JPS5872144A - Undercolor removal method and device - Google Patents

Abstract

PURPOSE:To make undercolor removal possible in a high ratio without making the hue achromatic, by controlling the undercolor removal quantity on the basis of the ratio of the primary color signal of each color to a black ink quantity signal or the like. CONSTITUTION:Three primary color signals from an original picture 1 due to a reading part 10 and a masking correcting circuit 20 are inputted to a black color calculating part 40 of an undercolor removing part 30, and a black ink quantity signal is formed through the calculating part 40 and a masking circuit 41. A ratio of each primary color signal to the black ink quantity signal is determined in a ratio calculating part 60, and removal black ink quantity calculating parts 45Y, 45M, and 45C of respective colors are controlled through undercolor removal controlling parts 70Y, 70M, and 70C in accordance with his ratio. Consequently, the undercolor removal considering the hue is performed in accordance with the ratio of each primary color signal to the black ink quantity signal by operational amplifiers 48Y, 48M, and 48C, and thus, undercolor removal is performed in a high ratio without making the hue achromatic, and transfer of inks is improved to economize in quantities of primary color inks. The similar result is obtained when the control based on the ratio of the black color signal to an average value of respective primary color signals is performed.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention processes color originals by color separation 1. 17 relates to an under color removal method and apparatus for obtaining signals corresponding to primary color ink amounts and black ink amounts based on signals obtained from the Furthermore, calculate the average value of each primary color signal corresponding to the average value of the color amount 17, find the ratio of the obtained black amount or average value signal and each primary color signal,
Control 12 controls the amount of black removed from the primary color ink based on the ratio, and when the color is close to an achromatic color, the difference in the amount of black removed from each primary color signal is reduced to approach a chromatic color. Undercolor removal is performed to increase the difference in the amount of black removed from the primary color signal, which prevents the sixth color from becoming achromatic, increases the total amount of undercolor removal, and improves ink transfer. This saves the amount of primary color ink.

Conventionally, when color printing a color original, color separation is performed using a color scanner such as that disclosed in U.S. Pat. No. 3,885,244 to create color separation plates of yellow, magenta, cyan, and black. is widely 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, as disclosed in the above-mentioned US patent specification, a color scanner first scans a color document through a color filter to obtain uncorrected three primary color signals, and then passes the obtained signals through a masking circuit to convert them into three primary color signals. From these three primary color signals, a black ink amount calculation circuit (for example, a minimum value detection circuit) obtains a black ink amount signal, which is corrected by a masking circuit, and a certain amount of black ink amount is removed from the three primary color signals. After obtaining primary color ink signals and obtaining signals corresponding to the amount of black ink and the amount of primary color ink, further gradation correction is performed, and based on the obtained signals, scanning exposure is performed on photosensitive film, such as city yellow, magenta, cyan, etc. This is to create color separation plates for each color of ink. Here, in particular, under color removal (U, C , R). 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 points and U and C commonly employed in conventional color scanners.

An undercolor removal configuration with R% adjustment will be described.

First, the corrected three primary color signals +y+ in the state shown in the first row
, ((Foundation), (C1 undercolor removal will be explained.

In the same figure, +S+, ((support) corresponds to the potential of the three primary color signals, and the three primary color signals (Yl, (I), (C1) are inverted signals, respectively, so the potential is high ( The closer to OV), the smaller the color amount of each of the three primary colors, and at OV, the color amount is 0%, and conversely, the lower the potential, the larger the total amount,
At -5V, the color amount is 100%.

The signal fKl corresponding to the black amount is obtained from these three primary color signals (■, tMI, fc'l. This signal (Kl is generally the maximum value of the three primary color signals (Yl, (Ml, tc'l) (the minimum value of the color amount) ).This black amount signal IKI is corrected by a masking circuit and is made into a corrected black amount signal (phantom'.) From this black amount signal tKl', a starting point amount (Sp ) is removed to obtain a black amount signal (K'-8p) related to undercolor removal.Generally, the starting point amount (sp) is about 30 to 40% with respect to 100% density. For better understanding, Fig. 1 shows an example in which 20% is adopted.Of course, the black amount signal (Kari' is the starting point (
Sp), the black amount signal (K
'-81)) is clipped to 0% (0■). Multiplying the obtained signal (K/-8p) KU,C,'R percent [%] (U p ) gives the obtained signal (
K'-8p') X (Up) with correction factor d,
Multiplying β and γ is the original six primary color signal tYl, (round, (removed from C1 to obtain the primary color ink amount signal (Y') (M') (C')
is obtained.

Although 20 to 30% is generally adopted as U, C, and R%, the illustrated example shows an example in which 50% is adopted.

Figure 1 fBl also shows the three primary colors (Yl, ((Foundation), (
The same starting point as the first position for C1, U
, C0R% indicates each signal after undercolor removal.

In such a conventional under color removal configuration, the amount of black removed from the primary color signal is the amount of black removed from each primary color signal (t'Al and fBl in FIG. 1, where K1' is the same and the black amount calculation formula is the same). It will be understood that both are the same.

Furthermore, in the conventional undercolor removal method, three primary colors [Y], (M
Even in the case of FIG. 1 (Bl) where there is a difference in the ratio of l and fcl, 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 C0R% is set to a high value, Figure 1 (primary color tY
l, (Ml, fcl have almost the same value (appears with its 3M color amount) t, 68ka1, □9.., E9.□9□6 For example, as shown in Figure 1 IBI, In the case of a yellowish-reddish gray, the color tone is not well reproduced and is reproduced in a color tone close to an achromatic color, so high U, (', R% is generally not adopted in the past.

The following are possible reasons why the color tone is not well reproduced and the color tone becomes close to achromatic color in the case as shown in FIG. 1 fB+.

First, the primary color signal from which the undercolor has been removed is output by a circuit such as a gradation correction unit as a halftone dot or continuous tone density in a non-linear conversion relationship as shown in Figure 6, and is applied to the printed object according to the output amount. Ink is applied 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, in the conventional undercolor removal method, calculation of undercolor removal is performed linearly, but conversion to halftone or continuous tone density and conversion to printing density and intensity are performed in a nonlinear manner, and the conversion relationship is It also varies depending on the plate-making conditions and printing conditions. Therefore, when the primary colors (Yl, (field, fcl) are approximately the same value (the color expressed by the three primary colors is achromatic or close to an achromatic color) as in +At in Figure 1, +Yl, +Ml after removing the undercolor, [The balance of the color amount of C1 does not change with each conversion and there is no problem, but as shown in Figure 1 fBl, if undercolor removal is performed when there is a hue such as a yellow-reddish tertiary color, non-linear The final printed material is produced through a conversion process based on relationships, so (■
, ((Incorporated), (Unlike the case where the undercolor is not removed, the color balance of C1 is different from that in which the color tone is not correctly reproduced and generally 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 runner-up problem, it is possible to use a masking circuit or the like to make more color corrections to strengthen the tone, but it is difficult to correct tertiary colors with low saturation by masking, so they are reproduced with good balance. It is difficult to do so.

On the other hand, if U, C, and R% are set to low values, a large amount of yellow, magenta, cyan, and black ink will be printed over and over again for achromatic colors, especially high-density achromatic colors (black or colors close to black). The drawbacks are that the transfer of ink to the paper during printing is poor, and because the removal rate is low, a large amount of expensive yellow, magenta, and cyan inks are required. Also, for achromatic colors, it is better to print mainly with black ink, which is an achromatic ink.

As mentioned above, conventional color scanners etc.

In C, R composition craftsmanship, U and C are used for one color manuscript.
, R% are multiplied by a constant value, which has the drawbacks mentioned above.

The present invention has been made in view of these drawbacks, and is shown in FIG.
)', the three primary colors [YI, (Ml, (If the color expressed by CI is an achromatic color or a color close to it, the under color is set at U, C, and R%, which is close to 100% for the primary color signal of each color. In addition, in the case of chromatic tertiary colors as shown in Figure 2 (B)', by removing the undercolor at U, C', and R% according to the primary color signal of each color, the conventional structure This solves the problem.

In the present invention, the black amount signal fKl' is determined by the average value (Gl) of each primary color signal (Yl, 2) and FC+, and the removed black amount is determined for each primary color signal by the ratio of these and each primary color signal. to control.

K for determining the average value ((g)) may be determined by the arithmetic mean or geometric mean ring of the color amounts of the three primary color signals.

In this case, the average value G is Y10M10 G-□ or G-V ■ Ma V Ma τ is given by

In the present invention, in this way, the black amount signal (K)' or the black amount signal (K)' and the average value (Gl are determined, and the black amount signal IK,)' or the average value signal fc)) and each primary color are The amount of undercolor removed from the three primary color signals is controlled by the ratio with the signal, so that the difference in the amount of undercolor removed from the six primary colors of each color is small, and as the color approaches the chromatic color, each color is To eliminate the drawbacks of the conventional undercolor removal configuration by increasing the difference in the amount of undercolor removal removed from primary color signals.

Although the black amount signal (Kl' or the average value signal (Gl) and the ratio of each primary color signal and U, 'C, R% may have a linear relationship, it is extremely important to be able to control them non-linearly. preferable.

The present invention will be described in detail below according to an embodiment shown in FIG. 5 in which the invention is applied to a scanner.

In this embodiment, the primary color signals fYl, (Ml, fcl
is an inverted signal similar to FIG. 1.2. However, for ease of understanding, the signals are displayed as positive values.

In addition, for the purpose of explanation, the reading section 00), mass ink correction section (a), gradation correction section (8o), recording section (9o), etc. that are generally employed in scanners may be referred to in the above-mentioned US patent specification, etc. Since this is well known, detailed explanation will be omitted.

In the reading section 00), the color original (
1) is mounted, and the document (1) is scanned to obtain uncorrected three primary color signals (Yl, fMl, (CI
is guided to the masking correction section (a).

Each color component yellow fyl, magenta (m), cyan (C), red (rl, blue ibl, green fg) is controlled by the masking circuit provided in this correction unit (201).
, black fkl, and white (@) are detected, and the original three primary color signals fY1.fM, fcl are corrected based on these color component signals to produce the corrected three primary color signals (■, ,(C)
Output.

This output signal (■, ((), IcI) is input to the next undercolor removal section (g).

In the under color removal section (to), the three primary colors - No. 1. Yl, (M
, fcl are input to the black amount calculation unit 4, the black amount is calculated and the black amount signal (Kl is outputted. This black amount calculation circuit detects the maximum value of the input signals IYI, (Ml, (C1) It is a circuit.

Since the signal (Y1% (goods), (C1) is a negative signal, in the circuit (4■), the minimum value of the color amount of the six primary colors (Y, M,
C) mini has been detected.

circuit (the black amount signal fKl obtained by 4G is set as the black amount signal IKI' corrected by 4υ and then becomes the starting point) (Sp) setting unit (42
1.

The S, p setting section (fourth is the Sp setting signal generator (43)
The output voltage of the generators (4, 1) can be adjusted manually, and the set output voltage, that is, the starting point signal (Sp) is converted into a black amount signal (K)' by an adder circuit (44). Since the black amount signal (K)' is a negative signal, the starting point signal (sp) is subtracted from the adder (44) as a result. Black amount related to U, C, H (K'-81
)) is output, and this signal is sent to the removal black amount calculation unit (4) for each color.
5Y), (45M), and (45C).

The removed black amount calculation unit (45Y), (45M), (
45C), the black amount (K'-3p) is determined by U';C,R% control section (70Y), (70M), (70
TJ, C', R% signals Ullll(Y, M,
By controlling according to C), the three primary color signals ■), (
(Goods), (The basic amount of black to be removed from C1 is calculated.

, this removal black amount calculation unit (45Y), (45M),
(45C) consists of a multiplication circuit, which outputs U, C, R [related black amount signal (K'-8p) and tJ, cR% signal Up (Y, M, The basic black amount (K'-8'p
) Xtjp (y.

M, C) are calculated. This signal (K'-8p)XUp
(Y, M, C) is an inversion circuit for each color (46Y),
(46M).

(46C) and the respective color adjusters (47Y)
.

(47M) and (47C), the correction factors d, β,
After being corrected by r, the operational amplifier (48Y), (48,M
), (48C) to the original three primary color signals (■, U, (C
1, which is essentially the original 3N color signal (Yl, ((
), the amount of black is removed from fcl.

In this way, the three primary color signals from which the undercolor has been removed, ie, the ink amount signals (Y') (M') (c') of the three primary colors, are obtained.

On the other hand, the black amount signal (K)' after being corrected by the masking circuit (41) K is input to the average value calculation unit 1) and used to calculate the average value +C++, and the average value signal obtained there is input to the ratio calculation section [0], or the black amount signal (Kl' is directly input to the ratio calculation section (60). FIG. 5 shows the latter case, and FIG. 6 shows the former case. The case is shown below.

The ratio calculation section uses the black amount signal (K)' and the primary color signal IY of each color.
I.

tM), , lC) or the average value signal (G
It calculates the ratio between l and the primary color signal of each color (Y'l, (goods), (C1, CK7Y), (KriM)
t CK7c) or (G/Y), (G/.

M), (G/C) are calculated.

The ratio signal obtained by the ratio calculation unit 160) is t for each color.
l, c, R% control section (70Y), (70M), (7
0C).

This U, C'', R% control section (+oy), (70
M) and (70C) provide a nonlinear factor to the ratio signal for each color in order to better control the calculation of the amount of black to be removed based on the ratio signal for each color.

In this embodiment, a characteristic curve setter (71Y
), (71M>, (71C) are provided, and several types of nonlinear amplifiers are provided which are switched by the setting devices (71Y), (71M), (71C)K, and the setting device (71C) is provided.
The characteristic curves (72a), (72b), (72C), etc. can be switched by switching by Y), (71M), and (71C). Characteristic curve (72a), (72
b)... is the ratio of the black amount signal diagram)' and the primary color signal of each color (K/y), (KPM) + (
When K/c) or grayness ((G) and the ratio of the primary color signal of each color (G/Y), (G/M), ((PC) is large, U, C, R% (Up) is high, When the ratio is small, it is designed to have low U, C, R%, and by setting these characteristic curves, nonlinearity is imparted to the ratio signal, and at the same time, the maximum U, C'.

R% and minimum U, C, R% are configured to be set. In other words, the characteristic curve (when 7 branches are set, the maximum U, C,
The R% is approximately 90% and the minimum U, C0R% is set to approximately 30%.

U, C, R% control section (70Y), (70M), (70C
) output signals U p' (Y, M, C) are sent to the removal black amount calculation unit (45Y) for each color (45Y), as described above.
45M) and (45C) to calculate the amount of black removed, and the thus obtained removed black amount signal is sent to the inversion circuits (46y) and (46M) for each color as described above.

(46C) and color adjuster (47Y), (46M),
(46C), operational amplifier (48Y), (48
M), (48C) and used to obtain ink amount signals (Y'), (M'), (C') of the three primary colors.

On the other hand, the black amount signal (Kl' is calculated by the ratio calculation section as in the case of Fig. 5), where the ratio is (K7y), (K'/M),
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 section - is (G/Y), (
yM), ((1/C), this ratio may be larger than 1, and the following problem may occur. In other words, in such a case, the ratio may be larger than 1. In the case of a color plate in which the primary color signal is large, the amount of black removed from the primary color signal becomes too thick, and therefore the amount of black ink may become insufficient.

Therefore, in such a case, the ratio signal obtained by the ratio calculation unit 1 (It) is input to the ratio signal comparison circuit/circuit, the maximum value (Ftrr+ax)' of the ratio signal is detected here, and this maximum value signal (Rmax) may be input to the black correction amount setting device (6).

The black correction amount setting device (Foundation) is used to set the amount by which black ink is increased in order to avoid a shortage of black ink when the maximum value Rmax of the ratio signal is greater than 1 by C (Rmax-1). ) is used to obtain a black correction amount signal for correcting the black amount signal (K)' so as to increase the amount of black ink. The black correction amount signal for increasing the amount of black ink based on (Rmax-1) is (Rm
ax-1). The black correction amount signal obtained by the black correction amount setting device is added to the black amount signal (Kl/) by the black amount signal correction circuit (64J) to obtain a corrected black amount signal (GA).

The three primary color signals from which the undercolor has been removed, that is, the ink amount signal (Y') (M') (c') of each color and the black ink amount signal (K') or (K") obtained as above, are gradation. After gradation correction is performed at the end of the correction section, the photosensitive film (5Y) (5M) (5C) (5
K) is exposed and recorded.

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' -8p) X f (K'/Y
)XdM' = M - (K' - Sp) X f (
K'/M) XβC'=C-(K'-8p)Xf(K1
7M)×γK” f ((Y, M+C) mini) or Y'=Y-(K'-Bp)xf(o/y)xαM'=
M-(K'-5p)x f(()7M)XβC'=
C-(K'-Sp) X, f (G/C) X r
K''-f(K') The apparatus of the embodiment has conventional U, C, and 'R% in order to be able to perform undercolor removal with constant values.

C, R switch (73Y), (75M), (73C), (
73K) is provided, and by switching the switch,
Removal black amount calculation unit (45Y), (45M), (4
5C) constant values of U, C', R% manually adjustable
It is configured to receive a signal.

Although the above-mentioned 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. As mentioned above, it is clear that the present invention 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 black amount removed from the primary color signal is performed based on the black amount signal and constant U, C'L R%, and the hue is not taken into account, so the amount of black removed from the primary color signal is low. Although there is a problem with ink transfer in achromatic areas when U, C, and R% are adopted, when high U, C, and R% are adopted, chromatic areas become achromatic, resulting in a favorable color tone. is not reproduced, so
In many cases, low U, C, and R% were adopted.

According to the present invention, the above problems are solved, and the black amount signal (K')
Even when the colors are 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, and conversely, the more chromatic the color, the more black is removed from the primary color signal of the main color. The difference between the amount of black and the amount of black removed from the enriched primary color signal becomes large. In this case, the amount of black removed from the primary color signal of the enriched color is thicker than the amount of black removed from the primary color signal of the main color. Therefore, the tone does not become achromatic, and the undercolor is removed at a high rate. Since it becomes possible to do
The ink transfer problem is solved.

[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. 6 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. 00)...Reading section (20)...Masking correction section (7)...Under color removal section (40...Black amount calculation section (4υ...Black amount signal masking circuit (4)...
21...Starting point setting section (45Y
), (45M), (45C)...Removed black amount calculation unit (1)...Average value calculation unit (70Y), (70
M), (7QC)...U. C, R% Control Department Patent Applicant Toppan Printing Co., Ltd. Representative Kazuo Suzuki

Claims (1)

[Claims] (1) In an undercolor removal method for obtaining signals corresponding to primary color ink amounts and black ink amounts based on signals obtained by color separation of a color original, The amount of black to be removed from the primary color signal of each color is controlled for each primary color signal based on the obtained ratio for each color. An undercolor removal method characterized by obtaining 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 under color removal method according to claim 1, wherein the average value signal is calculated from the geometric mean value of each primary color signal. (4) Separate the color original 1. In the under color removal device which obtains signals corresponding to the primary color ink amount and the black ink amount based on the signals obtained from the primary color signal, A ratio calculation unit that calculates the ratio of each color to the primary color signal, a removal black amount calculation unit that calculates the removal amount of black for each color based on the ratio signal from the ratio calculation unit, and a removal black amount signal from the removal black amount calculation unit. 1. A circuit for removing the amount of black from the primary color signal based on the signal 12, and controlling the amount of black removed for each color according to the ratio signal for each color.1. An undercolor removing device characterized in that the undercolor removing device obtains a signal corresponding to the amount of primary color ink. (5) The removed black amount calculation unit calculates UC8 from the ratio signal.
5. The undercolor removing device according to claim 4, further comprising a U, C, R% control section for obtaining an R% signal. (6) The undercolor removing apparatus according to claim 5, wherein the U, C, R % control section includes a nonlinear amplifier. (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 1. of the color original, a black amount calculation unit that calculates the black amount from the primary color signal; An average value calculation unit that calculates the average value of each primary color signal, a ratio calculation unit that calculates the ratio between the primary color signal and the average value signal from the average value calculation unit, and the amount of black removed for each color based on the ratio signal from the ratio calculation unit It is equipped with a circuit for removing the amount of black from the primary color signal based on the amount of black removed from the removed black amount calculation section, and a circuit for removing the amount of black from the primary color signal based on the amount of black removed from the amount of removed black. 1. An undercolor removing device characterized in that the amount is controlled to obtain a signal corresponding to the amount of primary color ink. (8) The removed black amount calculation section obtains a U.C, R% signal from the ratio signal. +' The undercolor removing device according to claim 7, characterized in that the device includes a C, R% control section. (9) The U, C, R% control section includes a nonlinear amplifier. (10) The undercolor removing device according to claim 7, wherein the ratio is a ratio of an average value signal to a primary color signal. αυ Compare whether the maximum value of the ratio of the average value signal to the primary color signal is greater than 1 or not 11. Only when it is greater than 1, the amount of black that corrects the corresponding signal for the amount of black ink 8. The undercolor removing device according to claim 7, further comprising a correction circuit.