JPH04180349A - Picture processing system - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Field of Industrial Application] This invention separates text, photographs, and halftone dots from a target image, and adaptively applies optimal image processing to each to reproduce a high-quality image. related to image processing methods.

[Conventional technology]

In order to obtain high-quality reproduced images in digital copying machines, facsimile machines, etc., it is desirable to adaptively apply optimal image processing to each of text, photographs, and halftone dots. In order to implement such processing, it is necessary to accurately separate each image region of the image, such as text, photographs, and halftone dots, as a preprocessing step.

Conventionally, as a method for accurately separating each image area from an image containing a mixture of text, photographs, and halftone dots, for example,
Binarization Processing Method for Images Containing Photographs and Halftone Dots'' (Preliminary Papers for the National Conference of the Japan Society of Image Electronics Engineers, 1989, pp. 91-94). This method performs edge detection of black and white transition points for each multiple pixel block to separate the text/halftone image from the continuous gradation image, and then converts the pixel block into a pattern matrix of binarized pixel patterns. The image is separated into an "R character image" and an "E halftone dot image" by coloring.

To separate the r character/halftone image J from the "continuous gradation image", first, the target image is divided into a plurality of blocks each having mxn pixels, and the average density is determined for each block. Next, when the average density is smaller than half of the dynamic range of density, a predetermined reference value is added to the average density, and when it is larger, it is subtracted, and the result is used as a parameter in the block.

When this parameter is included within the density distribution range of the block, it is determined that the image is an r character/halftone image, and when it is not included, it is determined that the image is a continuous gradation image J.

[To separate the character image J and the "halftone image," pixels within the block are binarized using the average density within the block as a threshold, the pattern of black pixels and white pixels within each block is examined, and the statistical value is Pattern matching ROM created from
When compared with the data, if it belongs to a character image, it is separated as an "E character image", and if it belongs to a halftone dot image, it is separated as a "halftone image".

In this way, among the separated image areas, the "character image" is subjected to binarization processing with etch emphasis, etc., and the halftone image J and the continuous gradation image J are smoothed and then subjected to pseudo-halftone processing.

[Problem to be solved by the invention]

According to the conventional method described above, since the etched portion of the character is separated as a "character image", the white background area is separated as a picture image (t!
8-point image or continuous grayscale image). For this reason, even though it is a white background area, there is a certain degree of density, so
Ink dots are placed here and there on the white background area of the reproduced image.
This causes the inconvenience that background stains become noticeable and the image quality deteriorates.

This invention detects a white background area when separating text, photographs, and halftone dots from an image containing a mixture of characters, photographs, and halftone dots, and reproduces an image without background smudges by reproducing the area in white. The purpose is to improve the quality of reproduced images.

[Means to solve the problem]

This invention provides an image processing method that prescans a target image, determines the image type based on various local feature values, and changes the reproduction method based on the determination result. a means for determining whether the target image is a halftone dot image during the main scan; a means for determining whether the target image is an edge portion during the main scan; A means for determining the attributes of each image area or pixel based on the determination result and switching the reproduction method; to play it.

[For production]

According to this invention, first, it is determined whether or not the target image includes a photographic image by pre-scanning, and if the photographic image is not included, the target image is a non-halftone area and a low density area at the time of main scanning. is played back with a white signal as a white background area. Therefore, the white background portion of the halftone dot/text mixed image can be reproduced using the white signal, and a high-quality image without background smear can be reproduced.

〔Example〕

FIG. 1 is a block diagram showing an embodiment of an image processing method according to the present invention. In the figure, blocks within the dotted line frame are blocks that operate during pre-scanning, and blocks within the chain line frame are blocks that operate during main scanning.

The prescan block includes an intermediate density area determination unit 1 that determines whether an input image obtained by reading a target document contains a photographic image (continuous grayscale image), and an intermediate density area determination unit It is comprised of a counter 2 that counts the determined number of areas, and a document recognition section 3 that determines from the count value of the counter 2 whether or not the target document is a mixed document including photographs.

This scan block includes a halftone dot separation section 4 that separates halftone dot areas from an input image, an etch separation section 5 that mainly separates edge portions of characters from an input image, and a white background determination section 6 that determines white background portions of an input image. , the determination result in pre-scanning and the halftone dot separation unit 4. Edge separation section 5. A determination unit 7 that determines the character part, picture part, and white background part of the input image based on the separation and determination results in the white background determination unit 6,
The dither processing unit 9 performs dither processing on the pattern portion of the image, and the judgment unit 70 selects either the MTF correction correction unit power or the output of the dither processing unit 9 based on the judgment result. It consists of a selection section 10 for selection.

In this configuration, first, the prescan block determines whether a photographic image (continuous grayscale image) is included in the input image. This determination is made based on the presence or absence of intermediate density. This method takes advantage of the fact that photographic images generally have areas of intermediate density, whereas character images and halftone dot images do not have a wide range of pixels of intermediate density. Specifically, when all pixels in a predetermined area (for example, 4×4 pixel size) of the input image have an intermediate density, the intermediate density area determining unit l determines that the input image is an intermediate density area, and when not, it determines that the area is an intermediate density area. Determined to be a non-intermediate density area. Then, the counter 2 counts the number of blocks determined to be in the intermediate density area, and if the count value is greater than a certain value, the document recognition unit 3 determines that the target document is a mixed document containing photographs; It is determined that the document does not contain photographs. Generally, a pattern image occupies an area of several centimeters squared or more, and if a halftone dot image with a minute area is detected during pre-scanning, it is determined to be erroneous separation and the document is recognized.

During the main scan, the input image is supplied in parallel to the halftone dot separation section 4, edge separation section 5, and white bet determination section 6, and the halftone dot separation section 4 determines the halftone dots depending on whether or not the density is at a peak. To separate. In this halftone dot separation section 4, halftone dot images are separated as halftone dots, and text/photo images are separated as non-halftone dots. This halftone dot separation unit 4 is disclosed in detail in Japanese Patent Application No. 1-278559 (title of invention: "Halftone Dot Area Separation Device") previously filed by the same applicant.

The etch separation unit 5 separates edges based on the connectivity of black pixels and white pixels that are ternarized (black/gray/white).

In this edge separation section 5, the etch portions of characters are separated as etch portions, the photographic images are separated as non-edge portions, and a portion of the halftone dot image is separated as non-edge portions. This etch separation section 5 is disclosed in detail in Japanese Patent Application No. 2-134054 (title of invention: ``Line Drawing Separation System'') previously filed by the same applicant.

The white background determination section 6 determines the white background based on the presence or absence of low-density pixels. Specifically, within a predetermined area,
When all the pixels have a low density, it is determined that the background is white; otherwise, it is determined that the background is non-white.

The white background determination section 6 determines the true white background area and the highlight area of the photographic image as a white background, and determines the highlight area of the halftone image as a non-white background area because minute dots are present in the document.

The determination unit 7 divides the input image into a text portion, a picture portion, and
Separate on white background. The method of separating each image area in the determination unit 7 is performed as follows.

First, when it is determined during pre-scanning that the input image does not include a photographic image, (a) If the input image has an edge area and is not a halftone dot, it is determined to be a text portion.

(b) If the input image is other than (a) and has a non-white background, it is determined to be a picture area.

(C) If the input image is a white background other than (a), it is determined to be a white background.

When it is determined during pre-scanning that a photographic image is included, (a) If the input image has an etched area and is not a halftone dot, it is determined to be a text portion.

(b) If the input image is a non-white background other than (al), it is determined to be a pattern area.

(C) If the input image is a white background other than (al), it is determined to be a picture area.

Selection section 0 selects the output of the MTF correction section 8 or the dither processing section 9 based on this determination result and outputs it to the outside as an output image. In other words, the character image in the input image is M
The TF correction unit 8 performs MTF correction, binarizes the signal, and outputs it as a signal with emphasis on resolution.The dither processing unit 9 performs dither processing on the pattern image and outputs it as a signal with emphasis on gradation.The white area is output as a white signal. .

〔Effect of the invention〕

According to this invention, it is determined whether the target image includes a photographic image through pre-scanning, and if the photographic image is not included, the target image is a non-halftone dot at the time of main scanning.
In addition, we made it possible to reproduce low-density areas using white signals, so
The white background part of an image containing halftone dots and text can be reproduced using a white signal, and a high-quality reproduced image without background smear can be obtained.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of an image processing method according to the present invention. DESCRIPTION OF SYMBOLS 1... Intermediate density area determination section, 2... Counter, 3...
. . . Original recognition section, 4. Halftone separation section, 5. Edge separation section, 6. White background determination section, 7.. Judgment section, 8..
- MTF correction section, 9... dither processing section, IO... selection section.

Claims (1)

[Claims] In an image processing method that prescans a target image, determines the image type based on various local feature amounts, and changes the reproduction method based on the determination result, whether or not the target image includes a photographic image at the time of the prescan. a means for determining whether the target image is a halftone image during the main scan, a means for determining whether the target image is an edge portion during the main scan, based on the determination results of each of the above means. means for determining the attributes of each image area or pixel and switching the reproduction method; and, if the target image does not include a photographic image, reproducing the non-halftone area and low density area in white during the main scan. An image processing method characterized by