JPH0696297B2 - Color printer output method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial field of application> The present invention inputs a full-color image (natural image with multi-gradation shading) obtained by an image pickup means such as a color camera or an image scanner to an image processor, The present invention relates to a color printer output method for processing the color space and outputting a full-color image with a color printer, and in particular, to high-contrast and high-quality image output of a color inkjet printer, a color fusion thermal transfer printer, or the like. A possible color printer output method.

<Prior Art> Usually, when performing color printing, as shown in FIG. 7, the color space of a full-color image obtained by the image pickup means 1 such as a color camera or an image scanner is processed by the image processor 2 and the result is obtained. Is output by the color printer 3. For such a color printer 3, one using three colors of yellow (Y), magenta (M), and cyan (C), or four colors of ink obtained by adding black (Bk) to these three colors is used. There is something I had. The color of each of these inks is not always an ideal spectral distribution, because there are many constraints associated with each printer, as described below.

In the case of a color inkjet printer, an ink liquid with low viscosity that does not cause clogging of the ink head, or an ink that allows the ink to properly permeate from the paper surface into the paper and form a dot diameter with an appropriate spread You need to choose the material.

In the case of a fusion-type color thermal transfer printer, the ink is heated by a small area head and transferred to the paper side, so it is necessary to select the ink material in consideration of the ink melting temperature, response time, adhesiveness with the paper, etc. There is.

Due to these constraints, the color of Bk ink is often thin in actual color printers. If the color of Bk ink is light, the contrast and image quality of full-color images will deteriorate.

In the case of a color printer, each ink is output as small 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 does not change It can be classified into one (binary system of 0 or 1).

When a full-color image is output using a color printer based on the principle of (b) above, a display method using pseudo halftone represented by a dither matrix method is used. This method is a method of expressing the grayscale information of each pixel forming an image by the size of the dot density in a certain fixed area. As an example of this method, a dither matrix (Bayer type) is shown in FIG. This method is devised so that when the density level of the ink of one color of each pixel is 16 levels from 0 to 15, the dots are dispersed as much as possible and output in a (4 × 4) matrix. Numerical values shown in FIG. 8 0 → 1 → 2 → 3
... indicates that the higher the density level of the R, G, B system, the less Bk dots are output.

By the way, as shown in FIG. 9, in a head 4 of a printer using four color inks, Y, M, C, and Bk ink heads 5 are arranged in a line in a vertical or horizontal direction. With respect to each of the head portions 5, 5, ..., That is, the pitch ΔP between the ink dots,
The minimum movement pitch ΔP in the X and Y directions is the same. Therefore, ink dots of different colors can be overlapped at the same place, but ink dots of the same color cannot be overlapped at the same place.

Then, as described above, in order to cover the fact that the Bk ink having a sufficient density cannot be obtained, the Bk ink and all the other Y, M, and C color inks are placed in the same place by using the heads of the above four color inks. There is a method of overlapping and outputting. However, in this system, for example, in the case of a color inkjet printer, since an amount of ink that exceeds the water absorption capacity of the paper is supplied, the dot diameter is not properly formed, and “bleeding” occurs, or the ink does not match the printer head. There is an inconvenience such as contact and stain the paper.

Therefore, in order to avoid such "bleeding" and stains on the paper, there is a method in which black ink and one of the other colors Y, M, and C are overlapped. However, for example, if Y dots are overlapped on Bk dots, the entire output image becomes yellowish, which is inconvenient. When C dots are overlapped, it becomes light blue, and when M dots are overlapped, it becomes purple.

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

<Problems to be Solved by the Invention> However, the method of alternately overlapping the Y, M, and C inks on the beam Bk ink dots as described above may have a cycle depending on the Y, M, and C inks depending on the output image. Therefore, there is a problem in that vertical streaks and horizontal streaks are conspicuous in the image output from the printer and the image quality is greatly impaired.

Therefore, an object of the present invention is to provide a color printer output method capable of obtaining a deep black color without impairing the color tone of the entire output image or the image, and capable of high-contrast and high-quality image output.

<Means for Solving the Problems> In order to achieve the above object, a color printer output method of the present invention is a dither matrix table that defines dots for outputting black ink to control the black density of a color image, and a black The dots that overlap ink and other colors of ink and the dots that contain only black ink are laid out and defined in correspondence with the dot output position of the printer paper, and the occurrence of the overlap of black ink with each of the other colors is defined. A color matrix table dedicated to black information, which is defined so that the probabilities are substantially equal, is provided, and black ink and other color inks are output and printed using this dither matrix table and color matrix table. It is characterized by

The dither matrix table is composed of an array of threshold values for defining dots that output black ink depending on the density level of an image. The dots to be overlapped with the ink of color are defined depending on the density level of the image.

<Function> The dither matrix table that defines the dots that output Bk ink, and the dots that overlap Bk ink and other colors of ink and the dots that contain only Bk ink are laid in correspondence with the dot output position on the printer paper. The color matrix table dedicated to black information, which is defined so that the occurrence probabilities of Bk ink and other colors of each other are almost equal, is used together with Bk ink and other color inks. Since the data is output, vertical stripes, horizontal stripes, etc. that greatly impair the image quality of the printer output do not occur. Further, the output image does not have a constant color tendency.

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

1 (a), (b), (c), and (d), m = 4, n =
4 shows an example of a color matrix table dedicated to black information of m rows and n columns in the case of 4. This color matrix table defines the dots in which the Bk ink and the other Y, M, C inks are overlapped and the dots of only the Bk ink are assigned to the printer paper. In the following, Yi
(I = 1 to 16) indicates that the Y ink is overlaid on the Bk ink. Similarly, Mi indicates that the M ink is overlaid on the Bk ink, and Ci indicates that the C ink is overlaid on the Bk ink. Oi indicates that only Bk ink is output and does not overlap with other color inks. i is the setting value of the Bayer type dither matrix table of FIG. 8, that is, R, G, B
The threshold values of the conversion formulas described later for converting from the system to the Y, M, C system are shown.

In the color matrix table of FIG. 1 (a),
The first row starts at the first column O ₀ and is in the order of O ₀ → C ₈ → M ₂ → Y ₁₀ .

The second row starts in the first column, M ₁₂ , and is in the order of M ₁₂ → Y ₄ → O ₁₄ → C ₆ .

The third row begins in the first column, C ₃ , and is in the order of C ₃ → O ₁₁ → Y ₁ → M ₉ .

The fourth row begins in the first column, Y ₁₅ , and is in the order of Y ₁₅ → M ₇ → C ₁₃ → O ₅ .

1 (a), (b), (c), (d) are all Y, M, C
Are evenly distributed in the color matrix table of 4 rows and 4 columns, so the output image is Y, M, C as described below.
It is possible to obtain a deep black color without causing any one of the above, or the vertical stripes and the horizontal stripes being conspicuous.

In the system as shown in FIG. 7, the image signals from the image processor 2 are R (red), G (green) and B.
Many are in the three primary color data format (blue). In such a case, the black color is represented by C = M = Y = 1 according to the theory of subtractive color mixture shown in FIG. In the case of outputting an image with four color inks of Y, M, C, and Bk according to the full-color image signal from the image processor 2, processing is performed using the dither matrix table as described in the prior art. The density of each ink is expressed by the dot density distribution of the ink.

Now, with respect to the R, G, B density information of the input image, using the values of the Bayer type dither matrix table of FIG. 8 as a threshold value, it is converted into Y, M, C, Bk by the following conversion formula. To do.

From the above equation (1), two-dimensional information R, G, B
When Y, M, C and Bk are created, it becomes as follows.

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

When the R, G, B density information of the input image is processed by the equation (1) using the values of the dither matrix table of FIG. 8 as threshold values, the distribution of the Bk ink dots is hatched in (a). As shown.

If the color matrix table dedicated to black information shown in FIG. 1A is applied to this FIG.
As shown in FIG. 3B, the Bk ink and other inks are overlaid on the hatched portions in FIG. That is,
In the first row of FIG. 3B, the M ink and the Bk ink are first overlapped at the location where the Bk ink is output, and the C ink and the Bk ink are overlapped at the next Bk ink location. At the next Bk ink location, M ink and Bk ink are overlaid again. That is, M ₂ → C ₈ →
It is output as M ₂ . This is because the color matrix table of FIG. 1 (a) shows dots and Bk in which Bk ink and M, Y, C ink are overlapped with respect to the position of the printer paper.
This is because the dots are assigned only to ink, and the color matrix table of FIG. 1 is applied to the dots outputting Bk ink by the dither matrix table of FIG.

In the second line, the ink that is overlaid on the first Bk ink is Y ink, and is overlaid in the order of Y ₄ → C ₆ → Y ₄ → O ₁₄ → C ₆ ... Or only Bk ink is output.

In the 3rd line, only Bk ink is output first, and O ₁₁ → M ₉ → O ₁₁ →
Only C ₃ ... and Bk ink are output, or Bk ink is overlapped with other color ink.

In line 4, C ink is overlaid on Bk ink.

The (4n + 1) th row uses the first row of the color matrix table, the (4n + 2) th uses the second row, and the (4n + 3) th row
Uses the 3rd row, the (4n + 4) uses the 4th row, and they are overlapped in the same manner. (N = 1,2,3 ...) As is easily understood from the above description, the dots from which the Bk ink is output are often spatially scattered by the processing using the dither matrix table. Moreover, when the input signal is an image image, the occurrence probability of Bk dots is
(1) above using the dither matrix table in the figure
When the color matrix table of FIG. 1 (a) is used by using the conversion equation of, O, M, C, Y are output with equal probability in both vertical and horizontal directions at any density level, as shown in FIG. Even at the density level, the color does not have a particular tendency.

In addition, the color matrix table has Y,
Since the colors of M and C are dispersed, even if there is periodicity in the distribution of Bk dots, the combination of Bk and other colors is properly mixed, so it appears as a streak of color to the human eye. Absent. If the Bk ink distribution has periodicity as shown in FIG. 6 (a) and the color matrix table dedicated to black information is defined as shown in FIG. It becomes like FIG. In this case, the image output by the color printer is Bk + Y,
Since Bk + M and Bk + C are continuously striped, black or Y-, M-, or C-colored streaks are conspicuous and the image quality is deteriorated. On the other hand, when the color matrix table of FIG. 1 (a) is used, the color periodicity is eliminated as shown in FIG. 6 (c), resulting in high image quality and a dark black appearance to the eyes.

Since the present invention processes the color information stored in the image memory, the matrix table is as shown in FIGS. 4 (b), (c) and (d) in addition to FIG. 4 (a). It is also within the scope of the present invention to replace only Bk + Y, Bk + M, Bk + C, and Bk, or replace the setting values of the dither matrix table and replace the color matrix table information such as Y, M, and C.

<Effects of the Invention> As is clear from the above, the color printer output method of the present invention is such that the dither matrix table defining the dots for outputting the black ink, the Bk ink, and the respective inks of other colors are overlapped. The Bk ink and other color inks are overlapped with each other by using the color matrix table exclusively for black information, which is defined by laying the dots corresponding to the dot output positions on the printer paper so that the occurrence probabilities are approximately equal. To output.

Therefore, according to the present invention, a dark black color is obtained, and the inks of other colors overlapping with Bk are spatially and randomly output, so that the printer output has a certain color tendency such as reddish or bluish. There is no tinge and no periodic color streaks appear in the printer output.

[Brief description of drawings]

1 (a), (b), (c) and (d) are diagrams showing an example of a color matrix table in one embodiment of the present invention, and FIG. 2 is a subtractive color mixture diagram used in a color printer,
FIG. 3 (a) is a diagram showing an example of black dot output locations,
FIG. 3 (b) is a diagram showing an output portion of ink to be overlaid, FIG. 4 is a diagram showing that the number of dots or Bk ink to be overlaid is increased as the density level of the image is lowered, and FIG. Is a diagram showing an example of a color matrix in which the same color is arranged in the same column, FIGS. 6 (a) and 6 (b) are diagrams showing examples of periodic black patterns and colors, and FIG. 6 (c).
Shows a non-periodic output example, FIG. 7 shows a general print system configuration, FIG. 8 shows a Bayer type dither matrix table, and FIG. 9 shows dots of a four-color ink head of a color printer. It is a figure which shows arrangement. DESCRIPTION OF SYMBOLS 1 ... Imaging means, 2 ... Image processor, 3 ... Color printer.

Claims (2)

[Claims] 1. A dither matrix table which defines dots for outputting black ink for controlling the black density of a color image, a dot in which black ink and inks of other colors are superposed, and a dot of only black ink. A color matrix table dedicated to black information is defined to cover the dot output position of the printer paper and define it so that the occurrence probability of overlapping of each other color and black ink is substantially equal, A color printer output method characterized in that black ink and inks of other colors are output and printed using the dither matrix table and the color matrix table. 2. The color printer output method according to claim 1, wherein the dither matrix table is a threshold value for defining dots for outputting black ink depending on a density level of an image. A color printer output method, which comprises an array and determines the overlapping dots of black ink and inks of other colors depending on the density level of the image using the dither matrix table and the color matrix table.