JPS6291076A - Image information output system - Google Patents

Abstract

PURPOSE:To obtain a half tone image having a good resolution and gradation characteristic and in which pitch nonuniformity is hard to be watched by dividing one picture element to be recorded into plural micro picture elements, and making fat the micro picture element in a line shape in a main scanning direction. CONSTITUTION:A dither matrix divides one picture element into the matrix of 4X4, and divides each element of the matrix into two image information and sets a multiple value as three values (0, 1/2 and 1). When the angle of a line screen is of 45 deg., after a line screen is formed by hitting four of 1/2 dot for the first, a 1/2 dot is fattened to one dot, and the dot is fattened in order in the sequence of numerals shown in figure corresponding to a density. Since the dither matrix is repeated two-dimensionally, a line 11 of 45 deg. is fattened in a rightward direction (the main scan direction).

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an image information output method that expresses density by changing the proportion of dots within a pixel based on gradation pixel signals.

[Prior Art] Conventionally, most printers and the like use a dither method of outputting a binary signal to perform gradation recording. However, with this method, there was a problem that the resolution deteriorated when trying to improve the gradation.6For example, to obtain 17 gradations including white, a 4x4 matrix is required, and to obtain 65 gradations, an 8x8 matrix is required. Since the number of dots increases in the middle of the matrix as the gradation increases, the resolution of the intermediate gradation tends to deteriorate as the matrix size increases.

For this reason, a method was devised that combines multilevel output and dithering to improve gradation without significantly reducing resolution. For example, in the case of a 4x4 matrix, only 17 gradations can be achieved with the z value, but 33 gradations can be achieved with 3 values, and 49 with 4 values.
If you change the gradation to 5 values, you can get 65 gradations.

Another method is to provide a plurality of dither matrices in which the number of dots increases, and to gradually shift the threshold values of each of these matrices to express gradation as a whole. For example, if gradation is expressed using four 4x4 dither matrices, the midtone resolution will be the same as when using a 4x4 dither matrix, and the number of gradations will be four times that when using a 4x4 matrix. .

Conventional dither matrix patterns can be roughly divided into dot-dispersed type (for example, Bayer type) and dot-concentrated type (for example, spiral type). It is known that the dot-dispersed type has better resolution and the dot-concentrated type has better gradation. Conversely, with the dot dispersion type, the dots are printed as far apart as possible, so the pitch of each printed dot gradually becomes finer until 50% of the area corresponding to the dither matrix is printed. The change in texture when printing is noticeable, and the actually printed dots are not square but rounded, so the gradation may be abrupt around 50% of the area depending on how each dot overlaps, etc. It had the disadvantage of changing to

On the other hand, in the case of the dot concentration type, pseudo halftone dots are formed in dither matrix units, so there is a drawback that the resolution of halftones is poor. In addition, in the case of laser printers, line-shaped unevenness (called pitch unevenness) occurs due to the tilting of the polygon scanner and uneven rotation of the photosensitive drum, etc., and in the case of thermal transfer printers, due to uneven paper feeding, which deteriorates the image quality. However, these pitch irregularities are particularly noticeable in the dot concentration type because the pseudo halftone dots are arranged in a vertical and horizontal grid pattern.

[Problems to be Solved by the Invention] It is an object of the present invention to provide an image information output method that eliminates the above-mentioned drawbacks, has good resolution and gradation, and makes pitch unevenness less noticeable.

[Means for solving the problem] As a means for solving this problem, for example, the method shown in FIG. 1(a)
The dither matrix shown in the example breaks down one pixel into a 4×4 matrix, and further divides each element of the matrix into 2
The pixel information is divided into two parts, and a numerical value corresponding to the gradation level is provided. This numerical array is set so that, when reproducing gradations, lines are formed in a direction at a predetermined angle with respect to the scanning line direction, and dots become thicker in the direction of the scanning line as the gradation increases.

L effect] In the configurations shown in FIGS. 1(a) and (b), as the gradation level increases, the scanning line is diagonally changed as shown in FIG. 1(b) according to the values of the matrix shown in FIG. 1(a). A straight line 11 is formed along the scanning lines, and the dots become thicker in the direction of the scanning line.

[Example] Hereinafter, an example of the present invention will be described in detail with reference to the accompanying drawings. In this embodiment, one pixel to be recorded is divided into a plurality of fine pixels, and the fine pixels are made thicker in a line shape in the main scanning direction, thereby obtaining a halftone image with good resolution and gradation.

[Example of dither matrix (Fig. 1) (a), (b)] Fig. 1 (a) is a dither matrix showing an example of the order in which dots are made thicker according to this embodiment.For simplicity, the dither matrix is 4. The case where the multi-values are 3friCO, 1/2 and 1) and the line screen angle is 45° is shown.

Figure 1 (b) is a diagram in which four 1/2 dots are first formed to form a line screen, and then the 172 dot of dot 10 is thickened to 1 dot. Make the dots thicker in order according to the concentration.

Furthermore, since the dither matrix is repeated two-dimensionally, the 45° line 11 becomes thicker in the right direction (main scanning direction) due to the dither matrix shown in FIG. 1(a).

[Comparison with other dither matrix patterns Figure 1 (a)
(b) - Figure 3 (a) (b) Next, as a comparative example, the second
Figure (a) shows the order of thickening the dots of the dot-dispersed type and the second
A dot pattern with up to the fifth dot in figure (b) (
Figure 3 (a) shows the order in which concentrated dots are thickened, and Figure 3 (b) shows the dot pattern (for 21/2 dots).
shows.

First, the lv tonality is compared with this example (Fig. 1 (a)
) (b)) After forming a line, the line becomes thicker little by little, so similar to the dot concentration type (Fig. 3 (a) and (b)), it is necessary to create a gentle gradation. obtain. On the other hand, in the dot dispersion type (Fig. 2 (a) and (b)), the dots are spaced as far apart as possible up to 50% of the area (checkered pattern), and then the dots are filled in between. , there is a drawback that the gradation changes suddenly before and after the surface v150%.

Next, let's compare the resolution. Dot concentrated type (Figure 3 (
In a) and (b)), pseudo halftone dots are formed in dither matrix units, and the pitch thereof is equal to the size of the dither matrix (a) (Fig. 1 (a) and (b)).
Now, we will form a 45° pseudo screen, and its pitch will be &
/J-2 is smaller than the dot concentrated type, so the resolution is improved. However, when the screen angle is 90°, the pitch of the pseudo screen is a, which is equal to the dot concentration type.

[Comparison of pitch unevenness Figures 4(a) and (b)] Also, as an example of comparing pitch unevenness, at a halftone level where 4 dots are printed in a 4x4 dither matrix, the pitch of the sub-scanning is 172 which is the normal pitch. The dot concentrated type (Fig. 4(b)
), the average density changes due to the overlap of the dots, and the pitch unevenness portion 41 is easily noticeable, but in this example (Fig. 4 (
In a)), there is no density change and the pitch unevenness 40 is not very noticeable.

Furthermore, when comparing changes in texture, with the dot dispersion type, the pitch of dots becomes finer until it reaches 50% of the area, so the change in texture is noticeable.
In this embodiment, after the lines are formed, the pitch of the lines is constant, so there is no change in texture.

[Example of forming a screen angle for color (Figure 5 (a)
(b))] The above is a black and white single color example, but the present invention can be applied to a color P.
When applied to A-tone recording, different pseudo screen angles can be formed for each color, and hue unevenness due to misregistration, pitch unevenness, etc. can be reduced.

5(a) and 5(b) are both based on a 3×3 matrix, and show the order in which the dots of the z value are placed.

Figure 5(a) shows an example of a 3x6 matrix with a screen angle of 26.6°; Figure 5(b)
) is a diagram showing an example of a case where a screen angle of 18.4° is formed using a 3×9 matrix.

When producing a full-color image using four colors: yellow (Y), magenta (M), cyan (C), and black (K), the screen angle should be, for example, 90' for Y, 63.4° for C, and 63.4° for C.
is 45° and 1M is 26.6°, and a matrix is provided for each color to process color image data.

Although the present embodiment has been described based on a 4×4 matrix, it is needless to say that the present invention is not limited to this.

[Effects of the Invention] As described above, according to the present invention, it is possible to provide an image information output method that has good resolution and gradation, and in which pitch unevenness is less noticeable.

[Brief explanation of drawings]

FIG. 1(a) is an example of a matrix showing the order in which the dots are thickened in this embodiment, and FIG. 1(b) is a pattern diagram when the order of FIG. 1<a) is reached up to 21/2 dots. , Figures 2 (a) and (b) are similarly dot-distributed matrix and pattern diagrams when up to 172 dots are printed, and Figure 3 (a) and (b) are similarly dot-concentrated matrix and 1/2 pattern diagrams. FIG. 4(a) is a diagram for explaining the pitch unevenness in this embodiment. FIG. 4(b) is a diagram showing the pitch unevenness in the case of the dot dispersion type. FIGS. 5(a) and 5(b) are diagrams showing an example of a case where screen angles are formed for color.

Claims (1)

[Claims] This is an image output method that reproduces gradations using gradation pixel signals.One pixel is decomposed into a matrix, and each element of the matrix is further divided into n pieces in the scanning line direction. An image information output method characterized in that a line is formed in a direction at a predetermined angle, and the dots are made thicker in the scanning line direction as the gradation increases.