JPH0253185A - Dot area deciding system - Google Patents

Abstract

PURPOSE:To shorten a time, which is needed when pattern matching processing is executed, by deciding whether an attention picture element belongs to a dot area or not on the basis of the number of picture elements in a concentration range, which is determined in advance, to exist in a block to include the attention picture element and spherical picture elements. CONSTITUTION:In block selection processing 3, the block to be composed of MXM picture elements with the attention picture element, which is shown by adding the mark of a double circle, as a center is calculated from the coordinates of this attention picture element. Then, the binarized concentration data of the picture elements, which are included in this block, are counted respectively by counters 41 and 42 in each '1' and '0'. In case of M=9, out of the 9X9=81 picture elements, the picture element of '1' to be shown by slanting lines, namely, a number (a) of the picture elements of low concentration to be counted by the '1' counter 41 is 16 and a number (b) of the picture elements of the high concentration to be counted by the '0' counter 42 is 64, for which 16 corresponding to the number (a) and the number 1 of the attention picture element itself are subtracted from the 81 picture elements. When the condition of (a)<(b), for example, is obtained for decision as the dot area, the condition of (a)=16 and (b)=64 is obtained. Then, since the condition of the (a)<(b) is estab lished, this attention picture element is decided as the picture element to belong to the dot area.

Description

[Detailed Description of the Invention] [Industrial Application Field] When an image containing a mixture of halftone dots and line drawings such as characters is reproduced by copying or the like, the quality of the reproduced image must be adjusted. In order to improve the image quality, it is desirable to perform moiré removal processing on areas that are expressed as halftone dots, and to perform sharpening processing on areas of line drawings such as characters.

Furthermore, even when transmitting images, the efficiency of data compression can be improved by applying encoding processing according to the characteristics of each area as described above.

The present invention relates to a halftone dot area determination method for separating halftone dot areas expressed as halftone dots from areas of line drawings such as other characters, as preprocessing for such processing.

[Conventional technology]

Japanese Patent Laid-Open No. 60-80365 discloses that after manually generated image data is binarized for each pixel using a fixed threshold value, a binarized image of, for example, 5 x 5 pixels including the pixel of interest is stored in advance. A region separation method is described in which a halftone dot area is detected when the number of pixels matching the halftone dot pattern exceeds a certain value.

[Problem to be solved by the invention]

However, in the above-mentioned conventional technology, when performing pattern matching between a binarized image and pre-stored halftone dot patterns, many halftone dot patterns must be prepared in order to perform accurate detection. It is necessary to keep
Therefore, there is a problem in that the time required to perform the pattern matching process becomes long.

[Means to solve problems]

Based on the number of pixels in a predetermined density range existing in a block including the pixel of interest and its surrounding pixels, it is determined whether the pixel of interest belongs to the halftone dot area.

[For production]

In the halftone image area, the density of the image is displayed by the size of the halftone dots, so the density of each pixel is a substantially constant value.

Therefore, if the density of pixels around the pixel of interest is approximately constant, it can be determined that the pixel of interest belongs to a halftone dot area.

〔Example〕

FIG. 1 shows a first embodiment of the present invention, which utilizes the fact that low-density pixels appear less frequently in halftone areas.

Image data consisting of manually generated density data for each pixel is 2
If the density of the pixel is low in the value converting means 1, it is "1";
If it is higher, it is binarized to "0" and then stored in the bitmap memory 2.

In the next block selection process 3, as shown in FIG. 2, a block consisting of MXM pixels centered on the pixel of interest marked with ◎ is calculated from the coordinates of this pixel of interest,
The binarized density data of the pixels included in this block are counted in units of "1" and "0" by counters 41 and 4□, respectively.

This figure 2 shows an example where M=9, and 9X9=8
Among one pixel, the number a of "1" pixels indicated by diagonal lines in Figure 2, that is, pixels with low density counted by the "1" counter 4□, is 16, which is counted by the "0" counter 4□. The number of pixels with high density is 8O-16 = 81 pixels minus 16, which corresponds to the above number a, and the number 1 of the pixel of interest itself.
It becomes 64.

If the condition for determining the pixel as a halftone dot area in the determining means 5 is, for example, a<b, then in this example, a=16°b=64, and the above condition a<b is satisfied, so this pixel of interest is a halftone dot region. It is determined that the pixel belongs to .

FIG. 3 shows a second embodiment that takes advantage of the high frequency of appearance of medium-density pixels in the halftone area. As shown, Th, <'l''h.

H by two thresholds Th and Th2 having the relationship of
, M, and L.

Conversion is performed by the binary converting means 12 so that if this ternary output is H or H, it becomes "0", and if it is M, it becomes 1'. In FIG. 3, the OR circuit 12. This binary conversion means 12 is shown as having a hardware configuration including.

Next, the output of the binary conversion means 12 is temporarily stored in the bitmap memory 13 as in the first embodiment, and in block selection processing 4, a block of M×M pixels centered on the pixel of interest is extracted.

Then, the number C of “1” pixels in this block is “
1" counter 15.1, and the number d of "0" in this block is counted by a "0" counter 15.degree..

For example, the number of pixels of this “1” is 0 of the total number of pixels.
．． If it is 5 or more, it is determined that the pixel belongs to the halftone area,
Moreover, if it is 0.5 or less, it is determined that the pixel belongs to a character area.

To quote the example of a 9 x 9 pixel block in Figure 2, if the number of pixels belonging to the medium density is 41 or more, it is determined that the pixel belongs to the halftone dot area, and if it is 40 or less, it is determined that the pixel belongs to the halftone dot area. It is determined that the pixel belongs to an area other than the point area.

Note that although the above embodiment has been explained as using a bitmap, this is for the purpose of making it easier to understand, and does not require, for example, that the data be developed as a bitmap on a bitmap memory. It goes without saying that the threshold value for binarization or ternarization, or the threshold value for determining a halftone area can be set as appropriate.

〔Effect of the invention〕

According to the present invention, a special effect is achieved in that it is possible to easily and efficiently determine whether a pixel belongs to a halftone dot area and a pixel belongs to an area other than the halftone dot area, such as a character area.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing an embodiment of the present invention, Fig. 2 is a diagram showing an example of a block, Fig. 3 is a diagram showing another embodiment of the invention, and Fig. 4 is a diagram showing an example of ternarization. It is a diagram.

Claims (1)

[Claims] The present invention is characterized in that it is determined whether or not the pixel of interest belongs to a halftone dot area based on the number of pixels in a predetermined density range existing in a block including the pixel of interest and its surrounding pixels. Halftone area determination method.