US3215030A

US3215030A - Color print simulator

Info

Publication number: US3215030A
Application number: US156006A
Authority: US
Inventors: Joseph G Jordan
Original assignee: Time Inc
Current assignee: TI Gotham Inc
Priority date: 1961-11-30
Filing date: 1961-11-30
Publication date: 1965-11-02
Anticipated expiration: 1982-11-02

Description

SEAR C r1 SUSHI Nov. 2, 1965 J- G. JORDAN COLOR PRINT SIMULATOR Filed Nov. :50, 1961 INVENTOR. JOSEPH. G. JORDAN hll A TTOR/VEYS United States Patent York Filed Nov. 30, 1961, Ser. No. 156,006 7 Claims. (Cl. 88-1) This invention relates to devices for analyzing the various color images on the separation image-bearing elements used in a multicolor printing process and, more particularly, to a new and improved device for analyzing such images to produce a visual representation of the results which will be obtained when they are combined in a print.

In multicolor printing processes, separate image-bearing elements such as continuous tone negative or positive transparencies are made in any of several ways as, for example, by photographing the object successively through different colored optical filters so that each of the elements contains the image information relating to only one of the various colors. From these elements, halftone plates or cylinders are made by a process which may involve many complex and time-consuming steps and it is impossible to ascertain what the final print will look like until these plates have been made and used to produce a proof. Once the process has been completed and the plates are made, however, the optimum point for introducing corrections into the separation images has passed and any necessary changes must then be made by hand on the engraved plates where the letterpress process is used, or, in the offset process, the plates must be made over, while, in gravure, the cylinders must be re-etched.

Various attempts have been made heretofore to predict the appearance of the proof or final print from the separation images at an earlier stage of the process, such as by substituting a simpler photographic process in place of the plate making and printing process or by photoelectric analysis of the various separation images point by point and, synthesis of a corresponding proof based upon an empirically determined relationship between the separations and a resulting print. In the former case, the absence of any photographic dyes or colorants sufliciently similar to printing ink makes the resulting approximation of the final print inaccurate while, in the latter case, the required machinery is complex and expensive.

Accordingly, it is an object of the present invention to provide a new and improved device for simulating accurately the appearance of a color print from separation images which avoids the above-mentioned disadvantages of the prior art.

Another object of the invention is to provide a new and improved color print simulator capable of synthesizing an accurate representation of a color print immediately and directly from color separation image-bearing elements without requiring any further processing of the images.

A further object of the invention is to provide a'new and improved coloeprwlator of the above character which is simple and inexpensive in structure and operation.

These and other objects of the invention are attained by dividing light from a source into two color components corresponding respectively to the reflection and absorption characteristics of one of the inks to be used in the printing process, projecting one of these components through a corresponding separation image-bearing element, recombining the color components, and then subjecting the combined light to similar successive operations involving each of the other separation image-bearing elements. The resulting image, which has been color modified in this manner may be viewed directly or projected onto a screen for viewing. In a particular device for carrying out the invention, dichroic mirrors are utilized to divide the light into color components corresponding to the reflection and absorption characteristics of the corresponding printing inks. Alternatively, optical color filters having the same characteristics may be used.

Further objects and advantages of the invention will be apparent from a reading of the following description in conjunction with the accompanying drawings in which:

FIG. 1 is a schematic view of a typical color print simulator arranged according to the invention;

FIG. 2 is a schematic view showing the arrangement of one form of light divider suitable for use in the system shown in FIG. 1, and;

FIG. 3 is a schematic diagram illustrating the relative dimensions of a portion of a simulator utilizing the light divider arrangement shown in FIG. 2.

In the representative embodiment of the color print simulator shown in FIG. 1, the images on three color separation

positive transparenices

10, 11, and 12 and a black printer positive transparency 13, from which printing plates or cylinders are to be made, are synthesized to project a color image accurately representing the appearance of the print which will be produced from the plates or cylinders onto a screen 14. To this end a conventional condensing lens 15 concentrates light from a source 16 through the black printer 13 onto an objective lens 17, which is the first imaging element of the system.

It will be understood of course, that if no black printer is used in the process, the element 13 is omitted from the system. Moreover, the transparencies 10-13 may be of either continuous tone images, as is usually the case in the gravure process, or halftone images as used in the offset process, for example. Also, although the simulator is described herein with reference to processes for preparing plates and cylinders for press printing, it will be understood that the invention is equally applicable to photographic or other processes wherein color prints are made from color separation images.

In accordance with the invention, the print simulator includes means for dividing light from the lens 17 into two components, one of which corresponds in color to the light absorbed by one of the printing inks used in the process and the other of which corresponds in color to the light reflected by the same ink. In the illustrated embodiment of the invention, this light dividing means comprises a dichroic mirror 18 which transmits a beam 19 of light having a particular spectral characteristic and reflects a beam 20 having a difierent spectral characteristic. Assuming the transparency 10 is the one from which a yellow ink printing plate is to be made, the dichroic mirror 18 has a spectral reflection distribution similar to the spectral absorption distribution of the yellow ink while its transmittance distribution is like the spectral reflection distribution of the yellow ink. Alternatively, if desired, the dichroic mirror 18 may be replaced by a half-silvered mirror and optical color filters having the required spectral transmittance characteristics may be interposed in the paths of the reflected and transmitted beams of light, but with this arrangement, a light source of considerably higher intensity must be used to obtain the same illuminance on the screen 14.

After being reflected by a mirror 21, the beam 20 passes through a field lens 22 which, in conjunction with the objective lens 17, superimposes an image of the black printer positive transparency 13 on the yellow separation positive 10 so that corresponding image portions coincide. In this way, the yellow separation positive absorbs light of the same spectral character and to the same extent at each point in the image as will be absorbed by the yellow ink in a print made from the separation image.

At the same time, the beam 19 transmitted by the dichroic mirror 18 and representing light of the quality which is reflected by the yellow ink passes through a field lens 23 identical to the lens 22 so that a corresponding aerial image 24'of the black printer 13 is formed. This light beam is then reflected by a mirror 25 and by a half-silvered mirror 26 which also transmits light in the beam 20 passed by the yellow transparency 10 so as to form a combined beam of light 27 wherein the yellow ink absorption information has been subtracted from the original light. Moreover, inasmuch as the light absorbed by a colored material is generally the color complement of the light reflected by the material, a positive complementary image-bearing color separation transparency (not shown) which has been made from the original object through a complementary color filter may, if desired, be interposed in the beam 19 to coincide with the aerial image 24 instead of the transparency 10 in the beam 20. V

In a similar manner the beam 27, after passing through an objective lens 28, is divided by a dichroic mirror 29 selected to have a spectral reflectance characteristic similar to the absorption characteristic of the magenta printing ink used in the process and a tranmittance characteristic like the spectral reflectance of that ink, the separation transparency 11 being the one from which the magenta printing plate is to be made. The reflected beam 31, after further reflection by a mirror 32, passes through a field lens 33 which, with the objective lens 28, superimposes the combined aerial image 24 and yellow separation image in the transparency 10 on the magenta separation positive 11 coincident with the image thereon, while the transmitted beam passes through a field lens 34 to form an aerial image 35 of the combined images 10 and 24. After reflection by a further mirror 36, the beam 30 is recombined with the beam 31 by a half-silvered mirror 37 to form a beam 38 wherein both the yellow and the magenta ink absorption information have been subtracted.

This combined beam 38 is likewise transmitted through an objective lens 39 and divided by a dichroic mirror 40 which passes a beam 41 having the cyan ink reflectance characteristic and reflects a beam 42 having the cyan ink absorption characteristic the latter beam being further reflected by a mirror 43 and imaged by a field lens 44 onto the cyan-separation positive 12. As in the preceding stages, the transmitted beam 41 is imaged by a field lens 45 to form an aerial image 46 and then deflected by a mirror 47 to a half-silvered mirror 48 which recombines the two beams. From this point, a projection lens 49 projects the recombined light onto the screen 14 to form an image which has the same color characteristics as the ultimate print will have. If desired, the screen 14 may be omitted and the lens 49 may be selected to permit a viewer to observe the combined image by looking toward the half-silvered mirror 48.

Although the image produced in the manner described above will represent reasonably accurately the color characteristics of a print made from the separation positive, its appearance will difier slightly from the actual print in certain respects. For example, the simulator does not make allowance for the changes in the halftone dot size effected in the plate making and printing processes or for the nonuniformity of ink film thickness across the dots, nor can it simulate the effect of ink trapping variations in printing or internal light scattering in the paper. Certain of these effects may, however, be introduced into the present system by conventional optical techniques, such as by varying the focus of the images on the separation elements, introducing flare or non-image-forming light into certain of the beams, 01'

making the spectral characteristics of the dichroic filters slightly difierent from those of the inks used in the process.

In order to produce a field of uniform color in the beams transmitted and reflected by a dichroic mirror, all of the light must be incident upon the mirror at approximately the same angle. To accomplish this in the present system, the

objective lenses

17, 28, and 39 which are schematically shown in FIG. 1, are preferably of the telecentric form shown in FIG. 2, having a positive component 50 and two

negative components

51 and 52, one for each emergent beam, the corresponding dichroic mirror 53 being located between the positive and negative components. This objective also includes an aperture stop 54 located in front of the positive component 50 adistance equal to the focal length of that element so that the principle rays from all points in the field of view emerge from the positive lens element in parallel directions so that they all strike the dichroic mirror 53 at the same angle. Although all the other rays from each point in the object have an angular distribution about the principal ray, this distribution will be the same for all parts of the field so that the color of the field in each of the divided beams is uniform throughout.

While this result might be accomplished by using a positive lens element alone, for one-to-one magnification this would require a dichroic mirror 53 larger than the object. Accordingly, the

negative elements

51 and 52 are included to increase the focal length of the system so that the positive element contributes relatively lower magnification and can be proportionately smaller. Another advantage of the telecentric objective is that, if the negative and positive components have the same numerical focal length, the addition of the negative component makes the objective of a form that is inherently free of astigmatism and field curvature.

In the schematic diagram shown in FIG. 3 the relative dimensions of a portion of a simulator utilizing a particular form. of telecentric objective are illustrated. In this case, the positive and

negative components

50 and 51 have a focal length of two units of length, such as inches, and are one unit in diameter and they are separated by one unit of distance. The aperture stop 54, which is two units distant from the positive element, preferably has an opening one-fifth unit in diameter so that one-to-one magnification with full field coverage is obtained for an object 55 having a maximum dimension of three units and located ten units away from the positive lens element.

Although the invention has been described herein with reference to specific embodiments, many modifications and variations therein will readily occur to those skilled in the art. Accordingly, all such variations and modifications are included within the intended scope of the 'invention as defined by the following claims.

I claim:

1. A device for simulating the appearance of a color print from a plurality of transparent color separation image-bearing elements each corresponding to one of a corresponding plurality of colored materials from which the color print is to be made comprising light source means, first light modulating means comprising light dividing means disposed at a first location for dividing light into two beams which follow different paths to a second location, one of which has a color characteristic approximately the same as that of light reflected by the corresponding colored material and the other of which has a color characteristic approximately the same as that of light absorbed by the corresponding colored material, a corresponding color separation image-bearing element interposed in the path of one of the two beams between the first and second location, and means disposed at the second location for recombining the two beams of light into a single beam, second light modulating means comprising light dividing means disposed at a third location for dividing light received from the second location into two beams which follow different paths to a fourth location, one of which has a color characteristic approximately the same as that of light reflected by a second corresponding colored material different from the colored material of the first light modulating means, and the other of which has a color characteristic approximately the same as that of light absorbed by the second corresponding colored material, a second corresponding color separation image-bearing element interposed in the path of one of the two beams between the third and fourth locations, and means disposed at the fourth location for recombining the two beams of light into a single beam whereby the appearance of a simulated color print can be previewed.

2. A device according to claim 1 wherein the corresponding color separation image-bearing element interposed in one of the two beams of the first and second light modulating means comprises means for supporting a corresponding positive transparency in the beam having a color characteristic approximately the same as that of light absorbed by the corresponding colored material.

3. A device according to claim 1 wherein each light dividing means comprises a dichroic mirror.

4. A device according to claim 3 including objective lens means comprising a positive lens element interposed in the light beam incident on the dichroic mirror of each modulating means to project all the principal rays toward the mirror in substanttially parallel directions and a negative lens element in each of the beams reflected and transmitted by the dichroic mirror.

5. A device according to claim 4 wherein the positive and negative lens elements have the same focal length and including aperture stop means interposed a distance equal to the focal length in front of the positive lens element.

6. A device according to claim 1 including a transparent black printer image-bearing element interposed in the path of light from the source.

7. In a process for simulating the appearance of a color print from a plurality of transparent color-separation image-bearing elements each corresponding to one of a corresponding plurality of colored materials from which the color print is to be made, the steps of dividing a beam of light at a first location into two beams which follow dilferent paths to a second location, one of which has a color characteristic approximately the same as that of light reflected by the corresponding colored material and the other of which has a color characteristic approximately the same as that of light absorbed by the corresponding colored material, transmitting one of the beams through a corresponding color separation imagebearing element located in the path of the beam between the first and second locations, recombining the two beams of light into a single beam at the second location, dividing the beam from the second location at a third location into two beams which follow difierent paths to a fourth location, one of which has a color characteristic approximately the same as that of light reflected by a second corresponding colored material different from that of the first-mentioned colored material and the other of which has a color characteristic approximately the same as that of light absorbed by the second corresponding colored material, transmitting one of the beams through a corresponding color separation image-bearing element located in the path of the beam between the third and fourth locations, and recombining the two beams of light at the fourth location whereby the appearance of a simulated color print can be previewed.

References Cited by the Examiner UNITED STATES PATENTS 2,961,920 1 1/60 Sachtleben 88-24 2,976,348 3/61 Bailey et al. 88-24 2,981,791 4/61 Dixon 88-24 2,983,824 5/61 Weeks et a1 88-1 2,985,065 5 61 Haynes et al. 88-24 3,019,703 2/62 Kilminster 8824 JEWELL H. PEDERSEN, Primary Examiner.

WILLIAM MISIEK, Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 5,215,030 November 2, 1965 Joseph G. Jordan It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 5, lines 20 and 21, strike out "means for supporting a"; line 30, for "substanttially" read substantially --c Signed and sealed this 23rd day of August 1966.

(SEAL) Attest:

ERNEST W. SWIDER EDWARD J. BRENNER Attesting Officer Commissioner of Patents

Claims

1. A DEVICE FOR SIMULATING THE APPEARANCE OF A COLOR PRINT FROM A PLURALITY OF TRANSPARENT COLOR SEPARATION IMAGE-BEARING ELEMENTS EACH CORRESPONDING TO ONE OF A CORRESPONDING PLURALITY OF COLORED MATERIALS FROM WHICH THE COLOR PRINT IS TO BE MADE COMPRISING LIGHT SOURCE MEANS, FIRST LIGHT MODULATING MEANS COMPRISING LIGHT DIVIDING MEANS DISPOSED AT A FIRST LOCATION FOR DIVIDING LIGHT INTO TWO BEAMS WHICH FOLLOW DIFFERENT PATHS TO A SECOND LOCATION, ONE OF WHICH HAS A COLOR CHARACTERISTIC APPROXIMATELY THE SAME AS THAT OF LIGHT REFLECTED BY THE CORRESPONDING COLORED MATERIAL AND THE OTHER OF WHICH HAS A COLOR CHARACTERISTIC APPROXIMATELY THE SAME AS THAT OF LIGHT ABSORBED BY THE CORRESPONDING COLORED MATERIAL, A CORRESPONDING COLOR SEPARATION IMAGE-BEARING ELEMENT INTERPOSED IN THE PATH OF ONE OF THE TWO BEAMS BETWEEN THE FIRST AND SECOND LOCATION, AND MEANS DISPOSED AT THE SECOND LOCATION FOR RECOMBINING THE TWO BEAMS OF LIGHT INTO A SINGLE BEAM, SECOND LIGHT MODULATING MEANS COMPRISING LIGHT DIVIDING MEANS DISPOSED AT A THIRD LOCATION FOR DIVIDING LIGHT RECEIVED FROM THE SECOND LOCATION INTO TWO BEAMS WHICH FOLLOW DIFFERENT PATHS TO A FOURTH LOCATION, ONE OF WHICH HAS A COLOR CHARACTERISTIC APPROXIMATELY THE SAME AS THAT OF LIGHT REFLECTED BY A SECOND CORRESPONDING COLORED MATERIAL DIFFERENT FROM THE COLORED MATERIAL OF THE FIRST LIGH TMODULATING MEANS, AND THE OTHER OF WHICH HAS A COLOR CHARACTERISTIC APPROXIMATELY THE SAME AS THAT OF LIGHT ABSORBED BY THE SECOND CORRESPONDING COLORED MATERIAL, A SECOND CORRESPONDING COLOR SEPARATION IMAGE-BEARING ELEMENT INTERPOSED IN THE PATH OF ONE OF THE TWO BEAMS BETWEEN THE THIRD AND FOURTH LOCATIONS, AND MEANS DISPOSED AT THE FOURTH LOCATION FOR RECOMBINING THE TWO BEAMS OF LIGHT INTO A SINGLE BEAM WHEREBY THE APPERANCE OF A SIMULATED COLOR PRINT BE PREVIEWED.