed on GAF P4 20x24tt line negative film, following which the color effects were composited on GAF HD 403 duplicating film for the four color separation negative films. Target color samples were obtained from the printer on coated web stock white paper (50 Ib.) which were draw downs of the four inks to be used in the printing of the maps, namely Acme Temp Yellow M76325-A, Acme Temp Proc. Warm Red M-79535, Acme Temp Blue M76326 and Acme Temp Black M-76990.The available illuminant light source was a GE tungsten map lamp rated at 100 watts at 20 volts, and the temperature thereof was measured to be 305or Kelvin by a Gossen color temperature meter. The primary color components of the various samples were then measured by a GAM reflection densitometer, Model GAM 126P. The yellow ink sample was found to have a gray level of 13, a density (proportionate percentage) of 23 (13.6%) for blue, 30 (17.8%) for magenta, and 11 6 (68.6%) for yellow. The magenta or warm red sample was found to have a gray level of 45, a density of 29 (11.3%) for blue, 134 (52.3%) for magenta, and 93 (36.3%) for yellow. The cyan or blue sample was found to have a gray level of 96, a density of 151 (60.2%) for blue, 64 (25.5%) for magenta, and 36 (14.3%) for yellow. The black ink sample was found to have a gray level of 189, a density of 193 (33.2%) for blue, 193 (33.2%) for magenta, and 1 96 (33.6%) for yellow.

The x, y and z co-ordinates of the ink samples were determined by reference to a data base (as in our Great Britain Appln. 14353. 78), or such can be determined directly by use of a spectrophotometer), as follows: Ink Sample x y z yellow .4973 .4614 .0275 magenta .6107 .3312 .0579 cyan .2245 .3193 .4560 black .4597 .4063 .1338 In this example, the filters chosen were the same as employed in the earlier example set forth, namely Kodak Wratten Photomechanical Filters Numbers 25 (red), 58 (green), and 478 (blue). In this example, the selected undeveloped photographic paper was Kodak Ektacolor RC 78, type NRC, manufactured by the Eastman Kodak Company.For this paper, the saturation times, adjusted as to each gray level, were determined as earlier set forth, for the red, green and blue filters, to be: Filter 25 Filter 58 Filter 478 For gray level (red) (green) (blue) 13 (yellow) 3.5 sec. 8.2 18.3 45 (magenta) 41.8 28.3 63.5 96 (cyan) 89.2 60.4 135.4 189 (black) 175.6 118.9 266.7 From the determined information as to the color component makeup of the samples, the characteristics of the available primary color filters, and the nature and saturation times of the given photographic paper in relation to the filters and illuminant source, the corresponding exposure times to substantially reproduce each target color on the photographic paper were determined, with reference to the color reference data base, to be:: Exposure Exposure Exposure Exposure of yellow of magenta of cyan of black separation separation separation separation Filters film film film film 25 (red) 0.2 sec. none 103.7 85.7 58 (green) none 53.0 5.9 52.6 47B (blue) 36.3 19.0 4.2 46.1 To extend the exposure times for improved control thereof in a manner known per se, each filter pack had included therewith a neutral density filter of 1.50 rating, to reduce the intensity of the light from the illuminant source, and also an ultraviolet absorbing filter, utilizing filters for these purposes which are commercially available from Eastman Kodak Company.

The photographic paper was exposed to the illuminant source successively through each filter for each of the indicated times for each separation film in succession. Exposure times were controlled semi-automatically by a DIT 200 timer, marketed by Sergeant-Welch Company. With the photographic paper thus exposed, it was then developed in the conventional manner, according to the manufacturer's specifications. The exposure and development cycle was completed in about fifteen minutes, and can be even faster if neutral density filters are reduced or not used. Upon drying, the developed photographic paper provided an accurate color proof of the proposed printing run based on the color separation negatives at hand, using the selected inks and printed on the type of paper presented.

Fig. 2 diagrammatically shows the overall color printing reproduction procedure utilizing the color proofing technique shown and discussed in connection with Fig. 1. Proceeding from a color original of either a two dimensional or three dimensional nature, four color separation films are prepared in a manner conventional per se, such as by photography. As known, these separation films can be either positives or negatives and of a screened or half or continuous tone character. The color separation films may then either go directly to a printer who does his own color proofing, or to a specialty color proofing shop where the color proof is prepared for subsequent approval and delivery to a printing house.Given a set of color separation films and certain candidate inks and paper or like base on which the color reproduction is to be printed, the printer or color proofer prepares swatches of the inks on the printing base or reasonable facsimile thereof and then proceeds with the production of one or more color proofs, following the procedure illustrated and discussed in connection with Fig. 1. The resulting proof or proofs are then inspected and approved by the printing buyer, such as an advertising agency or the like. Printing plates in the respective colors are then prepared from the respective color separation films in a manner conventional per se, such as by known etching processes, and the resulting printing plates are utilized along with the respective selected inks and the selected paper or like printing base during the printing run, also in the manner conventional per se.

In utilizing this color proofing technique, it will be readily understood that it is applicable to a wide variety of color proofing needs, such as in the reproduction of original works or art or other art work, colored signs, sample variations for textiles, wallpaper variations, paint or color swatches, variations in rug pattern colors, plastics, or anything requiring a visual sample or samples of what a finished product might look like in color.Reproducing colors of natural products such as fruits or vegetables, or a glass of wine, for example, is also an application of the present technique, where the color components of the natural product can be measured with a spectrophotometer and the colors reproduced on photographic paper by the target color reproduction technique of the present invention, then reproduced from given inks as a printed color reproduction, with the colors of the printed reproduction when printed being "proofed" in relation to selected inks by the color proofing technique of the present invention.

Various modifications, further adaptations and variations will readily occur to those skilled in the arts to which the invention is addressed. Thus, simply by way of further example, it will be recognized that other coloring agents, such as pigments or dyes rather than printer's inks, may be equally well addressed by the target color reproduction technique of the present invention, and that the nature of the base to which the inks or the like (e.g. pigments or dyes) are to be applied may be readily varied.

Thus, the particular nature of the printing paper (matte or glossy, for example), or other texture of the print base (which may be three dimensional such as equipment fronts or calculator keys or the like), can widely vary in practice and can be readily matched or at least closely simulated in practice of this color proofing technique.

In utilizing the present invention, it is an important advantage and characteristic that the determination of the target color color constituents can take into account the color of the paper or other printing base itself, which of course contributes its colors to the colors of the ink or the like swatches.

Rather than requiring any particular color proofing films and any particular type of film or paper on which the color proof is to be developed, the color proofing technique of the present invention may be used with any photosensitive photographic paper of any texture, it being recognized of course that undeveloped photographic paper is commercially available or can be made to order in a wide variety of colors, textures and configurations and is considerably more economic consumable than the specially prepared photopolymeric materials heretofore required for pre-press color proofing.

The color proofing technique of the present invention, by means of which a color proof is obtained by successive exposure of undeveloped photographic paper to an illuminant light source through color separation films successively placed in register on the photographic paper and through successive color filters for successive exposure times calculated to substantially reproduce each color associated with each color separation film on the photographic paper when developed, is not necessarily limited to any particular technique for determining the color or color component makeup of the ink or the like with which each color separation film is correlated.Thus, in a given instance, the correlation between a given ink or the like and a given color separation film, in terms of the filters and exposure times necessary to substantially reproduce the ink color on a particular given photographic paper or the like, may be determined as a factory specification or be otherwise available to the color proofer.It is contemplated, for example, that a manufacturer and materials supplier to the color proofing and printing trade can provide the trade with a color proofing "package" involving an inventory of printer's inks or the like, an inventory of colored filters and illuminant source or sources, an inventory of types of undeveloped photosensitive photographic paper, and a computer or like equipment pre-programmed to correlate any particular ink and any particular paper with the available illuminant source(s) and color filters, and provide the appropriate corresponding filter exposure times, such computing or like equipment as funished by the manufacturer providing to the color proofer a direct readout of the photographic paper to be used and the illuminant source, filters, and associated exposure times to be used in the given instance.It is further contemplated that, with these outputs, such an equipment could be automated in the sense that exposure of the paper through each color separation film and its associated group of filters would be automatically controlled by the equipment.

At the beginning of a run the color proofer manually inputs to the equipment the identity of the target colors to be reproduced (e.g. the printer's inks or the like to be used during the printing run), the nature of the paper to be used during the printing run, and possibly any corrective inputs desired such as modifications in hue or tone. The pre-programmed equipment would then automatically determine the illuminant source, the group of filters and exposure times to be used to reproduce the color of each given ink or the like, and on demand would automatically sequence the filter exposures through each separation film.Operation of the equipment would involve the color proofer simply sequentially registering the first color separation film with the photographic paper, then activating the equipment to perform the filter exposure sequence associated with the ink correlated with that separation film, then removing the first separation film from the paper and registering the second separation film therewith, then again activating the equipment to perform the associated filter exposure sequence for the ink correlated with the second film, and so on until the paper is fully exposed through all separation films and associated filters. Following the exposure cycles, then, such equipment could also be automated to automatically develop the photographic paper and deliver the developed photographic media to the color proofer as the finished color proof.

From the foregoing, various further applications, modifications and adaptations of the method disclosed by the foregoing preferred embodiments of the present invention will be apparent to those skilled in the art to which the present invention is addressed, within the scope of the following claims.

Claims (19)

Claims

1. The method of color proofing a set of multi-color separation films, comprising: (a) successively exposing an undeveloped color photosensitive surface to an illuminant light source through each color separation film in sequence, with the light source being exposed to the film and photosensitive media in each instance through successive color filters and for associated successive exposure times substantially reproducing each color image associated with each color separation film on the photosensitive media when developed; and (b) developing the photosensitive surface to provide the color proof.

2. The method of claim 1, wherein each color reproduced in relation to each color separation film substantially reproduces the color of the ink or the like to be used with a printing plate prepared from such color separation film.

3. The method of claim 1 or 2, wherein said color photosensitive surface is paper or the like simulating the surface on which printing is to occur using plates prepared from the set of color separation films.

4. Color proof, prepared according to the method of any of claims 1, 2 and 3.

5. The method of pre-press color proofing a set of color separation films from which printing plates are to be made for color printing of a multi-color image on a paper or like printing base with a given set of printer's inks or the like, said method comprising: (a) preparing samples of the given inks or the like on the printing base or equivalent thereof; (b) determining the primary color component makeup of each sample in relation to a given illuminant source and from a color reference data base based on such illuminant source, determining a group of color filters and associated color filter exposure times appropriate to substantially reproduce each sample color on a selected photographic paper when the paper is exposed to the illuminant source through such filters for such exposure times;; (c) exposing the undeveloped photographic paper to the light source in sequence through each color separation film and its associated group of color filters for the determined respective filter exposure times to substantially reproduce each separation film color image in the associated sample color on the photographic paper when developed; and (d) developing the exposed photographic paper to provide a pre-press color proof.

6. A color proof, produced by the method of claim 5.

7. Printed material, produced by use of said printer's inks or the like and printing plates made from the set of color separation films color proofed as set forth in claim 5.

8. The method of claim 5, wherein the color component makeup of each sample is determined spectrophotometrically.

9. The method of claim 5, as applied to color proofing a set of color separation films based on colored pictorial material.

10. The method of claim 5, as applied to color proofing a set of color separation films based on graphic art work.

11. The method of claim 5, as applied to color proofing a set of color separation films based on a three-dimensional object.

12. The method of claim 5, as applied to color proofing a set of color separation films based on a color dyed textile or fabric.

13. The method of claim 5, as applied to color proofing a set of color separation films based on pigmented paint.

14. The method of claim 5, as applied to color proofing a set of color separation films based on color dyed carpet or rug material.

15. A method of obtaining target colors on color photosensitive photographic media, utilizing a light source and color filters, said method comprising: (a) preparing a color reference data base expressing the primary color component makeup of a plurality of colors illuminated by a given light source, (b) determining from the data base the primary color component makeup of each target color under illumination by the given light source, (c) selecting a group of up to three filters capable of reproducing each target color by appropriate sequential exposures and development of photographic material, (d) determining from the primary color component makeup of each filter under illumination by the given light source and from the sensitivity of the photographic material to light from the given source filtered by each filter the color filter exposure times appropriate to substantially reproduce each target color on the photographic media when developed, (e) partially masking and exposing the undeveloped color sensitive photographic media the illuminant source in sequence through each group of color filters for the determined exposure time for each filter, to substantially reproduce each target color on the respective unmasked portions of the photographic media when developed, and (f) developing the exposed photographic media.

1 6. The method of claim 1 5, as applied to the preparation of a color proof from a set of color separation films, comprising: (a) determining from printer's ink swatches of respective primary color and black inks the color component makeup of each in relation to the illuminant source; (b) determining from the color components of the inks and from the color reference data base, the respective color filters and respective exposure times appropriate to reproduce each target color on the photographic media when developed; (c) exposing the photographic media to the illuminant source through each color separation film and its associated group of color filters for the determined respective exposure times to substantially reproduce each separation film color image in the associated target color on the photographic media when developed; and (d) developing the exposed photographic media to provide the color proof.

17. Color proof media, produced by the method of claim 16.

18. Printed media, produced by use of printer's inks and printing plates made from the set of color separation films color proofed as set forth in claim 16.

19. A method of color proofing a set of multi-color separation films substantially as hereinbefore described with reference to Fig. 1 or Fig. 2 of the accompanying drawings.