JP3303990B2 - Image signal processing device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image signal processing apparatus which is applied to an image reading apparatus such as a facsimile, a copying machine, etc. and binarizes an image signal.

[0002]

2. Description of the Related Art In the above-mentioned conventional image signal processing apparatus, as shown in Japanese Patent Application Laid-Open No. 60-74775, an image signal is compared with a predetermined threshold value. If it is white, it is binarized. The threshold is usually fixed, but there is also a method of changing the threshold according to a shading waveform to binarize.

[0003]

In the above-described binarization method in the conventional image signal processing apparatus, the threshold value is fixed or only changed according to the shading waveform. Is reduced due to the deterioration of the MTF (modulation transfer function), and the level difference between black and white is reduced.
There is a problem that characters are blurred, broken lines, and broken lines occur.

[0004] It is an object of the present invention to provide an image signal processing apparatus that performs an appropriate binarization process on an image signal.

[0005]

In order to achieve the above object, the present invention provides a plurality of binarizing sections for binarizing an image signal by comparing them with different threshold values, Correspond to each
To set up has been binarized data, respectively before line outputted from the binarization unit, current line, next line and the next pixel, current
As a matrix of 3 × 3 pixels consisting of the pixel and the previous pixel
Output line buffer section and these line buffers
Output pattern and 3x3 image stored in advance
Select a pattern detection section for matrix ratio <br/> compare a predetermined character-line pattern consisting of hydrogen, one of the binarized data from the binarizing unit by comparison of the pattern detection unit And a selector for outputting the data.

[0006] In addition, the selection unit has already selected and decided.
A line buffer for storing the binarized data of the previous line
And stores the binarized data of the previous line in each of the binarized units.
Commonly used for line buffers
Before the line buffer section as a 3 × 3 pixel matrix
The data is output to the pattern detection unit .

Further, in the pattern detecting section, the center
A 3 × 3 pixel matrix with pixels as target pixels
It is characterized by performing a comparison .

[0008]

According to the above means, the image signal is binarized at different threshold values, and each pattern composed of a plurality of pixels of the binarized data for each different threshold value is obtained.
For example, by comparing with a pattern appearing in the outline of a character or a thin line, when the pattern matches, it is determined that the character or the line portion is present, and the corresponding binarized data is selected and output to output a thin character or a thin line. Black level binarized data is reliably output to an image signal, and appropriate binarization processing is performed.

Further, by performing the pattern comparison in a 3 × 3 matrix, efficient pattern comparison can be performed.

A storage unit for storing binarized data by commonly using binarized data relating to a previously selected and determined previous pixel (previous line) as pattern detection data of each binarized data. Can be reduced, and at least one piece of data is already selected and determined, so that the detection accuracy is improved.

[0011]

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

FIG. 1 is a block diagram showing the configuration of a first embodiment of the present invention. Reference numeral 1 denotes an A / D (analog / digital) converter for converting an image signal from an image reading section (not shown) into a digital signal. In this embodiment, all white is set to "0", all black is set to "15", and intermediate levels between them are indicated by "1 to 14".

Further, 2 is a plurality (3 is used in this embodiment)
, Each of the binarization circuits 2 has a different threshold value. In the present embodiment, the threshold values are “8” and “7”.
"6" is set.

Reference numeral 3 denotes a line buffer, which is a storage unit provided two by two in each binarizing circuit 2. The two line buffers 3 and one output line 4 will be described later in detail. 3x
Three matrix data is output.

Reference numeral 5 denotes a pattern detection circuit provided corresponding to each binarization circuit 2. The pattern detection circuit 5 receives the 3 × 3 matrix data of the binarized data. Reference numeral 6 denotes a selection circuit that selects and outputs appropriate binarized data of the binarization circuit 2 based on a comparison result in each pattern detection circuit 5 described later.

Next, the operation of the first embodiment will be described.

An image signal converted into a digital signal by the A / D converter 1 enters three binarizing circuits 2 having different threshold values and is binarized. The data binarized by each binarization circuit 2 is stored in the line buffer 3 and, as shown in FIG. 2, the previous line, the current line, the next line and the next pixel, the current pixel, the previous pixel. And a matrix of 3 × 3 pixels is formed.

In FIG. 2, the center pixel is the pixel of interest (the pixel of interest), and each number indicates an example of the output level of the binarized data. The threshold value of each binarization circuit 2 is "8""7"
Since it is "6", the state of the matrix input to each pattern detection circuit 5 is as shown in FIGS. 3A to 3C at the output level of FIG. 3A to 3C, hatched portions indicate black pixels and white portions indicate white pixels.

That is, in the binarization circuit 2 having a threshold value of "8", one black pixel is provided (FIG. 3A), and in the binarization circuit 2 having a threshold value of "7", the black pixel is provided. In the binarization circuit 2 having three pixels (FIG. 3B) and a threshold value of "6", there are four black pixels (FIG. 3C).

The pattern detection circuit 5 stores typical patterns appearing in thin characters and character outlines shown in FIGS. 4A to 4D. 4A to 4D, a hatched portion indicates a black pixel, and a white background portion indicates a white pixel. In the pattern detection circuit 5, the patterns shown in FIGS.
It is compared and detected whether or not the matrix output which is the comparison target pattern of (c) matches, and the binarization data of the binarization circuit 2 relating to the matched matrix output is selected from the selection circuit 6 according to the comparison result. Is output.

In this embodiment, since the patterns in FIG. 3C and FIG. 4C match, the binarized data from the binarizing circuit 2 with the threshold value "6" is output. If there is no matching pattern or if there are a plurality of matching patterns, a default value is selected.

As described above, binarization is performed on the image signal using a plurality of thresholds, and a pattern that matches a pattern such as a character contour or a thin line is selected from patterns based on the binary data based on each threshold. Therefore, the correspondence between characters and lines corresponding to the binarized data is appropriately determined, and even if the level difference between the black level and the white level is small in the binarized data such as thin characters and lines, the black level Is output accurately, and it is possible to prevent the occurrence of blurred characters, broken lines, and broken lines in the output image.

Further, since the coincidence between the binary data in the matrix and the pattern is detected by the pattern detection circuit 5, efficient and accurate detection becomes possible.

FIG. 5 is a block diagram showing the configuration of the second embodiment of the present invention. The basic configuration is the same as that of the first embodiment. The binarized data is stored and commonly used for the matrix output of FIG. 2, and the number of line buffers provided for each binarizing circuit 2 is reduced. Further, since the binarized data of the previous line is data that has already been selected and determined, the detection accuracy can be improved.

The range of application can be expanded by changing the threshold value of the binarization circuit 2 as appropriate. Further, the number of the binarization circuits 2 is not limited to three in the above embodiment. Similarly, the pattern and matrix outputs are 3
It is not limited to a matrix of × 3.

[0026]

As described in the foregoing, according to the image signal processing equipment of the present invention, by binarizing an image signal at a plurality of different threshold values, the binary data by each different threshold
The previous line, current line, next line and next pixel,
3x3 pixel matrix pattern consisting of pixel and previous pixel
And this matrix pattern is predetermined
By comparing with a predetermined character / line pattern composed of a matrix of 3 × 3 pixels, the determination of the character and line portion of the binarized data, that is, the determination of the black data can be reliably performed. Black level binarized data can be reliably output from the signal, and the occurrence of blurred characters, broken lines, and crushed characters in the output image can be prevented.

The attention of the center pixel of the comparison of the previous Symbol pattern or
Efficient pattern comparison can be performed by using a matrix of 3 × 3 pixels as pixels .

[0028] Furthermore, by using the binary data according to one <br/> and to previous line detection data before Symbol pattern, it is possible to reduce the number of installation such as a line buffer for patterning Moreover, since the binarized data has already been selected and determined, the detection accuracy is improved.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of an image signal processing device according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram of matrix output.

FIG. 3 is an explanatory diagram of each matrix output binarized by different threshold values.

FIG. 4 is an explanatory diagram of a character / line pattern.

FIG. 5 is a block diagram illustrating a configuration of an image signal processing device according to a second embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... A / D converter, 2 ... Binary circuit, 3,13 ... Line buffer, 4 ... Output line, 5 ... Pattern detection circuit,
6 ... Selection circuit.

Claims (3)

(57) [Claims] 1. A plurality of binarization units for comparing image signals with different threshold values and binarizing the image signals, and corresponding to each of the binarization units.
To set up has been binarized data, respectively before line outputted from the binarization unit, current line, next line and the next pixel, current
As a matrix of 3 × 3 pixels consisting of the pixel and the previous pixel
Output line buffer section and these line buffers
Output pattern and 3x3 image stored in advance
Select a pattern detection section for matrix ratio <br/> compare a predetermined character-line pattern consisting of hydrogen, one of the binarized data from the binarizing unit by comparison of the pattern detection unit An image signal processing device, comprising: 2. Before being already selected and determined by the selection unit.
Equipped with a line buffer to store the binary data of the line
The binarized data of the previous line corresponds to each of the binarized units.
This line is used in common for the line buffer
From the in-buffer section as a 3 × 3 pixel matrix
Claim 1 Symbol for and outputs the pattern detection unit
Placing the image signal processing apparatus. 3. A pattern detecting section, comprising : a central pixel;
Pattern ratio in a 3 × 3 pixel matrix with
The image signal processing apparatus according to claim 1 or 2, wherein the configured to perform compare.