JP2766031B2 - Image processing apparatus and image processing method - Google Patents

Description

The present invention relates to an image processing apparatus for binarizing image information represented by gradation or multi-valued information.

(B) Conventional technology When image information obtained by an image reading device such as an image scanner or a digital copying machine that optically reads an image of a document is binarized, unnatural irregularities are generated in a portion that is originally a straight line. Or a white or black isolated point of about one pixel may occur.

Therefore, for example, in Japanese Patent Application Laid-Open No. 58-212260, a threshold value for white and a threshold value for black are set in addition to a threshold value for binarizing image information, and unevenness or isolation is set for the binarized image information. An area where a point can occur is determined, and discontinuous pixels and isolated points are corrected in the area by two threshold values.

In addition, a method has been considered in which pattern matching is performed in a specific range centering on a target pixel, and continuity with surrounding pixels is checked to correct image information.

(C) Problems to be solved by the invention However, in the above-mentioned Japanese Patent Application Laid-Open No. 58-212260,
The correction must be performed in both the main scanning direction and the sub-scanning direction, and the correction is performed using a threshold different from the binarized threshold in an area where irregularities and isolated points may occur. Complex and efficient binarization could not be performed.

Also, in correction by simple pattern matching, if the pattern to be determined is small, the number of determination errors increases,
If the pattern to be discriminated is increased to reduce the discrimination error, a large table of the pattern as a reference for comparison is required, and the circuit becomes large in scale.

The present invention has been made in view of such a point, and provides an image processing apparatus and a processing method thereof capable of removing irregularities and isolated points with high accuracy by simple processing using a relatively small pattern matching table. Is what you do.

(D) Means for Solving the Problems An image processing apparatus according to the present invention includes a binarizing unit (1) for binarizing a pixel of image information with a predetermined threshold value, and a difference between the pixel value and the threshold value. Binarization error detection means (5) for outputting a binarization error determination signal indicating a possibility of a binarization error occurring from
Pattern matching means (2) for outputting a continuity judgment signal indicating the continuity between the pixel binarized by the binarization means and its neighboring pixels, and the binarization error judgment signal And inversion control means (6) for inverting the binary information of the pixel based on the continuity determination signal.

Further, the image processing method of the present invention binarizes a pixel of image information with a predetermined threshold, detects a possibility of a binarization error from a difference between the pixel value and the threshold, and performs binarization. Detecting the continuity between the extracted pixel and its binarized neighboring pixels, and inverting the binary information of the pixel according to the possibility of the occurrence of the binarization error and the continuity. And

(E) Function In the present invention, the binarization means (1) binarizes the pixel of the image information with a predetermined threshold value, and indicates a possibility that a binarization error may occur from a difference between the pixel value and the threshold value. A binarization error detection unit (5) outputs a binarization error determination signal, and indicates a continuity between the pixel binarized by the binarization unit (1) and its neighboring pixels binarized. The pattern determination means (2) outputs the gender determination signal, and the inversion control means (6) inverts the binary information of the pixel based on the binarization error determination signal and the continuity determination signal.

Further, in the present invention, the pixels of the image information are binarized with a predetermined threshold, and the possibility of a binarization error occurring is detected from the difference between the pixel value and the threshold, and the binarization is further performed. The continuity between the pixel and its binarized peripheral pixels is detected. Then, the binary information of the pixel is inverted according to the possibility that the binarization error occurs and the continuity.

(F) Embodiment FIG. 1 is a schematic configuration diagram showing an embodiment of an image processing apparatus according to the present invention. In the present embodiment, as shown in FIG. 3, pattern matching is performed using a 9-pixel (3.times.3) pattern including a target pixel as a center and eight neighboring pixels adjacent to the target pixel as a pattern table. Alternatively, pattern matching may be performed using a larger pattern table.

(1) Although not shown, image information from an image reading device such as an image scanner that optically reads an image of a document and outputs image information in which each pixel is represented by multi-valued (or gradation) digital information. Is a binarization circuit as binarization means for binarizing each pixel based on a preset threshold value and outputting image information as binary information.

(2) a pattern matching means for checking the continuity between the pixel of interest and surrounding pixels from a pattern centered on the pixel of interest in the image information binarized by the binarization circuit (1). A pattern matching circuit that outputs a continuity determination signal indicating whether or not to invert the target pixel based on continuity according to a pattern such as whether the target pixel is uneven or an isolated point with respect to surrounding pixels; And a pattern access unit (4) for accessing a pattern table unit (3) using a pattern centered on the target pixel as an address.

The pattern access unit (4) has six latches (4) for storing binary information of pixels for pattern matching.
a) to (4f), two line memories (4g) and (4h) each formed of a shift register for holding image information in the sub-scanning direction, and a latch (4c) for storing binary information of a pixel of interest. Inversion processing section (4i) for inverting the stored binary information of the target pixel in accordance with an inversion control signal described later.
And outputs image information that has been subjected to correction such as removal of irregularities and isolated points.

(5) generates a binarization error determination signal indicating a possibility that a binarization error will occur from the difference between the multi-value information of the pixel of interest and the threshold for binarization in the binarization circuit (1); This is a binarization error detection circuit as binarization error detection means for outputting in five stages (see FIG. 2) according to the difference.

Since the binarization error determination signal is more likely to be erroneously binarized into white or black as the multi-value information is closer to the threshold,
The smaller the absolute value of the difference, the higher the level.
In the present embodiment, it is set that the level 5 is most likely to be erroneously binarized, the level 1 is set as the least likely, and the level 5, the level 4, and the level 3 are set.
At high levels, the width of the corresponding difference is set narrow.

(6) The continuity judgment signal output from the pattern table section (3) of the pattern matching circuit (2) and the binarization error judgment signal output from the binarization error detection circuit (5) are input. As the continuity determination signal indicating that the pixel of interest is an uneven point or an isolated point and needs to be inverted, and the binarization of “5” level that is most likely to cause a binarization error An inversion control circuit as inversion control means for outputting an inversion control signal for inverting the binary signal of the target pixel only when an error determination signal is input.

In such a device, image information (multi-valued information) of an image read by an image reading device such as an image scanner (not shown) is sent to a binarization circuit (1) and a binarization error detection circuit (5). Is entered.

In the binarization circuit (1), each input pixel sequentially performs binarization on image information represented by multi-value information, and each pixel outputs image information of binary information.

Further, in the binarization error detection circuit (5), the difference between the threshold value for binarization in the binarization circuit (1) and the multi-value information of each pixel is obtained, and as shown in FIG. 2 according to the difference
It determines the possibility of occurrence of a binarization error, and outputs a binarization error determination signal of any one of five levels.

The image information binarized by the binarization circuit (1) is input to the pattern matching circuit (2), and the pattern access unit (4) uses, as an address, image information in a range where pattern matching centering on the pixel of interest is performed. From the pattern table unit (3) to determine whether or not the pixel of interest becomes irregularities or isolated points with respect to surrounding pixels and thus lacks continuity. A continuity determination signal indicating the necessity of inverting image information (binary information) of a pixel is output.

The pattern lacking continuity that requires inverting the image information (binary information) of the pixel of interest includes two lines perpendicular to the peripheral pixel, the pixel of interest (FIG. 3A), and the pixel of one line of the peripheral pixel. There are a target pixel (FIG. 3B), only the target pixel (FIG. 3C), and the like. In such a pattern, a continuity determination signal is output to invert the binary information of the target pixel. Of course, a continuity determination signal is also output for inverting the pattern shown in FIG. 3, that is, a pattern rotated by 90 °, 180 °, and 270 ° to invert the binary information of the target pixel.

The inversion control circuit (6) receives the binarization error determination signal from the binarization error detection circuit (5) and the continuity determination signal from the pattern matching circuit (2), and determines the binarization error. If the signal indicates that the binarization error of level 5 is most likely to occur and the continuity determination signal is in a state where the binary information of the pixel of interest should be inverted, the inversion processing unit (4i) And outputs an inversion control signal.

Then, the inversion processing section (4i) inverts and outputs the stored binary information of the target pixel. As a result, a correction is made for an erroneously binarized pixel, such as unevenness or an isolated point, which lacks continuity with surrounding pixels.

For example, in the case of the pattern shown in FIG. 3B, when the target pixel as shown in FIG. 4A should be considered to be incorrectly binarized, the target pixel as shown in FIG. 4B is properly binarized. There are times when you should think. Uniquely, inverting the target pixel in the pattern of FIG. 3B would be inconvenient in FIG. 4B. However, in the present invention, the level of the binarization error determination signal of the target pixel is also referred to. By doing so, the inversion control can be performed with high accuracy.

That is, when the level of the binarization error determination signal is 1 to 4 in the case of the pattern of FIG.
When the binary information of the pixel is not inverted as a binarized one (for example, in a state as shown in FIG. 4B) and the level of the binarization error determination signal is 5, the target pixel is erroneously binarized. Then, the binary information of the pixel is inverted (for example, the state of FIG. 4A).

When unnecessary irregularities and isolated points are often found in the image information (binary information) obtained by performing the correction as described above, the most recent inversion is performed by an input instruction from the operator. It is also possible to make corrections for removing irregularities and isolated points again by setting the levels of the binarization error determination signal to 5 and 4.

(G) Effects of the present invention As apparent from the above description, the present invention
The inversion control of a pixel that is converted into a concavity and convexity or an isolated point is performed based on the possibility that a binarization error may occur based on the difference between the pixel value and a threshold value for binarization. Go by continuity. Therefore, irregularities and isolated points can be removed with high accuracy by simple processing. Further, a relatively small pattern matching table is sufficient for checking the continuity between the pixel and its surrounding pixels, which can contribute to the miniaturization of the circuit.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment of an image processing apparatus according to the present invention, FIG. 2 is a diagram for explaining the level of a binarization error determination signal, and FIG. 3 is a pattern requiring inversion control. FIG. 4 is a diagram showing an example of the state of a pattern matching table and its surrounding pixels. (1) ... binarization circuit (binary means), (2) ... pattern matching circuit (pattern matching means),
(3) ... pattern table section, (4) ... pattern access section, (4i) ... inversion processing section, (5) ... binary error detection circuit (binary error detection means), (6) ... Inversion control circuit (inversion control means).

Claims (2)

(57) [Claims] 1. A binarizing means for binarizing a pixel of image information with a predetermined threshold value, and a binarization error determination indicating a possibility that a binarization error occurs from a difference between the pixel value and the threshold value. A binarization error detection unit that outputs a signal; a pattern matching unit that outputs a continuity determination signal indicating the continuity between the pixel binarized by the binarization unit and its neighboring pixels binarized; An image processing apparatus comprising: an inversion control unit that inverts binary information of the pixel based on the binarization error determination signal and the continuity determination signal. 2. A method for binarizing a pixel of image information with a predetermined threshold value, detecting a possibility of occurrence of a binarization error from a difference between the value of the pixel and the threshold value, and detecting the binarized pixel. Image processing for detecting the continuity of the pixel and its neighboring pixels, and inverting the binary information of the pixel in accordance with the possibility of occurrence of the binarization error and the continuity. Method.