JPS63296947A - Color recording system - Google Patents

Abstract

PURPOSE:To enable a saturation gap not to be generated between a chromatic color area and a black color area by reproducing an accurate color, by a method wherein saturation is obtained from three color color signals, besides the signal is converted to a plurality of chromatic color material signals, an adding print quantity of black is determined according to a color material and the saturation abovementioned and thereafter, a quantity to be removed of under color is determined. CONSTITUTION:Original information which was decomposed into three colors and read, is parallel outputted as three color signal of red, green, and blue, is outputted as a signal normalized to 0-1 with an equivalent neutral density conversion circuit 6 and is divided into two parts. One part is inputted to a masking circuit 7, and the other is inputted to a saturation detection means 8 to perform a specific operation. A saturation signal c is outputted to be inputted to a coefficient decision device 9. The coefficient decision circuit 9 performs a specific operation, outputs a coefficient signal to a black adding circuit 11 and besides, outputs a coefficient signal for removal of under color to an under color removal circuit 12. Besides, the signal inputted to the masking circuit 7 is converted to an ink signal by a known method, is inputted to the under color removal circuit 12 and at the same time, is inputted to a minimum value detection means 10. Then, said signal is outputted to the under color removal circuit 12 via the black adding circuit 11.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a color recording system that reproduces colors using a plurality of color materials including black, such as ink, and particularly when printing with undercolor removal. The present invention relates to a color image processing method for determining the amount of inking.

[Conventional technology]

Conventionally, in printing technology, four-color printing is usually used when reproducing color original images. i.e. yellow, magenta,
Color separation plates are created for printing inks of cyan and black colors. This is because, for example, in the case of three-color printing of yellow, magenta, and cyan, the ink does not have perfect color characteristics and cannot meet the ideal printing conditions, resulting in a reproduced image with poor contrast. This is because there is no

Further, during four-color printing, so-called undercolor removal may be performed on other printing inks, that is, yellow, magenta, and cyan printing inks. When this undercolor removal is performed, the achromatic portion is printed with only black ink, so the color reproduction range in the low brightness portion is widened, and gray stability can be maintained relatively high. Further, there is an effect that printing becomes reliable and the amount of ink used is reduced.

In this way, there are various advantages when performing four-color printing by removing the undercolor.

However, when performing four-color printing, there is a problem in that it is difficult to determine the amount of undercolor to be removed and the amount of black to be added, that is, the amount of black overprinting.

In order to solve this problem, a method for determining the amount of undercolor removal and the amount of blackening in a color scanner for printing has been proposed in Japanese Patent Laid-Open No. 57-173838 and Japanese Patent Laid-Open No. 58-190951.
This method is disclosed in Japanese Patent Application Laid-Open No. 58-211757, etc.

The method disclosed in Japanese Unexamined Patent Publication No. 57-173838 is characterized in that undercolor removal is carried out separately for an achromatic color area and a chromatic color area. This method reproduces an achromatic color area with only black, and further changes the amount of black printing with a gradient in a transition area from a chromatic color area to an achromatic color area.

Also, JP-A-58-190951, JP-A-58-190951,
No. 211757 discloses that depending on the gradation value, the amount of black printing,
A method for determining the amount of undercolor removal is shown. This method achieves a completely achromatic structure up to a gray value corresponding to the overlay of the black ink used, and increases the color component of the chromatic ink in the shadow area above this gray value. In other words, up to a certain level of density that can be reproduced with black ink, black is reproduced only with black ink, and for black densities higher than that, high-density black is reproduced by adding equal amounts of inks of the other three colors. There is.

In addition, methods for determining the amount of blackening and undercolor removal in digital color recording methods such as inkjet, thermal transfer recording, and laser color xerography are described in, for example, Japanese Patent Laid-Open No.
It is disclosed in JP-A No. 161981, JP-A-59-163973, and the like.

The method disclosed in JP-A-59-161981 is to obtain the amount of black overprint by multiplying the minimum value of the color data of cyan, magenta, and yellow by a certain constant, and calculate this amount of black overprint from each color data. Performs undercolor removal.

Furthermore, the method disclosed in Japanese Patent Application Laid-Open No. 59-163973 determines two chromatic inks to be combined with black based on the reflectance of multiple color inks, and prevents the chromatic inks and black ink from overlapping. By recording as follows,
Amount of black printing using a simple calculation method.

The amount of undercolor removal is determined.

[Problem that the invention seeks to solve]

However, the method disclosed in JP-A-57-173838 that performs undercolor removal by distinguishing between gray areas and colored areas requires a large number of coefficients when determining the amount of black overprinting and the amount of undercolor removal. do. Determination of these coefficients can still only be done empirically, and the amount of inking described above,
The difficulty of determining the amount of undercolor removal cannot be resolved.

Also, JP-A-58-190951, JP-A-58-190951,
No. 211757 discloses that depending on the gradation value, the amount of black printing,
Although it is shown that the under color removal amount is determined, these publications only describe the processing method in the black reproduction section, and when there is a transition from the chromatic color area to the black reproduction area, that is, In an image where the saturation changes gradually, such as a general picture, there is a risk that a false contour of color, that is, a saturation gap will occur.

Furthermore, the method disclosed in Japanese Patent Application Laid-Open No. 59-161981 is generally called fixed rate undercolor removal and undercolor addition.
In this case, there is a problem that accurate color reproduction cannot be performed. Regarding the reason why accurate color reproduction cannot be achieved, see, for example, "Study of ink-marking in printing (I) J, Proceedings of the 1st Color Engineering Conference 9, 4th Society of Optics, 1984.
It is described in 1-7 etc.

Furthermore, in the method disclosed in Japanese Patent Application Laid-Open No. 59-163973, calculations are performed based on the principle of average additive color mixture, so there is a problem that accurate color reproduction cannot be performed during actual printing. This is known to be caused by light penetration and diffusion efficiency inside the desk, for example, J, ^
, C. Yule, "Theory of Color Reproduction", Printing Society Publishing Department, February 1971, p.24
7-248.

In view of the shortcomings of the prior art described above, the present invention provides a black ink that does not require empirical adjustment, can perform accurate color reproduction through simple calculations, and does not create a saturation gap between the chromatic color area and the black area. The object of the present invention is to provide a color recording method that performs overprinting and undercolor removal.

[Means for solving problems]

In order to achieve the above object, the color recording method of the present invention has the following features:
Calculating the saturation from the three-color color signals from the human-powered device, converting the three-color color signals into color material signals of a plurality of chromatic colors, determining the amount of inking according to the color material signals and the saturation, and It is characterized by determining the amount of undercolor removal.

[Effect]

In the present invention, the blackening amount is determined based on the saturation of the document detected from the three-color color signals and the coloring material signal obtained by converting the three-color color signals, for example, by calculating an approximate formula. . At this time, the black printing amount is determined not only according to the color material signal, but also
It also changes depending on the saturation. Therefore, even if the image changes continuously from a highly chromatic area to an achromatic area, the amount of ink printing for optimal color reproduction is continuously determined, without creating a saturation gap. Smooth color reproduction is possible. Furthermore, since the amount of undercolor removal also changes depending on the saturation, the optimum amount of undercolor removal is determined in a continuous area from the colored area to the black area.

Here, the theoretical background on which the present invention is based will be explained using an example in which ink is used as a coloring material.

Now, consider the case where a color image is reproduced by combining a plurality of chromatic inks as shown in FIG.

FIG. 2(a) shows the cyan ink portion 1. The area ratio of the magenta ink part 2 is 100%, and only the yellow ink part 3 is 10%.
This is a case where it is not 0%, and shows a form that expresses colors with high saturation. Hereinafter, this will be referred to as form A.

In addition, the cyan ink portion 1. Magenta ink section 2. This is a case where the yellow ink portions 3 have the same area ratio, and shows a form expressing an achromatic color. From now on, shape this! ! It's called SB. Note that in Figure 2, etc., numeral 4 indicates a blank section.

The conditions for performing ink reprinting on these image formats A and B to match the format using three-color ink are shown below.

In the form shown in FIG. 2(a), since cyan and magenta are superimposed on the smallest dot part of the three colors, that is, the yellow ink part 3, the part of the surface laY of the smallest dot part is black. . Therefore, the inking amount is a.

, it is sufficient to simply replace the yellow ink amount a.

Note that for the sake of simplicity, it is assumed here that the ink amount and area correspond, and are given the same reference numerals.

In addition, the amount of undercolor removal is determined by the Neugebauer (Neu
gebauer's formula, DeMichel
), the area remains the same except for the smallest dot part.

Formulating the above results in equation (1).

Note that a C+ allr a Y is the cyan, magenta, and yellow ink portions 1.2.3 before blackening in Fig. 2.
represents the area of art aci all+ art is black after ink printing.

Represents the area of cyan, magenta, and occupancy.

In order to generalize this formula, the size relationship of the three color dots can be expressed as maximum area a□, , intermediate area a1jld + minimum area awl
When expressed as □, the formula (2) is obtained.

In addition, aIIlaX+ al@ld+ almlm is
This is the area after black printing corresponding to allAII+aald+amin.

Next, consider the form shown in FIG. 2(b).

When considering this form B, the Neugebauer equation is effective, and the average reflectance R of the image shown in FIG. 2(b) can be obtained by equation (3).

Here, s Rc, RXI Ry+ 'R1+ RG*
R1+ RXI RCHY is cyan, magenta, yellow, cyan/magenta overprint area, magenta/yellow overprint area,
It represents the reflectance of the yellow/cyan overprinted area, the white paper, and the cyan/magenta/yellow overprinted area, respectively. Further, a represents the area ratio of cyan, magenta, and yellow.

Here, the shape shown in FIG. 2(b)! ! Let us consider the case where blackening is performed at IB. Since form B is an achromatic color, when only one color of yellow in the yellow ink portion 3 is replaced with black, the other two colors, cyan and magenta, need to be completely removed under color. In other words, the undercolor removal amount is 100%.
It is necessary to Hence the shape! ! The formula obtained by blackening IB becomes formula (4).

R=(1ax)・Rw+ax・Rx ”・(4) However, R11 is the reflectance of black. In order for the colors before and after black printing to match in terms of colorimetry, formula (3) must be used.
, the right sides of (4) must be equal. Here, if formula (3) = formula (4) is formulated, formula (5) is obtained.

a t = (Rcxv Rw)−'X (a”(
Rcxv Rs Ra Rt+Rc+Rx+Ry
Rw) + a”・(3Rw −2Rc −2RII
-2RY+R1+RG+R1)+ a・(-3Rw+
RC+lI++RY))・ ・ ・ ・ ・ ・ ・(
5) Therefore, the blacking amount a is the three-color area ratio a before blacking
The relationship is cubic. Let each coefficient be α9 β, r
Then, RCIIyIlw RCIImarR.

3Rw +Rc +RIl +L γ =□ Rcwv Ry (6) From the calculation of the above formula, the following formula (7) is derived for each coefficient.

In addition, in the inequality part that includes an equal sign, each equality is cyan,
This only holds true if the magenta and yellow coloring materials are rectangular dyes with ideal rectangular spectral density distributions, and is an inequality sign in the case of general coloring materials.

Therefore, from equations (5), (6), and (7),
The amounts of black, cyan, magenta, and yellow ink when form B is overprinted with black are expressed by the following equations.

Equation (8) will be further considered.

The area a of ink printing is alII, , = 0 or am+++
When =1, al=asl+.

Now, if a+alh is set as P, then from equation (7), am am1m≧0 (however, 0≦amlh≦1) holds true.

The amount of black overprinting has been described above, and next, the amount of undercolor removal will be described.

If we organize the amount of undercolor removal for the above forms A and B,
In form A, which is a highly chromatic case, the under color removal amount is 0 from equation (2), and in form A, which is an achromatic case, the under color removal amount is 100% from equation (8). It turns out that it has to be.

Form A is the color area asl of the smallest dot. is completely included in the area a+aax+ *1d of the other two colors. Analysis of such a case has already been carried out, and it is said that the following relationship holds true for the maximum color area a+1IlaX after removing the undercolor.

(For example, see "First Color Engineering Conference 1-7 Consideration of Smear Insertion in Printing (I)").

1-a In the description of the wing tip, in the case of form A, it was assumed that a 1laX = a ll11411 = 1, that is, the undercolor removal amount was 0, but the same result can be obtained from equation (9). It will be done.

However, form B1, i.e. a m a X = a a l d = a w
Considering the case where a l h = a, as mentioned above, generally except for rectangular pigments, a, ≧alIlI.

(However, the equality sign holds true only when al,=sail 1), so according to equation (9), alaax<O.

However, in reality, this cannot happen.

The reason why such a problem occurs in equation (9) is explained as follows.

Equation (9) holds true under the condition that the area am1m is completely included in the area allAI+, but for form B
In this case, the area a□ is not necessarily included in the areas a, □, but rather there are many areas where the area 8m1m exists alone. The magnitude of such an inclusion relationship is generally known as the Demichel relationship. Such a difference in the inclusion relationship causes a problem in equation (9).

Therefore, if we consider undercolor removal from the perspective of preserving saturation before and after ink printing, the following can be considered regarding the form.

Before ink printing, the area where the area amIn exhibits saturation is amtn (1 ama
x”amid), and the area where the area amlaM exhibits saturation is amax(1amid'amtj).

After black printing, the smallest area aslh is replaced by black area a1, so there is no part where area a1ゎ exhibits saturation, and after black printing, there is a part where area a1ma+1 exhibits saturation. alaax(1ax).

Therefore, in order to equalize the colors before and after ink printing, the saturation must also be preserved, which can be formulated as follows.

al+aax(1au) =a+max(1amid' aat,,)amIn(
11aax'amid) ``aaaX asllll''``'αO, that is, -a1.

Formula (10a) has form B1, that is, a wax =
When a mid = a IIIR = a is substituted, alsax = o, and the same result as the above equation (8) is obtained.

Therefore, when determining the undercolor removal amount, three color inks that do not include black I allall alllld + aalh
An algorithm for undercolor removal must be incorporated in consideration of the inclusion relationship.

In addition, in the above description, the maximum area a. Although the above has been described for X, exactly the same result can be obtained for the intermediate area amid.

From the above-described analysis of the highly chromatic color form and the achromatic color form B, it can be seen that the following conditions are required for the amount of ink printing and the amount of undercolor removal in order to perform accurate color reproduction.

Condition (i): The black printing amount a is always a, ≧a m I n for the minimum value a*lh of the three color ink amounts for achromatic colors.
As the color becomes higher, a K'= a mi
It is necessary to set it to n.

Condition (i): For highly chromatic colors, the undercolor removal amount must be 0, and for achromatic colors, the undercolor removal amount must be 100%.

To confirm this, we used color printing to create three-color printing samples of cyan, magenta, and yellow, as well as overprinting samples of two of cyan, magenta, yellow, and black, and evaluated the color characteristics using Munsell Hue. , Munsell Baliney, Munsell chromatography measurement, on the other hand, the halftone area ratio ac of each color ink,
a,, at, and ax were measured. The relationship between the minimum ink amounts a and le of the three-color sample and the blackening amount a was actually measured for the pair of the three-color sample and the blackening sample obtained in this way, which have the same color.

Figure 3 is a three-dimensional graph showing the actual measurement results. The difference a wal between the black printing amount a and the minimum value a + mln of the three color samples is taken.

As can be seen from this graph, lamlh is always positive, and when the Munsell Baliney is the same, it can be seen that as the Munsell chroma, that is, the saturation increases, the aK a pass r+ monotonically decreases. Therefore, the above condition (i
> was confirmed to be correct from the results of actual measurements.

However, as it is, in color recording devices,
Munsell hinney, Munsell value, and Munsell chroma must always be determined, which is not practical.

Therefore, the saturation C on the X axis shown in FIG.

Substitute with

First, saturation e is calculated from the three color signals R, G, and B using the following equation.

-A-B However, it is assumed that the maximum value of the signals R, G, and B is standardized to 1.

The minimum value a of the ink signal for each saturation obtained in this way
Figure 4 shows the results of determining the amount of blackening using slh.

In the figure, the horizontal axis indicates the minimum value a1 of the ink signals of the three colors. .

, and the vertical axis shows the minimum value a of the three color signals from the black printing amount a,
1. ．． This is the result obtained by subtracting a@lr+ and regressing the measured data shown in FIG. 3 using equation (8).

The correlation coefficient of the regression equation for the measured data at this time is 99
．． It was 8%. From FIG. 4, a, ≧amIn,
It can be seen that as the saturation increases, il,=a, .

Next, af obtained by regressing the measured data using equation (8)
Figure 5 shows the relationship between the coefficient α of iln3 and the coefficient β of amlh'' and each saturation obtained from the human color signals R, G, and B using equation (9).As can be seen from the figure, the coefficient α .

β is a monotonous function for each saturation, and both converge to 0 as the saturation approaches 1. On the other hand, a+sa
x a@1n=0, α>0. β<0. Note that these coefficients α and β can be approximated by, for example, a quadratic equation.

Since the blackening amount a1 was determined as described above, the undercolor removal amount was next confirmed.

The confirmation method was to use the same sample as the one used to check the blackening amount, and to check whether the blackening sample aIllaX+
A method was used to compare at and afiaX+ amin of color-matched samples.

The comparison results are shown in FIG. In the figure, the horizontal axis represents the saturation signal obtained from the three color signals R, G, and B using the formula Ql) when determining the amount of blackening. The vertical axis also shows the maximum ink amount a1 after black printing calculated using equations (9) and (10a). The difference between A and I and the maximum ink amount obtained by actually measuring the inking sample is calculated. In Fig. 6, the difference between the calculated value of equation (9) and the measured value is represented by a solid line, and the equation (
The difference between the calculated value and the measured value of lea) is shown by a broken line.

From FIG. 6, we can see that when the saturation signal is small, that is, when the color is close to achromatic, Equation (10a) applies well, and when the saturation signal is large, that is, when the color becomes highly chromatic, Equation (10a) applies well.
It can be seen that 9) applies well. This is considered to be due to the inclusion relationship between the amounts of ink of the three colors as described above.

Therefore, in this embodiment, equation (9) and equation (10a) are used depending on the saturation signal. This can be formulated as the following equation.

allllll)l: hl(go)'(amax-ak)+(1-hl('
)) ”(a, am, -amtjl-al.

......However, hl(0) = 0. hl(1) = 1.
Let hl be a monotone function.

That is, the maximum value signal a. When 8 is large, (a□Eak)/(1ak) is dominant, and when it is small, (a---a-+-)/(1ak) is dominant. Naori can be approximated by, for example, h,=a x ax2.

The difference between the measured value and the actual value in the formula beating is shown by the dashed-dotted line in FIG. When formula 112+ was used, good agreement with actual measurements was obtained with a correlation coefficient of 99.6%.

In this way, regarding undercolor removal, as a result of actual measurements, a□,
It has been found that it is necessary to perform 100% undercolor removal when -a, , , is below a certain value. Note that this constant value changes depending on the recording method.

In the above, the area a□8 of the maximum color was used to determine the amount of undercolor removal, but it goes without saying that the same applies to the area Amid of the other color. In addition, at this time as well, the function h1
A function h2 similar to is used.

From the above, in a color recording system that reproduces colors using color materials such as inks of multiple colors including black, for example, if the following processing is performed, only relatively simple calculations are required, and no empirical adjustment is required. Therefore, accurate colorimetric color reproduction can be performed. Furthermore, continuous changes in saturation are possible even in the changing area between the colored area and the black area.

That is, the three color signals from the input device are converted into saturation signals, and ink signals of multiple colors excluding black corresponding to the ink dot area ratio of each color aC+ a)
(1) Ink signals ac, a
Maximum value a□8 of mo aY and maximum 111f direct a-t-wo detection L, (11) From the difference between both amam amIn, black printing ma
Find the coefficients α and β of the formula representing k, (iii) From the coefficients α and β and the minimum value a all, determine the blacking amount a by the following formula, ak = (X' a ya I n '+β+H111
2+(1-a-β)'amIn(iv) the maximum value a
From sax, determine the coefficient h (where h: h, , h2) necessary to obtain the undercolor removal amount, and (v) calculate the coefficient h, the black overprint amount a1, and the three-color ink signal a.
From llall+aald+aalh, the undercolor removal amount is determined based on the following equation.

1 1 to 8m alatl, = 0 However, h, , h2 is a function of saturation C. Here, an approximate expression is obtained from the measurement results of color-matching the reproduced image by ink printing and the reproduced image by three-color ink. By doing so, accurate colorimetric color reproduction can be performed. Also, ama, 1aal.

corresponds to the saturation, so even in the area where the colored area changes and the black area, the coefficients α and β change according to the saturation, and the optimal inking amount ak is continuously determined, resulting in continuous chroma. It is possible to change the degree.

Furthermore, since the amount of undercolor removal is controlled based on a coefficient corresponding to the saturation, it is possible to determine the optimum amount of undercolor removal in a continuous area from the colored area to the black area. For example, when the saturation is low, the undercolor removal amount is set to 100%, and when the saturation is high, the undercolor removal amount is set to 0, and the undercolor removal amount is continuously changed according to the saturation. , a black-printed image that is color-matched to the reproduced image using three-color ink is obtained.

〔Example〕

DETAILED DESCRIPTION OF THE INVENTION Hereinafter, features of the present invention will be specifically described based on examples with reference to the drawings.

FIG. 1 shows an example of a color recording apparatus for implementing the color recording method of the present invention.

In the figure, 5 is an input device such as a reading device that separates and reads manuscript information into three colors, and the read manuscript information is
For example, it is converted into a digital signal by an A/D converter (not shown) provided in the human-powered device 5, and output in parallel as three color signals R, G, and B of red, green, and blue.

The color signals R, G, and B are processed by an equivalent neutral density conversion circuit (in the figure,
The signals Rt, Gt, Bl are converted into equivalent neutral concentration by 6 (shown in the END conversion circuit) and normalized to 0 to 1.
is output as

These normalized signals R,,G,,B, are divided into two parts, one of which is input to the masking circuit 7, and the other to the saturation detection means 8.

The saturation detection means 8 includes a comparator, an adder, and a subtracter 9 branch circuits (not shown), performs the following calculations, and outputs a saturation signal C.

A = max (Rl+ G l+ B I) B = +
+++n (RI, G i B + )L=-A+B-A-B The saturation signal e obtained in this way is sent to the coefficient determiner 9
is input.

The coefficient determiner 9 is composed of a subtracter and a multiplier (not shown), performs the following calculations, and outputs coefficient signals α and β to the inking circuit IO.

α ・=・ p ・ ('!! -1)' However, P is a positive constant set in the coefficient determiner β=q・(go-l)
2 However, q is a negative constant set in the coefficient determiner.The above formula approximates the changes in coefficients α and β using a quadratic formula,
Constants p and q are determined depending on the coloring material.

Further, the coefficient determiner 9 performs the following calculation and outputs a coefficient signal for undercolor removal to the undercolor removal circuit 12.

h=62 On the other hand, R,, G,, B input to the masking circuit 7
The l signal is converted into cyan, magenta, and yellow ink signals C, M, and Y in a well-known manner. These ink signals C,
M and Y are input to the under color removal circuit 12 and also manually input to the minimum value detection means 10.

The minimum value detection means 10 is composed of, for example, two stages of comparators (not shown) each for detecting the minimum value, and first two of the three signals are detected by the previous stage comparator. Compare the size and select the smaller output. Next, the comparator in the subsequent stage compares the output of the comparator in the previous stage with the remaining signals, thereby outputting the minimum value signal a1 of the ink signals C, M, and Y.

This minimum value signal amin is input manually to the inking circuit 11.

The inking circuit 11 includes a subtracter and an adder (not shown).

It is composed of a multiplier, and performs the following calculation using the coefficient signals α and β manually inputted from the coefficient determiner 9 and the minimum value signal aalr+ manually inputted from the minimum value detection means 10 to obtain a black printing signal. After obtaining the black printing signal a, the black printing signal a is outputted to the undercolor removal circuit 12.

a,=jlrla,l,'+β'alal112+
(1-α-β)astn The undercolor removal circuit 12 uses the ink signals C, M, and Y from the masking circuit 7 and the blackening signal a from the inking circuit 11 to remove the undercolor using the following procedure. The removal is performed and only the positive signal a, ,a, is output.

That is, first, the calculation of 1-a value is performed, and the signal a lc+ a 1llI+ a
Find IY. However, the suffix i of all+al is one of C, M, or Y, and h is a function of the saturation C.

Next, only the positive signal al+a2 of the signals a le+ a lX+ a IT is output.

Through the above operations, achromatic signals, cyan and magenta, are generated from the three color signals R, G, and B.

Two of the yellow colors and black are converted into color signals al+a2+aK, and the outputs are sent to the printer section to perform color recording.

As mentioned above, in this embodiment, the amount of inking and undercolor removal is determined based on saturation, so it is easy to make adjustments according to human senses. If you want to increase or decrease the color, just adjust the amount of inking based on the saturation.

Although the above embodiments have been explained by taking a printer using ink as an example, the present invention is not limited to this, and the present invention is also applicable to digital color recording methods such as inkjet, thermal transfer recording, and laser color xerography. be able to.

〔Effect of the invention〕

As described above, according to the present invention, the blacking amount is determined according to the color material signals of a plurality of chromatic colors obtained by converting the three-color color signals and the saturation detected based on the three-color color signals. That's what I do. For example, if you calculate the coefficients of an equation that approximates the amount of blacking from the ink signals of each color, and calculate the blacking signal based on the minimum value of the ink signals of each color using this approximation formula, each of the coefficients will be calculated based on the saturation. It changes depending on. therefore,
The amount of inking also changes continuously, and the saturation can change continuously between the colored area and the black area, and no saturation gap occurs.

Furthermore, since the amount of undercolor removal is also controlled according to the saturation, the optimal amount of undercolor removal can be continuously obtained from the colored area to the black area. Furthermore, according to the present invention, all the coefficients necessary for the calculation are generated within the circuit, so there is no need for complicated adjustment work, and the calculation can be performed using a relatively simple circuit.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing an embodiment of the present invention, FIG. 2 is an explanatory diagram showing a recording format for explaining the theoretical background of the present invention, and FIG. 3 is a diagram showing a recording format for explaining the theoretical background of the present invention. Figure 4 is a graph showing the relationship between the minimum value of the ink signal, the difference between the inking signal and the minimum value of the ink signal, and the saturation. Figure 5 is the graph showing the change in the coefficient of the approximation formula. Graph shown, No. 6
The figure is a graph showing the relationship between saturation and the amount of color ink after blackening. 1. Nijian ink section 2: Magenta ink section 3: Yellow ink section 4: Blank section Patent applicant: Fuji Xerox Co., Ltd.
Masato Kobori (and 2 others)
Figure 1 Figure 2 (cl) (b) Figure 3 Munsell chroma Figure 4 Ok-〇nnn (%) Figure 5 α・β 6th factor

Claims (1)

[Claims] 1. Determining saturation from three color signals from an input device, and converting the three color signals into color material signals of a plurality of chromatic colors;
A color recording method characterized in that an amount of inking is determined according to the color material signal and the saturation, and an amount of undercolor removal is determined. 2. The color recording method according to claim 1, wherein the plurality of chromatic color material signals correspond to the halftone area ratio of each color material. 3. The scope of claims characterized in that, when the black overprint amount is a_k and the minimum value of the plurality of chromatic color material signals is a_m_i_n, the black overprint amount a_k is determined by the following formula: The color recording method described in item 1. a_k=α・a_m_i_n^3+β・a_m_i_n
^2+(1-α-β)・a_m_i_n However, when α and β are coefficients 4 and the saturation is ■, the coefficients α and β are each expressed by the following functions. The color recording method according to item 3 of the range. α=f(■) However, f is a monotonically decreasing function for ■When ■=0, α>0 β=g(■) However, g is a monotonically increasing function for ■When ■=0, β 5. The color recording method according to claim 3, wherein the relationship between the black printing amount a_k and the minimum value a_m_i_n is a_k≧a_m_i_n. 6. Let the black printing amount be a_k, and let the maximum value, intermediate value, and minimum value of the plurality of chromatic color material signals be a_m_a_x, a
2. The color recording method according to claim 1, wherein the undercolor removal amount is determined by the following equation, where _m_i_d and a_m_i_n are represented by the following equation. a_1_m_a_x=[h_1(■)・(a_m_a_
x-a_k)+(1-h_1(■))・(a_m_a_
x-a_m_i_n)]/1-a_k a_1_m_i_d=[h_2(■)・(a_m_i_
d-a_k)+(1-h_2(■))・(a_m_i_
d-a_m_i_n)]/1-a_k a_1_m_i_n=0 However, h_1, h_2 are functions of saturation ■, a_1_m_a
_x, a_1_m_i_d, a_1_m_i_n are the three-color ink amounts 7 of maximum, middle, and minimum dots after black printing, and the functions h_1 and h_2 are monotonically increasing functions of the saturation (■), and it is assumed that the following conditions are satisfied. A color recording method according to claim 6, which is characterized by: h_1(0)=0 h_2(0)=0 h_1(1)=1 h_2(1)=1