JP2521744B2 - Image processing device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing apparatus, and more particularly to an image processing apparatus that identifies an image area in a document and performs image processing corresponding to the area.

[Prior Art] Conventionally, in this type of image processing apparatus, as shown in FIG.
The original is read by the input sensor 71 such as CCD, and the image data is converted into a digital signal by the A / D converter 72. This digital signal is subjected to gradation correction such as contrast adjustment by the gradation correction circuit 73, converted into dot ON / OFF signals by the binarization circuit 74, and output as an image by the binary printer 75. There is.

A typical binarization method in the binarization circuit 74 is as follows.
There are a method of binarizing with a fixed threshold (fixed threshold method) and a method of binarizing with the dither method.

The former can obtain good image quality when reproducing characters, line drawings, etc. in a document, but has a problem that halftone portions such as photographs in a document have no gradation and the image quality deteriorates. On the other hand, in the latter case, the gradation property in the halftone portion is improved, but there is a problem that the image quality is deteriorated due to the cutout of characters and line drawings and the generation of moire fringes in halftone dot photographs of a specific screen ruling.

[Problems to be Solved by the Invention] Therefore, when characters, line drawings, photographs, and halftone dots coexist in the same document, each image area is identified and the optimum binarization processing corresponding to the area is performed. Need to be applied. That is, a binarization method that emphasizes resolution over gradation is used for character / line drawings, and a binary value that emphasizes gradation over resolution for halftone images such as photographic images. Adopt a method of computerization. On the other hand, for the halftone dot photograph, it is necessary to suppress the high frequency component of the image that causes the moire and then use the binarization method that produces the gradation.

The present invention has been made in view of the above conventional example, and an object of the present invention is to provide an image processing apparatus capable of identifying the type of an image area so that halftone processing of image data suitable for each image area can be performed. And

[Means for Solving Problems] In order to achieve the above object, the image processing apparatus of the present invention has the following configuration. That is, input means for inputting multivalued image information, identification means for identifying the type of image area of the multivalued image information, and halftone processing for performing halftone processing on the multivalued image information corresponding to the image area. An image processing apparatus comprising: a means for calculating the average value of the multi-valued image information in units of a predetermined pixel block, and the identification means for comparing the average value with the multi-valued image information. The first comparison means, the second comparison means for comparing the difference between the average value and the multi-valued image information with a predetermined threshold value, and the comparison output of the first and second comparison means. It is provided with means for converting multi-valued image information into binary data, and detection means for detecting continuity of the binary data in the row direction or the column direction.

[Operation] The average value of the multi-valued image information is calculated in a predetermined pixel block unit, the average value is compared with the multi-valued image information, and the difference between the average value and the multi-valued image information is set as a predetermined threshold value. Compare. Multivalued image information is converted into binary data based on these two comparison outputs, continuity in the row direction or column direction of the binary data is detected, and the image of the multivalued image information is based on the continuity. Identify the area type. Then, it operates so as to perform halftone processing on the multivalued image information corresponding to the image area.

Embodiments Embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[Description of Configuration of Image Processing Apparatus (FIG. 1)] FIG. 1 is a block diagram showing a schematic configuration of the image processing apparatus of the present embodiment.

For example, the image signal photoelectrically read by the input sensor unit 1 such as CCD is converted into digital image data 7 by the A / D converter 2.
Is converted to. Now, assuming that the A / D converter has 8 bits, the digital image data 7 becomes a density signal of 256 gradations.
The gradation correction circuit 3 performs gradation processing such as contrast adjustment and brightness (luminance) adjustment on the input image data 7, and outputs gradation-corrected image data 6.

The tone-corrected image data 6 is input to the character processing circuit 4, the halftone processing circuit 5, and the character area determination circuit 8. The character area determination circuit 8 determines whether it is a character area or a halftone area. By outputting the determination signal 9 and switching the switch 10, the output of the corresponding processing circuit 4 or 5 is sent to the printer section 11 which is a binary printer. Output to form an image.

The character processing circuit 4 compares a certain threshold value with the image data 6, and outputs "1" when the image data 6 is larger, and outputs "0" when the image data 6 is smaller. As a result, images such as characters and line drawings are output clearly. On the other hand, the halftone processing circuit 5 sequentially compares the threshold values shown in the dither matrix with the image data 6 by the dither method. When the image data 6 is large, "1" is set, and conversely, the image data 6 is set. When it is small, "0" is output. Thereby, a halftone image such as a photograph can be reproduced with good gradation. Further, in the halftone processing circuit 5, after removing the high frequency component of the image which causes the moire of the halftone image by a low pass filter such as a smoothing filter, a good image with less moire for performing the above-mentioned dither processing is obtained. Can be reproduced.

[Explanation of Character Area Judgment Circuit (FIGS. 2 to 6)] FIG. 2 is a block diagram of the character area judgment circuit 8, and the same parts as those in FIG.

Reference numeral 21 denotes a binarization circuit whose detailed block diagram is shown in FIG. 3, in which multivalued image data 6 is input and converted into binarized data 24. Reference numeral 22 is a line buffer including a line buffer for at least three lines, which inputs the binarized data 24 and stores the binary data 24 for three lines. The judging device 23 is 2
The continuity of the black “1” pixels of the binarized data 24 is checked. When there is continuity, the judgment signal 9 is set to “1” as a character area, and when there is no continuity, the judgment signal 9 is set to “halftone area”. Set to 0 ". Therefore, the switch 10 is switched to the side a when the judgment signal 9 is "1" and to the side b when the judgment signal 9 is "0".

FIG. 3 is a block diagram of the binarization circuit 21 of the character area determination circuit 8.

The averaging circuit 31 inputs the image data 6, calculates an average value 37 of the image densities of m × n pixel blocks, and outputs it. The comparator 32 compares the average value 37 with the image data 6 and outputs a signal "1" when the image data 6 is larger, and "0" when it is smaller.
Is output. The density difference detection circuit 33 takes the difference between the image data 6 and the average value 37, and outputs a signal 35 of "1" when the difference is larger than the threshold value and "0" when the difference is smaller than the threshold value.

 This relationship is expressed by the following equation.

| D−AV | ≦ T ... B = 0 | D−AV |> T ... B = 1 where D is the value of the image data 6, AV is the average value, and T is the threshold value.

FIG. 4A is a diagram showing the relationship between the input signal and the output signal in the modifier 36.

The area where the signal 35 is “0”, that is, the area where the local density difference of the image is small corresponds to the continuous tone photographic area or the background area, and the area where the signal 35 is “1” is the local density difference of the image. Is a large area and corresponds to a halftone dot image area and a character area. As is clear from this figure, when the signal 35 is "0", the corrector 36
The binarized data 24, which is the output of, becomes "1", and when the signal 35 is "1", the binarized data 24 is determined corresponding to the signal 34.

The binary data 24 thus obtained can separate the dots of halftone dots and the black pixel portions of characters.

FIG. 4B is a diagram showing a specific circuit example of the modifier 36.

FIG. 5 (A) is a diagram showing an example of the binarization result of the halftone dot image, in which halftone dot black pixels are scattered. Further, FIG. 5B is a diagram showing an example of the binarization result of the character image, which is shown as a series of black pixels in the character portion.

Therefore, in order to separate the halftone dot image and the character image, the continuity of the black pixels in the row direction and the column direction is counted, the image area with a predetermined continuity is defined as the character area, and the image area without continuity is defined as the halftone dot. It can be seen that it may be determined that the area.

 FIG. 6 is a diagram showing a specific circuit example of the judging device 23.

The pixel row 61 that is continuous in the horizontal direction is ANDed for 3 pixels by the AND circuit 63, and when 3 consecutive pixels are “1”, the data is “1”.
Is stored in the buffer 65. On the other hand, the pixel row 62 continuous in the vertical direction is ANDed by three vertical pixels in the AND circuit 64, and when three consecutive pixels in the column direction are “1”, the data “1” is stored in the buffer 68. It

The AND circuits 67 and 68 read out three consecutive data from the buffers 65 and 66, respectively, and when all the three consecutive data are "1", the output becomes "1". . OR circuit 69 is AN
Since the outputs of the D circuits 67 and 68 are ORed together, if either the horizontal direction or the vertical direction is continuous, it is determined to be a character or line drawing area, and the determination signal 9 becomes "1".

By performing this determination processing by the determiner 23 while shifting it by one pixel, it is possible to perform area determination over the entire input image area.

In the present embodiment, the continuity of 3 pixels in the horizontal direction, the vertical direction, is detected, but the continuity detection of more pixels (for example, about 5 pixels) and the continuity detection in the oblique 2 directions are performed.
Further accurate character detection is possible.

As described above, according to the present embodiment, the photograph area, the character area, and the halftone dot photograph area are identified, and the binarized data corresponding to the type of each area is selected and printed out. , It has become possible to obtain a layer of good image quality in any image.

[Advantages of the Invention] As described above, according to the present invention, it is possible to determine the type of image data and perform the halftone process corresponding to the type of image.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of an image processing apparatus according to an embodiment of the present invention, FIG. 2 is a block diagram of a character area determination circuit, and FIG. 3 is a block diagram of a binarization circuit of a character area determination circuit. FIG. 4 (A) is a diagram showing the relationship of input / output data of the corrector, FIG. 4 (B) is a diagram showing a concrete circuit example of the corrector, and FIGS. 5 (A) and 5 (B) are FIG. 6 is a block diagram showing a binarization example of a halftone image and a character image, FIG. 6 is a block diagram of a judging device for detecting continuity of black pixels, and FIG. 7 is a block diagram showing a schematic configuration of a conventional image processing apparatus. It is a figure. In the figure, 1 ... Input sensor section, 2 ... A / D converter, 3 ...
Gradation correction circuit, 4 ... Character processing circuit, 5 ... Halftone processing circuit, 6 ... Image data, 8 ... Character area determination circuit, 9
...... Judgment signal, 10 ...... Switch, 11 ...... Printer section, 21
...... Binarization circuit, 22 ...... Line buffer, 23 …… Judger, 24 …… Binarized data, 31 …… Averaging circuit, 32 …… Comparator, 33 …… Density difference detection circuit, 36 …… Corrector, 37 ... average value, 65,66 ... buffer.

Claims (1)

(57) [Claims] 1. Input means for inputting multi-valued image information; identification means for identifying the type of image area of the multi-valued image information;
An image processing apparatus comprising: a halftone processing unit that performs a halftone process on the multivalued image information corresponding to the image area, wherein the identifying unit is an average value of the multivalued image information in a unit of a predetermined pixel block. Calculating means, first comparing means for comparing the average value with the multivalued image information, and second comparing means for comparing a difference between the average value and the multivalued image information with a predetermined threshold value. Means, means for converting the multivalued image information into binary data based on the comparison output of the first and second comparing means, and detection of continuity in the row direction or column direction of the binary data. An image processing apparatus, comprising: a detection unit, wherein the type of the image area is identified based on the continuity of the binary data.