JPS63205237A - Image processing apparatus - Google Patents

Abstract

PURPOSE:To perform the binarization processing in accordance with the type of an image, by converting multivalue image data to binary data on the basis of the compared outputs of the first and second comparing means and detecting the continuity of the binary data in line and row directions. CONSTITUTION:A character processing circuit 4 compares a specific threshold value with image data 6 to sharply output the image of a character or line drawing. A medium constrast processing circuit 5 successively compares the threshold value shown by a dither matrix with the image data 6 according to a dither method to reproduce the medium contrast image of a photograph or the like with good gradation. In a character region judge circuit 8, the multivalue image data 6 are converted to binarized data 24 by a binarization circuit 21 and the binary data 24 corresponding to three lines are stored in a line buffer 22. A judge device 23 sets a judge signal 9 to '1' and sets the same to '0' at the time of a medium contrast region. A switch 10 is changed over by the judge signal 9 and the output of the processing circuit 4 or 5 is outputted to a printing part 11.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] 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] As shown in FIG. 7, in a conventional image processing apparatus of this type, an input sensor 71 such as a CCD reads a document, and the image data is converted into a digital signal by an A/D converter. This digital signal undergoes gradation correction such as contrast adjustment in a gradation correction circuit 73, is converted into a dot ON10FF signal in a binarization circuit 74, and is output as an image by a binary printer 75. There is.

Typical binarization methods in the binarization circuit 74 include:
There are a method of binarizing using a fixed threshold value (fixed threshold method) and a method of binarizing using a dither method.

The former method provides good image quality when reproducing characters, line drawings, etc. in a document, but there is a problem in that halftone areas such as photographs in the document lose gradation and the image quality deteriorates. On the other hand, in the latter case, the gradation quality in the half-tone area is improved, but the problem is that the image quality deteriorates due to cut-off of characters and line drawings and the occurrence of moiré fringes in halftone photographs with a certain number of screen lines.

[Problems to be solved by the invention] For this reason, when characters, line drawings, photographs, and halftone photographs coexist in the same document, each image area is identified and the optimal binarization process corresponding to that area is performed. It is necessary to apply That is,
For text and line drawings, focus on resolution over gradation 2
For halftone images such as photographic images, a binarization method that emphasizes gradation rather than resolution is used. On the other hand, for halftone photographs, it is necessary to suppress high-frequency components of the image that cause moiré, and then apply a binarization method that produces 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 device that can identify the type of image area so that image data suitable for each image area can be binarized. shall be.

[Means for Solving the 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 multi-value image information, identification means for identifying the type of image area of the multi-value image information, and binarization for binarizing the multi-value image information corresponding to the image area. an image processing device comprising: means for calculating an average value of the multivalued image information in units of predetermined pixel blocks; and a calculation means for comparing the average value with the multivalued image information. a first comparison means, a second comparison means that compares the difference between the average value and the multi-value image information with a threshold value, and a second comparison means that compares the difference between the average value and the multi-value image information with a threshold; means for converting intermediate machine information into binary data;
and detection means for detecting continuity of the binary data in the row direction or column direction.

[Operation] In the above configuration, the identification means calculates the average value of the multi-value image information in a predetermined pixel block, compares the average value with the multi-value image information, and compares the average value with the multi-value image information. Compare the difference with the threshold. Multivalued image information is converted into binary data based on the comparison outputs of the first and second comparison means, continuity of the binary data in the row direction or column direction is detected, and based on the continuity, Identify the type of image region. Based on this identification information, it operates to perform processing corresponding to the type of image data.

[Embodiments] Hereinafter, embodiments of the present invention will be described in detail 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 this embodiment.

For example, an image signal photoelectrically read by an input sensor section 1 such as a CCD is converted into digital image data by an A/D converter 2. For example, if the A/D converter is 8 bits, the digital image data 7 will be a density signal of 256 gradations. The gradation correction circuit 3 performs gradation processing such as contrast adjustment and brightness adjustment on the input image data, and outputs gradation-corrected image data 6.

The tone-corrected image data 6 is input to a character processing circuit 4, a halftone processing circuit 5, and a character area determination circuit 8. This character area determination circuit 8 determines whether the area is a character area or a halftone area, and by outputting a determination signal 9 and switching a 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 and 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 "O" when the image data 6 is smaller. Images such as characters and line drawings are clearly output.On the other hand, the halftone processing circuit 5 uses a dither method to sequentially compare the darkness values indicated by the dither matrix with the image data 6, and when the image data 6 is large, '1' is output; conversely, when image data 6 is smaller, '0' is output. Thereby, halftone images such as photographs can be reproduced with good gradation. Further, in the halftone processing circuit 5, after removing high-frequency components of the image that cause moiré in the halftone image using a low-pass filter such as a smoothing filter, a good image with less moiré is obtained for performing the dither processing described above. Can be reproduced.

[Description of character area determination circuit (FIGS. 2 to 6)] FIG. 2 is a block diagram of the character area determination circuit 8, and parts common to those in FIG. 1 are designated by the same reference numerals.

Reference numeral 21 denotes a binarization circuit whose detailed block diagram is shown in FIG. 22 is a line buffer containing line buffers for at least three lines, and the binarized data 24
is input and three lines of binary data 24 are stored. The determiner 23 checks the continuity of black "1" pixels in the binarized data 24, and if there is continuity, determines the determination signal 9 as a character area.
1", and when there is no continuity, the judgment signal 9 is set to "0" as a halftone area. Therefore, the switch 10 sets the judgment signal 9 to "0".
When is "1", it is switched to the a side, and when it is "o", it is switched to the b side.

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 and outputs the average value 37 of the image density of the m×n pixel block. The comparator 32 compares the average value 37 and the image data 6, and when the image data 6 is larger, it is 1°°, and when it is smaller, it is 1°.
A signal 34 of "0" is output. Also, a concentration difference detection circuit 33
Then, the difference between the image data 6 and the average value 37 is taken, and when this difference is larger than the threshold value, a signal 35 of 1° is output, and when it is smaller, a signal 35 of “0” is output.

This relationship is expressed as follows.

l D-AV l≦T ・B=O +D-AVI>T ・B=1 Here, D is the value of the image data 6, AV is the average value, and T is the threshold value.

FIG. 4(A) is a diagram showing the relationship between the input signal and the output signal in the corrector 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 a continuous tone photographic area or the background area, and the area where the signal 35 is "1" is the area where the local density difference of the image is small. This area is large and corresponds to the halftone image area and character area. As is clear from the figure, when the signal 35 is 0'', the binary data 24 that is the output of the corrector 36 becomes 1'', and when the signal 35 is 1'', the binary data 24 corresponds to the signal 34. converted data 24 is determined.

The binarized data 24 obtained in this manner allows separation of halftone dots and black pixel portions of characters.

FIG. 4(B) is a diagram showing a specific circuit example of the corrector 36.

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

Therefore, to separate a halftone image and a character image, count the continuity of black pixels in the row and column directions, set the image area with a predetermined continuity as a character area, and set the image area without continuity as a halftone area. It turns out that it is sufficient to judge that.

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

Three pixels of the horizontally continuous pixel column 61 are ANDed by an AND circuit 63, and when three consecutive pixels are "1", data "1" is stored in the buffer 65. On the other hand, the vertically continuous pixel column 62 is connected to the vertically continuous pixel column 62 by an AND circuit 64.
The AND for the pixels is taken, and three consecutive pixels in the column direction are "1".
”, data '1' is stored in the buffer 68.

AND circuits 67 and 68 each read three consecutive pieces of data from buffers 65 and 66, and when the three consecutive pieces of data are all 1'', their output becomes ``1''.

Since the OR circuit 69 takes the logical sum of the outputs of the AND circuits 67 and 68, if either the horizontal direction or the vertical direction is continuous, it is determined that it is a character or line drawing area, and the judgment signal 9 is output.
becomes 1″.

By executing this determination process by the determiner 23 while shifting one pixel at a time, it is possible to perform area determination over the entire input image area.

In this example, continuity of 3 pixels in the horizontal and vertical directions was detected, but by detecting continuity of more pixels (for example, about 5 pixels) and in two diagonal directions, even higher precision can be achieved. Good character detection becomes possible.

As explained above, according to this embodiment, by identifying photographic areas, character areas, and halftone photographic areas, and selecting and printing out data that has been subjected to binarization processing corresponding to the type of each area, , it has become possible to obtain images of good quality no matter what type of image.

[Effects of the Invention] As described above, according to the present invention, the type of image data can be determined and the binarization process corresponding to the type of image can be performed.

[Brief explanation of the drawing]

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 the character area determination circuit. , FIG. 4(A) is a diagram showing the relationship between input and output data of the corrector, FIG. 4(B) is a diagram showing a specific circuit example of the corrector, and FIGS. 5(A) and (B) are FIG. 6 is a block diagram of a determiner that detects the continuity of black pixels, and FIG. 7 is a block diagram showing a schematic configuration of a conventional image processing device. It is a diagram. 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...Judgment device, 24...
Binarized data, 31... Averaging circuit, 32... Comparator, 33... Concentration difference detection circuit, 36... Corrector, 3
7...Average value, 65.66...Buffer. Figure 3 (A) (B) Figure 5 Figure 4 (A) Figure 4 (8)

Claims (1)

[Scope of Claims] Input means for inputting multivalued image information, identification means for identifying the type of image area of the multivalued image information, and binarization of the multivalued image information corresponding to the image area. an image processing device comprising: a binarization means for converting the multi-value image information into a binary image; a first comparison means for comparing the difference between the average value and the multivalued image information with a threshold; and a second comparison means for comparing the difference between the average value and the multivalued image information with a threshold, means for converting the multivalued image information into binary data;
Detecting means for detecting continuity of the binary data in the row direction or column direction, and the type of the image area is identified based on the continuity of the binary data. Device.