JPS6080365A - Processor of pseudo medium gradation picture - Google Patents

Abstract

PURPOSE:To obtain a pseudo medium gradation processor without moire by comparing an input picture signal with plural patterns stored in advance and switching to output a pseudo medium gradation signal and a binary-coded signal with a fixed threshold value in response to the compared output. CONSTITUTION:A picture signal inputted from a terminal 11 is binary-coded by a fixed threshold value binary-coding circuit 12 and further the coincidence/dissidence with a pattern to be subjected to plural pseudo medium gradation stored in advance is detected at a plural pattern collating circuit 13. Then an area extracting circuit 14 counts the number of picture elements which is at the surrounding of a noted picture element, e.g., within a range of 5X5 picture elements and where the plural pattern collection circuit 13 discriminates that the expression of pseudo medium gradation value is suitable are counted, and when the number obtains a prescribed value or over, it is discriminated that the area is entirely an area to be subjected to the pseudo medium gradation expression. The output from a pseudo medium gradation circuit 15 and the output from the fixed threshold binary-coding circuit 12 are switched to be extracted from the result of discrimination.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a circuit that adaptively converts an image signal containing a mixture of halftone photographs and line drawings such as characters into pseudo halftones.

Pseudo-halftone expression is often used in recording devices that have only black and white binary expressiveness. A technique typified by systematic dithering is also used in facsimile. If the input image is a mixture of halftone photographs and line drawings such as characters, binarization using a fixed threshold will reproduce fine details in the line drawings well, but depending on the number of lines in the input halftone photographs, Moiré may occur or false contours may appear. Furthermore, in the case of binarization using the systematic dithering method, problems occur such as moiré and insufficient resolution in line drawings, making characters illegible.

SUMMARY OF THE INVENTION An object of the present invention is to provide a pseudo-halftone processing device that overcomes the drawbacks of the prior art described above, preserves both resolution and halftone expression, and does not cause moire.

According to the present invention, number 1 is a means for binarizing an input image signal with a fixed threshold value, and a comparison between a spatial pattern constituted by the binary image signal and a plurality of pre-stored patterns of halftone dot manuscripts. means for detecting pixels in which the pattern of the image signal matches the pattern of the halftone photograph; means for converting the input image signal into pseudo-halftone; and means for converting the detected number of pixels into a predetermined area. unit, and according to the counted value, the grayscale image signal (p) and the binary image signal based on the fixed threshold value are switched and outputted. The image processing device is turned off.

A detailed description will be given below with reference to the drawings.

FIG. 1 is a block diagram showing an example of the invention. The image signal input from the terminal 11 is sent to the fixed threshold binarization circuit 1.
2, it is compared with a fixed threshold value and binarized. A plurality of pattern matching circuit 13 detects whether or not this binary image signal matches a plurality of pre-stored patterns to which pseudo halftoning is to be performed.

In the area extraction circuit 14, the area around the pixel of interest, for example, 5×5
The number of pixels within the pixel range for which pseudo halftone expression is determined to be suitable by the multiple pattern matching circuit 13 is counted. This may be done by adding 255 pixels, or by using an integrating circuit with a feedback loop. Then, the number of pixels determined to be subjected to pseudo-halftone conversion in the area surrounding the pixel of interest is counted, and if the number exceeds a certain value, it is determined that the entire area is an area that should be subjected to pseudo-halftone expression. . A certain value means, for example, if we are counting the number of pattern matching pixels in an area that includes one period of expected halftone dots, if the halftone period is 4 pixels and the area is 5 x 5 pixels, then the area is If the area is to be represented as a pseudo-halftone, the number of pixels that should match the pattern is at least 4, so 4 is selected. By doing this, it is possible to prevent a portion of fine text from being mistakenly determined to be a halftone dot.

On the other hand, the input image signal is subjected to pseudo-halftone conversion in a pseudo-halftone conversion circuit 15 . The image signal selection circuit 16 receives the output of the area extraction circuit 14 and selects either the binary image signal or the pseudo halftone image signal.

FIG. 2 shows an example of the configuration of the fixed threshold value binarization circuit shown in FIG. 1. The image signal inputted from the terminal 21 is compared with a fixed threshold value supplied from the terminal 22 by the comparator 24, and the result is outputted to the terminal 23.

FIG. 3 shows an example of the configuration of the multiple pattern matching circuit 13 shown in FIG. 1. H1 to H4 on the same scanning line as the pixel of interest shown in FIG. Moreover, -scanning line delay elements 34A to 34D and one pixel delay elements 33E to 33
By N, D1 to D4 located in the upper left direction from the pixel of interest X shown in FIG. 4 are obtained, and the exclusive OR with X is obtained.

The above exclusive logic 1" powerful read-only memory 36
Enter the address. This read-only memory 36
In order to determine whether the pixel of interest should be made into a pseudo-halftone, compare the exclusive OR patterns of H~H4, D0~D4, and the image of interest XX with the patterns that frequently appear in halftone photographs with multiple A types of lines. Before deciding whether or not there is, the criterion for this judgment is the presence or absence of moiré. For example, in the case of sampling at a density of 16 lines, if the halftone photograph has 120 lines or less, it is better to perform binarization using a fixed threshold for better halftone expression. If the number of lines is greater than that, it is determined that pseudo-halftoning such as re-halftoning is appropriate. Furthermore, if it does not match the halftone dot pattern, it is determined that it is based on a line drawing and that binarization using a fixed threshold is appropriate. This judgment signal is output to terminal 32.

In this embodiment, a pattern of four pixels each is referred to in both the scanning reduction direction and the diagonal direction, but more pixels than this may be referred to.

FIG. 5 shows an example of the configuration of the pseudo halftoning circuit 15 shown in FIG. 1. A pixel-by-pixel gate clock and a scanning m-unit clock are inputted to terminals 53 and 54 from pixel clock generators (not shown), respectively, and a pixel counter 57 and a scanning line counter 5
8. For example, when using a 4x4 pixel systematic dithering method, each counter has 4 pixels of each clock.
The remainder is output and input into the read-only memory 56. The read-only memory 56 has each threshold value of a 4×4 dither matrix written therein, which is read out and compared with the image signal input from the terminal 51 by the comparator 55, resulting in a pseudo halftone. The image signal is output to the terminal 52.

FIG. 6 shows an example of the configuration of the image signal selection circuit 16 shown in FIG. 1. fixed threshold binarization which is the output of the region extraction circuit 14;
A pseudo halftoning switching signal is input from the terminal 64, and in accordance with that signal, the 2
The multiplexer 65 selects either the value image signal or the pseudo-halftone image signal input from the terminal 62.
Output to 3.

According to the above-described pseudo-halftone image processing device, moiré can be suppressed without impairing the rich gradation expression of halftone photographs, and the pseudo-halftone image processing device can suppress the moiré without impairing the rich gradation expression provided by halftone photographs, and the pseudo-halftone image processing device can suppress resolution even in line drawings such as characters. A tone image is obtained.

[Brief explanation of the drawing]

FIG. 1 is a clock diagram of an embodiment of a pseudo halftone image processing device according to the present invention, FIG. 2 is a block diagram of a binarization circuit using a fixed threshold of 1, and FIG. 3 is a block diagram of a multiple pattern matching circuit. Fig. 4 is a diagram showing the positional relationship between pixels used for pattern matching and the pixel of interest, Fig. 5 is a block diagram of the pseudo halftoning circuit, and Fig. 6 is a block diagram of the image signal selection circuit. 13 is a binarizer with a fixed threshold value, 13 is a multiple pattern matching circuit, 14 is an area extraction circuit, 15 is a pseudo halftoning circuit, 16 is an image signal selection circuit, 24 is a comparator, 33A...33N is one pixel delay element, 34A
...34D is a one-pixel delay element, 35A...
・35H is an exclusive OR circuit, 36 is a read-only memory, 55 is a comparator, 56 is a read-only memory, 57.58
is a counter, and 65 is a multiplexer. Figure 4 Figure 5 Transcript Figure 4ll

Claims (1)

[Claims] In an apparatus for adaptively binarizing an image containing a mixture of halftone photographs and line drawings such as characters, there is provided a means for binarizing the input image signal using a fixed threshold, and a spatial pattern constituted by the binary image signal. means for detecting pixels in which the pattern of the image signal and the pattern of the halftone photograph match by comparing them with patterns of a plurality of halftone photographs that have been typed in advance; and pseudo halftoning the input image signal. means for counting the detected pixel convergence in units of a predetermined area, and generating the pseudo halftone image signal and the buried film according to the counted value.