JPH0678140A - Picture processor - Google Patents

Abstract

PURPOSE:To prevent the loss in the shapes of character or line drawing edges in the binarization processing of the error diffusing system which reduces the occurrence of moire. CONSTITUTION:A comparator 2a as the binarizing means of the error diffusing system, a comparator 2b as the simple binarizing means of the simple binarizing system, a correlation discriminating circuit 8 which discriminates character or line drawing edges in two-dimensional direction with a noticed picture element as the center, and a selector 5 which selects the binarized signal of the comparator 2a or the comparator 2b as the discrimination result are provided. An inputted picture signal is binarized by the error diffusing system and the simple binarizing system and is inputted to the selector 5. The selector 5 selects the binarization processing adapted to the input picture signal by a discrimination signal (s) from the correlation discriminating circuit 8 which indicates whether the periphery of the noticed picture element is the edge of a character or a line drawing or not.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing apparatus for processing a read image signal in an image scanner, a facsimile and the like, and more particularly to an image processing apparatus for performing binarization processing by an error diffusion method.

[0002]

2. Description of the Related Art Halftone dot processing and systematic dithering method are widely used as a processing method for pseudo-representing an image including continuous gradation by a binary image. In addition to these processing methods, an error diffusion method has been used in recent years.

A conventional image processing apparatus using this error diffusion method stores an error between an input and an output when a pixel around a target pixel is binarized, and binarizes the target pixel. Sometimes, the error is utilized to match the average luminance level between the input image and the output image to express pseudo halftone. B. Proposed by Schroder. ("Images From Comp
uters ", IEEE Spectrum, vol.
6, 1969) Since halftone dots are widely used in ordinary printed matter to express pseudo halftone, moire may occur when handled as a document such as an image scanner or a facsimile.

This moiré is noticeable when the halftone dot period of the input image and the sampling period of the image input device are close to each other or have an integral multiple relationship. Moire appears as a striped pattern that does not exist in the input image at all, which not only embarrasses the operator but also deteriorates the image quality.

The mechanism of moire generation is described in J.
M. It is described in detail by White. ("Re
center Advances in Threshold
ding Technologies for facsi
Mile ", Journalof Applied P
photographic Engineering, A
pr. 1980)

This conventional image processing apparatus stores the error between the input and the output when the peripheral pixels of the target pixel are binarized, and binarizes the target pixel. Sometimes the error is utilized to match the average luminance level between the input image and the output image to express a pseudo halftone, so that the moire reduction effect on the halftone dot original is great, but On the other hand, there is a drawback that the edge shapes of characters and line drawings are destroyed, so the operator has to decide whether or not to use selectively for images in which halftone pictures and characters and line drawings are mixed. There is a point.

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image processing apparatus which solves the above problems and reduces the edge collapse of a character / line drawing.

[0007]

An image processing apparatus according to the present invention is an image processing apparatus for inputting an image signal represented by halftone or pseudo-halftone and performing binary image processing, in which the input image signal and the binary image are processed. Detecting the error with the output binary image signal of the binarizing means, the binarizing means by the error diffusion method realized by adding the error to the next input image signal,
A simple binarizing means for the input image signal by a simple binarizing method, a judging means for judging a character / line drawing edge in a two-dimensional direction centering on a pixel of interest, and an error diffusion method by the output of this judging means. And a selection means for selecting either the binarized image signal or the binarized image signal according to the simple binarization method.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings.

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

[0010] In FIG. 1, a delay circuit 4 for outputting a delay error signal D ₅ delayed one pixel of the error signal D _4, a multi-level image signal D ₀ inputted from an input terminal T ₁ and the delay error signal D ₅ an addition circuit 1a outputs the multi-valued image signal D ₁ by adding the threshold T for the error diffusion method multivalued image signal D ₁
And Konpereta 2a which was binarized compared to H ₁ outputs a binary image signal D _2, multi-value image signals D ₁ and comparator 2
and a sign inverting circuit 3 and the output signal D ₃ and the multi-level image signal D ₁ of the sign inversion circuit 3 inverts a binary image signal D ₂ for detecting an error between the binary image signal D ₂ of the output of a An error detecting means comprising an adder circuit 1b for adding (when the input image signal D ₁ is on the white side of a preset threshold value TH ₁ the difference between the input image signal D ₁ and the perfect white level is regarded as the white side error, When the value is on the black side of the threshold value TH ₁ , the difference from the full black level is output as a black side error.), The input multi-valued image signal D ₀ and the threshold value TH for the simple binarization method.
Binary image by a simple binarization method compared to _second image signals D ₆
And a register 6a for storing predetermined pixel signals adjacent to each other around the target pixel in the two-dimensional direction via the line memories 7a to 7d pixel by pixel.
˜6e, a correlation determination circuit 8 that determines the correlation in the two-dimensional direction in the pixel signals output from the registers 6a to 6e, and outputs a signal indicating the correlation, and the determination of the correlation determines whether the character / line drawing In the case of an edge, the binarized image signal D ₆ of the binarization processing by the simple binarization method is output, and in the case other than the character / line drawing edge, the binarization by the error diffusion method is binarized. And a selector 5 that appropriately selects the output of the image signal D ₂ .

In FIG. 1, in this embodiment, a function of determining whether or not the target pixel is an edge of a character / line drawing by referring to a peripheral area of the target pixel and a two-dimensional area of 5 pixels × 5 pixels have.

Next, the operation of this embodiment will be described.

[0013] In FIG. 1, the input terminal T ₁ is input multivalue image signal D _0, the input terminal T ₂ Error diffusion threshold value TH ₁ is input. The adder circuit 1a adds the multi-valued image signal D ₀ and the error signal D ₅ supplied from the delay circuit 4, and supplies the multi-valued image signal D ₁ to the comparator 2a and the adder circuit 1b.

The comparator 2a has a threshold value TH ₁ for the error diffusion method applied to the input terminal T ₂ and a multi-valued image signal D ₁
Are compared and binarized to supply the binary image signal D ₂ to the selector 5 and the sign inverting circuit 3. Sign inversion circuit 3
Converts the binary image signal D ₂ from a positive value to a negative value and supplies it to the adding circuit 1b.

The adder circuit 1b adds the multi-valued image signal D ₁ and the negative binary image signal D ₃ and supplies a new error signal D ₄ to the delay circuit 4. The delay circuit 4 has a delay of one pixel.

By repeating the above operation, the binary image signal in which the error in the error diffusion method is corrected is sequentially input to the selector 5.

On the other hand, the multi-valued image signal D ₀ input from the input terminal T ₁ is binarized by the threshold value TH ₂ for the simple binarization method input from the input terminal T ₃ in the comparator 2b. The signal D ₆ is input to the selector 5.

Here, the line memories 7a to 7d and
The shift registers 6a to 6e output pixel signals for referencing the peripheral 5 pixels centering on the pixel of interest, and the correlation determination circuit 8
At, it is determined whether or not it is an edge of a character / line drawing, and the result is supplied to the selector 5 as a determination signal S. The correlation determination circuit 8 is composed of a ROM or the like. In the selector 5, in response to the determination signal S from the correlation determination circuit 8, in the case of a character / line drawing edge, the simple binarization method output
If it is not a line drawing edge, the error diffusion method is selected.

FIG. 2 shows an example of character / line drawing edge judgment by the correlation judging circuit according to this embodiment. FIGS. 2 (a) to (d) are diagrams showing the case of character / line drawing edges, and (e) to (h) are shown. It is a figure which shows the case where it is not a character line drawing edge.

In the above-described embodiment, the error diffusion method that refers to one pixel is taken as an example, and the determination of the edge of the character / line drawing is explained by taking 5 pixels × 5 pixels as an example. However, even if more pixels are referred to. The present invention can be similarly implemented.

[0021]

As described above, the pixel processing apparatus of the present invention is an image processing apparatus which receives an image signal represented by halftone or pseudo-halftone and performs a binary image processing, in combination with the input image signal. Binarizing means by an error diffusion method realized by detecting an error from the binary image signal output from the binarizing means and adding the error to the next input image signal, and an input image by the simple binarizing method Means for simple binarization of signals,
A determination means for determining a character / line drawing edge in a two-dimensional direction centering on the pixel of interest, and an output of this determination means whether the image is a binary image signal by an error diffusion method or a binary image signal by a simple binary method. By providing the selecting means for selecting either one, it is possible to reduce the edge collapse of the character / line image, reduce the occurrence of moire in the halftone dot photograph portion, and improve the quality of the output binary image. Have.

[Brief description of drawings]

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

FIG. 2 shows an example of character / line drawing edge judgment by a correlation judging circuit in the present embodiment, (a) to (d) are diagrams showing a case of character / line drawing edges, and (e) to (h) are characters / line drawing edges. It is a figure which shows the case where it is not a line drawing edge.

[Explanation of symbols]

S determination signal T _1, T _2, T ₃ input terminal T ₄ output terminals 1a, 1b adder circuit 2a, 2b comparator 3 sign inverting circuit 4 delay circuit 5 selector 6a~6e shift register 7a~7d line memory 8 correlation determination circuit

Claims (1)

[Claims] 1. An image processing apparatus for inputting an image signal represented by a halftone or pseudo halftone and performing a binary image processing, wherein an error between an input image signal and an output binary image signal of a binarizing means is eliminated. The binarizing means by the error diffusion method realized by detecting and adding the error to the next input image signal, the simple binarizing means of the input image signal by the simple binarizing method, and the target pixel Characters in the two-dimensional direction centered on
A determination means for determining a line drawing edge, and a selection means for selecting either a binarized image signal by the error diffusion method or a binarized image signal by the simple binarization method by the output of the determination means. An image processing apparatus comprising: