JPH0585892B2 - - Google Patents

Description

[Detailed description of the invention]

Technical field In color printing, the present invention processes primary color signals of cyan, magenta, yellow, and black obtained from a set of four color separation plates of cyan, magenta, yellow, and black using a subtractive color method. The present invention relates to a circuit that converts into color signals of red, green, and blue, which are the three primary colors of the additive color method. Prior Art There are several types of color reproduction methods as described above depending on the underlying coloring technique, but the present invention is based on Neugebauer's theory, which is a halftone color reproduction method. Even in the method of configuring the color reproduction process based on Neugebauer's theory, there are various variations depending on how the theoretical formula is handled. According to an example of the prior art, cyan, magenta,
Primary color signals c representing cyan, magenta, yellow, and ink obtained by scanning four color-separated transparent images of yellow and ink using a flying spot scanner;
Take out m, y, bl, and from this, the secondary color signal cm,
Create nine signals representing my, yc, the tertiary color signal cmy, and the paper color, create tristimulus values The three primary colors R, G,
It depends on the method of converting to B signal. This method not only requires nine multiplier circuits, making the circuit configuration complicated, but also requires the use of the primary, secondary, tertiary colors, and paper color in determining the tristimulus values. When adjusting the mixing ratio, no matter which color is adjusted, R, G, and B all change, making adjustment extremely difficult and requiring a high degree of skill. As a countermeasure to the above problem, the present applicant modified the Neugebauer equation to simplify the circuit configuration, requiring only seven multiplier circuits, and converting each R, G, and B signal into a primary color and a secondary color. Completed a method that could independently adjust color, tertiary color, and paper color, and published JP-A-56-
The details were disclosed in Publication No. 123540. In this method, when the dot area ratios obtained from cyan, magenta, yellow, and black halftone documents are respectively c, m, y, and bl, the reflectance R due to red light is expressed by the following equation. R = (1-bl) {1-(α ₁ c + α ₂ m + α ₃ y −α ₅ cm − α ₆ cy-α ₇ my −α ₈ cmy)} + α ₄ bl = (1-bl) (1c″) + α ₄ bl ...(1) Here, α ₁ to α ₈ are constants. Similarly, the following formula holds true for green G and blue B. G = (1-bl) (1-m'') + β ₄ bl ……(2) B=(1−bl)(1−y″)+γ ₄ bl ……(3) The color reproduction circuit is constructed using equations (1), (2), and (3). is Fig. 1. Fig. 1 shows a color reproduction circuit described in Japanese Unexamined Patent Publication No. 123540/1983.1.
The next color signals c, m, y, bl are multiplied in the color collector 1 using four multipliers 6 to 9 to produce signals of the second colors cm, cy, my and the third color cmy.
That is, in the color corrector 1, the primary color, secondary color, and tertiary color signals are each expressed by the above equation.
The coefficients α ₁ to α ₈ , β ₁ to β ₈ and γ ₁ to γ ₈ (all 1 or less) of each term of c″, m″, and y″ are set by the variable resistor 10 to
16, 17-23 and 24-30, and these signals are added by adder 2 to obtain c''
Signals of m″ and y″ are obtained respectively. Furthermore, the tendency for the gradation to decrease in the transition from a high-density secondary color to a tertiary color can also be corrected by adjusting these coefficients. Output c″ of adder 2,
m″, y″, bl are inverters 31 to 34 of subtracter 3
The output signal (1-c″), (1-c″) is inverted by
m''), (1-y''), and (1-bl), respectively.
These outputs are supplied to the first black mixer 4 and multiplied by its multipliers 35 to 37 to produce output signals (1-bl) (1-c''), (1-bl) (1-m'' ), (1
−
bl) (1-y'') respectively. That is, the outputs of the inverters 31, 32 and 33 of the subtracter 3 are input to the outputs of the multipliers 35, 36, 37 of the first black mixer 4.
the inverter 34 of the subtracter 3.
is supplied to the other input side of the multipliers 35, 36 and 37 of the first black mixer 4.
Signal (1-bl) on the output side of 5, 36 and 37
(1-c″), (1-bl) (1-m″) and (1-bl)
(1-y'') respectively. These outputs are supplied to the second black mixing regulator 5, and black signals α ₄ bl, β ₄ bl, and γ ₄ bl, which are output signals, are added.
The coefficient α ₄ is given by the above equation, and therefore the added black ink is adjusted to a predetermined value by the variable resistor 38. Green and blue colors are the same as explained above for red color, and variable resistor 3
It can be adjusted by 9 and 40. The outputs R, G, and B of the variable resistors 38 to 40 of the second black mixing regulator 5 are further supplied to a paper color corrector, and are matched to the color of the paper by the variable resistor. The output of the paper color corrector feeds into a monitor gamma corrector before being applied to the monitor. The reason for this is that the gamma of CRT monitors is generally said to be 2.2, so in order to correct this and make it 1, it is necessary to perform inverse conversion through a non-linear circuit having gamma characteristics of 0.45.
The output of this monitor gamma corrector is amplified by a video amplifier and then supplied to a color monitor to display a desired color video. The color reproduction circuit shown in Figure 1 is
Although the circuit configuration is simpler than those shown in No. 4777 and No. 51-5305, there are a total of four multipliers in the color collector 1 and three in the first black mixer 4. We need as many as seven. Purpose of the Invention The purpose of the present invention is to simplify the construction and reduce the cost by reducing the number of multipliers, which are complicated and expensive, to only three, and to make the construction simple and inexpensive. It is an object of the present invention to provide a color reproduction circuit for color printing separation plates that can be sufficiently used for applications where color reproducibility is not so important, such as a plate inspection device for printing separation plates. Summary of the Invention The color reproduction circuit for color printing separations according to the present invention includes primary color signals c representing halftone area ratios obtained from cyan, magenta, yellow, and black color printing separations;
An input terminal receives each of the primary color signals c, m, and y, and outputs signals by adjusting the levels of the primary color signals c, m, and y according to predetermined coefficients α ₁ , β ₁ , and γ ₁ .
A level adjuster that outputs cα ₁ , mβ ₁ , yγ ₁ , and a signal cα ₁ , which is output from this level adjuster.
In response to mβ ₁ , yγ _{1 ,} three primary color signals (1−cα ₁ ), (1−
mβ ₁ ), (1−yγ ₁ ) as well as receiving the black signal bl and outputting a signal (1−bl); 1-bl) to obtain the signal (1-cα ₁ ) (1-bl), (1-mβ ₁ )
(1-bl), (1-yγ ₁ )(1-bl), and these signals (1-cα ₁ )(1-bl), ( 1-
By adding the black signal bl to each of mβ ₁ ) (1-bl) and (1-yγ ₁ ) (1-bl) at a predetermined ratio, the signal (1-cα ₁ ) (1-bl) + α ₄ is obtained. bl, (1−mβ ₁ )(1−b
l)
+β ₄ bl, (1-yγ ₁ ) (1-bl) + γ ₄ bl; and the signal (1-cα ₁ ) (1-bl) + α ₄ bl, (1-
mβ ₁ ) (1-bl) + β ₄ bl, (1-yγ ₁ ) (1-bl) +
γ ₄
The present invention is characterized by comprising a color mixer that receives BL and mixes them at a predetermined ratio to output additive color signals of red, green, and blue having intermediate colors. Further, the color reproduction circuit for color printing separations according to the present invention has primary color signals c, which represent halftone area ratios obtained from cyan, magenta, yellow, and black color printing separations;
An input terminal receives each of the primary color signals c, m, and y, and outputs signals by adjusting the levels of the primary color signals c, m, and y according to predetermined coefficients α ₁ , β ₁ , and γ ₁ .
A level adjuster that outputs cα ₁ , mβ ₁ , yγ ₁ , and a signal cα ₁ , which is output from this level adjuster.
In response to mβ ₁ , yγ _{1 ,} three primary color signals (1−cα ₁ ), (1−
mβ ₁ ), (1−yγ ₁ ), and a subtractor having four inverters that receives the black color map signal bl and outputs a signal (1−bl), and these three primary color signals (1−cα ₁ ), (1−mβ ₁ ),
(1-yγ ₁ ) in a predetermined ratio and outputs additive color signals of red, green, and blue, and the three colors red, green, and blue output from this color mixer. Multiply each of the signals by the signal (1-bl) 3
a first black mixer having three multipliers; the black signal BL is added to each of the three color signals output from the first black mixer at a predetermined ratio to produce intermediate colors of red and green; The apparatus is characterized in that it includes a second black mixer that outputs a blue color signal. Embodiment In the color printing separation plate reproduction circuit according to the present invention, approximate calculations are performed by modifying the Neugebauer's theoretical formula described in the above-mentioned Japanese Patent Application Laid-Open No. 56-1235400 so as to simplify the circuit configuration. However, in the above equation (1), the secondary colors cm, cy, my
If you omit the and tertiary color cmy, it becomes as follows. R=(1-bl) {1-(α ₁ c+α ₂ m+α ₃ y)}+
α ₄
bl...(1)' The parentheses in the above equation mean that the primary colors c, m, and y are mixed at the ratios of α ₁ , α ₂ , and α _{3 ,} respectively. (1)
Compared to the parentheses in the expression, since the secondary and tertiary colors with negative signs disappear, the level of C'' becomes too high and the secondary and tertiary colors are not reproduced.In the present invention, as described above, Instead of mixing the primary color and adding it to the subtractor, add the primary color directly to the subtractor and add 3.
The primary color signals R ₀ , G ₀ , B ₀ are obtained, the black color signal is mixed to obtain intermediate color signals R′, G′, B′, and these color signals R′, G′, B′ are The color signals R'', G'', and B'' having intermediate colors are obtained by mixing them in proportion. This processing process is expressed as follows: R' = (1 - bl) ( 1−α ₁ c)+α ₄ bl……(4) G′=(1−bl)(1−β ₁ m)+β ₄ bl……(5) B′=(1−bl)(1−γ ₁ y)+γ ₄ bl……(6) R″=k ₁ R′+k ₂ G′+k ₃ B′ ……(7) G″=k ₄ R′+k ₅ G′+k ₆ B′ ……(8) B″=k ₇ R′+k ₈ G′+k ₉ B′ ……(9) In equations (4), (5), and (6), c, m, and y are respectively red, green, and This means that only components other than blue are reflected. That is, R ₀ =1−α ₁ c,
G ₀ = 1-β ₁ m, B ₀ = 1-γ ₁ y are each 1, meaning that components other than red, green, and blue are subtracted from the reflected light of all wavelengths. No. 3
Becomes a primary color signal. Therefore, when observing these three primary color signals R ₀ , G ₀ , B ₀ on a color monitor, 3
A brightly colored screen consisting only of primary colors can be observed.
(1-bl) and the terms α ₄ bl, β ₄ bl, and γ ₄ bl mean giving a mixture of ink colors, so R', G', and B' are the tones that are close to the three primary colors with ink added to them. Become something.
R′, G′, and B′ color mixture ratio in equations (7), (8), and (9)
k ₁ to _{k 3} , k ₄ to k ₆ , k ₇ to k ₉ are the reds included in the secondary colors my, cy, cm obtained by the ink used,
Shows the percentage of green and blue reflected light. This value is calculated by creating the secondary color using the ink actually used for printing.
It is sufficient to measure the density of red, green, and blue for each secondary color, calculate the transmittance from this, and normalize this transmittance. If the measured values are listed in the ink catalog, you can use them as is. By providing color mixture in this manner, secondary colors can be produced that are substantially close to primary colors. 3
The next color can be developed by adding ink color. Furthermore, in order to obtain color reproduction close to the original image, correction for the paper color and gamma correction for the color reproduction characteristics of the monitor can also be added. FIG. 2 shows the configuration of an example of the color reproduction circuit of the present invention. In this example, cyan, magenta,
Primary color signals c, m, y, and bl representing the halftone dot area ratio obtained by scanning four printed separation plates of yellow and black are applied to a level adjuster 51, and each is connected to a variable resistor 52.
α ₁ c, β ₁ m, and γ ₁ y are created by ~54. Next, the primary color signals α ₁ c, β ₁ whose levels have been adjusted in this way
m, γ ₁ y and black signal bl are supplied to the subtracter 55, and the inverters 56 to 59 convert them into (1-
α ₁ c), (1-β ₁ m), (1-γ ₁ y), (1-bl)
Create. Furthermore, these signals are applied to multipliers 61 to 63.
(1-bl)
(1-α ₁ c), (1-bl) (1-β ₁ m), (1-bl)
Create (1-γ ₁ y). These signals and the black color signal bl are further supplied to a second black color mixer 64 including variable resistors 65 to 67, and intermediate three primary color signals R', G', Create B′. In the present invention, an intermediate color is added to these three primary color signals R', G', B', and for this purpose these signals are supplied to a color mixer 68 having matrix resistors 69-77. The ratio of color mixing in the color mixer 68 is determined by the amounts of red, green, and blue reflected by the secondary colors my, cy, and cm of the ink used. For example, "Theory of Color Reproduction" by Jiyoung Yule,
(Published by Printing Society Publishing Department, February 5, 1971) No. 149
The coefficients k ₁ to k ₉ determined by the matrix resistors 69 to 77 are calculated from the red, green, and blue density data for MY, CY, and CM listed as typical process ink densities on the page. The values are as shown in the table below.

【table】

[Table] The values of the matrix resistors 69 to 77 of the mixer 68 may be calculated by a known method so as to satisfy the values of K ₁ to _{k 9} above. Further, in terms of the circuit configuration, the second black mixer 64 and the color mixer 68 may be combined into one matrix resistor. FIG. 3 shows another embodiment of a color reproduction circuit implementing the color reproduction method of the present invention. In the embodiment shown in FIG. 2, the color mixer 68 is placed after the second black mixer 64, but in this example, the color mixer 68 is placed in the subtracter 5.
5 and the first black mixer 60. As is clear from equations (4) to (9) above, even if you reproduce an intermediate color by mixing the primary color signals before mixing the ink color, and then add the ink color, red and green, which have intermediate colors, will not be reproduced. , blue color signals R″, G″, B″ can be obtained. Red, green, and blue color image signals obtained in this way
In order to obtain even more similar color tones by supplying R″, G″, and B″ to an RGB display, it is desirable to add correction for the color of the paper and the coloring characteristics of the display. It can be constructed by a similar matrix resistor.Furthermore,
This correction matrix resistor may be combined with the matrix resistor of the color mixer to form a single matrix resistor. Effects of the Invention Although the color tone of the image on the display obtained by the present invention has some secondary colors that are less similar than the original image, the primary colors are vividly reproduced and at first glance. The color tone is almost the same as that of the image reproduced by the circuit shown in FIG. On the other hand, the circuit does not require four multipliers, has fewer adjustment parts, and has a significantly simpler configuration, making the device smaller and cheaper and easier to adjust. Therefore, it is most suitable for applications such as an inspection device for color printing separation plates, where it is sufficient to judge whether the printed separation plates of each part of the layout are correct or not. In addition, it can be used in applications where only primary colors need to be reproduced, or applications where some reduction in the reproducibility of some secondary colors is acceptable, and the effect can be quite large.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing the configuration of a conventional color reproduction circuit, FIG. 2 is a circuit diagram showing the configuration of an example of the color reproduction circuit for color printing separation plates according to the present invention, and FIG. 3 is a circuit diagram showing the configuration of another example of the circuit. It is. 51...Level adjuster, 53...Subtractor, 60
...First black mixer, 64...Second black mixer, 68
...color mixer.

Claims (1)

[Claims] 1. A primary color signal c representing the halftone area ratio obtained from cyan, magenta, yellow, and black color printing separation plates,
An input terminal receives each of the primary color signals c, m, and y, and outputs signals by adjusting the levels of the primary color signals c, m, and y according to predetermined coefficients α ₁ , β ₁ , and γ ₁ .
A level adjuster that outputs cα ₁ , mβ ₁ , yγ ₁ , and a signal cα ₁ , which is output from this level adjuster.
In response to mβ ₁ , yγ _{1 ,} three primary color signals (1−cα ₁ ), (1−
mβ ₁ ), (1−yγ ₁ ) as well as receiving the black signal bl and outputting a signal (1−bl); 1-bl) to obtain the signal (1-cα ₁ ) (1-bl), (1-mβ ₁ )
(1-bl), (1-yγ ₁ )(1-bl), and these signals (1-cα ₁ )(1-bl), ( 1-
By adding the black signal bl to each of mβ ₁ ) (1-bl) and (1-yγ ₁ ) (1-bl) at a predetermined ratio, the signal (1-cα ₁ ) (1-bl) + α ₄ is obtained. bl, (1−mβ ₁ )(1−b
l)
+β ₄ bl, (1-yγ ₁ ) (1-bl) + γ ₄ bl; and the signal (1-cα ₁ ) (1-bl) + α ₄ bl, (1-
mβ ₁ ) (1-bl) + β ₄ bl, (1-yγ ₁ ) (1-bl) +
γ ₄
and a mixer that receives BL and mixes them in a predetermined ratio to output additive red, green, and blue color signals having intermediate colors. . 2 Primary color signal c representing the halftone area ratio obtained from the cyan, magenta, yellow, and black color printing separation plates,
An input terminal receives each of the primary color signals c, m, and y, and outputs signals by adjusting the levels of the primary color signals c, m, and y according to predetermined coefficients α ₁ , β ₁ , and γ ₁ .
A level adjuster that outputs cα ₁ , mβ ₁ , yγ ₁ , and a signal cα ₁ , which is output from this level adjuster.
In response to mβ ₁ , yγ _{1 ,} three primary color signals (1−cα ₁ ), (1−
mβ ₁ ), (1−yγ ₁ ), and a subtractor having four inverters that receives the black color map signal bl and outputs a signal (1−bl), and these three primary color signals (1−cα ₁ ), (1−mβ),
(1yγ ₁ ) is mixed in a predetermined ratio to create red using the additive coloring method.
A color mixer that outputs green and blue color signals, and 3 that multiplies each of the three color signals of red, green, and blue output from this color mixer by the signal (1-bl).
a first black mixer having three multipliers; the black signal BL is added to each of the three color signals output from the first black mixer at a predetermined ratio to produce intermediate colors of red and green; A color reproduction circuit for a color printing separation plate, comprising a second black mixer that outputs a blue color signal.