JPH024552A - Color printer output system - Google Patents

Abstract

PURPOSE:To obtain a dense black color by overprinting black ink and other color inks by using both a dither matrix table for defining a black ink output dot and a color matrix table only for black information. CONSTITUTION:In order to control the black density of a color image, a dither matrix table for defining a dot for outputting black ink, a dot for superposing black ink and other color ink, and a dot of only black ink are assigned for a printer sheet to be regularly defined, and color matrix tables (a)-(d) only for black information so defined that probabilities of overprinting other color and black inks become uniform. Then, black ink and other color inks are output. Thus, a dense black is obtained, and other color ink to be superposed with black are output at random in space. Accordingly, its output does not become a predetermined trend of redlike or bluelike, and it can prevented periodic color stripe from presenting.

Description

[Detailed Description of the Invention] <Industrial Application Field> This invention inputs a full-color image (natural image with multi-tone gradation) obtained by an imaging means such as a color camera or an image scanner to an image processor, Regarding the color printer output method that processes the color space and outputs a full-color image on a color printer, it is particularly useful for making the image output of color inkjet printers, color melting type thermal transfer printers, etc., high contrast and high image quality. Concerning possible color printer output methods.

<Conventional technology> Normally, when performing color printing, as shown in FIG. is outputted by color printer 3. Such a color printer 3 uses three colors: yellow (Y), magenta (M), and cyan (C), or uses black (Bk) in addition to these three colors.
There is one that uses four colors of ink with the addition of . The color of each of these inks usually does not necessarily have an ideal spectral distribution because there are many constraints associated with each printer, such as (1) and (2) below as examples.

■ In the case of color inkjet printers, ink liquid with low viscosity that does not clog the ink head, and ink that permeates properly from the paper surface into the paper and spreads appropriately to form dots are used. You need to choose an ink material.

■ In the case of melt-type color thermal transfer printers, the ink is heated by a small-area head and transferred to the lower side, so ink materials are selected by considering the ink's melting temperature, response time, adhesion to paper, etc. There is a need.

Due to these constraints, the color of Bk ink often appears dull in actual color printers.

If the color of the Bk ink is dull, the contrast and image quality of full-color images will deteriorate.

In addition, in the case of color printers, each ink is output as minute dots on paper by some means, but in these cases, (a) the ink density of each dot changes (b) the ink density of each dot changes. It can be classified as boring (binary 0 or l).

When a full-color image is output using a color printer based on the principle (b) above, a pseudo halftone display system, typically a dither matrix system, is used. This method expresses the shading information of each pixel constituting an image by the size of the dot density in a certain plane. As an example of this method, FIG. 8 shows a dither matrix (Bayer type). This method uses (4×
The matrix 4) is designed to output dots as dispersed as possible. Numerical value 0→l shown in Figure 8
→2-3... indicates that the higher the density level of R, G, and B systems, the fewer Bk dots are output.

By the way, as shown in FIG. 9, the head 4 of a printer using four color inks has Y, M, C, and Bk ink head sections 5 arranged in a vertical or horizontal line.
is scanned in the X direction and the Y direction relative to the paper, and each head $5.5. ..., that is, the pitch ΔP between ink dots, and the minimum movement pitch ΔP in the X and Y directions are made to be the same. Therefore, ink dots of different colors can be overlapped at the same location, but ink dots of the same color cannot be overlapped at the same location.

In order to compensate for the fact that Bk ink of sufficient density cannot be obtained as described above, the above-mentioned four-color ink heads are used to print Bk ink and other Y and M inks.

There is a method that outputs all three colors of ink at the same location, overlapping each other. However, with this method, for example, in the case of a color ink jet printer, an amount of ink is supplied that exceeds the water absorption capacity of the paper, so dots of an appropriate diameter are not formed, resulting in "bleeding" and ink spilling onto the printer head. This may cause the inconvenience of staining the paper due to contact with the paper.

Therefore, in order to avoid such "bleeding" and staining of the paper, there is a method in which black ink is overlaid with one of the other colors of Y, M, and C. However, if, for example, a Y dot is always superimposed on a dot in I3, the entire output image will have a yellowish tinge, which is inconvenient. Also, if you overlap the C dots, it will look light blue, and if you overlap the M dots, it will look purple (
Become.

In order to eliminate this inconvenience, there is a method in which Y, M, and C inks are alternately superimposed on Bk ink dots.

<Invention or problem to be solved> However, in this way, Y ink dots are alternately printed on Bk ink dots.
, M, and C inks overlap, depending on the output image, there may be periodicity in the way the Y, M, and C inks are overlaid, so vertical and horizontal streaks will be noticeable in the printer output image, and the image quality will be significantly impaired. There is a problem.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a color printer output method that can obtain a deep black color without impairing the tone or image of the entire output image, and can output an image with high contrast and high quality.

<Means for Solving the Problems> In order to achieve the above object, the present invention provides a dither matrix table that defines dots for outputting black ink in order to control the black density of a color image, and a dither matrix table that defines dots for outputting black ink and other colors. In addition to regularly defining dots with overlapping ink and dots with only black ink on the printer paper,
A color matrix table dedicated to black information is provided, which is defined so that the probability of occurrence of overlap between black ink and each other color is approximately equal, and using this dither matrix table and color matrix table, black ink and It is characterized by being able to print using ink of other colors.

Effect〉 If we create a dither matrix table that defines dots that output Bk ink, dots that overlap Bk ink and ink of other colors, and dots that contain only Bk ink, and regularly define them by allocating them to the printer paper, we get ( In addition, by using a color matrix table dedicated to black information that defines the probability of occurrence of overlapping of Bk ink and other colors to be approximately equal, the ink and (ya color ink) are output in 13. Therefore, vertical stripes, horizontal stripes, etc. that greatly impair the image quality of the printer output do not occur.Furthermore, the output image does not have a fixed color tendency.

<Example> Hereinafter, the present invention will be explained in detail with reference to illustrated embodiments.

In the second supervision drawings (a), (b), (c), and (d), m=4. An example of a color matrix table dedicated to black information in m rows and n columns when n=4 is shown.

This color matrix table contains Bk ink and other Y,
Overlapping dots of M and C inks and dots of only Bk ink are allocated and defined on printer paper. In the following, Yi (i=1-16) indicates that Y ink is superimposed on Bk ink. Similarly, Mi indicates that M ink is superimposed on Bk ink, and C4 indicates that C ink is superimposed on Bk ink. O
i indicates that only ink is output to I3 and that ink of other colors does not overlap. i indicates the setting value of the Bayer type dither matrix table in FIG. 8, that is, the threshold value of the conversion formula described later for converting from the R, G, B system to the Y, M, C system.

In the color matrix table of FIG. 1(a),
The first row starts at the first column C6, Oo-C8-M2→Y
, +1.

The second row starts from the first column M, M12→Y4→014
→The order is Co.

The third row starts in the first column C3, C3-o++-+Y+
→The order is MO.

The 4th row starts from the ” column Yes, Y15-M7→C1
The order is 3 → 05.

In Figure 1 (a), (b), (c), and (d), Y, M, and C are evenly distributed in a color matrix table with 4 rows and 4 columns, so the output is as described below. It is possible to obtain a deep black color without any of the colors of the image h'Y, M, or C appearing, or without noticeable vertical or horizontal stripes.

In the system shown in FIG. 7, the image signals from the image processor 2 are R (red), G (green), B (
Many of them are in the three primary color data format (blue). In such a case, black can be represented by C=M=Y=1 according to the theory of subtractive color mixture shown in FIG. Y, M, C according to the full color image signal from the image processor 2.

When outputting an image using the four-color ink of I3, processing using a dither matrix table is performed to express the light and shade of each ink using the dot density distribution of the ink, as described in the conventional technology section. .

Now, for the R, G, and B density information of the human image, the eighth
Using the value of the Bayer dither matrix table shown in the figure as a threshold value, Y is calculated using the following conversion formula.

Convert to M, C, I3k.

When the two-dimensional information v, M: c, Bk is created from the two-dimensional information r(, G, B) using the above equation (1), the following is obtained.

When the color data of G is smaller than the setting value of the dither table, the color information of M is created. When the color data of B is smaller than the setting value of the dither table, the color information of Y is created, and the color data of R is set as the dither table. When the value is smaller than the setting value of the table, C color information is generated, and when M, Y, and C are all set to 1, Bk color information is generated.

Then, when the R, G, and B density information of the input image is processed using equation (1) using the values of the dither matrix table shown in FIG. 8 as thresholds, the distribution of Bk ink dots is hatched as shown in FIG. It will be shown as follows.

If the color matrix table dedicated to black information shown in FIG. 1(a) is applied to this FIG. 3(a), the third
As shown in FIG. 3(b), Bk ink and other inks are applied over the hatched area in FIG. 3(a). That is, in the first line of FIG. 3(b), at the location where Bk ink is output, first the M ink and I3 are overlapped, and at the next Bk ink location, the C ink and Bk ink are overlapped. Then, at the next Bk ink location, the M ink and the ink on r3 are again superimposed and burned.

That is, it should be output as M,→Cl1-M. This is because the color matrix table in Figure 1(a) shows Bk ink, M, Y, and C in relation to the position of the printer paper.
The dots that overlap with ink and the dots of only Bk ink are assigned, and the dither matrix table shown in Fig. 2 is used to assign this second dot to the dot that outputs Bk ink.
This is because the color matrix table shown in the figure is applied.

In the second line, the ink that overlaps the first Bk ink is Y ink, Y4→C8→Y4→014-'C8
... or only Bk ink is output.

The third line is ``At first only Bk ink is output, 01゜→M
9→01l-+C3... only Bk ink is output,
Or use other colors of ink and Bk ink on top of each other.

In the 4th line, the C ink should overlap the Bk ink.

The (4n+1)th row uses the first row of the color matrix table, the (4n+2)th row uses the second row, and the (4n+2)th row uses the second row.
+3) uses the 3rd row, and (4n+ 4) uses the 4th row, each of which is overlapped in the same way.

(n=1, 2.3...) As is easily understood from the above explanation, the dots where Bk ink is output are often spatially scattered due to processing using a dither matrix table. Moreover, when the input signal is an image, the probability of occurrence of Bk dots is
Using the dither matrix table shown in Figure 8,
Using the conversion formula 1) and the color matrix table shown in Figure 1(a), the vertical and horizontal directions O, M, C, and Y are output with equal probability at any density level, as shown in Figure 4. , there is no particular color trend at any density level.

In addition, the above color matrix table has Y in each row and each column.
, M, and C colors are dispersed, so even if there is periodicity in the distribution of Bk dots, the combinations of Bk and other colors will be mixed appropriately, so that they will appear as streaks of color to the human eye. can not see. If the distribution of Bk ink is periodic as shown in Figure 6(a), and the color matrix table dedicated to black information is defined as shown in Figure 5, the pattern after overlapping will be The result will be as shown in Figure 6 (b). In this case, if you look at the same row of images output by a color printer, there will be continuous bands of Bk+Y, Bk10M, Bk+C, so it will be black and Y.
Alternatively, M or C colored streaks become noticeable and the image quality deteriorates. On the other hand, if the color matrix table shown in FIG. 1(a) is used, the periodicity of colors as shown in FIG. 6(C) is eliminated, resulting in high image quality, which appears to the eye as deep black.

Since this invention processes color information stored in an image memory, the color matrix table is shown in FIGS. 4(b), (c), (d) in addition to FIG. 4(a).
) where only Bk+Y, Bk+M, Bk+C5Bk are simply replaced, or where the setting values of the dither matrix table are changed and color matrix table information such as Y, M, C, etc. is replaced, also falling within the scope of this invention. .

<Effects of the Invention> As is clear from the above, the color printer output method of the present invention uses a dither matrix table that defines dots for outputting black ink, and overlaps each of the Bk ink and the pond color ink. Bk ink and other color inks are overlapped by using a color matrix table exclusively for black information, which is regularly defined by allocating dots on the printer paper so that the probability of their occurrence is approximately equal. This is what is output.

Therefore, according to the present invention, a deep black color is obtained, and since the ink of other colors that overlap with Bk are output spatially randomly, the printer output has a certain color tendency such as reddish or bluish. There is no color tinge, and no periodic color streaks appear on the printer output.

[Brief explanation of the drawing]

FIGS. 1(a), (b), (c), and (d) are diagrams showing an example of a color matrix table in an embodiment of the present invention, FIG. 2 is a subtractive color mixture diagram used in a color printer, and FIG. Figure (a) shows an example of the output location of black dots, Figure 3 (b) shows the output location of overlapping ink, and Figure 4 shows the output location of overlapping ink as the density level of the image decreases. Figure 5 is a diagram showing an example of a color matrix in which the same color is arranged in the same column, Figure 6 (a)
, (b) is a diagram showing an example of periodic black pattern and color output, Figure 6 (C) is a diagram showing an example of non-periodic output, Figure 7 is a configuration diagram of a general printing system, FIG. 8 is a diagram showing a Bayer type dither matrix table, and FIG. 9 is a diagram showing the dot arrangement of a four-color ink head of a color printer. l...imaging means, 2...image processor, 3...color printer. Figure 7

Claims (2)

[Claims] (1) A dither matrix table that defines dots that output black ink to control the black density of color images, dots that overlap black ink and ink of other colors, and dots that use only black ink on printer paper. A color matrix table dedicated to black information is provided, which is allocated and defined regularly, and is defined so that the probability of occurrence of overlapping with each other color and black ink is approximately equal, and this dither matrix table and color matrix A color printer output method characterized in that black ink and ink of other colors are output and printed using a table. (2) In the color printer output method according to claim 1, the dither matrix table is formed from an array of threshold values for defining dots for outputting black ink depending on the density level of the image. This is a color printer output method that uses the dither matrix table and color matrix table to determine dots for overlapping black ink and ink of other colors depending on the density level of the image.