JPH01114159A - Intermediate tone picture processing method - Google Patents

Abstract

PURPOSE:To eliminate flickering of the screen and to obtain a picture with high quality by using dither matrices adjacent in lateral direction in the state of deviation in longitudinal direction in using the dither matrix to generate a binary intermediate picture. CONSTITUTION:A dither matrix memory 5 outputs a threshold value sequentially from the left end of the 1st row of the 1st dither matrix in the right direction and then from the left end of the 1st row of the 2nd dither matrix in the right direction in response to the pattern address generated from an address generating circuit 6. The operation above is repeated to a digital signal by one row and then the processing is advanced to the 2nd row and the 3rd row of the matrix. Then the threshold value outputted sequentially from the memory 5 and the digital signal outputted from a correction circuit 4 are compared by a comparator circuit 8 and only when the level of the digital signal is larger than the threshold value, a black picture element signal is outputted. Since the black picture elements exist scattering, the object is attained.

Description

DETAILED DESCRIPTION OF THE INVENTION G) Industrial Application Field The present invention relates to a halftone image processing method for generating a binary halftone image using a dither matrix.

(b) Conventional technical information filing devices or facsimile devices optically read an image from a document and decompose it into dot-shaped pixels.
Image processing is performed in which each pixel is converted into a binary signal of black and white.

Furthermore, in this type of image processing, for grayscale images such as photographs, binarization processing is performed using a dither method using a dither matrix to obtain a pseudo binary halftone signal. Regarding such dither method, please refer to rF published by Nikkan Kogyo Shimbun.
“Image signal processing for AX, OA” (1981)
As shown in detail in the article ``Pseudo-halftone display using a binary display device for halftone images'' on pages 16 to 25 of the issue (published on October 20th), as shown in Figure 5, various A 4 by 4 matrix (in this case, a spiral matrix) consisting of threshold values is taken as one unit, and such a matrix is arranged vertically and horizontally in the same way as shown in Figure 6, and the read image is divided into two.
It converts it into a value signal.

4. Problems to be Solved by the Invention By the way, when an image with a uniform density level of 4 (light gray) is converted into a binary signal using the dither matrix shown in Fig. 6, the pattern shown in Fig. 7 is obtained. In order to display this on a CRT display with half the resolution, if the odd rows and odd columns are thinned out, the pattern will be as shown in Figure 8, with black pixels appearing in every -row (and -column). The image will be displayed.

However, displays on CRT displays are generally performed using an interlaced method, alternately using odd and even lines. Therefore, as shown in FIG. 8, an image with black pixels in each line is On the CRT display, a dark screen (display on odd-numbered lines) and a bright screen (display on even-numbered lines) are alternately displayed, and the screen flickers.

This flickering state of the screen is caused by the density level 7 in the IJ mask usage pattern (Fig. 6).
A similar problem occurs when each image up to (gray) is converted into a binary signal.

Furthermore, even in the original pattern shown in FIG. 6 which is not thinned out, the quality cannot be said to be good because the black pixels are concentrated in a predetermined row.

An object of the present invention is to eliminate screen flickering and obtain high quality images.

In an apparatus for generating a binary halftone image using an IJ matrix, the dither matrices that are adjacent in the horizontal direction are used with a shift in the vertical direction. It is characterized by

(e) Effect: As in the present invention, by using dither matrices that are adjacent in the horizontal direction and shifted in the vertical direction, black pixels appear distributed over many rows.

(f) Embodiment FIG. 1 is a block diagram showing an embodiment of an image reading apparatus using the method of the present invention. (1) is a reading sensor consisting of a C0D (charge-coupled device) or the like that converts an image on a document (not shown) into an electrical signal, (2) is an amplifier circuit that amplifies the electrical signal to a predetermined level, and (3) is (4) is a correction circuit that performs shading correction of the digital signal, etc.; (5) is a dither matrix memory that stores a predetermined dither matrix; 6) is dither matrix memory (5)
An address generation circuit that outputs a pattern address to (7)
) controls the operation of the A/D conversion circuit (3) and the correction circuit (4), and also controls the address generation circuit (6) so that the pattern address corresponding to the control is output from the address generation circuit (6). The control circuit (8) compares the digital signal given from the correction circuit (4) with the threshold value read from the dither matrix memory (5), and outputs the black pixel signal only when the level of the digital signal is higher than the threshold value. (9) is an output interface that outputs black and white binary signals, and the output of this output interface is displayed on a CRT display (not shown). (not available) will be displayed.

As shown in FIG.
As shown in the figure, the dither matrix for one unit having a size of 4 by 4 is used shifted in the vertical direction (shifted by two rows in this embodiment).

For this purpose, the dither matrix memory (5) contains a second
As shown by the dashed frame in the figure, the first pattern in the normal state
A dither matrix and a second dither matrix formed by shifting the dither matrix by two lines are described.

The operation of such an image reading device will be explained below. When a document (not shown) is set at a predetermined position, a reading sensor (1) converts the image on the document line by line into analog electrical signals. This analog electrical signal is amplified to a predetermined level by the amplifier circuit (2), and then the A/D conversion circuit (
3), where the digital signal is converted into a digital signal.The digital signal is input to a correction circuit (4) and undergoes correction processing such as shading correction. At this time, the control circuit (7) controls the operation of the A/D conversion circuit (A/D conversion circuit) and the correction circuit (4), and in response to this control, an appropriate pattern address is generated from the address generation circuit (6). The operation of the address generation circuit (6) is controlled so that the address generation circuit (6)

According to the pattern address generated from the address generation circuit (6) in F of such control, the dither matrix memory (5)
) is read from the left end of the first row of the first dither matrix in the vertical and rightward directions, and sequentially outputs the threshold values from the left end of the first row of the second dither matrix to the right. This operation is repeated for one row of digital signals, and then
In this way, the threshold value sequentially output from the dither matrix memory (5) and the digital signal output from the correction circuit (4) are transferred to the comparison circuit (
8), and a black pixel signal is output only when the level of the digital signal is greater than the threshold value. For example, when an image with a density level of 4 is converted into a binary signal using the dithering device (IJ) shown in FIG. 2 of this embodiment, as shown in FIG. appeared in
Good quality halftone images can be obtained.

Furthermore, if the odd rows and odd columns of this image are thinned out, black pixels will appear in both the odd and even rows, as shown in Figure 4.
No flickering occurs when displayed on a display.

Note that the size of the dither matrix and the shift imaginary are not limited to those in this embodiment, and may be set as appropriate.

(G) Effects of the Invention According to the present invention, dither matrices that are adjacent in the horizontal direction are used in a state that they are shifted in the vertical direction, so that the black pixels are not concentrated in a predetermined row but are dispersed. Become. Therefore, flicker-free screen display and high-quality images can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an image reading device according to the present invention, FIG. 2 is a schematic diagram showing how a dither matrix is used in the method of the present invention, and FIG. 3 is an example of a halftone image obtained by the method of the present invention. 4 is a schematic diagram showing an image after the halftone image has been thinned out, FIG. 5 is a schematic diagram showing a typical example of a dither matrix, and FIG. 6 is a conventional dither matrix.) FIG. 7 is a schematic diagram showing an example of a halftone image obtained in the conventional example, and FIG. 8 is a schematic diagram showing an image after thinning processing of this halftone image. (Li...reading sensor, (5)...dither matrix memory, (8)
...comparison circuit,

Claims (1)

[Claims] (1) A halftone image processing method, characterized in that in a device that generates a binary halftone image using dither matrices, the dither matrices that are adjacent in the horizontal direction are used in a state that they are shifted in the vertical direction. .