JPH0347619B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a color image recording method, and more particularly to a color image recording method in which a color image is recorded according to an electrophotographic method using a laser beam modulated by image input.

In recent years, it has been considered that electrophotographic color copiers could be used as color CRT output printers or color facsimile terminals by writing with a laser beam. This is because it is expected to be used in many applications as a device that can quickly convert computer output signals into color images, but most of these devices are pseudocolor and cannot be used as full color images. Printers have not yet been realized.

The reason for this is mainly due to the characteristics inherent in electrophotography, and the reproducibility of intermediate colors is poor and no technical solution has been achieved in this respect. That is, latent image,
When considering the characteristics of each electrophotographic process, including image forming processes such as development and transfer, as an image recording system rather than ideal, the output value relative to the input is nonlinear, and the input spatial frequency (MTF
This is because the higher the value), the lower the response becomes.

Therefore, with conventional analog image recording (luminance modulation) methods and image processing techniques, it is not possible to obtain images with sufficient gradation even in monochromatic colors. Have difficulty.

The present invention has been made in view of these points,
An object of the present invention is to provide a color image recording method capable of recording a full-color image with high gradation.

In order to achieve the above object, the color image recording method of the present invention separates input color image data into a plurality of chromatic color components and a black component, and develops a dot pattern by applying a predetermined matrix to each of the components. , a recording method for recording a color image by overlapping such patterns, characterized in that the size of the matrix for the black component is smaller than the size of the matrix for the chromatic color component.

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 shows a color electrophotographic recording apparatus employing the method of the present invention. In FIG. 1, a semiconductor laser light source unit 1 is provided, from which a collimated light beam modulated by an image signal is emitted.
This light beam is deflected by an optical deflector such as a rotating polygon mirror, passes through an imaging lens 3, and an image is formed on a photosensitive drum 4. In that case, the photosensitive drum 4 is neutralized by the pre-static eliminator 4a, then uniformly charged by the primary charger 4b, and then statically removed by the static eliminator 4c in accordance with the light beam, so that static electricity corresponding to the image is generated on the photosensitive drum 4. A latent image is formed. Subsequently, the latent image thus formed is developed by the developing devices 5a to 5d.

The developing units 5a to 5d are Y (yellow) and M, respectively.
(magenta), C (cyan), and Bl (black) toners are included, and one of them is selected. In other words, the input signal is separated into four colors, Y, M, C, and Bl, and the semiconductor laser light source unit 1 is used for each color.
A modulated beam corresponding to each color is emitted from the unit, and a developing device corresponding to that color is driven. The toner images of each color developed on the photosensitive drum in this manner are transferred to the recording paper 7 wound around the transfer drum 6 in an overlapping manner each time. The radius ratio between the photosensitive drum 4 and the transfer drum 6 is 2:1, and an image is recorded on each half of the photosensitive drum. That is, while development is being performed on one half of the photosensitive drum 4, charging or latent image formation is performed on the other half of the circumference.

FIG. 2 illustrates image processing using the density pattern method, which is an embodiment of the recording method of the present invention. The input signal Xi10, which is converted into an electrical signal based on the luminance information at a certain point i sampled in the image separated into each color, is sent to a comparator 1.
1 is compared with a comparison value Ci12 having a certain value, and an output Yi13 is obtained based on the magnitude relationship. The comparison value Ci is generally called a comparison matrix due to its j×k matrix configuration as shown in FIG. 3B, and the input signal shown in FIG. 3A is
Xi is compared with each component of this comparison matrix Ci (j, k), and an output Yi (j, k) is obtained in which the black level (i.e., 1) is achieved only at the larger component. accordingly
Yi also has a j×k matrix configuration.

This type of method is generally called the density pattern method, in which one output pixel is set to j for each input pixel.
Each element of the submatrix divided into ×k submatrices (this is called a micropixel)
This is a method of systematically filling in the areas.

The output Yi thus obtained is stored in the line memory 14 as shown in FIG.
The capacity of this line memory 14 is j× for one pixel.
If one line is made up of k bits and one line is made up of l pixels, then generally it will be j x (k x l) bits/line. These bits are regularly stored in j rows and k×l columns, and by operating each row j times, one line of image is recorded by the recording device.

For example, as shown in FIG.
Assume that Xi=5.3×1/16 and the comparison matrix Ci is a 4×4 matrix with Ci=1/16×13 4 8 12 9 0 3 7 5 1 2 11 14 10 6 15. however,
Here, it is assumed that the maximum value of the input signal is Xi, max=1.0. The resulting output signal Yi is Yi=0 1 0 0 0 1 1 0 1 1 1 0 0 0 0 0. Using this method, each pixel i=1.2......
1 and stores the result in the line memory 14.

FIG. 4 shows an enlarged example of an image output for one color when an image is output using such a method. When performing color recording, recording is performed by outputting images for each color of Y, M, C, and Bl and overlapping them. In FIG. 3c, the entire 4.times.4 matrix corresponds to one input pixel, and the entire matrix is called a pixel, and the small section for each element is called a micropixel. In FIG. 4, the diagonal line 20 corresponds to the shaded area in FIG. 3c.

In this embodiment, the pattern created by these fine pixels corresponds to the dot pattern of the present invention.

When one output pixel is formed using a 4.times.4 matrix using the method described above, 16 gradations can be obtained if the pixel is large. However, when the pixels are made smaller, the gradation decreases for the following reasons. That is, the fifth
As shown in the figure, the MPF values of latent images and development transfer in electrophotography decrease as the spatial frequency increases. Therefore, when the pixels become smaller, each fine pixel is not filled in faithfully, and an increase or decrease in one fine pixel does not appear as a change in the recorded output.

Therefore, even if it is configured with a 4×4 matrix,
16 gradations cannot be obtained.

On the other hand, as a human visual characteristic, a lot of gradation is required for low-frequency components with low spatial frequencies (for example, the skin of a person's face), but gradation is required for high spatial frequency components (contours, etc.). It is known that less tonality is better.

In the above-mentioned method, if the resolution is to be increased for each color of Y, M, C, and Bl, it is necessary to reduce the size of the pixel. In such a case, gradation is impaired and color reproducibility cannot be obtained.

A feature of one embodiment of the present invention is that the Y, M, and C output methods are performed using a large matrix size, and the Bl output method is performed using a small matrix size, thereby improving both color reproducibility and resolution. The point is to make sure you are satisfied.

FIG. 6 shows this pixel size, where (A) shows the pixel size for Y, M, and C, and (B) shows the pixel size for Bl. For example, one side A in (A) is
0.4 mm, and one side B in (B) is, for example, 0.2 mm.

Each of them is composed of a 4×4 matrix and is independently recorded using the density pattern method described above.

When performing laser beam scanning, recording is performed using thin (B) fine pixels (50 μm per piece) as a reference.

In other words, one pixel in the main scanning direction is 50 μm,
The feed pitch is also 50 μm. Therefore, for the 0.4 mm pixel (fine pixel 100 μm) in (A), it is sufficient to record by scanning twice as many times. As a result of color recording at such a pixel size, the reproducibility of image gradation is sufficiently satisfied for each of the colors Y, M, and C. These are Y,
M and C are recorded overlappingly with their centers shifted from each other (shifting their centers is not necessarily essential).

On the other hand, since the pixels of Bl are smaller, the gradation decreases.In electrophotography, this decrease in gradation is mainly noticeable in the white side. Therefore, the recorded image for Bl becomes information mainly containing contour components.

By superimposing this on the Y, M, and C images, an image with sufficient color reproducibility and resolution can be obtained.

In this method of outputting by changing the pixel size, the luminance information input values for each color (blue, green, red) are stored in the memory in small pixel units, and only when recording black, the brightness information input values for each color (blue, green, red) are stored in the memory in small pixel units. It is calculated from the R signal, and other color components (Y, M, C) are obtained by taking the average value of several pixels.

As described above, according to one embodiment of the present invention, a color image is recorded by overlapping the output matrix with different pixel sizes for each color, so human visual characteristics are taken into account. It is possible to provide full-color images with high gradation.

It is worth mentioning that such a method is not necessarily applied only to electrophotography, but can also be applied to nonlinear systems or other systems where the MTF value decreases as the spatial frequency decreases, and similar effects can be obtained. Not even.

As explained above, according to the present invention, a matrix pattern is applied depending on the color, and the resulting dot patterns for each color are superimposed to record a color image, so there is gradation. In addition, color reproduction with good resolution can be performed.

Furthermore, according to the present invention, the size of the matrix for the black component, which has a large effect on resolution, is made smaller than the size of the matrix for the chromatic color component, which has a large effect on gradation reproducibility. It is possible to improve reproducibility and improve the resolution of color images.

[Brief explanation of drawings]

FIG. 1 is a layout configuration diagram showing a schematic configuration of a color copying apparatus using the method of the present invention, FIG. 2 is a block circuit diagram showing image processing by the density pattern method, and FIGS. 3 A to C are density pattern FIG. 4 is an explanatory diagram showing an enlarged image output processed by the density pattern method. FIG. 5 is a table showing the response to spatial frequency. FIG. 6A , B are explanatory diagrams showing changing the size of the output pixel depending on the color. 1...Light source unit, 2...Light deflector, 3...
Lens, 4...Photosensitive drum, 4a-4c...Charger, 5a-5d...Developer, 6...Transfer drum,
7... Recording paper, Xi... Input pixel, Ci... Comparison matrix, Yi... Output pixel.

Claims (1)

[Claims] 1 A recording method that separates input color image data into multiple chromatic color components and black components, develops a dot pattern by applying a predetermined matrix to each component, and records a color image by overlapping these patterns. A color image recording method, characterized in that the size of the matrix for the black component is smaller than the size of the matrix for the chromatic color component.