JPS61114650A - Reproducing method of intermediate gradation picture - Google Patents

Abstract

PURPOSE:To make lateral stripes inconspicuous in a reproduced intermediate gradation picture by using a dither pattern whose output picture element period is (n) times the number of faces of a scanner (n is a positive integer) to process an intermediate gradation picture signal to be reproduced to control a luminescence body. CONSTITUTION:In turning the scanner 3 once, the number of times of scanning the same as the number of faces of the scanner 3 is attained and the scanning (scanning by the same reflecting face) in the same state at each number of times is repeated. For example, when the number of faces of the scanner 3 is 4 and the period in the picture element concentration by the dither pattern 6 is 4, a lateral stripe 7 appears at a period the same period as the picture element concentration, and since each lateral stripe 7 is generated by the reflecting light on the same face of the scanner 3, the lateral stripe has the same width without width change and any lateral stripe 7 is made inconspicuous.

Description

[Detailed Description of the Invention] Technical Field> The present invention relates to a method for reproducing halftone images, and more specifically, the present invention relates to a method for reproducing a halftone image.
This invention relates to a method for reproducing halftones on a platform scanned by a scanner consisting of a rotating polygon mirror.

<Prior Art> Conventionally, a device in which light from a light emitting body controlled by an image signal to be reproduced is scanned by a scanner made of a rotating polygon mirror has been applied to, for example, a Leb beam printer.

The above scanner has multiple reflective surfaces, and if each reflective surface is formed parallel to the rotation center axis, the scanning beam will always be irradiated in a predetermined positional relationship, resulting in a good A reproduced image can be obtained. However, in scanners currently in general use, not all reflective surfaces are formed parallel to the rotation center axis, and are tilted to some extent, and each reflective surface has a different inclination. Generally, the position where the scanning beam is irradiated changes for each reflecting surface. That is, the interval between the irradiation positions of the scanning beams between adjacent reflecting surfaces varies from one reflecting surface to another, causing a reduction in the quality of reproduced images. In particular, when a halftone image is reproduced using a dither pattern, the inclination of the reflective surface clearly appears as horizontal stripes in the re-flattened image, causing a reduction in the quality of the reproduced halftone image.

In order to prevent the above-mentioned horizontal streaks from occurring, it is possible to improve the accuracy of the skiving itself so that all non-conforming surfaces are parallel to the rotation center axis, but highly accurate scanners are extremely expensive. Moreover, even if the accuracy is increased, there is no guarantee that the inclination of each reflecting surface will be eliminated, and the width of the horizontal stripes will only become smaller, so this cannot be a practical solution. Also,
Although it is conceivable to install a device to correct the tilt of the scanner, the problem is that the device itself is complicated and expensive.

Purpose> This invention was made in view of the above problems.
The purpose of the present invention is to provide a method for reproducing halftone images that makes horizontal stripes in reproduced halftone images inconspicuous using a simple method without requiring improvements to the scanner itself or a gap correction device. There is.

<Configuration> In order to achieve the above object, the method for reproducing a halftone image of the present invention reproduces a halftone image signal to be reproduced with an output pixel period n times the number of scanner surfaces (where n is a positive integer). ) to control the light emitting body, and horizontal stripes will occur every several times on the scanner surface, but since the output pixel period is n times the number of times the scanner scans, The horizontal stripes that occur in each pixel period are the same and have the same width, and the horizontal stripes in the reproduced halftone image are hardly noticeable as they degrade the image quality.
The quality of reproduced halftone images can be improved.

However, it is preferable to use a dot-concentrated dither pattern as this is effective in improving the quality of reproduced halftone images.

<Example> Hereinafter, embodiments will be described in detail with reference to the accompanying drawings showing examples.

FIG. 3 is a schematic diagram showing an image reproducing device, in which output light from a laser light source (1) as a light emitter is passed through a scanner (2) consisting of a rotating polygon mirror ( 3) The image is formed on the reflective surface (31) of U, the reflective surface (31)
The reflected light is focused onto a scanned medium (5) by a condenser (4) consisting of a lens or the like. Note that (32) is the rotation center axis of the scanner 1F (3), and the scanner (3) is rotated at a predetermined speed about the rotation center @ (32) by a drive source (not shown). Further, the scanner (3) has a plurality of reflective surfaces (31) on its outer peripheral surface, and the scanning speed can be set by the rotation speed, and the scanning width can be set by the number of reflective surfaces (31).

Therefore, by rotating the scanner (3) once, it is possible to perform scanning the same number of times as the number of surfaces of the scanner (3), and scanning in the same state (scanning with the same reflective surface) is repeated each time. It turns out.

Figure 1 is a diagram showing the relationship between the number of scans by the scanner (3) and the D1 Avatar (6).
The number of planes is 4, and the period of pixel concentration by dither pattern (6) is 4.

In the same figure, (7) shows the part where horizontal stripes occur.
appears, and each horizontal stripe occurrence part (sword is formed by the light reflected by the same surface of the scanner (3), so
It has the same width with no wide/narrow variations, especially where any horizontal lines occur (the sword alone is not noticeable).

Figure 2 is also a diagram showing the relationship between the number of scans by the scanner (3) and the dither pattern (6), where the number of scans by the scanner (3) is 4 and the period of pixel concentration by the dither pattern (6) is 8. It shows the case.

In this case, the part where horizontal stripes occur (71 is the scanner (3)
This will appear every two rotations of the sword, but since each horizontal stripe is formed by the light reflected from the same surface of the sugi turtle su (3), it is assumed that the width is the same with no change in width or width. t5, in particular, any part where horizontal streaks occur (only 71 is not noticeable).

FIG. 4 is a diagram showing the relationship between the number of scans by Sugi 17 (3) and the γ iser pattern (6). , shows a case where the period of pixel concentration by dither pattern (6) is 2.

In this case, the horizontal stripe occurrence portion (sword) appears twice during one rotation of the scan f(3), and this horizontal stripe occurrence portion C sword is formed by a different reflective surface every other time. , the horizontal stripe occurrence area that changes in width and narrowness in the reproduced image ('7
), and the wider horizontal stripe area (the sword) is particularly noticeable, reducing the quality of the reproduced halftone image.

As is clear from the above 31 marks, Fig. 1 and Fig. 2
In the embodiment shown in the figure, the quality of the reproduced halftone image can be improved by making the width of the horizontal stripe generation portion the same for all Cs.

However, if the output pixel period becomes too large, the resolution of the image itself will decrease, so it is preferable not to increase the number of scanner surfaces too much and to use a dither pattern in which the period of pixel concentration is not too large.

As described above, the present invention processes a halftone image signal to be reproduced into a light emitter by processing a dither pattern T in which the output pixel period is n times the number of scanner surfaces (where n is a positive integer). As a result, the width of the horizontal stripes occurring in the reproduced halftone image remains the same without changing in width or width, so that any horizontal stripes are not noticeable. This has the unique effect of increasing the quality of reproduced halftone images.

[Brief explanation of drawings]

Figures 1 and 2 are diagrams showing the relationship between the number of scans by the scanner (3) and the dither pattern (6), Figure 3 is a schematic diagram showing the image recirculation device, and Figure 4 is a diagram showing the relationship between the number of scans by the scanner (3) and the dither pattern (6). FIG. 3 is a conventional diagram showing the relationship between the number of scans and the Didi pattern (6). (1)...Rede light source as a light emitter, (3)...
Scanner, (6)...dither pattern,
, 1(7)...Horizontal streak occurrence area, (31)...
・Reflective surface diagram 1

Claims (1)

[Claims] 1. Controlled by the halftone image signal to be reproduced A rotating polygon mirror What is scanned by a scanner? In the above, the halftone image signal to be reproduced is The output pixel period is equal to the number of scanner surfaces. Dither that is multiplied by n (where n is a positive integer) You can control the light emitter by processing it with a pattern. A method for reproducing halftone images characterized by: 2. Dither pattern with concentrated dots According to claim 1 above, How to reproduce halftone images.