GB2061060A

GB2061060A - Masking arrangement for color printing

Info

Publication number: GB2061060A
Application number: GB8037146A
Authority: GB
Original assignee: Toppan Printing Co Ltd
Current assignee: Toppan Inc
Priority date: 1978-01-20
Filing date: 1979-01-18
Publication date: 1981-05-07
Also published as: CH633139A5; GB2061061B; GB2022352B; NL7900451A; DE2902245B2; GB2061060B; GB2022352A; DE2953088C2; DE2902245A1; GB2061061A; DE2902245C3

Abstract

Pairs of signals of Y and M, Y and C, and C and M are formed by combining two members out of Y, M and C image signals. The minimum and maximum selected signals from the combinations are generated along with minimum and maximum selected signals from the three Y, M and C image signals. The signals of cyan, magenta and yellow colors are detected and generated by subtracting the minimum selected signals of the combined signals from the minimum selected signal of three Y, M and C signals. The signals of red, green and blue colors are detected and generated by subtracting the maximum selected signals of the combined signals from the maximum selected signal of three Y, M and C signals. The hues, saturations and brightnesses of the six color signals are controlled and the six color controlled signals are added to the Y, M and C image signals.

Description

1 GB 2 061 060 A 1

SPECIFICATION

Improvements in or relating to color separation This invention relates to a masking device and a method of masking for forming the pairs of signals Y and M, 5 M and C, and C and Y.

When colored pictures are printed by using colored originals such as color photographs, the color separation films are prepared by separating the colors of originals with using a color separation device such as a color scanner.

The present invention relates to an apparatus for determining the color separation conditions, in which a 10 color original is firstly scanned to obtain electrical signals of the image, the image signals are corrected so as to be printed desirably, and in order to develop the image on a color monitor in the state similar to the actually printed image, the above corrected image signals are further corrected. By developing thus corrected image signals on the color monitor, the conditions for the color separation process can be determined. The present invention further relates to the method for the above color signal correction and the 15 matrix circuit which is used in the above apparatus. 2) Description of prior art

In the case that a color original such as a color photograph is printed, the printing operation comprises the following three steps in general cases. The first step is a color separation step in which the color separation films are prepared by separating the colors of an original picture with using a color separation device such as 20 a color scanner. The second step is a plate making step in which the printing plates for practical printing are prepared from the color separation films. The third step is a practical printing step in which the printing plates are attached to a printing press and printed matters are then produced.

While, in the above series of steps, the fully colored products are obtained only in the final practical printing step and colored materials are not obtained in the intermediate steps, therefore, it is quite difficult to 25 estimate whether the final printings have good colors or not.

For example, in the case that the tone of color is not desirable in the original picture, each color is corrected in the intermediate steps (mainly in the color separation step), however, it is difficult to judge whether such correction is adequate or not.

Since the state of color of the final printings is hardly presumed in the intermediate steps, the so-called 30 previewing apparatus have been proposed recently, in which apparatus the image that is similarto the image to be actually printed is developed on a color television screen so as to check up the colors of image in each step.

Exemplified as the apparatus to check up whether the image to be printed from the color separation films are desirable or not, are the previewing apparatus of Hazeltine Research, Inc. as disclosed in United States 35 Patent No. 3,131,252 and the apparatus of the present applicant which is disclosed in United States Patent No. 3,972,066. Further, as the apparatus for determining the conditions in color separation step by previewing, there are exemplified an apparatus of DrAng. Rudolf Hell GmbH as disclosed in West German Offeniegungsschrift No. 2607623. In this apparatus of Hell GmbH, a previewing device and a color scanning device are combined in in-line.

In the previewing apparatus of this kind, the most important fact is that how the image on the color television monitor is made similar to the actually printed image. Further, when the apparatus of this kind is put in the actual process, the apparatus is regulated in compliance with several conditions (by regulating correction factors), and the second important fact is that such the regulation is easily carried out.

By the way, the above-mentioned Hazeltine's apparatus was put on the market, however, they are sold very few, now, because the resemblance of color is not good.

Further, the apparatus of Hell GmbH are also sold on the market now, however, the resemblance of color is not satisfactory and the regulation of the apparatus is quite troublesome. In the previewing apparatus of the present applicant for checking up color separation films, is obtaining favorable reputations in the relevant field because the method of simulation as disclosed in the United States Patent is quite satisfactory.

According to one aspect of the present invention there is provided a masking device which comprises means for forming the pairs of signals of Y and M, M and C, and C and Y by combining two members out of Y, M and C image signals and for generating the minimum selected signals from said combinations, means for generating another minimum selected signal from said three Y, M and C image signals, means for detecting and generating the signals of cyan, magenta and yellow colors by subtracting said former 55 minimum selected signals of said combined signals respectively from said latter minimum selected signal of three Y, M and C signals, means for controlling the hues, saturations and brightnesses of said cyan, magenta and yellow color signals and means for adding the color correction signals of said cyan, magenta and yellow color controlled signals to said Y, M and C image signals.

Another aspect of the invention provides a masking device which comprises means for forming the pairs 60 of signals of Y and M, M and C, and C and Y by combining two members out of Y, M and C image signals and for generating the minimum selected signals and maximum selected signals from said combinations, means for generating other minimum selected signal and maximum selected signal from said three Y, M and C image signals, means for detecting and generating the signals of cyan, magenta and yellow colors by subtracting said former minimum selected signals of said combined signals respectively from said latter 2 GB 2 061060 A 2 minimum selected signal of three Y, M and C signals, means for detecting and generating the signals of red, green and blue colors by subtracting said former maximum selected signals of said combined signals respectively from said latter maximum selected signal of three Y, M and C signals, means for controlling the hues, saturations and brightnesses of said six color signals and means for adding the color correction signals of said six color controlled signals to said Y, M and C signals.

In yet another aspect the invention provides a method of masking, which method comprises forming the pairs of signals of Y and M, M and C, and C and Y by combining two members out of Y, M and C image signals generating the minimum selected signals from said combinations, generating another minimum selected signal from said three Y, M and C image signals, detecting and generating the signals of cyan, magenta and yellow colors by subtracting said former minimum selected signals of said combined signals respectively from said latter minimum selected signal of three Y, M and C signals, controlling the hues, saturations and brightnesses of said cyan, magenta and yellow colour signals and adding the color correction signal of said cyan, magenta and yellow color controlled signals to said Y, M and C image signals.

A further aspect of the invention provides a method of masking, which method comprises forming the pairs of signals of Y and M, M and C and C and Y by combining two members out of Y, M and C image signals, generating the minimum selected signals and maximum selected signals from said combination, generating other minimum selected signal and maximum selected signal from said three Y, M and C image signals, detect;.-9 and generating the signals of cyan, magenta and yellow colors by subtracting said former minimum selected signals of said combined signals respectively from said latter minimum selected signal of three Y, M and C signals, detecting and generating the signals of red, green and blue colors by subtracting 20 said former maximum selected signals of said combined signals respectively from said latter maximum selected signal of three Y, M and C signals, controlling the hues, saturations and brightnesses of said six color signals and adding the color correction signals of said six color controlled signals to said Y, M and C signals.

It is, therefore, the primary object of the present invention to provide a novel and improved apparatus for 25 use in the color separation work of the color printing.

Another object of the present invention is to provide an apparatus for determining the color separation conditions on which the image developed on a color monitor of the apparatus is made quite similar to the image to be printed.

A further object of the present invention is to provide such an apparatus which can be operated easily, 30 effectively and reliably.

Still a further object of the present invention is to provide a method for correcting color signals and matrix circuits which are used in the above-mentioned apparatus.

In accordance with the present invention, the apparatus for determining the color separation conditions is provided with a scanning section, masking circuits, under-color removal circuits, clip circuits, gradation 35 correcting circuits, color correcting circuits, matrix circuits and a color monitor of a color Braun tube.

These and other objects and features of the present invention will be more clearly apparent to those skilled in the art by the following detailed description of the invention with reference to the accompanying drawings, in which:

Figure 1 is a block diagram of an embodiment of the color separation condition determining apparatus 40 including a schematic plan view of the operation panel according to the present invention; Figure 2 is a block diagram showing the rotating mechanism of a filter device; Figure 3 is a plan view of a filter disc; Figure 4 is a wave form chart which is obtained by using the filter device shown in Figure 2; Figure 5 is a diagram of black and white level controlling circuits and white level controlling circuits for 45 color image signals; Figure 6 is a diagram of clip circuits; Figure 7 is a block diagram of color correcting circuits; Figure 8 to Figure 11 show the constitution of the masking circuits, in which:

Figure 8 is a schematic illustration of color bars; Figure 9 and Figure 10 are charts of image signals; Figure 11 is a block diagram of the masking circuit; and Figure 12 is a block diagram of the circuits for indicating a gray scale on a color monitor.

When a color original such as a color photograph is color-printed, color separation films of four colors, yellow (hereinafter referred to as "y"), magenta (hereinafter referred to as "M"), cyan (hereinafter referred to 55 as "C") and black (hereinafter referred to as "Be"), are prepared by using a color separation apparatus such as a color scanner. The printing plates that are used in the practical printing are prepared from these four color separation films. The printing plates are attached to a printing press and the printing operation is carried out in the succeeding step.

If the color gradation of the color original is not good, the color or gradation correction is performed in 60 orderto obtain good final printings. This color or gradation correction is done mainly in the color separation step, while the correction to some degree is possible also in the plate making step, by means of dot etching.

It should be noted, however, that, when the color correction is carried out, it is difficult to presume the corrected color of final printings in connection with a certain degree of the color correction. That is, the color separation films obtained in the color separation step are four black silver images of Y, M. C and Bt having 65 15, z 3 GB 2 061 060 A 3 corresponding densities. Therefore, it is difficult to imagne the printed full color image from these four silver images.

In order to eliminate the above difficulty, several previewing apparatus are proposed as described in the foregoing paragraph of the prior art. The largest problem in the devices of this kind is that the image formed on a color monitor is hardly made similar to the actually printed image. That is, the image on the color monitor is made by providing the color Braun tube with three primary colors of red (hereinafter referred to as "R"), blue (hereinafter referred to as "B") and green (hereinafter referred to as "G") as an additive mixture. While, the printed image is mainly represented on the surface of printing paper by the subtractive mixture of Y, M, C and BI. Accordingly, between the image of color monitor and printed paper, the color mixing methods and the used primary colors are different. Furthermore, assuming that there are two electric signals 10 of 10 % and 15 % corresponding to the respective color densities, when they are combined by additive mixture (that is, on a Braun tube), they are represented as the respective densities of 10 % and 15 %. Meanwhile, in the printed matters, the colors are represented in a overlapped state so that they are not felt as their densities of 10 % and 15 % and they becomes the densities of somewhat lower degrees.

As described above, the representation of colors on printings is fundamentally different from that of color 15 Braun tube. Therefore, it is quite difficult to make the image on the color monitor similar to the printed image.

In the apparatus for determining the color separation conditions of the present invention, a color original is scanned by a color separation device such as a TY. camera, and an image which is similar to the image to be printed is developed on a color monitor by applying necessary color corrections, thereby confirming whether the color correction is adequate or not. In other words, with watching the color monitor, several correction knobs are manipulated so as to control the image on the color monitor into the most desirable state, and the values of correction in the actual color separation can be obtained from the values of turning the knobs (corrected values in the apparatus).

In the following, the present invention will be described in more detail with reference to the accompanying 25 drawings.

Figure 1 shows the apparatus for determining color separation conditions of the present invention in a block diagram. A color original is scanned in a scanning section 100 which produces synchronous Y, M and C image signals. A scanning bed 101 is provided with a light source 104 having a stable light quantity and a light diffusion sheet. Placed on the diffusion sheet is a film stand 102 made of a transparent glass plate. A 30 color original 103 such as a color film to be printed is put on the film stand 102. The color original 103 may be of positive type or negative type. Above the film stand 102, a television camera 110 is installed so as to scann the color original 103.

In front of the camera tube of the television camera 110, a filter 111 of three colors of R, B and G are built in.

Further, attached in front of the filter 111 is a zoom lense 112. This filter 111 is provided with color filter elements of red 111 R, green 111 G and blue 111 B which is disposed at angles of 120'. This filter 111 is rotated about its center in synchronism with the scanning of each color. For example, when Y signals are obtained, the original is scanned through the filter element 111 B. Like wise, the M signals are obtained through the filter element 111 G and the C signals, through the filter element 111 R.

The image signals of the color original 103 that are obtained in the above scanning are memorized in a 40 memory 140 through a camera control 120 and a black and white level controlling circuit 130. The camera control 120 performs the beam adjustment for converting the image signals into those corresponding to positive type ones and the controlling of electrical focuses and nega- posi converting. In the black and white level controlling circuit 130, the output reference signals of 0 % and 100 % delivered from the camera are adjusted to their respective levels of 0 % and 100 % by means of knobs 904 and 905. That is, the controlling 45 circuit 130 is so operated thatthe signal treating system may have a certain function to such as variation of light intensity orfading of filter elements. The memory 140 memorizes the scanned image signals Y, M and C sequentiaily, In this embodiment, a magnetic disc memory is employed, however, an]C memory may also be used.

In the above camera scanning, when a record switch 908 on the control panel 900 is depressed, the filter 50 111 is automatically rotated by an electric motor and the respective Y, M and C image signals of the color original 103 is stored into the memory 140. The output signals delivered from the memory 140 are controlled into the image signals of a certain level range by the black and white level controlling circuit 150 with the manipulation of knobs 906 and 907. These black and white level controlling circuits 130 and 150 controls the output signals relative to the reference signals, in other words, they control the image signals into a certain 55 level range in the system.

The output signals of the controlling circuit 150 are further led into a white level controlling circuit 160 of color image and in this controlling circuit 160, the white levels of input signals are regulated by means of the knobs 909 and 910.

By the way, in this embodiment, the Y, M and C color image signals are obtained by turning a filter device 60 with using a single camera, the obtained signals are stored in the memory and the three color image signals are delivered synchronously from the memory, that is, the so-called sequentially memorizing system. It should be noted, however, that the synchronous three color image signals can be obtained if three image pickup tubes are used without the use of the memory device. As compared with the latter system, the dispersion in qualities of cameras can be eliminated in the former system so that the controlling operation is 65 4 GB 2 061 060 A easier when it is applied to the practical printing process and the maintenance of devices is also easy.

The synchronized Y, M and C image signals are applied to a masking circuit 200 from the memory 140 through the controlling circuits 150 and 160. The masking circuit 200 receiving the inputs of Y, M and C image signals, detects the component of yellow, magenta, cyan, blue, green and red colors and performs the correction of the respective color components. The device of this kind is used in color scanners. The controlling knobs 922 are used for correcting the color components of yellow, magenta, cyan, blue, green and red colors.

There is provided a U.C.R. (under-color removal) circuit 280 on the stage next to the masking circuit 200. Further, next to the U.C.R. circuit 280, a U.C.R. control confirmation circuit 290 is connected. This circuit 290 judges whether the rate of U.C.R. and U separation are proper or not, which have been set by means of the controlling knobs 924 for the cut points of U.C.R. and the controlling knobs 925 of the percentages of U.C. R. More particularly, by manipulating the changeover knob 923, it is possible to develop the combined image of Y, M and C, to develop the image of only Bt and furtherto develop the combined image of Y, M, C and Be on the color monitor.

The image signals of Y, M, C and Bt are then applied to a clip circuit 300. In the masking circuit 200, complicated signal treatment is done, for example, the image signals of Y, M, C and Be are added to or subtracted from one another, or they are multiplied by correction factors, so that the image signals of Y, M, C, and Be are mixed with the signal components of below or above 0 % to 100 % level range. Thus, this clip circuit 300 clips these electric signals which are outside the range of 0 % to 100 %. The clip circuit 301 in a later stage is also provided forthe same purpose.

A gradation correcting circuit 400 corrects the gradation of Y, M, C and Be image signals. When the correcting knobs 926 are manipulated, the compression, highlight, shadow, contrast and pedestal levels of each image signal are corrected.

The color correcting circuit 500 on the next stage converts the respective image signals of Y, M, C and Be of the printing system into the image signals of Y, M, C and Be of the color monitor. More particularly, when 25 the Y, M, C and B( signals of printing system are converted into the image signals of R, B and G only by the matrix circuit, the portions of secondary, tertiary and quaternary colors become dark or blackish colors.

Therefore, some degree of the secondary, tertiary and quaternary color components are deducted from the former Y, M and C signals, thereby lightening the secondary, tertiary and quaternary colors and making the portions of secondary, tertiary and quaternary colors on the color monitor resemble to the actually printed 30 colors.

As this color correcting circuit, the secondary and tertiary color correcting circuit as disclosed in U.S.

Patent No. 3,972,066 may be employed. Further, the secondary, tertiary and quaternary color correcting circuit as disclosed in the later part may also be used, which provides more preferable resemblance.

The matrix circuit 600 is the next stage calculates the color components contained in the respective color 35 image signals of Y, M, C and Be and converts them into R, G and B image signals. This matrix circuit is disclosed in U. S. Patent No. 3,972,066 as filed by the same applicant as that of the present application and other references, accordingly, detailed description thereon will be omitted. The output signals from this matrix circuit 600 are applied to the color monitor 800 having a color Braun tube by way of a gray scale mixing circuit 700. In order to perform comparative inspection of color density (particularly highlight color 40 density) on the screen 801 of the color monitor with a gray scale 701, the gray scale 701 indicated on the screen is made movable by the grayscale mixing circuit 700.

That is, it is difficult to know correctly the densities of colors on the screen 801, however, when a certain gray scale is developed on the same screen, it becomes possible to know the degree of density of color on the screen. Accordingly, the density of the colorto be printed can also be known from the color that is 45 indicated on the monitor screen.

By the way, the reference numeral 805 denotes an oscilloscope which is used for observing the wave forms of input signals, corrected curves, and the densities of signals at various positions. In the drawing, the input terminal of the oscilloscope 805 is connected to the output terminal of the clip circuit 301, however, it can be connected to other various stages by means of the changeover switches 912 to 916.

4 In the following, the respective devices of the apparatus of the invention will be described in detail.

Figure 2 shows a block diagram of the filter 111 and other devices which rotates the Y, M and C filter 111 built in the camera 110 synchronously with the scanning of the original image. The light source 104 illuminates the color original 103. The color original 103 is scanned by a monochromatic camera tube 110 through the filter disc 111 having filter elements of 111 R, 111 G and 111 B with rotating the filter disc 111 by an 55 electric motor. The image signals which are taken by the monochromatic camera tube 110 are applied to image signal amplifying circuits 116 and 117 to be amplified. The output signals from the image signal amplifying circuit 116 are applied to the clip circuit 118 which functions as a comparator. The image signals which are regulated in the clip circuit 118 are applied to a logical circuit 119, in which the control signals are produced, which signals are used when the output image signals delivered from the image signal amplifying 60 circuit 117 are stored into the memory device 140.

In the following, Figure 3 showing the details of the filter disc 111 will be described. A hole 11 la is defined in the filterdisc 11 land apertures 11 ld are formed between boundaries 111 band the attached filter elements 11 lc. The light rays from the light source 104 can be passed through the apertures 11 ld byway of the color original 103. The apertures 11 ld are through holes or of transparent plates having a certain density65 GB 2 061 060 A 5 such as gray scales which do not constitute the R, G and B monochromatic filters. With this filter disc 111, the output image signals obtained by the monochromatic camera tube 110 becomes the state as shown in Figure 4. More particularly, in the period Tw of the image signals which corresponds to the aperture 111 cl, the signal level is higher than the detecting levels. By discriminating such the higher signals by means of the clip circuit 118 which has a clip voltage Vc1p, the rotation timing pulses having a cycle corresponding to the rotational speed of the filter disc 111 can be obtained. Further, since the filter disc 111 is provided with the apertures at regular intervals of 120'when recording is performed on the basis of the pulses given by the clip circuit 118, the image signals, that is, the picture images are not effected adversely because the image signals corresponding to the periods Tw of the apertures 111 cl together with the boundaries 111 b are not recorded in the memory device 140.

Bythe way, the hole 11 la in Figure 3 is used as the detecting hole for reset pulse after each rotation of the filter disc 111.

As described above, the filter disc 111 having the above structure does not require the hale for detecting the rotational speed, accordingly, it can be easily attached without the necessity of locating work.

-15 Furthermore, unfading gray scales are fitted into the apertures and periodically detected so as to compare 15 with the transmitted light rays through the filters R, G and B, therefore, the degree of fading in each of the filters R, G and B can be known.

The black and white level controlling circuit 150 and the white level controlling circuit 160 for color image are shown in Figure 5. The input, for example, Y signals are applied to a gain controlling circuit 151 and they are regulated by variable resistors 152,153, 161 and 162, thereby controlling the levels of the signals. The 20 variable resistor 152 is connected to the GAIN knob 906 of the memory, the variable resistor 153 is connected to the PED knob 907 of the memory, the variable resistor 161 is connected to the GAIN knob 909 of SET, and the variable resistor 162 is connected to the ALL knob 910 of the SET.

Further, the black and white controlling circuit 130 is also provided with a regulating circuit of gain controlling circuit, so that the adjustment is possible by means of the GAIN knob 904 and the PED knob 905 25 of CAMERA. The inputs of 0 % level signals and 100 % level signals are applied to the camera 110 and the outputs of each stage are adjusted to the range of 0 %to 100 %, thereby obtaining the constant state of camera scanning.

Still further, since the portions to be printed as white have different densities in accordance with the scanning conditions of the color original 103, it is necessary to determine the level of density of the color 30 original that must be printed white (no ink is printed on the printing). The above is set by means of the SET GAIN knobs 909 and 910.

Now, the clip circuits 300 and 301 will be described in the following. As described in the foregoing, when several electric signals are treated by adding, subtracting and multiplying, the signals outside the range of 0 %to 100 %are produced. Especially, if the signals over 100 %level are produced, the fluorescent substance 35 of the Braun tube of the monitor 800 continues the light emission until it is saturated and the portions which must become white do not become white but are colored or the color reversion is caused to occur. These facts are not desirable for obtaining the similarity of image so that the signals which exceed about 100 % level are clipped. In the practical operation, the clipping is made at 102 % level.

Further, the positions of the clip circuits are not restricted to thoseshown in Figure 1 and the clip circuits 40 may be reduced to one.

Shown in Figure 6 is an embodiment of the clip circuit 301. The reference numerals 370,371 and 372 denote input terminals for R signal, G signals and B signals, respectively. The reference numerals 373 - 378 denote transistors, 379 denotes a variable resistor, and 380, 381 and 382 denote the output terminals for R signals, G signals and B signals, respectively.

In the operation of the device shown in Figure 6, the transistors 374, 376 and 378 are applied with a clip voltage through the variable resistor 379 and the emitters and the collectors of the transistors are commonly connected to those of other transistors 373, 375 and 377. When the input signals of R, G and B are applied to the transistors 373, 375 and 377 by way of the input terminals 370, 371 and 372, the output signals obtained from the output terminals 380, 381 and 382 are clipped. By the way, the other clip circuit 300 is used for the 50 four image signals and the functions thereof are just the same as those of the above embodiment.

In the following, the color correction circuit 500 will be described. In the aforementioned U.S. Patent No.

3,972,066 owned by the present applicant, it is described that the image on the color monitor can be made more similar to the printed image when the secondary and tertiary colors are corrected during the conversion of printing type image signals into video type image signals, more particularly, the secondary 55 and tertiary color components are detected from the input Y, M and C image signals and the secondary and tertiary color components are eliminated from the input Y, M and C signals to some extent. Since the resemblance of image can well be attained only by the correction of the secondary and tertiary colors, the embodiment of the present invention may be provided with the secondary and tertiary color correcting circuit, however, in order to obtain more preferable results, the secondary, tertiary and quaternary color correcting circuit may be provided, which will be described in the following.

Figure 7 is a block diagram of the secondary, tertiary and quaternary color correction circuit. The inputs of Y, M, C and B( image signals are applied to the clamping output amplifiers 502, 503, 504 and 505 and the % level of the image signals are fixed to a certain d.c. voltage, and the pulses P, having a level corresponding to the 100 %level of Y, M, C and &are added to the retrace periods of the image signals.

6 GB 2 061 060 A 6 These Y, M, C and Bt image signals have reversed levels so that, when a signal level is high, the value of density is low.

The outputs from the clamping output amplifiers 502 - 504 are applied to secondary composite signal detecting circuits 506 - 508. These circuits 506 - 508 include NAM (non- additively mixing) circuits, that is, the circuits which produce their outputs by detecting a higher signal (when input signals are two) orthe highest 5 signal (when input signals are three or more). Accordingly, secondary color signals---TY,-WC-and -CY are obtained from the respective circuits 506 - 508.

The outputs of the clamping output amplifiers 502 - 504 are applied to a tertiary color composite signal detecting circuit 509 which contains also the NAM circuit and produces the output of tertiary color signals _YMC.

The reference numerals 510 - 512 denote pure secondary color composing, circuits which remove tertiary color components from secondary color components. By receiving the above- mentioned secondary color signals -YM, -WC-and - and the signal of -YMC as input signals, the circuits produce the outputs of _jW -177 -MC 1 --C +YWC a n d -ZY--4-Y -MC.

The quaternary color composing circuit 513 also includes the NAM circuit and it receives the inputs of Y, 15 M, C and Bt signals to produce quaternary color signal -YMCRe.

On the assumption thatthe pure secondary color components are represented by r, g and b, the tertiary color component, by bl, and the quaternary color component, by bV, the inputs of these secondary, tertiary and quarternary color components are applied to the adders 514 - 516 and the secondary, tertiary and quarternary color components are multiplied by correction factors of a, P, y, 6, and E, thereby correcting the 20 original image signals of Y, M and C.

When the corrected, Y, M and C signals are represented by Y', M'and C', respectively, the functions may be shown by the following equations:

Y' =Y +r xa+gxr:)+bixb+bi'XE M'=M+r Xa+bxy+bl Xb+bl' XE C, =C +gxp+bxy+bl Xb+bl'XE 11 In the above equations Y, M and Care reversed image signals are r, g, b, bland bl' are positive secondary, tertiary and quaternary color signals, accordingly, the right sides of the above equations mean that some 30 degree of the secondary, tertiary and quaternary color components are removed from the image signals of Y, M and C.

By correcting with the above-described correcting circuits 500, the portions of secondary, tertiary and quaternary color components of the image on the color monitor 800 become brighter, which image resembles to the image that is actually printed.

The masking circuit 200 will be described in the following. Even though the masking circuits of color scanners may be used, a new type masking circuit will be proposed herein.

Shown in Figure 8 are color bar images and when the color bars are scanned by a video camera and converted into electric signals, the signals of Y, M and C shown in Figure 9 are obtained. The Y, M and C image signals are reversed signals so that if the density is high, the level is low.

The present invention is described with reference to the color correction signal diagram of Figure 10. By using the means which detect only the signals of minimum levels and produce outputs (minimum value NAM), the input signals of Y, M and C as shown in Figure 10 are detected and the minimum NAM signals of Figure 10, YM, MC and CYare obtained by the combintions of Y and M, M and C, and C and Y. Further, the minimum NAM signal, YMC of the combination of Y, M and C is also detected.

As shown in Figure 10, it should be noted that YMC contains all the colors other than white of the color bars and YM contains all the colors other than white and cyan. Therefore, only the reverse signal of cyan can be detected by YM - YMC. In like manner as above, the reversed signal of yellow and the reversed signal of magnets are separately detected by MC YMC and Cy- YMC. Therefore, the colors of cyan, yellow and magenta can be corrected separately by multiplying proper factors.

Figure 11 shows the block diagram of an embodiment of the masking circuit. In Figure 11, the reference numerals 251, 251' and 251" denote clamping output amplifiers, 252, 252', 257' and 253 denote maximum value selecting circuits, 254, 254% 254" and 255 denote minimum value selecting circuits, 256, 256', 256", 257, 257' and 257' denote circuits for addition and positive and negative correction signal generation, 258 denotes a controlling circuit and 259, 259' and 259' denote addition circuits.

The input terminals 250,250'and 25T' in Figure 11 are applied with the Y, M and C signals of Figure 9 and Figure 10. The reference numerals 251, 25Vand 251" are clamping output amplifiers which fix the Y, M and C signals to a certain d.c. voltage. The outputs of clamping output amplifiers 251, 25Vand 25V are connected to maximum value selecting circuits 252, 252', 25Z and 253, and minimum value selecting circuits 254,254', 250and 255. Each of the maximum value selecting circuits 252,252', 25T' and 253 detects the signals of YM, 60 WC-and-C-Y-of Figure 9, at the same time, they detect YMC signal to reverse it into -YMC signal. Each of the minimum value selecting circuits 254,254', 254" and 255 detects the signals of YM, MC and CYof Figure 10, atthe same time, they detect YMC signal to reverse it into - YMC signal. The reference numerals 256,256' and 256" denote addition and negative and positive correction signal generating circuits, in which the outputs of maximum value selecting circuits 252, 252' and 25T' and the output of the other maximum value 65 - 7 GB 2 061 060 A 7 selecting circuit 253 are added together, then they produce negative and positive correction signals of 1-(YM 7m- - -Y-MC-} WC - YWC), WC- - -YM-C-}, a n d(-CY - -Y-M-C),-(-Y YM C}. Th e ref e re n ce n u m e ra 1 s - MC),WM- 257, 257' and 257' also denote addition and negative and positive correction signal generating circuits, in which the outputs of the minimum value selecting circuits 254, 254' and 254!'and the output of the other minimum value selecting circuit 255 are added together and they produce negative and positive correction signals of 'HYM - YMC), YM- YMC},{-(MC- YMCLMCYMC},and{-(CY- YMC),CY- YMC1.

The relations between the correction signals and colors are as follows:

WM - YMC = r...... red color M-C - YMC = b.... blue color 10 CY- YMC = b.... green color -(YM - YMC) =c.... cyan color -(MC - YMC) = y.... yellowcolor -(CY- YMC) =m.... magenta color -15 15 The reference numeral 258 denotes controlling circuits, which determine the addition ratios of the output correction signals r, b, g, c, y and m of the above correction signal generating circuits 256, 256', 256", 257, 257'and 257' to the signals of Y, M and C of Figures 9 and 10. The reference numerals 259,259' and 259' denote addition circuits. In the addition circuit 259, the output of the clamping output amplifier 251 and the controlled correction signals of r, b, g, c, y and m of the controlling circuit 258 are subjected to addition (or subtraction) to generate the corrected Y'signal. In like manner, the addition circuits 259' and 259' add (or subtract) respectively the controlled correction signals of the controlling circuits 258 to (or from) the outputs of the clamping output amplifiers 251' and 25V, and they generates the corrected M' and C' signals.

The present invention will be described further taking an example of a color of cyan. When the cyan color 25 of Figure 8 is reproduced on the color monitor, the portions of Y, M and C signals of Figure 10 which correspond to the cyan color are supplied to the color monitor. When the portions of Y, M and C signals of Figure 9 corresponding to the cyan color are varied in signal ratios, the brightness, saturation and hue of cyan color on the color monitor can be changed.

In Figure 10, -(YM - YMC) = c is cyan color. The addition or subtraction ratio of the positive or negative 30 correction signal to cyan color generated by the correction signal generating circuit 257 of Figure 11, is regulated by the controlling circuit 258, then the correction signal is added to Y, M and C signals by the addition circuits 259, 259' and 259' to produce Y', M' and C'signals. Further, the signals of Y', M' and C' of Figure 11 is applied to the color monitor and the controlling of the cyan color is done by means of the controlling circuit 258, thereby changing the brightness, saturation and hue of the cyan color. When a correction signal of +c is added to the signal C among the signals Y, M and C of Figure 10, the cyan in Figure 8 becomes white. To the contrary, when -c signals is added to Y and M signals among the Y, M and C signals, the cyan in Figure 8 becomes black.

By means of the above-described masking circuit, the colors of cyan, magenta and yellow are detected separately and the lightness, saturation and hue of each color of the red, green, blue, cyan magenta and yellow, can be varied without changing the achromatic color portions. Accordingly, this masking circuit is quite effective.

In the following, the gray scale mixing circuit 700 will be described. As shown in Figure 12, gate pulses are generated at each horizontal or vertical period by a gray scale gate pulse generator 703 and a portion of image signals that are applied to the gray scale generating circuit 700 is removed, and the gray scale signal 45 that is produced by the gray scale signal generator 704 is added to the above removed portion of the image signals. Therefore, the gray scale is indicated on the color monitor 800.

This gray scale 701 can be developed on the color monitor screen, and if not desired, the gray scale 701 can be eliminated by means of the switch 917. Further, the gray scale on the screen can be moved horizontally by a knob 918.

Though the density measuring device is not described in the above disclosure with regard to the correction condition determining apparatus of the present invention, the density measuring device as disclosed in U. S. Patent, No. 4,123,171 filed by the present applicant, may be built in the apparatus of the present invention. The knobs 919 and 921 are used for shifting the cross bar of density measuring device.

Further, though not being described in the above embodiment, as disclosed in U.S. Patent 3,972,066, several correction conditions can be separately set in compliance with the printing system employing the apparatus of the present invention, such as the method of printing, the kinds of ink and paper and so forth.

The method for using the apparatus of the present invention for determining the correction conditions of color separation will be described in the following.

The signal treatment system of the present apparatus is made constant by setting all the color control 60 knobs 922 and the gradation knobs 926 to zero, then the regulating the knobs 904, 905, 906 and 907 applying the inputs of standard density signals. In accordance with the employed system of printing, the correction factors are adjusted.

After that, a color original 103 to be printed is put on the film stand 102. Further, the set gain knobs 909 and 910 are adjusted to determine the white level and observe the image developed on the color monitor 800. 65 8 GB 2 061 060 A 8 If the image on the monitor is not desirable, an adequate image is produced by manipulating the color control knobs 922 and gradation knobs 926. It goes without saying that, when the image on the color monitor is judged whether it is good or not, the above-mentioned gray scale 701 and density meter may be employed if necessary.

With the quantities of theturning of knobs 909,910, 922 and 926,the degrees of correction in the color 5 separation work of a color original, that is, the correcting conditions, can be obtained.

Although the present invention has been described in connection with a preferred embodiment thereof, many variations and modifications will now become apparent to those skilled in the art. It is preferred, therefore, that the present invention be limited not by the specific disclosure herein but only bythe appended claims.

Claims

1. A masking device which comprises means for forming the pairs of signals of Y and M, M and C, and C and Y by combining two members out of Y, M and C image signals and for generating the minimum selected 15 signals from said combinations, means for generating another minimum selected signal from said three Y, M and C image signals, means for detecting and generating the signals of cyan, magenta and yellow colors by subtracting said former minimum selected signals of said combined signals respectively from said latter minimum selected signal of three Y, M and C signals, means for controlling the hues, saturations and brightnesses of said cyan, magenta and yellow color signals and means for adding the color correction signals of said cyan, magenta and yellow color controlled signals to said Y, M and C image signals.

2. The masking device which comprises means for forming the pairs of signals of Y and M, M and C, and C and Y by combining two members out of Y, M and C image signals and for generating the minimum selected signals and maximum selected signals from said combinations, means for generating other minimum selected signal and maximum selected signal from said three Y, M and C image signals, means for 25 detecting and generating the signals of cyan, magenta and yellow colors by subtracting said former minimum selected signals of said combined signals respectively from said latter minimum selected signal of three Y, M and C signals, means for detecting and generating the signals of red, green and blue colors by subtracting said former maximum selected signals of said combined signals respectively from said latter maximum selected signal of three Y, M and C signals, means for controlling the hues, saturations and brightnesses of said six color signals and means for adding the color correction signals of said six color controlled signals to said Y, M and C signals.

3. A method of masking, which method comprises forming the pairs of signals of Y and M, M and C, and C and Y by combining two members out of Y, M and C image signals, generating the minimum selected signals from said combinations, generating another minimum selected signal from said three Y, M and C 35 image signals, detecting and generating the signals of cyan, magenta and yellow colors by subtracting said former minimum selected signals of said combined signals respectively from said latter minimum selected signal of three Y, M and C signals, controlling the hues, saturations and brightnesses of said cyan, magenta and yellow color signals and adding the color correction signals of said cyan, magenta and yellow color controlled signals to said Y, M and C image signals.

4. A method of masking, which method comprises forming the pairs of signals of Y and M, M and C and C and Y by combining two members out of Y, M and C image signals generating the minimum selected signals and maximum selected signals from said combinations, generating other minimum selected signal and maximum selected signal from said three Y, M and C image signals, detecting and generating the signals of cyan, magenta and yellow colors by subtracting said former minimum selected signals of said combined 45 signals respectively from said latter minimum selected signal of three Y, M and C signals, detecting and generating the signals of red, green and blue colors by subtracting said former maximum selected signals of said combined signals respectively from said latter maximum selected signal of three Y, M and C signals, controlling the hues, saturations and brightnesses of said six color signals and adding the color correction signals of said six color controlled signals to said Y, M and C signals.

5. A masking device, substantially as hereinbefore described with reference to, and as shown in, Figures 1 and 8 to 11 of the accompanying drawings.

6. A method of masking, substantially as hereinbefore described with reference to Figures land 8 to 11 of the accompanying drawings.

7. Any novel feature or novel combination of features disclosed herein.

Printed for Her Majesty's Stationery Office. by Croydon Printing Company Limited, Croydon, Surrey, 1981. Published by The Patent Office, 25 Southampton Buildings. London, WC2A lAY, from which copies may be obtained.

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