JPH01222575A - Binarizing circuit for picture signal - Google Patents

Abstract

PURPOSE:To reproduce an original with mixture of a character and an intermediate tone picture with excellent picture quality by outputting a character or an intermediate tone binarizing signal selectively in the unit of picture elements in response to the total sum of density difference absolute values between a noted picture element and its adjacent picture elements. CONSTITUTION:An output of the 1st binarizing circuit 3 deciding the white or black level of the noted picture element is selected depending on an output of a 2-dimension edge emphasis circuit 2 giving an emphasis signal emphasizing the density of the noted picture element in response to the density difference between the noted picture element and the adjacent four picture elements and on an output of an averaging circuit 1 giving a density mean value in the area around the noted picture element. Moreover, the output of a dither circuit 4 giving the 2nd binarizing signal being the result of binarizing the noted picture element based on the threshold level of the dither matrix varying periodically in the main scanning and the subscanning directions is outputted by selecting with the output of the differential circuit 6 outputted the total sum of the density difference absolute value between the noted picture element and the adjacent 4 picture elements. Thus, the intermediate tone and the character are reproduced in an excellent way.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an image signal binarization circuit, and more particularly to an image signal binarization circuit that reads and binarizes a document containing halftones.

[Conventional technology]

FIG. 2 is a block diagram of an example of a conventional image signal binarization circuit, and FIG. 3 is a layout diagram of four pixels adjacent to a pixel of interest. This will be explained with reference to FIGS. 2 and 3.

Four pixels a· adjacent to the image signal 32 of the pixel of interest X.

A two-dimensional edge emphasis circuit 22 outputs an emphasis signal 35 that emphasizes the density of the pixel of interest X according to the density difference with the image signals 31 and 33 of b, c, and d, and peripheral pixels a to d of the pixel of interest X.
an average value circuit 21 that outputs an average density value 34 of the density average value 34; and a binarization circuit 23 that outputs a first binary signal 36 that determines black and white of the pixel of interest X based on the emphasis signal 35 and the average density value 34.
and a dither circuit 24 that compares the image signal 32 of the pixel of interest X with a threshold value of a dither matrix that changes periodically in the main scanning and sub-scanning directions and outputs a second binary signal 37, and a switching signal 38. The selector circuit 25 outputs a signal 39 selecting the first or second binary signal.

[Problem to be solved by the invention]

The conventional image signal binarization circuit described above switches and outputs the first binarized signal 36 for a character original and the second binarized signal 37 for a halftone original.
There is a problem in that when the digitized signal 36 is selected, halftones cannot be reproduced well, and when the second binary signal 37 is selected, characters cannot be reproduced well.

[Means to solve the problem]

The image signal binarization circuit of the present invention includes a two-dimensional edge emphasis circuit that outputs an emphasis signal that emphasizes the density of the pixel of interest according to the density difference between the pixel of interest and four adjacent pixels; an average value circuit that outputs a density average value of a surrounding area; a binarization circuit that outputs a first binary signal that determines whether the pixel of interest is black or white based on the emphasis signal and the average density value; and the pixel of interest. and a differential circuit that outputs the sum of the absolute value of the density difference between the pixel and four adjacent pixels; The present invention includes a dither circuit that outputs two binary signals, and a selector circuit that selects and outputs the first or second binary signal according to the total sum value.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a block diagram of one embodiment of the present invention.

Four pixels a adjacent to the pixel of interest X and the image signal 12.

A two-dimensional edge emphasis circuit 2 that outputs an emphasis signal 15 that emphasizes the density of the pixel of interest X according to the density difference with the image signals 11.13 of b, c, and d, and peripheral pixels a% d of the pixel of interest X
an average value circuit 1 that outputs a density average value 14 of , and a binarization circuit 3 that outputs a first binarized signal 16 that determines whether black or white of the pixel of interest X is determined based on the emphasis signal 15 and the density average value 14;
A dither circuit 4 that compares the image signal 12 of the pixel of interest X with a threshold value of a dither matrix that changes periodically in the main scanning and sub-scanning directions and outputs a second binary signal 17;
and the image signals 11.13 of the four adjacent pixels a to d.
8, the first or second binarized signal 16 or 17
and a selector 5 that outputs a signal 19 selecting the selected one.

Next, the operation will be explained. Multivalued image signal 11°12.
13 is input to the average value circuit 1 and the two-dimensional edge emphasis circuit 2. The image signal 12 indicates the density of the target pixel X shown in FIG. 3, the image signal 11 indicates the density of pixels a and b one line before and after the target pixel The density of right pixels c and d is shown.

The two-dimensional edge enhancement circuit 2 selects a pixel of interest X and four surrounding pixels a.
, b, c, and d, an emphasized signal 15(y) is output, which has been corrected by calculations such as equation (1).

y=2x-0, 25(a+b+c+d)-(1) FIG. 4 is a layout diagram showing an example of the pixels in the peripheral area of the pixel of interest. X is the pixel of interest, x-1...x+5 and x+1...x
+5 is the pixel column on the left and right of X, a-5...a+5 and b-
5...b+5 are pixel columns one line before and after the pixel column of X, and a total of 33 pixels are arranged, including 11 pixels in the main scanning direction and 3 pixels in the sub-scanning direction. Average value circuit 1 is 3
Average density value data from image signals 11 to 13 of 3 pixels (2)
The density average value 14 obtained by calculating the formula is output.

The binarization circuit 3 converts the density average value 14(x) and the emphasis signal 14
A first binary signal 16 is output in which black and white of the pixel of interest X is determined according to the value of (y).

FIG. 5 is a correlation diagram between the density average value r and the emphasis signal 15 for explaining the operation of this embodiment. When data and y are above the polygonal line i shown in FIG. 5, the black level is binarized, and when it is below, the white level is binarized, and the first binarized signal 16 corresponding to a character original is output.

The dither circuit 4 is a circuit corresponding to a halftone original, and compares the image signal 12 of the pixel of interest with a preset threshold of a dither matrix and outputs a second binary signal 17 capable of reproducing halftones. .

The difference circuit 6 calculates the sum value 18 (L) of the absolute value of the density difference between the pixel of interest and four adjacent pixels using equation (3).

L= l x-a l + l x-b l+ l x
−c l + l x−d l −(3>This total value (L) is a parameter for determining whether the image to be read is a character or a halftone image. In other words, if the value of (L) is large, it is a character image. , if it is small, it is determined that it is a halftone image.

In this way, the selector 5 can output the signal 19 of the first or second binarized signal 16 or 17 depending on the summation value 18 (L). .

〔Effect of the invention〕

As explained above, the present invention selects and outputs a binary signal of a character or a halftone in pixel units according to the sum total of the absolute value of the density difference between a pixel of interest and an adjacent pixel. This has the effect of reproducing originals with mixed tones with good image quality.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 is a block diagram of an example of a conventional image signal binarization circuit, FIG. 3 is a layout diagram of four pixels adjacent to a pixel of interest, and FIG. The figure is a layout diagram showing an example of the pixels in the peripheral area of the pixel of interest, and FIG. 5 is a correlation diagram between the density average value X and the emphasis signal 15 for explaining the operation of this embodiment. 1.21...Average value circuit, 2.22...Two-dimensional edge emphasis circuit, 3.23...Binarization circuit, 4,24...
- Dither circuit, 5.25...Selector, 6...Differential circuit.

Claims (1)

[Claims] a two-dimensional edge emphasis circuit that outputs an emphasis signal that emphasizes the density of the pixel of interest according to the density difference between the pixel of interest and four adjacent pixels; and an average value circuit that outputs an average density value of the surrounding area of the pixel of interest. a binarization circuit that outputs a first binarized signal that determines whether the pixel of interest is black or white based on the emphasis signal and the average density value;
a difference circuit that outputs a total value of the absolute value of the density difference with the pixel;
The pixel of interest is binarized based on the threshold value of the dither matrix that changes periodically in the main scanning and sub-scanning directions.
An image signal binarization circuit comprising: a dither circuit that outputs a digitized signal; and a selector circuit that selects and outputs the first or second binarized signal according to the total sum value.