JPS6347191B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an undercolor removal method and apparatus for obtaining signals corresponding to primary color ink amounts and black ink amounts based on signals obtained by color separation of a color original, and in particular, to a method and apparatus for calculating the black amount based on color separation signals. Alternatively, in addition to the black amount, calculate the average value of each primary color signal corresponding to the average value of the color amount, find the ratio of the obtained black amount or average value signal and each primary color signal, and calculate the ratio based on the ratio. When the color is close to achromatic, the difference in the amount of black removed from each primary color signal is reduced, and as the color approaches a chromatic color, the amount of black removed from each primary color signal is decreased. Undercolor removal is performed to increase the difference, preventing tertiary colors from becoming achromatic and increasing the total amount of undercolor removal, improving ink transfer and saving primary color ink. It is. Conventionally, when printing a color original in color, it has been widely used to perform color separation using a color scanner as disclosed in U.S. Pat. No. 3,885,244 to create color separation plates of yellow, magenta, cyan, and black. Are known. A practical version is created from this separated version, and the practical version is mounted on a printing machine to perform color printing. By the way, the color scanner
As disclosed in the above-mentioned US patent specification, first, a color original is scanned through a color filter to obtain uncorrected three primary color signals, and the obtained signals are passed through a masking circuit to obtain three primary color signals. A black ink amount signal is obtained from the primary color signal by a black ink amount calculation circuit (for example, a minimum value detection circuit), and a masking circuit performs correction, and a certain amount of black ink amount is removed from the three primary color signals to obtain a three primary color ink signal. After obtaining signals corresponding to the amount of black ink and primary color ink, further gradation correction is performed, and scanning exposure is performed on photosensitive film based on the obtained signals to produce each color of yellow, magenta, cyan, and black. This is to create color separation plates. In particular, obtaining a signal corresponding to the amount of black ink from the three primary color signals and removing a certain amount of the amount of black ink from the three primary color signals to obtain a signal corresponding to the amount of primary color ink is generally referred to as under color removal (UCR). I'm calling. The present invention relates to improvements in such undercolor removal. An example in which the present invention is applied to a color scanner will be described below. Here, the starting point and UCR% commonly adopted in conventional color scanners
A regulated undercolor removal configuration is described. First, the corrected three primary color signals Y in the state shown in FIG. 1A,
Undercolor removal for M and C will be explained. In the figure, S, T, and U correspond to the potentials of the three primary color signals, and the three primary color signals Y, M, and C are inverted signals, so their potentials are high (close to OV).
Therefore, the color amount of each of the three primary colors is small, and the color amount is 0% at 0V, and conversely, the lower the potential, the larger the color amount, and at -5V, the color amount is 100%. A signal K corresponding to the amount of black is obtained from these three primary color signals Y, M, and C. This signal K can generally be obtained by detecting the maximum value (maximum value of color amount) of the three primary color signals Y, M, and C. This black amount signal K is corrected by a masking circuit to become a corrected black amount signal K'. The starting point amount (Sp) is removed from this black amount signal K' to obtain a black amount signal (K'-Sp) related to undercolor removal. Generally, the starting point amount (Sp) is about 30 to 40% of the full concentration of 100%, but for better understanding, FIG. 1 shows an example in which 20% is used. Of course, when the black amount signal K' does not reach the starting point (Sp), the black amount signal (K'-Sp) related to undercolor removal is clipped to 0% (0V). The obtained signal (K′-
Sp) is multiplied by UCR percentage [%] (Up), and the obtained signal (K'-Sp) x (Up) is multiplied by correction factors α, β, γ, and the original three primary color signal Y
The primary color ink amount signals Y′, M′, are removed from M and C.
C′ is obtained. Although 20 to 30% is generally adopted as the UCR%, the illustrated example shows an example in which 50% is adopted. Figure 1B also uses the same starting point as Figure 1A for the three primary colors Y, M, and C shown in the same figure, and UCR.
Each signal after undercolor removal is shown in %. In such a conventional undercolor removal configuration, the amount of black removed from the primary color signals is the same for each primary color signal in FIGS. 1A and B, where the black amount signal K' is the same and the black amount calculation formula is the same. One thing will be understood. Furthermore, in the conventional undercolor removal method, three primary colors Y,
Even in the case of FIG. 1B where there is a difference in the ratio of M and C, the amount of black removed from each primary color signal is the same. The drawbacks of the conventional undercolor removal structure as described above are as follows. That is, in order to increase the removal ratio, U.
If CR% is set to a high value, there will be a problem if the primary colors Y, M, and C have approximately the same value (the color expressed by the amount of the three primary colors is achromatic or close to an achromatic color) as shown in Figure 1 A. However, as shown in Figure 1B, for example, in the case of a yellowish-reddish gray, the tone is not well reproduced and is reproduced as a tone close to an achromatic color, so conventionally, generally high UCR% is Not adopted. The following are possible reasons why the color tone is not well reproduced and the color tone becomes almost achromatic in the case shown in FIG. 1B. First, the primary color signal from which the undercolor has been removed is output as halftone dot or continuous tone density by a circuit such as a gradation correction section using a non-linear conversion relationship as shown in FIG.
Ink is applied to the printing material according to this output amount to form the density of each color component. In this case, each color ink contains other color components as shown in FIG. 4, for example. In this way, conventional undercolor removal methods calculate linear undercolor removal, but conversion to halftone or continuous tone density and conversion to print density are performed in a nonlinear manner, and the conversion relationship is also different from platemaking. It is not constant depending on the conditions and printing conditions. Therefore, as shown in Figure 1A, the primary color Y,
If M and C have almost the same value (the color expressed by the three primary colors is achromatic or close to achromatic), the color balance of Y, M, and C after removing the undercolor will depend on each conversion. However, as shown in Figure 1B, if the undercolor is removed when there is a yellow-red tertiary color, the final printed matter will undergo a conversion process based on a non-linear relationship. The color balance of Y, M, and C is different from the case where the undercolor is not removed, and the color tone is not reproduced correctly, and generally the color tends to become achromatic. Furthermore, if a large amount of undercolor removal is performed, the black ink area becomes large, which also tends to reduce the hue of the three primary color inks. As a countermeasure to the above-mentioned drawbacks, it is possible to use a masking circuit to make more color corrections to intensify the tone, but it is difficult to correct tertiary colors with low saturation by masking, so it is necessary to reproduce them with good balance. That is difficult. On the other hand, if UCR% is set to a low value, a large amount of yellow, magenta, cyan, and black ink will be overprinted for achromatic colors, especially high-density achromatic colors (black or colors close to black), which will cause problems during printing. The disadvantages are that the ink transfer to the paper is poor and that a large amount of expensive yellow, magenta, and cyan ink is required due to the low removal rate. Also, for the expression of achromatic colors, it is better to mainly print with black ink, which is an achromatic ink, for a more preferable tone expression. As mentioned above, the U.S. of conventional color scanners, etc.
In the CR configuration, U.
Since CR% is multiplied by a fixed value, it has the drawbacks mentioned above. The present invention has been made in view of such drawbacks, and when the colors represented by the three primary colors Y, M, and C are achromatic colors or colors close to them as shown in FIG. 2 A', the primary color signal of each color is Remove undercolor with UCR% close to %,
Further, in the case of chromatic tertiary colors as shown in FIG. 2B', the problems of the conventional structure are solved by removing the undercolor at a UCR percentage corresponding to the primary color signal of each color. In the present invention, the black amount signal K' or the average value G of each of the primary color signals Y, M, and C is determined, and the amount of black to be removed is controlled for each primary color signal based on the ratio between these and each primary color signal. The average value G may be determined by the arithmetic mean or geometric mean of the color amounts of the three primary color signals. In this case, the average value G is G=Y+M+C/3 or

It is given by [Formula]. In the present invention, the black amount signal is
K' or black amount signal K' and the average value G are determined, and the amount of undercolor removed from the three primary color signals is controlled by the ratio of this black amount signal K' or average value signal G and each primary color signal. The closer a color is to a chromatic color, the smaller the difference in the amount of undercolor removed from each of the three primary colors, and as the color approaches a chromatic color, the difference in the amount of undercolor removed from each primary color signal becomes larger. To overcome the drawbacks of an undercolor removal configuration. Although the ratio between the black amount signal K' or the average value signal G and each primary color signal and U, C, and R% may have a linear relationship, it is extremely preferable to control them non-linearly. The present invention will be described in detail below with reference to an embodiment shown in FIG. 5 in which the present invention is applied to a scanner. In this embodiment, the primary color signals Y, M, and C are inverted signals as in FIGS. 1 and 2. However, for ease of understanding, the signals are displayed as positive values. Furthermore, in the description, the reading section 10, masking correction section 20, gradation correction section 80, recording section 90, etc., which are generally employed in scanners, are well known from the above-mentioned US patent specifications, so details will be omitted. Further explanation will be omitted. A color original 1 is mounted on an original cylinder 11 in a reading section 10 , and uncorrected three primary color signals Y, M, and C obtained by scanning the original 1 are guided to a masking correction section 20 . Each color component yellow y, magenta m, cyan c, red r, blue b, green g, black k,
White w is detected and the original three primary color signals Y, M, C are corrected based on these color component signals.
Outputs primary color signals Y, M, and C. These output signals Y, M, and C are sent to the next undercolor removing section 30.
is input to. In the under color removing section 30, the three primary color signals Y, M,
C is input to the black amount calculating section 40, the black amount is calculated, and a black amount signal K is output. This black amount calculation circuit 4
0 is a circuit that detects the maximum value of input signals Y, M, and C. Since the signals Y, M, and C are negative signals,
As a result, the circuit 40 has detected the minimum value (Y, M, C) mini of the color amounts of the three primary colors. The black amount signal K obtained by the circuit 40 is converted into a corrected black amount signal K' by a black amount signal masking circuit 41 and then input to the starting point [Sp] setting section 42 . The Sp setting section 42 is provided with an Sp setting signal generator 43, and the output voltage of the generator 43 can be manually adjusted.
is added to the black amount signal K'. Since the black amount signal K' is a negative signal, the starting point signal (Sp) is subtracted by the adder 44, and the black amount (K'-Sp) related to the UCR is output from the adder 44. ) is output, and the signal is input to the removed black amount calculation units 45Y, 45M, and 45C for each color. The removal black amount calculation units 45Y, 45M, and 45C calculate the black amount (K'-Sp) by calculating the UCR for each color, which will be described later.
UCR% from % control parts 70Y, 70M, 70C
By controlling based on the signal Up (Y, M, C), the basic amount of black to be removed from the three primary color signals Y, M, C is calculated. The removed black amount calculation units 45Y, 45M, and 45C are composed of multiplication circuits, and are calculated using the black amount signal (K′-Sp) related to UCR and the UCR% from the UCR% setting unit 70.
The basic black amount (K'-Sp) x Up (Y, M,
C) is calculated. This signal (K′-Sp) Up (Y,
M, C) are inversion circuits 46Y, 46M, 4 for each color.
6C and the respective color adjusters 47Y, 4
After being corrected by correction factors α, β, and γ at 7M and 47C, it is added to the original three primary color signals Y, M, and C via operational amplifiers 48Y, 48M, and 48C, so that the original three primary color signals Y, The amount of black is removed from M and C. In this way, three primary color signals from which the undercolor has been removed, ie, three primary color ink amount signals Y', M', and C' are obtained. On the other hand, the black amount signal K' after being corrected by the masking circuit 41 is input to the average value calculation section 61 and used to calculate the average value G, and the average value signal obtained there is input to the ratio calculation section 60. Will it be done?
Alternatively, the black amount signal K' is directly input to the ratio calculating section 60. Figure 5 shows the latter case, and Figure 6 shows the latter case.
The figure shows the former case. The ratio calculation unit 60 calculates the ratio between the black amount signal K' and the primary color signals Y, M, and C of each color, or the ratio between the average value signal G and the primary color signals Y, M, and C of each color (K '/Y), (K'/M), (K'/C) or (G/Y), (G/M), (G/C) are calculated. The ratio signal obtained by the ratio calculation unit 60 is input to the UCR% control units 70Y, 70M, and 70C for each color. The UCR% control units 70Y, 70M, and 70C provide a nonlinear factor to the ratio signal for each color in order to more preferably control the black removal amount calculation based on the ratio signal for each color.
In this embodiment, a characteristic curve setter 7 for each color is used.
1Y, 71M, and 71C are provided, and several types of nonlinear amplifiers that are switched by the setting devices 71Y, 71M, and 71C are provided.
The characteristic curves 72a, 7 are changed by switching by M, 71C.
2b, 72c... can be switched. Characteristic curves 72a, 72b, ... are black amount signals as shown in the figure.
The ratio of K′ to the primary color signal of each color (K′/Y), (K′/
M), (K'/C) or the ratio of grayness G to the primary color signal of each color (G/Y), (G/M), (G/C) is large, resulting in a high UCR% (Up), and the above Designed to have low UCR% when the ratio is small,
By setting these characteristic curves, nonlinearity is imparted to the ratio signal, and at the same time, the maximum UCR% and the minimum UCR% are set. That is, when the characteristic curve 72b is set, the maximum UCR% is approximately 90%, and the minimum UCR% is approximately 30%. The output signals Up (Y, M, C) from the UCR% control units 70Y, 70M, and 70C are input to the removed black amount calculation units 45Y, 45M, and 45C for each color as described above, and the removed black amount is calculated. The obtained removed black amount signal is sent to the inversion circuit 46Y for each color as described above.
46M, 46C and color adjusters 47Y, 46M,
Operational amplifier 48Y, 48M, 48C via 46C
The ink amount signals of the three primary colors Y′, M′,
It is used to find C′. On the other hand, the black amount signal K' has the ratios calculated by the ratio calculation section (K'/Y), (K'/M), as in the case of Fig. 5.
There is no problem in the case of (K'/C), but as in the case of FIG. 6, the ratio calculated by the ratio calculation unit 60 is (G/
In the case of Y), (G/M), and (G/C), this ratio may be larger than 1, which may cause the following problem. That is, in such a case, the amount of black removed from the primary color signal in a color plate where the ratio is greater than 1 becomes too large, and therefore the amount of black ink may become insufficient. Therefore, in such a case, the ratio signal obtained by the ratio calculation section 60 is input to the ratio signal comparison circuit 62, where the maximum value (Rmax) of the ratio signal is detected, and this maximum value signal (Rmax) is It may also be input to the black correction amount setting device 63. The black correction amount setter 63 sets the maximum value Rmax of the ratio signal.
This is to set the amount to increase the amount of black ink in order to avoid the amount of black ink from running out when is larger than 1. This is to obtain a black correction amount signal for correcting the amount signal K'.
The black correction amount signal for increasing the amount of black ink based on (Rmax-1) can have a non-linear relationship with (Rmax-1). The black correction amount signal obtained by the black correction amount setting device is added to the black amount signal K' in the black amount signal correction circuit 64 to obtain the corrected black amount signal K''. The three primary color signals from which the colors have been removed, that is, the ink amount signals Y', M', and C' of each color and the black ink amount signal K' or K'' are subjected to gradation correction in a gradation correction section 80 and then input to a recording section 90. , photosensitive films 5Y, 5M, 5 mounted on the recording cylinder 91 in the recording section 90.
C, 5K exposure recording. The ink amount signals for each color obtained in this manner according to the embodiment of the present invention are as follows. Y'=Y-(K'-Sp)×f(K'/Y)×α M'=M-(K'-Sp)×f(K'/M)×β C'=C-(K' -Sp) x f (K'/M) x γ K' = f ((Y, M, C) mini) or Y' = Y - (K' - Sp) x f (G/Y) x α M' =M-(K′-Sp)×f(G/M)×β C′=C-(K′-Sp)×f(G/C)×γ K″=f(K′) The device has a conventional UCR percentage so that it can perform undercolor removal at a constant value.
Switches 73Y, 73M, 73C, and 73K are provided, and by switching the switch, a UCR% signal of a constant value that can be manually adjusted is input to the black removal amount calculation units 45Y, 45M, and 45C. has been done. Although the above embodiment has been described in detail with respect to an example in which the present invention is applied to a color scanner, it goes without saying that the present invention can be applied to other similar color separation devices, etc. However, it is clear that it can also be applied to digital processing methods. Since the present invention has the above structure, it has excellent practical effects as shown below. That is, in the conventional undercolor removal configuration, the amount of black removed from the primary color signal is performed based on the amount of black signal and a constant UCR%, and the hue is not taken into account, resulting in a low U.
When CR% is adopted, it is high despite the problem of ink transfer in achromatic color areas.
When UCR% is used, chromatic parts become achromatic and desirable tones cannot be reproduced, so in many cases a low UCR% was used. According to the present invention, the above problems are solved and the black amount signal is
Even when K′ is equal, the closer the color is to an achromatic color, the more the amount of black removed from each primary color signal approaches the same amount; conversely, as the color becomes chromatic, the primary color signal of the main color The difference between the amount of black removed from the dark primary color signal and the amount of black removed from the murky primary color signal becomes large. In this case, the amount of black removed from the primary color signal of the murky color is larger than the amount of black removed from the primary color signal of the main color. Therefore, the color tone does not become achromatic, and it is possible to remove the undercolor at a high rate, thereby solving the problem of ink transfer.

[Brief explanation of the drawing]

The drawings are for explaining the present invention, and FIG. 1 is a signal explanatory diagram showing a conventional undercolor removal configuration, and FIG. 2 is a signal explanatory diagram showing an undercolor removal configuration of the present invention corresponding to FIG. 1. , Fig. 3 is a graph showing the conversion relationship of the signal after undercolor removal to output halftone dots or density, Fig. 4 is an explanatory diagram of the color components of each primary color ink, and Fig. 5 is the undercolor removal device of the present invention. FIG. 6 is a block diagram of another embodiment. 10...reading unit, 20...masking correction unit,
30...undercolor removal section, 40...black amount calculation section, 41
...Black signal masking circuit, 42...Starting point setting section, 45Y, 45M, 45C
...Black removal amount calculation unit, 61...Average value calculation unit, 7
0Y, 70M, 70C...UCR% control section.

Claims (1)

[Claims] 1. In an undercolor removal method for obtaining signals corresponding to the amount of primary color ink and the amount of black ink based on the signals obtained by color separation of a color document, the primary colors obtained by color separation are provided. Determine the black amount signal or the average value signal of the black amount signal and each primary color signal from the signal, and determine the ratio of the primary color signal of each color obtained by color separation to the black amount signal or the average value signal, and each obtained color 1. An undercolor removal method comprising controlling the amount of ink removed from the primary color signal of each color based on the ratio of each primary color signal to obtain a signal corresponding to the amount of primary color ink. 2. The undercolor removal method according to claim 1, wherein the average value signal is calculated from an arithmetic average value of each primary color signal. 3. The undercolor removal method according to claim 1, wherein the average value signal is calculated from the geometric mean value of each primary color signal. 4. In an under color removal device that obtains signals corresponding to primary color ink amounts and black ink amounts based on signals obtained by color separation of a color original, a black amount calculation unit that calculates black amount from primary color signals; a ratio calculation unit that calculates the ratio between the black amount signal from the color filter and the primary color signal of each color, a removal black amount calculation unit that calculates the removal black amount for each color based on the ratio signal from the ratio calculation unit, and a removal black amount calculation unit The present invention includes a circuit that removes the amount of black from the primary color signal based on the amount of black removed from the primary color signal, and controls the amount of black removed for each color according to the ratio signal for each color to obtain a signal corresponding to the amount of primary color ink. Characteristic undercolor removal device. 5 The removed black amount calculation unit calculates the amount of black removed from the ratio signal.
5. The undercolor removing device according to claim 4, further comprising a UCR% control unit that obtains a UCR% signal. 6. The undercolor removing apparatus according to claim 5, wherein the UCR% control section includes a nonlinear amplifier. 7. In the under color removal device that obtains signals corresponding to the primary color ink amount and the black ink amount based on the signals obtained by color separation of the color original, a black amount calculating section that calculates the black amount from the primary color signal; An average value calculation section that calculates the average value of the primary color signal, a ratio calculation section that calculates the ratio between the primary color signal and the average value signal from the average value calculation section, and a removal amount of black for each color based on the ratio signal from the ratio calculation section. A removal black amount calculation unit that calculates the removal black amount, and a circuit that removes the black amount from the primary color signal based on the removal black amount signal from the removal black amount, and controls the removal black amount for each color according to the ratio signal for each color. An undercolor removing device characterized in that the undercolor removing device obtains a signal corresponding to the amount of primary color ink. 8 The removed black amount calculation section calculates the amount of black removed from the ratio signal.
8. The undercolor removing device according to claim 7, further comprising a UCR% control unit that obtains a UCR% signal. 9. The undercolor removing apparatus according to claim 8, wherein the UCR% control section includes a nonlinear amplifier. 10. Claim 7, wherein the ratio is a ratio of the average value signal to the primary color signal.
Undercolor removal device as described in Section 1. 11 A black amount correction circuit that compares whether the maximum value of the ratio of the average value signal to the primary color signal is greater than 1 and corrects the signal corresponding to the amount of black ink only when it is greater than 1. An undercolor removing device according to claim 7, characterized in that the device includes: