JPH0548894A - Picture processor - Google Patents

Abstract

PURPOSE:To provide a picture processor by which a moire noise generated at the time of operating a halftone processing to dot pictures can be effectively suppressed, and the indefiniteness of on edge in the dot picture can be suppressed. CONSTITUTION:This device is equipped with a block dividing circuit 3 which divides a picture into blocks of prescribed sizes, dot adaptability calculating circuit 6 which calculates a dot adaptability from pixel data in the blocks, and number of line detecting circuit 5 which detects the number of lines of the dot pictures in the blocks. The smoothing processing of a characteristic corresponding to the dot adaptability calculated by the dot adaptability calculating circuit 6 and the number of lines detected by the number of line detecting circuit 5 is operated to the pictures in the blocks.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing apparatus for outputting a halftone dot photograph to a CRT, a printer or the like in electronic files, digital copying machines, facsimiles, scanners and the like.

[0002]

2. Description of the Related Art When outputting a halftone dot image read by an image sensor to a CRT or a printer, if halftone processing such as dither processing is performed as it is, moire noise is generated, so that a reproduced image of high quality is obtained. For this purpose, it is necessary to remove (blurr) high frequency components by applying a low-pass filter having a frequency characteristic corresponding to the number of lines of the halftone picture, and then perform halftone processing and output.

[0003]

However, it is difficult for an operator to detect the number of lines of a halftone dot photograph, and in practice, a low-pass filter having a constant frequency characteristic is used for processing. At present, the image is blurred more than necessary depending on the number of halftone dots.

Further, even if a low-pass filter having an optimum frequency characteristic is used, it is inevitable that the edge portion of the halftone dot image is blurred, and a high quality image cannot be reproduced.

The present invention has been made in view of such circumstances, and it is possible to effectively suppress moire noise generated when halftone processing is performed on a halftone dot photograph, and to blur an edge of a halftone dot photograph. An object of the present invention is to provide an image processing device capable of suppressing the above.

[0006]

An image processing apparatus of the present invention comprises an image dividing means for dividing an image into blocks of a predetermined size, and a halftone dot matching degree calculating means for calculating a halftone dot matching degree from pixel data in the block. And a line number detecting means for detecting the number of lines of the halftone dot photograph in the block, and a halftone dot compatibility calculated by the halftone dot compatibility calculating means and a characteristic corresponding to the number of lines detected by the halftone dot detecting means. And a smoothing means for performing a smoothing process on the image in the block.

[0007]

In the image processing apparatus of the present invention having the above structure,
Since the smoothing process is performed only on the blocks that are determined to be suitable for the halftone dot by the halftone dot compatibility calculation means, excessive blurring such as edges in the halftone dot photograph can be suppressed.
Further, since the optimum smoothing processing is performed according to the number of lines detected by the line number detecting means (a low-pass filter having an optimum characteristic is selected in the embodiment), moire noise is effectively reduced. ..

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the configuration of an embodiment of the image processing apparatus of the present invention. The image signal input from the image sensor 1 is digitized by the A / D converter 2 and further divided into blocks of a predetermined size by a block division circuit, and each divided block is sequentially temporarily stored in the block memory 4. It

The line number detection circuit 5 detects the number of lines of halftone dots from the pixel data in the block stored in the block memory 4. In the case of a halftone picture, the density waveform of the pixels in the block is as shown in FIG. When the number of pixels in the main scanning direction of the block is N, the resolution of the image sensor is dpi, and the number of pulses (peaks) having a maximum value observed in the block is n, the line number detection circuit 5 calculates the line by the following equation. Calculate the number. Number of lines = n × dpi / N

The halftone dot compatibility calculation circuit is provided in the block memory 4
Read the pixel data in the block stored in
The difference between the maximum value of the concentration waveform in FIG. 2 and the minimum value on the left or right of the concentration waveform, that is, the amplitude of the concentration waveform (in other words, the height of the pulse) is calculated, and the average value is compared with a threshold value to match the halftone dot. Determine the degree.

The output terminal of the block memory 4 is connected to the input terminal of the switch SW1. The output terminal O of the switch SW1 is directly connected to the input terminal of the dither circuit 8. The output terminal A of the switch SW1 is connected to the input terminal of the dither circuit 8 via the optimum digital low-pass filter 7a when the number of halftone dots is 60. The output terminal B of the switch SW1 is connected to the input terminal of the dither circuit 8 via the optimum digital low-pass filter 7b when the number of halftone dots is 85. The output terminal C of the switch SW1 is connected to the input terminal of the dither circuit 8 via the optimum digital low-pass filter 7c when the number of halftone dots is 135.

The switch SW1 connects any one of the output terminals O, A, B and C to the input terminal in accordance with the output of the line number detection circuit 5 and the output of the halftone dot compatibility calculation circuit 6.

Next, the operation of the embodiment of FIG. 1 configured as described above will be described. When the halftone dot compatibility calculation circuit 6 outputs to the switch SW1 a signal indicating that the pixel data stored in the block memory 4 does not match the halftone dot, the switch SW1 connects its input terminal and the output terminal O to each other. To As a result, the pixel data stored in the block memory 4 is not subjected to smoothing processing, and the dither circuit 8
Is supplied to. Therefore, the edges and the like in the halftone dot photograph are supplied to the dither circuit 8 without being subjected to the smoothing processing (without being passed through the low-pass filter), so that the blurring of the edges and the like can be avoided.

When the halftone dot compatibility calculation circuit 6 outputs to the switch SW1 a signal indicating that the pixel data stored in the block memory 4 matches the halftone dot, the switch SW1
Depending on the number of lines detected by the line number detection circuit 5,
The input terminal is connected to any one of the output terminals A, B and C. Therefore, the pixel data stored in the block memory 4 is stored in the low-pass filters 7a, 7b and 7
After being passed through a low-pass filter that is most suitable for the number of halftone dot lines in c, it is supplied to the dither circuit 8. Therefore, since the image data is subjected to optimum smoothing processing, moire noise can be effectively reduced. ..

The halftone dot compatibility calculating circuit 6 may add the absolute values of the density differences from all the pixels for the pixels in the block, and compare the added value with a threshold value to determine the adaptability. ..

Further, the halftone dot fitness calculating circuit 6 determines the halftone dot fitness by using the halftone dot fixed value obtained by fuzzy inference from the feature of the signal waveform showing the pixel density or the pixel in the block. May be.

In the embodiment shown in FIG. 1, a digital low-pass filter is used because a filter is applied after A / D conversion, but a plurality of analog low-pass filters having different characteristics are prepared. Alternatively, these filters may be switched according to the dot compatibility and the number of dot lines to be used for smoothing the analog image signal, and the smoothed analog image signal may be A / D converted.

In the embodiment shown in FIG. 1, a plurality of low-pass filters having different characteristics are switched. However, even if a low-pass filter whose characteristics dynamically change according to the detected halftone dot number is used. Good.

Further, in the embodiment of FIG. 1, the number of lines is detected for each divided block and the low pass filter is switched. However, after the number of lines is determined in the first several blocks, the low pass filter to be used is used. May be fixed.

[0020]

As is apparent from the above description, according to the image processing apparatus of the present invention, the smoothness corresponding to the halftone dot conformity (that is, the necessity of smoothing) of the image block and the number of lines of the halftone dot is used. Since the image processing in the block is performed, smoothing processing can be performed according to the area of the halftone dot photograph with many high frequency components excluding the edges etc., so moire noise can be effectively reduced. In addition, it is possible to suppress blurring such as edges.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of an image processing apparatus of the present invention.

FIG. 2 is a waveform diagram showing pixel density in a block.

[Explanation of symbols]

 3 block division circuit 5 halftone dot frequency detection circuit 6 halftone dot compatibility calculation circuit 7a, 7b, 7c low pass filter

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Toru Fujii, No. 10 Hanazono Dodo-cho, Ukyo-ku, Kyoto City, Kyoto Prefecture Omron Co., Ltd. Co., Ltd. (72) Hajime Okumura Hajime Okumura, No. 10 Hanazono Dodo-cho, Ukyo-ku, Kyoto City, Kyoto Prefecture OMRON Corporation

Claims (4)

[Claims] 1. An image dividing means for dividing an image into blocks of a predetermined size, a halftone dot matching degree calculating means for calculating a halftone dot matching degree from pixel data in the block, and a line of a halftone dot photograph in the block. Within the block, the number of lines detecting means for detecting the number, and the smoothing process of the characteristic according to the number of lines detected by the number of lines detecting part and the number of lines detecting part An image processing apparatus comprising: a smoothing unit that applies an image. 2. The image processing apparatus according to claim 1, wherein the line number detecting unit detects the line number by counting pulses of a waveform showing a pixel density in the block. 3. The halftone dot matching degree calculating means calculates the halftone dot matching degree based on the magnitude of the amplitude of a waveform indicating the pixel density in the block. Image processing device. 4. The halftone dot compatibility is calculated by the halftone dot suitability calculating means using a halftone dot definite value obtained by fuzzy inference from the characteristics of a signal waveform indicating pixel density or pixels in the block. The image processing apparatus according to claim 1, wherein the image processing apparatus determines.