JPH0591305A - Color expressing method - Google Patents

Abstract

PURPOSE:To provide the color expressing method which prevents the occurrence of moire and improves the resolution of a picture. CONSTITUTION:In the electrophotographic device provided with line heads which arrange picture element constituting elements formed by one exposure of an end face light emission type EL element in the subscanning direction to form one picture element, the combination of plural colors and the area ratios of these colors are changed with one picture element as the unit with respect to each color data based on picture data and the arrangement of colors is changed for each color data to set many picture element patterns in a memory, and color data corresponding to picture data is discriminated by a discriminating means 2, and a picture element pattern is selected and called from the memory in accordance with color data outputted from the discriminating means 2 and random numbers outputted from a random number generating means 4, and line heads are driven based on the selected picture element pattern.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color expression method in an electrophotographic apparatus in which an edge emitting EL element is caused to emit light for exposure.

[0002]

2. Description of the Related Art Conventionally, an image is expressed by assembling a large number of pixels, but a spot of light emitted from an LED is set as one pixel and a color image is formed by changing the optical density according to the color to be expressed. There is also a method of expressing an intermediate color by a pattern in which the area ratio of different primary colors per unit area is changed.

[0003]

Conventionally, when intermediate colors having the same optical density are continuous in a relatively large image, patterns having the same area ratio of different primary colors per unit area are continuous, resulting in a stripe pattern. There is a problem that moire occurs as if there is a pattern. When the spot of the light emitted from the LED is one pixel (one dot), a plurality of dots are required to represent the minimum unit image in order to express the gradation, resulting in extremely low resolution.

[0004]

SUMMARY OF THE INVENTION The present invention is an edge-emitting type E
In an electrophotographic apparatus having a line head that forms one pixel by arranging pixel constituent elements formed by a single exposure of an L element in the sub-scanning direction, a plurality of colors of a plurality of colors are set for each pixel for each color data based on image data. While changing the combination and the area ratio of these colors, the arrangement of the colors is changed for each of the color data, a large number of pixel patterns are set in the memory, and the color data corresponding to the image data is determined by the determination means,
The pixel pattern is selected by the color data output from the discriminating means and the random number output from the random number generating means, is called from the memory, and the line head is driven based on the selected pixel pattern.

[0005]

According to the image data, not only the combination of a plurality of colors in each pixel and the pixel pattern in which the area ratio of these colors is changed are selected, but also the image data of the same color data (color level) is selected. Even when they are continuous, it is possible to randomly select a pixel pattern in which the color arrangement is changed in units of one pixel and output it from the line head, and therefore it is possible to prevent the occurrence of moire. Further, since the color level of the intermediate color can be expressed in gradation in units of 1 pixel (1 dot), the resolution of the image can be increased.

[0006]

An embodiment of the present invention will be described with reference to the drawings. As shown in FIG. 2, a host computer 1 for outputting image data is sequentially connected with a system controller 2 as a discriminating means, a library controller 3, and a random number generator 4 as a random number generating means. Also, the library controller 3 includes a pixel pattern library 5
And the selector 6 are sequentially connected. This selector 6
The line buffer 7 _1, 7 ₂ ... and 7 _k, and the line head driver 8 _1, 8 ₂ ... 8 _k, the line head 9 _1, 9 ₂ ... 9 _k
And are connected in sequence. These line heads 9 ₁ ,
9 ₂ ... 9 _k are separately provided corresponding to black and other color images, and are formed by arranging a large number of edge emitting EL elements on a straight line.

The pixel pattern library 5 functions as a memory for storing the set pixel pattern. That is, as shown in Table 1, the pixel pattern library 5 is set as a matrix by the color data L output from the system controller 2 and the random numbers 1 to 12 output from the random number generator 4. The stored many pixel patterns are stored.

[0008]

[Table 1]

An image of the pixel pattern is shown in FIG. The level of the color data L on the vertical axis in Table 1 is 0.
3 to 4 and L = 0 is shown in FIG.
L = 1 is shown in FIG. 3 (b), and L = 2 is shown in FIG. 3 (c).
In addition, L = 3 corresponds to (d) of FIG. 3 and L = 4 corresponds to (e) of FIG. In FIG. 3, the shaded portion has a blue distribution, and the white portion has a yellow distribution.
For the sake of explanation, Table 1 and FIG. 3 show only pixel patterns of yellow and blue and their intermediate colors, but actually, pixel patterns including other primary colors are also stored.

One pixel is formed by arranging four pixel constituent elements, which are formed by emitting light from the edge emitting EL element once, in the sub-scanning direction. That is, a photoconductor (not shown) on which an electrostatic latent image is formed by receiving light.
One pixel is formed by causing the edge-emitting EL element to emit light four times in the process of rotating, and a large number of edge-emitting EL elements arranged on a line are responsible for this operation to form a continuous pixel image. Is formed.

FIG. 3 corresponding to color data L = 0 in Table 1
In (a) in Fig. 3, N in which yellow is arranged in one pixel
O. 1 is a pixel pattern.

FIG. 3 corresponding to color data L = 1 in Table 1
(B) shows a green pixel pattern close to yellow, in which yellow is arranged with an area of 3/4 of one pixel, blue is arranged with an area of ¼, and
Even if the same color data level is used, the number of NO. 2 to NO. It is divided into four types of pixel patterns of five.

FIG. 3 corresponding to color data L = 2 in Table 1
(C) shows a pixel pattern of green, which is an intermediate color between yellow and blue, in which yellow is arranged with an area of two quarters and blue is arranged with an area of two quarters in one pixel,
Furthermore, even if the level of the same color data is changed, the NO. 6 to NO. It is divided into six kinds of 11 pixel patterns.

FIG. 3 corresponding to the color data L = 3 in Table 1.
(D) shows a pixel pattern of an intermediate color close to blue. Blue is arranged with an area of 3/4 of one pixel, yellow is arranged with an area of ¼, and
Even if the same color data level is used, the number of NO. 12 to NO. It is divided into four types of 15 pixel patterns.

FIG. 3 corresponding to the color data L = 4 in Table 1.
(E) is the case of NO. 16 pixel patterns.

Incidentally, in FIG. 3, NO. 1 to NO. The code of 16 corresponds to the code of the pixel patterns 1 to 16 shown in Table 1 in a matrix.

Next, an actual color expression method will be described with reference to the flowchart shown in FIG. When the image data is input from the host computer 1, the system controller 2 outputs the color data L corresponding to this image data. Library controller 3 that has input this output
Is the pattern No. of the pixel pattern library 5. Using the table (Table 1), the color data L of 0 to 4 and the random number R randomly output from the random number generator 4 are used to generate the pattern No. To decide. Due to this determination, the specific pixel pattern called from the pixel pattern library 5 is selected by the selector 6 according to its color level.
Is output to any of the line buffers 7 ₁ , 7 ₂ , ... 7 _k , and the line heads 9 ₁ , 9 ₂ ... 9 _k are driven by any of the line head drivers 8 ₁ , 8 ₂ ... 8 _k .

As described above, 1 corresponding to the image data
In addition to selecting a pixel pattern in which the combination of a plurality of colors and the area ratio of these colors are changed on a pixel-by-pixel basis, even if image data of the same color data (color level) continues, It is possible to randomly select pixel patterns with different arrangements and output them from the line heads 9 ₁ , 9 _2, ... 9 _k . An example thereof is shown in FIG. FIG. 4 shows L
= 2, the image is formed by forming pixels in a matrix based on image data having the same color data, but even if the area ratio of yellow (white portions) and blue (hatched portions) of each pixel is the same. Since the arrangement changes randomly, it is possible to prevent the occurrence of moire that is seen as a striped pattern.

Further, as shown in FIG. 5A, in the case of expressing the yellow of the white part, the blue of the shaded part, and the intermediate color thereof in four gradations, the color of the intermediate color in units of one pixel (1 dot). Since the levels can be expressed in gradation, the resolution of the image can be increased. On the other hand, FIG.
As shown in (b), in the case where a conventional LED is used to express yellow in a white part, blue in a shaded part, and an intermediate color thereof in four gradations, the minimum unit of an image is 4 pixels (4 dots). ) Is required and the resolution is extremely low.

[0020]

The present invention is based on image data in an electrophotographic apparatus having a line head for forming one pixel by arranging pixel constituent elements formed by one exposure of an edge emitting EL element in the sub-scanning direction. A plurality of pixel patterns are set in a memory by changing a combination of a plurality of colors and an area ratio of these colors in each pixel for each color data, changing the arrangement of the colors for each color data, and corresponding to image data. Color data is discriminated by the discriminating means, the pixel pattern is selected by the color data output from the discriminating means and the random number output from the random number generating means, and the pixel pattern is called from the memory, and a line is selected based on the selected pixel pattern. Since the head is driven, a pixel in which a combination of a plurality of colors and an area ratio of these colors are changed for each pixel corresponding to image data In addition to selecting the turn, even when the image data of the same color data (color level) continues, it is possible to randomly select a pixel pattern in which the color arrangement is changed on a pixel-by-pixel basis and output it from the line head. Therefore, the occurrence of moire can be prevented, and the color level of the intermediate color can be expressed in gradation in units of 1 pixel (1 dot), so that the image resolution can be increased. Have.

[Brief description of drawings]

FIG. 1 is a flowchart from selection of an image pattern to output.

FIG. 2 is a block diagram showing an electronic circuit.

FIG. 3 is an explanatory diagram showing an image pattern divided for each color data.

FIG. 4 is an explanatory diagram showing a part of an image.

FIG. 5 is an explanatory diagram showing a comparison of the minimum unit image area between the present proposal and the conventional example.

[Explanation of symbols]

 2 discrimination means 4 random number generation means 5 memory

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Claims (1)

[Claims] 1. An electrophotographic apparatus having a line head for forming one pixel by arranging pixel constituent elements formed by one exposure of an edge emitting EL element in the sub-scanning direction,
A plurality of pixel patterns are set in a memory by changing a combination of a plurality of colors and an area ratio of these colors for each pixel for each color data based on the image data and changing the arrangement of the colors for each color data. The color data corresponding to the data is discriminated by the discriminating means, the pixel pattern is selected by the color data output from the discriminating means and the random number output from the random number generating means, and the selected pixel pattern is called from the memory. A color expression method characterized in that the line head is driven based on the above.