JPH08307675A - Image processing unit - Google Patents

Abstract

PURPOSE: To attain binarization for an image in which missing of a thin line or unsharpened edge is not in existence. CONSTITUTION: A picture element discrimination section 11 uses an intermediate tone binarization section 12 being a 1st binarization means to binarize an input image when the picture element level of the input image is within a range between two threshold levels T0 and T1. Furthermore, when the picture element level of the input image is at the outside of the range, a binarization section 13 being a 2nd binarization means executes the binarization.

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 converting a multivalued image into a binary image.

[0002]

2. Description of the Related Art Conventionally, a multi-valued image is converted into a binary image by turning on / off a plurality of pixels of the binary image corresponding to the gradation of each pixel of the multi-valued image. .
In such an image binarization method, a plurality of binary pixels are required to represent one pixel of the input image. Therefore, in order to make the number of pixels of the input image and the output image equal, Need to be thinned out.

As a method of thinning out a multi-valued image, for example,
A method of taking any pixel value in the pixel block as a representative value and a method of taking an average value in the pixel block as a representative value are used.

[0004]

However, in the above-mentioned conventional method, there is a problem that thin lines of an image are missing or edges are blunted by thinning out a multi-valued image.

The present invention has been made in view of the above problems, and it is an object of the present invention to enable binarization of an image without thin lines or blunt edges without reducing the processing speed. Image processing apparatus.

[0006]

[Means for Solving the Problems] and

To achieve the above object, the present invention comprises at least two first and second binarizing means, and the image processing for converting a multi-valued image into a binary image by the binarizing means. In the apparatus, means for determining whether or not the pixel value indicated by the input multi-valued image is within a predetermined range; and if the pixel value is within the predetermined range, the first binarizing means. In the first conversion means for converting the multi-valued image into a binary image, and when the pixel value is out of the predetermined range, the second binarization means converts the multi-valued image into a binary image. Second conversion means for converting to an image.

The above-mentioned structure functions to perform binarization of an image having no thin lines and no blunt edges without reducing the processing speed.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. [First Embodiment] FIG. 1 is a block diagram showing the arrangement of an image processing apparatus according to the first embodiment of the present invention. In the figure, reference numeral 10 is an image input unit for inputting a multi-valued image, 11
Is a pixel value determination unit that switches the subsequent binarization unit according to the pixel value of the input image from the image input unit 10. The image processing apparatus according to the present exemplary embodiment includes a halftone binarizing unit 12 that functions as a first binarizing unit that is excellent in reproducing halftones as a binarizing unit, and a first binarizing unit that is excellent in reproducing edges. An edge binarization unit 13 as a binarization unit for 2 is provided. The image binarized by these binarizing units is output from the image output unit 14.

FIG. 2 is a diagram showing a pixel block which is an image processing unit in this embodiment. The image processing apparatus according to the present embodiment performs processing in units of four pixels having the positional relationship shown in FIG. That is, each pixel of the input image has a value indicating a gradation value (density, density, brightness, saturation, hue, chromaticity, etc.), for example, an integer value from 0 to 255. Further, each pixel of the output image has a value corresponding to two states of ON and OFF, for example, 1 and 0.

If the pixel value of the input image is a value within the range of two threshold values T0 to T1, the pixel value judging section 11 shown in FIG. 1 is a halftone binarizing section which is a first binarizing means. 2 at 12
The binarization is performed, and if the pixel value of the input image is a value outside this range, the edge binarization unit 1 which is the second binarization unit.
3 functions to perform binarization.

The threshold value T0 is a value near the minimum pixel value of the input image, and the threshold value T1 is a value near the maximum pixel value of the input image. For example, if the range of possible pixel values of the input image is 0 to 255, T0 = 5, T
Specify as 1 = 250. The pixel used for this pixel value determination is any one of the four pixels 20 to 23 in FIG. 2, and for example, the upper left pixel 20 is used.

Halftone binarization unit 1 which is the first binarization means
In step 2, binarization is performed by the density pattern method. Here, for example, (a) to (e) of FIG. 3 (reference numerals 30 to 34)
As shown in, the pixel values of the input image are classified into five levels, and the density pattern corresponding to each level is obtained as a binary image. In the example of the density pattern shown in FIG. 3, the number of ON pixels is increased at each stage. The pixel value used for this binarization is any one of the four pixels shown in FIG. 2, and for example, the upper left pixel 20 is used.

Further, the edge binarization unit 13 which is the second binarization means performs binarization with a fixed threshold value. That is, if the pixel value of the input image is larger than the threshold value T, the pixel value of the binary image is turned on, and if the pixel value of the input image is smaller than the threshold value T, the pixel value of the binary image is turned off.

The above-mentioned threshold value T is from T0 to T1.
If the value is within the range of, and the value is as described above, a value such as 128 is used. The edge binarization unit 13 binarizes the four pixels, which are processing units, with the above-mentioned fixed thresholds, and performs four binarization of four pixels.
Get the value image.

As described above, according to this embodiment,
By applying a binarization method suitable for each of the edge portion and the halftone portion according to the pixel value of the input image, it is possible to binarize an image without missing thin lines or blunt edges without slowing down the processing speed. can do. [Second Embodiment] The second embodiment of the present invention will be described below.

In the first embodiment, the above-mentioned density pattern method is used in the first binarizing means (halftone binarizing unit 12), but the present invention is not limited to this. You may process by another pseudo halftone expression system.

FIG. 4 is a block diagram showing the arrangement of an image processing apparatus for carrying out the image processing method according to the present embodiment, which uses a pseudo halftone expression method different from the binarization according to the first embodiment. is there. In the figure, the same components as those of the image processing apparatus according to the first embodiment shown in FIG. 1 are designated by the same reference numerals, and the description thereof will be omitted here.

In FIG. 4, reference numeral 41 is a binarization error correction unit for correcting an error caused by binarization, and 42.
Is a binarization error storage unit for feeding back an error caused by binarization.

That is, when the pixel value determining unit 11 determines that the pixel value of the image input from the image input unit 10 is within the specified range, the binarization error correction is performed on this pixel value. The unit 41 adds the accumulated error stored in the binarization error storage unit 42. Next, the halftone binarization unit 43 binarizes the pixel values to which the error has been added.

Here, for example, density patterns are assigned as follows. These density patterns are, for example,
This is a pattern having a binary pixel arrangement as shown in FIG.

[0021] Specifically, if the pixel value to which the error is added is 208, the density pattern 33 in FIG. 3 is selected.

The binarization error storage unit 42 compares the difference between the pixel value to which the error is added by the binarization error correction unit 41 and the minimum value of the error-added pixel values corresponding to the selected density pattern. That is, in the above example, 208-192 = 16 is stored as an error.

At this time, the error may be divided into a plurality of areas and stored. For example, as shown in FIG. 5, there is a configuration in which an error is multiplied by a predetermined coefficient and divided into four directions. In the figure, reference numeral 50 is a pixel block currently being processed, and 51 is a pixel block to be processed next. In the above example, since the error is 16, the binarization error storage unit 42 sets 16 as the error of the next pixel block.
× 7/16 = 7 is stored, and in the processing of the next pixel block, the binarization error correction unit 41 adds the above error 7 to the input pixel value.

As described above, according to this embodiment,
Performs error correction particularly suitable for the halftone part of the input image 2
By applying the binarization method, the gradation reproducibility of the halftone image can be improved. [Third Embodiment] In the first and second embodiments, the second binarizing means (edge binarizing unit 13) performs binarization with a fixed threshold value. The present invention is not limited to this, and another binarization method may be used.

Since the image processing apparatus according to this embodiment has the same configuration as the image processing apparatus according to the first embodiment shown in FIG. 1, its illustration and description are omitted here.

In the present embodiment, the pixel value judging section 11
When it is determined that the pixel value of the input image is a pixel value outside the specified range, the output pixel value is determined for each pixel of this pixel block by a different threshold value.

FIG. 6 is a diagram showing an example of a threshold mask according to this embodiment. In the figure, the threshold at the position of reference numeral 70 is 51, the threshold at the position of 71 is 153, the threshold at the position of 72 is 204, and the threshold at the position of 73 is 102. Then, the edge binarization unit 13, which is the second binarization unit, compares the input pixel value with the above threshold value for each pixel of this pixel block, and if the input pixel value is larger than the threshold value, the on 2 Given a value image and the input pixel value is less than the threshold,
Gives an off binary image.

By adopting the above-mentioned structure, it is possible to improve the reproducibility even when there are pixels of intermediate gradation in the pixel block determined as the edge portion.

In each of the above embodiments, the processing unit (pixel block) is four pixels, which are two pixels in the vertical and horizontal directions. However, the processing unit is not limited to this and may be configured by combining any number of pixels and positions. Further, by applying the image processing according to each of the above embodiments to each color component of the image,
The present invention can be applied to a color multi-valued image.

The present invention may be applied to a system composed of a plurality of devices or an apparatus composed of one device. Further, it goes without saying that the present invention can be applied to the case where it is achieved by supplying a program to a system or an apparatus.

[0031]

As described above, according to the present invention,
By performing different binarization conversion on the edge portion or the halftone portion depending on the pixel value of the input image, it is possible to perform high-speed image binarization without missing fine lines or dull edges.

[0032]

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an image processing apparatus according to a first embodiment of the present invention.

FIG. 2 is a diagram showing an example of a pixel block which is a processing unit in the first embodiment.

FIG. 3 is a diagram showing an example of a density pattern according to the first embodiment.

FIG. 4 is a block diagram showing a configuration of an image processing apparatus according to a second embodiment.

FIG. 5 is a diagram showing an example of an error diffusion coefficient according to the second embodiment.

FIG. 6 is a diagram showing an example of a threshold mask according to a third embodiment.

[Explanation of symbols]

 10 Image Input Section 11 Pixel Value Judgment Section 12 Halftone Binarization Section 13 Edge Binarization Section 14 Image Output Section 41 Binarization Error Correction Section 42 Binarization Error Storage Section 43 Halftone Binarization Section

Claims (6)

[Claims] 1. An image processing apparatus, comprising at least two first and second binarizing means, wherein the binarizing means converts a multivalued image into a binary image. A unit that determines whether the pixel value shown is within a predetermined range; and if the pixel value is within the predetermined range, the first binarization unit converts the multi-valued image into a binary image. First to convert to
Second converting means for converting the multi-valued image into a binary image by the second binarizing means when the pixel value is out of the predetermined range.
An image processing apparatus, comprising: 2. The image processing apparatus according to claim 1, wherein the first binarizing unit converts the multivalued image into a binary image by a density pattern method. 3. The first binarization unit further includes a unit that stores an error between tone values of an input image and an output image, and a unit that corrects the pixel value based on the stored error. The image processing device according to claim 2, wherein 4. The image processing apparatus according to claim 1, wherein the second binarizing unit converts the multivalued image into a binary image by a systematic dither method. 5. The image processing apparatus according to claim 4, wherein the conversion performed by the second binarizing unit is a conversion based on a fixed threshold value. 6. The image processing apparatus according to claim 4, wherein the conversion by the second binarization unit is a conversion using a different threshold value for each pixel of the pixel block.