JPS614370A - Picture processing system - Google Patents

Abstract

PURPOSE:To obtain pictures of high quality and reduce influences of erroneous discrimination by making a sharp distinction between character areas and half- tone areas with respect to picture blocks and applying OR data between binarized picture data and picture data subjected to dither processing to blocks of character areas. CONSTITUTION:Picture information in a block memory 11 is binarized with a certain threshold of a fixed threshold memory 12 by a fixed threshold binarizing circuit 13 and is stored in a binary picture memory 16, and meanwhile, picture information in the block memory 11 is subjected to dither processing by an organic dither processing circuit 15 and is stored in a binary picture memory 17. A picture quality discriminating circuit 20 refers to picture information in the memory 11 to discriminate a noticed block as a half-tone area or a character area and transmits the discrimination signal to a selecting circuit 19. If the discrimination signal indicates a half-tone area, the circuit 19 outputs the binary picture in the memory 17; but if this signal indicates a character area, the circuit 19 obtains the signal of OR between binary pictures stored in memories 16 and 17 by an OR circuit 18 and uses this signal as the output signal.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to an image processing method that obtains a halftone image through binarization processing.

More specifically, the present invention divides an image into blocks each consisting of a plurality of pixels, determines whether each block is a character area or a halftone area, and applies a different image reproduction method to each block. The present invention relates to an image processing method to which the present invention is applied.

[Prior art]

Conventionally, in this type of image processing method, ■ For a block determined to be a character area, a binary image is output by converting the original image information into a binary image using a predetermined fixed threshold; For blocks determined to be regions, a binary image obtained by subjecting the original image information to systematic dithering and converting it into a binary image is output.

FIG. 1 is an example of original image information, and shows an example in which a character image with a pixel value of 180 appears at the right end of a halftone image with pixel values of 50 to 60. The image shown in the first figure is divided into blocks of 4 pixels vertically and 8 pixels horizontally, and each block is determined whether it is a halftone area or a character area based on the difference between the maximum value and minimum value within the block. (Unexamined Japanese Patent Publication No. 1983)
As shown in FIG. 2, the left block is determined to be a halftone area (H), and the left block is determined to be a character area (B).

FIG. 3 is an example of a systematic dither matrix with 32 thresholds. 4(A) is an image obtained by binarizing the original image shown in FIG. 1 with a fixed threshold value of 128, and FIG. 4(B) is an image obtained by converting the original image shown in FIG. An image obtained by binarizing the original image shown in the figure is shown.

FIG. 4(C) is a result of combining and outputting the images of FIG. 4(A) and FIG. 4(B) block by block according to the determination results shown in FIG. 2. Here, since the left block in FIG. 1 is determined to be in the halftone area, the left block in FIG. 4(B) is selected for the left block in FIG. 4(C),
In addition, since the right block in Figure 1 has been determined to be a character area, the right block in Figure 4 (C) is compared to Figure 4 (A).
The right block is selected.

Due to such area determination, the deterioration of the text portion that occurs noticeably in the systematic dither processing (see black area 5 shown in FIG. 4) is greatly improved as seen in black area 8.
On the other hand, the intermediate tone around the characters 4 ＃(ah...oo4□
, 1,141m (C 43), and as a result, the area around the literature section becomes white, creating a discontinuity with the background, resulting in an extremely unnatural reproduced image.

〔the purpose〕

The purpose of the present invention is to obtain high-quality reproduced images and The objective is to provide an image processing device that can perform

Another object of the present invention is to define a halftone area as a character area. The present invention is characterized in that logical sum data of image data that has been binarized using a predetermined fixed threshold value and image data that has been dithered is applied to the image block that has been determined to be.

The present invention will be described in detail below with reference to the drawings.

〔Example〕

FIG. 5 is a block diagram showing one embodiment of the present invention.

In this figure, 9 and 10 are image memories that store image information, 11 is a block memory that is connected to the image memories 9 and 1O and takes out the image information of the block of interest, 12 is a memory that stores a fixed threshold value, and 13 is a block memory that stores image information. A fixed threshold binarization circuit that binarizes the image information in the block memory 11 using a threshold value in the memory 12; 14 is a memory that stores the threshold value of an organized dither matrix; 15 is a block according to the contents of the memory 14; Circuits 16 and 17 that perform systematic dither processing on image information in memory 11
is a memory for storing a binary image; 18 is a logical sum circuit that calculates a logical sum; and 19 is a logical sum circuit that selects the output of the logical sum circuit 18 or the output of the binary image memory 17 based on a judgment signal from the image quality judgment circuit 20. A selection circuit 20 is an image quality determination circuit that determines whether the area is a halftone area or a character area based on the contents of the block memory 11, and 21 and 22 are switches.

In this configuration, when the switches 21 and 22 are in the first position, image information read from the original is stored in the image memory 9. When the l block is composed of 4 x 8 32 pixels, the switch 21 is switched from the a side to the b side, and the switch 22 is switched from the b side to the a side at the time when image information corresponding to 4 scanning lines is stored. In turn, this allows continuous input and continuous processing.

The contents of image memories 9 and 10 are transferred to block memory 11 in l block units. Further, the image information in the block memory 11 is stored in the fixed threshold memory 12 by the fixed threshold value binarization circuit 13, is binarized with a certain threshold value, and is stored in the binary image memory 16. At the same time, systematic dither processing is performed by the systematic dither threshold memory 15 and stored in the binary image memory 17.

The image quality determination circuit 20 refers to the image information in the block memory 11, determines whether the blow 2 of interest is a halftone area or a character area, and sends a determination signal to the selection circuit 19.

The selection circuit 19 outputs the binary image stored in the binary image memory 17 when the determination signal indicates a halftone area, and on the other hand, outputs the binary image stored in the binary image memory 17 when the determination signal indicates a character area. A signal obtained by ORing the binary images stored in the image memories 1B and 17 is sent to the OR circuit 18.
This is used as the output signal.

When the image information shown in the first figure is input to the embodiment shown in the fifth figure, the image information is first stored in the image memory 9 or 10. When the judgment block is 4×8, the image information of the left block in FIG. 1 is first transferred to the block memory 11.

Assuming that a threshold value 128 is stored in the fixed threshold memory 12, the image information in the block memory 11 is binarized by the fixed threshold z-value converting circuit 13 and stored in the binary image memory 16. Ru. In this case, the contents of the binary image memory 1B are the images shown in the left block of FIG. 4(A).

- Assuming that the dither threshold shown in FIG. 3 is stored in the systematic dither threshold memory 14, the image information in the block memory 11 is subjected to systematic dither processing by the systematic dither processing circuit 15. and stored in the binary image memory 17. The contents of the binary image memory 17 are shown in FIG. 4(B).
This is the image shown in the left block.

In parallel with the above-mentioned binarization process, the image quality determination circuit 20 performs image quality determination based on the contents of the block memory 11, and determines that the image is in the halftone area as shown in the left block of FIG. , sends a signal to the selection circuit 18. Upon receiving the signal determined to be in the halftone area, the selection circuit 18 outputs the contents of the binary image memory 17 as an output signal.

Processing then moves to the right block in FIG. The block memory 11 stores the image of the right blow in FIG.
It reads from 0 and then performs exactly the same processing as described above. In the case of the right block, the binary image shown in the right block of FIG. 4(A) is stored in the binary image memory 16, and the binary image shown in the right block of FIG. 4(B) is stored in the binary image memory I7. This is a binary image shown in the right block of . Further, the image quality determination circuit 20 sends a determination signal indicating that the area is a character area to the selection circuit 18, as shown in the right block of FIG.

The selection circuit 18° that has received the determination signal indicating that it is a character area,
In this case, the output of the OR circuit 18 is selected and used as the output signal.

FIG. 6 is a diagram showing the processing results of the image information shown in FIG. 1. That is, as a result of the processing according to this embodiment, a black area 25 indicating halftone information appears in the right block, which prevents whitening around the character area 26 and significantly improves the image quality.

Here, the image quality determination circuit 20 includes a CPU, a ROM,
.

It can take various forms, such as a microcomputer with RAM or the like, or a logic circuit. For example, when an image quality determination circuit is configured using a microcomputer, the image quality of one program can be determined using the following procedure.

FIG. 7 shows an example of such an image quality determination procedure for identifying a halftone image area when the number of white pixels is equal to mn. First, in step S1, switch 7
1-bit binary image information I* for one pixel is read out from the image memory on the side selected by , and then it is determined whether or not the information corresponds to a white pixel. Here, if the determination is affirmative, the count value C is incremented by +1 and the process proceeds to step S4, and if the determination is negative, the process directly proceeds to step S4. In step S4, it is determined whether or not the reading process for l blocks has been completed, and if it is determined that the reading process has been completed, the process advances to step S5.

In step S5, it is determined whether the count value C is equal to 0 or mn. If the determination is affirmative, step S6
If the determination is negative, the process advances to step S7, in which it is determined that the relevant process is a halftone image area or a z-value image area, and an identification signal to that effect is sent to the selection circuit 16. Send′. Next, in step S8, the count value C is cleared, and the image quality determination process for one block is completed.

In the above embodiment, an example was shown in which the image quality was determined based on the image information stored in the block memory 11, but the method is not limited to such a determination method. The determination may be made using a targeted algorithm.

It is also possible to output dithered data by directly inputting image information as an address into a memory such as a ROM, or to output data processed using a fixed threshold value. .

〔effect〕

As explained above, according to the present invention, for a block determined to be a character area, the logic between image data binarized using a fixed threshold value and image data binarized using a systematic dither method is determined. By using a simple processing method of calculating the sum and outputting it, it is possible to obtain the special effect of preventing the white background around the literature section, maintaining continuity with the halftone area, and greatly contributing to improving image quality.

Furthermore, according to the present invention, even if a halftone area is incorrectly determined to be a character area, the systematic dithering method is used to calculate the binary value (OR with the image), so image quality deterioration due to the incorrect determination is significantly reduced. It is possible to obtain the effect of

[Brief explanation of the drawing]

Figure 1 is a diagram showing an example of image information, Figure 2 is a diagram showing the results of image quality determination, Figure 3 is a diagram showing systematic dither threshold values, and Figure 4 (A).
is a diagram showing an image in which the image information shown in the first figure is binarized using a fixed threshold value of 128, and FIG. 4(C) is a diagram showing an image reproduction state according to the conventional example. FIG. 5 is a diagram showing an embodiment of the present invention. FIG. 6 is a diagram showing an image reproduction state according to the present embodiment. FIG. 7 is a flowchart showing the image quality determination procedure in this embodiment. 910... Image memory, 11... Block memory, 12... Fixed threshold memory, 13... Fixed threshold binarization circuit, 14... Systematic dither threshold memory, 15 ... Systematic dither processing circuit, 18.17 ... Binary image memory, 18 ... OR circuit. 19...Selection circuit, 21, 22...Switch.

Claims (1)

[Claims] An image block consisting of multiple pixels is determined as either a text area or a halftone area, and the image block determined to be a text area is dithered with binarized image data using a predetermined fixed threshold. An image processing method characterized by applying logical sum data with image data.