JPH0696296B2 - Color printer output method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention processes a full-color image input from a color camera or an image scanner with an image processor,
The present invention relates to a color printer output method for outputting the result with a color printer, and more particularly to a color printer output method for giving high contrast and high image quality to a color inkjet printer, a color fusion type thermal transfer printer, and the like.

<Prior Art> Normally, when performing color printing, as shown in FIG. 6, a full color image input from a color camera or an image scanner 1 is processed by an image processor 2,
The result 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 necessarily an ideal spectral distribution, because there are many constraints associated with each printer, such as the following.

In the case of a color inkjet printer, an ink liquid with low viscosity so that the ink head does not become clogged, or an ink material that allows the ink to properly penetrate from the cover surface into the paper and form a dot diameter with a suitable spread Need to choose.

In the case of a melt-type color thermal transfer printer, the ink is heated with a minute area head and transferred to the paper side, so it is necessary to select the ink material after considering the ink melting temperature, the response time and the adhesiveness with the paper. is there.

Therefore, in the case of outputting a natural image having a multi-level gradation of several thousand colors or more, that is, a full-color image, the color of the Bk ink whose contrast has a great effect on the image quality is often thin in the case of an actual color printer.

In the case of a color printer, each ink is output as small dots on the 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 of 0 or 1).

When a natural image of each gradation, that is, a full-color image is output using a color printer based on the above principle (b), 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. For example, when the gray level of ink of one color for each pixel is 16 levels from 0 to 15, (4
FIG. 7 shows an example of dot output in the matrix of (4). FIG. 7 (a) shows a case where the dot arrangement of the ink to be output is lined up in order from the edge as the density level increases (darkens) in the order of 0 → 1 → 2 →. Due to the periodicity of the dot arrangement, vertical or horizontal stripes are often seen in part or all of the output image, and the image quality can be greatly impaired. For this reason, in many cases, dots are arranged discontinuously as shown in FIG. 7 (b).

<Problems to be Solved by the Invention> Generally, as shown in FIG. 8, a printer head has Y, MC, and Bk ink heads 4 arranged in a line in a vertical or horizontal direction. Are relatively scanned in the X and Y directions, respectively, and the pitch between the ink dots 5, 5, ... Is the same as the minimum movement pitch (Δp) in the X and Y directions. Therefore, ink dots of different colors can be stacked at the same place, but inks of the same color cannot be stacked at the same place. On the other hand, even with the four-color ink system in which black ink is introduced to obtain a high cost last as described above, there are many cases in which "black" with sufficient density cannot be obtained due to various restrictions.

From this, it is possible to mix black ink and other inks in order to obtain "black" with sufficient density.

As one of the lines, it is a method to output black ink and other Y, M.C. However, in the case of this method, 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, an appropriate dot diameter is not formed, “bleeding” occurs, and the ink does not stick to the printer head. There is an inconvenience such as contact and stain the paper.

In addition, in order to avoid such "bleeding" and stains on paper, when one color of black ink and other Y, MC is overlapped, for example, if Y dots are always overlapped at Bk dots, The whole output image becomes yellowish and becomes inconvenient.
At the same time, when C dots are overlapped, it becomes bluish, and when M dots are overlapped, it becomes reddish.

In order to eliminate such inconvenience, when the Y and MC inks are alternately overlaid on the Bk ink dots, there is a periodicity in the Y, MC ink overlay method depending on the output image.
There is a problem that the vertical and horizontal stripes 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 dark black color without impairing the color tone of the entire output image or the image.

<Means for Solving the Problems> In order to achieve the above object, the color printer output method of the present invention is a color printer output method in which a head scans a printer sheet in two directions orthogonal to each other and prints. A color matrix table is defined in which the above-mentioned regulation of overlapping is defined so that the occurrence probability of overlapping of ink dots with a plurality of color ink dots is substantially equal in the above two directions, and black ink and color are based on this color matrix table. The feature is that the ink is output and printed.

Further, from the above, the color matrix table is characterized by having a portion where a black ink dot and a plurality of color ink dots are overlapped with each other and a portion where only a black ink dot is formed.

<Operation> In a color printer output method in which a head scans and prints on a printing paper in two directions orthogonal to each other, the probability of occurrence of overlapping of black ink dots with a plurality of color ink dots is substantially equal in the two directions. The black ink and the color ink are output and printed based on the color matrix table which defines the above rule of overlapping. Therefore, a deep black color can be obtained without impairing the color tone and image quality of the entire output image. <Example> The present invention will be described in detail below with reference to the illustrated example.

The present embodiment is provided with a table of m rows × n columns as a color matrix table that defines a rule of stacking when stacking ink dots of other colors on Bk ink dots.
Based on this table, black ink and color ink are output and printed, dark black and then high contrast,
I try to get high image quality.

FIG. 1 shows an example of a color matrix dedicated to black information when m = 3 and n = 3. In this color matrix, the vertical first row begins with the first column Y ₁ , Y ₁ , M ₁ ,
The order is C ₁ . Also, the vertical second row is in the order of C ₂ , Y ₂ , and M ₂ starting from the first column C ₂ , and the vertical third row is starting from the first column M ₃ and is M ₃ , C ₃ , Y. It is in order of ₃ . Here, Yi (i = 1 to 3) indicates that the yellow ink is overlaid on the Bk ink, Mi (i = 1 to 3) is the magenta ink, and Ci (i = 1 to 3) is the ink. It shows that each cyan ink is overlaid on Bk ink. In this way, since the Y and MC arrays are shifted one by one in the row direction and one in the column direction, one of the Y and MC colors is tinted, and vertical and horizontal stripes are noticeable, as described below. It is possible to obtain a dark black color.

In the system as shown in FIG. 3, the image signals from the image processor 2 are R (red), G (green) B.
Many are in the three primary color data format (blue). In such a case, black is R = G = according to the theory of additive color mixture.
It is represented by B = 0. In the case of outputting an image with four color inks of Y, MC, and Bk according to the full-color image signal from the image processor 2 as described above, the dither processing or the like is performed as described in the related art to change the density of each ink. It is represented by the dot density distribution of the ink.

Now, it is assumed that the Bk ink dot distribution is hatched in FIG. 2A as a result of dithering according to the input image signal. When the color matrix table dedicated to black information shown in FIG. 1 is applied to this image, as shown in FIG. 2 (b) at the hatched portion, as shown in FIG.
Bk ink and other ink are layered.

That is, in the first line of FIG. 2 (b), the Y ₁ ink is first overlaid at the location where the Bk ink dot is output, then the M ₁ ink at the location of the Bk ink dot, and the next Bk ink. C ₁ ink is overlaid on each dot. In the next Bk Ink Dot,
The Y ₁ ink is overlaid, and then Y ₁ , M ₁ , and C ₁ are sequentially overlaid in this order. In the second line, the ink overlaid on the first Bk ink dot is the C ₂ ink, and thereafter, as in the first line, C ₂ , Y ₂ , and M ₂ are repeatedly overlaid in order. Also, in the third line, the M ₃ ink dot is similarly overlaid on the Bk ink dot first, and the following M ₃ , C ₃ ,
Repeatedly repeated in the order of Y ₃ . Thus, the (3n + 1) th (n = 1,2 ...) Row is the same as the first row, the (3n + 2) th row is the second row, and the third (n + 1) th row is the third row.
Stacked in the same way as rows.

In this way, Bk dots are often spatially scattered by the dither process, and other ink dots that overlap each Bk dot are output with equal probability in both the X and Y directions. It does not have a particular color tendency. Moreover, this color matrix is Y, M for each row and each column.
Since the color of C is shifted, even if the distribution of Bk dots has periodicity, the combination of Bk and other colors is properly mixed, and it cannot be seen as streaks or stripes to the human eye. .

If the distribution of Bk ink has periodicity as shown in FIG. 4 (a), the color matrix dedicated to the black signal is the third color matrix.
If the pattern is defined as shown in the figure, the pattern after overlapping is as shown in FIG. 4 (b). That is, if the images output by the color printer are viewed in the same column, Bk and Y, Bk and M,
Since the bands of Bk and C continue, black and Y or M or C colored stripes are conspicuous and the image quality is deteriorated. On the other hand, the first
When the color matrix shown in FIG. 4 is used, the result is as shown in FIG. 4C, and since the color periodicity is eliminated, it looks dark black to the eyes.

FIG. 5 shows a color matrix dedicated to black information, FIG. 5 (a) shows a (4 × 4) matrix, and FIG. 5 (b) shows a (6 × 6) matrix. In FIGS. 5A and 5B, On (n = 1,2, ..., 5,6) locations are locations where only Bk ink dots are present and other color inks are not overlaid. In this way, it is the first to provide a part of the Bk ink dot only without overlapping other inks.
This is to make it possible to alleviate the case where black is too dark in the color matrix shown in the figure.

In this way, the black ink and the Y, MC ink dots are based on the color matrix that defines the locations where the Bk ink dots and the Y, MC ink dots overlap with each other are almost equal, and where only the Bk ink does not overlap. When you output and print, a constant color tendency such as yellow, red, blue, etc. does not occur, no periodic color stripes or stripes appear, and black does not become excessively dark. Is obtained.

The color matrix shown in FIGS. 1 and 5 may be properly used depending on the ink characteristics of the printer. Further, it is possible to select various color matrices to select the optimum black density.

<Effects of the Invention> As is apparent from the above, the color printer output method of the present invention is a color printer output method in which a head scans and prints on a printer paper in two directions orthogonal to each other. The color matrix table is provided by defining the above rule of overlapping so that the occurrence probabilities of overlapping with the color ink dots are substantially equal in the above two directions, and black ink and color ink are output based on this color matrix table. Since the image is printed by printing, a dark black color can be obtained without impairing the color tone and image quality of the entire output image, and an image with high contrast and high image quality can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a color matrix in one embodiment of the present invention, FIG. 2 (a) is a diagram showing an example of black dot output locations, and FIG. 2 (b) is FIG. 2 (a). FIG. 4 is a diagram showing the output of ink that is overlaid on the output portion of FIG. 1 based on the color matrix shown in FIG. 1, and FIG. 3 is a diagram showing an example of a color matrix in which the same color is arranged in the same column, FIG. Is a diagram showing an output example of a periodic black pattern, FIG. 5 is a diagram showing an example of a color matrix in another embodiment of the present invention, FIG. 6 is a configuration diagram of a general print system, and FIG. FIG. 6 is a diagram showing a grayscale expression matrix by dot output of the printer shown in FIG. 6, and FIG. 8 is a diagram showing dot arrangement of the four-color ink head of the printer.

Claims (2)

[Claims] 1. In a color printer output method in which a head scans and prints on a printer paper in two directions orthogonal to each other, a probability of occurrence of superposition of black ink dots and a plurality of color ink dots in the above two directions. A color printer output method comprising a color matrix table in which the above-mentioned rule of overlapping is defined so as to be substantially equal, and black ink and color ink are output and printed based on this color matrix table. 2. The color matrix table according to claim 1, wherein the color matrix table has a portion where a black ink dot and a plurality of color ink dots are overlapped with each other, and a portion where only a black ink dot is formed. Color printer output method described.