JP3059282B2 - Binary image scaling 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 processing apparatus,
In particular, the present invention relates to a binary image scaling device that performs scaling processing on a binarized input image.

[0002]

2. Description of the Related Art Conventionally, in a device for processing binarized image information such as a facsimile apparatus, a scaling process (enlargement or reduction) or a pixel density conversion process is performed on a binary image. For example, in a communication method called memory communication in facsimile, binarized image data is temporarily stored in a memory, and communication is started after a predetermined time has elapsed. After the start of communication, the specification of the other party is known. For example, if the size of the other party's printer is smaller than the size of the document to be transmitted, reduction / magnification processing is performed on the binary data stored in the memory.

As a reduction / magnification processing method for this purpose, there is a simple so-called “thinning-out method” in which one pixel is discarded for several pixels of the original image. Moiré occurs in a picture image that has been blurred, crushed, or dithered, and the texture of the error-diffused picture image is disturbed, resulting in a large deterioration in image quality. Hereinafter, such an image processed by the dither method, the error diffusion method, or the like is referred to as a pseudo halftone image or a pattern image.

In addition, some scaling methods such as a projection method and a logical sum method have been proposed, but none of these methods can scale a character or a pseudo halftone image to high quality.

[0005]

Therefore, conventionally, in order to perform high-quality scaling processing on an image in which characters and pseudo halftones are mixed, is the input binary image a character image? There is one in which an image area is determined to be a pseudo halftone image and a processing method is switched for each pixel or area based on the determination result (for example, see Japanese Patent Application Laid-Open No.
11877 and 3-73666).

However, it is very difficult to accurately perform the above-described image area determination.
There is a problem that the image quality is degraded due to the disorder of the edge of the character or the texture of the pseudo halftone. In particular, as a result of the erroneous determination, pseudo halftone processing is partially performed even on an image in which the entire screen is composed of characters, so that characters are blurred, and compared with the above-described conventional simple thinning method. However, the image quality is greatly deteriorated.

Further, even if the image type (character or pseudo halftone) is the same, the cause of the image quality degradation differs depending on the magnification. Conventionally, an optimum scaling process is selected in consideration of the image type and the magnification. As a result, there is a problem that high-quality scaling cannot be performed.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a binary image scaling device for performing a high-quality scaling process by selecting an optimum scaling method for the determined image type and magnification. It is in.

[0009]

To SUMMARY OF THE INVENTION To achieve the above object, in the first aspect of the present invention, the first binary image, scaling processing to binary to a second binary image having different pixel density Image transformation
In the doubling device , based on different magnification processing methods
A plurality of scaling processing means for performing scaling processing, and determining whether or not a pseudo halftone area is included in the first binary image
Determining means, means for storing a magnification of the scaling processing, and selecting means for selecting one of the scaling processing means according to the determination result of the determining means and the stored magnification. I have. The invention according to claim 2 is characterized in that the determination means detects a changed pixel in the first binary image and makes a determination based on density information of the changed pixel. The invention according to claim 3 is characterized in that the determination means makes the determination based on the code amount of the first binary image. According to the fourth aspect of the present invention, the stored
Magnification is 90% or more, when the determination means determines not include the pseudo halftone region in said first binary image, said selection means, scaling processing based on the logical sum method
It is characterized in that scaling processing means is selected.

[0010]

The selecting section selects the scaling means based on the judgment result from the pseudo half tone judging section. That is, when the pseudo halftone determination unit determines that the image type is only characters, the entire image is scaled by the logical sum method, and when it is determined that the image includes a pseudo halftone, the entire image is processed. Is subjected to multi-value scaling processing. Further, the selection unit can select a scaling unit using the scaling ratio . As a result, the scaling processing means is switched based on the information on whether or not a pseudo halftone is included and the scaling factor , so that the optimum scaling processing method is selected for the type and scaling factor of the image. It is possible,
High quality scaling processing is possible.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be specifically described below with reference to the drawings. FIG. 1 is a block diagram of an embodiment of the present invention. In FIG. 1, reference numeral 1 denotes a pseudo halftone determining unit that determines whether or not an area subjected to pseudo halftone processing is included in an input binary image, and 2 denotes a magnification storage for storing a magnification for performing a scaling process. And 3, a plurality of scaling processing units for performing scaling processing by a nearest neighbor method, a logical sum method, a multi-valued scaling processing, etc., and 4 an output of the pseudo halftone determination unit 1 and an output of the scaling storage unit 2. Is a selection unit that drives the selector according to (1) and selects the scaling unit 3.

Hereinafter, the embodiment of the present invention will be described in detail. The pseudo-halftone judging section 1 judges whether or not an input image has a pseudo-halftone-processed area. Then, one of the following four determination methods is used. That is,

[0013] First determination method: The first method uses information designated by a user for key input. In a facsimile apparatus, when an operation of storing an image in a memory after reading a document with a scanner and performing binarization processing, the user is prompted to select whether to perform character processing on the entire surface or to perform pseudo halftone mixed processing. For example, a "character mode" button and a "pattern mixed mode" button are provided in the key input section, and when a binarized image is stored in the memory, which mode has been binarized is stored in the memory. It is stored at a predetermined position. Then, when performing the scaling process at the time of transmission, the pseudo halftone determining unit 1 refers to the stored mode and does not include the pseudo halftone if the binarization is performed in the character mode. Is determined. Thus, according to the first determination method, the key input information
To determine whether pseudo halftones are included
The user is free to choose the scaling method
Can be.

Second determination method: In general, a pseudo halftone image has a feature that black and white pixels are more dispersed than a character image. Therefore, in the present embodiment, it is determined whether the character is a character or a pseudo halftone based on the degree of the dispersion. That is, as shown in FIG. 2, when one or more of the four pixels a, b, c, and d at the top, bottom, left, and right of a certain pixel P have different pixel values from the pixel P, the pixel P is changed to a changed pixel. That. Then, the pseudo half tone determination unit 1
Then, the original image is divided into small areas of, for example, 5 × 5 pixels,
The number of changed pixels in each of the divided areas is counted, and if the counted value is equal to or greater than a predetermined threshold, it is determined that a pseudo halftone is included.

Third determination method: This method takes into account the distribution of changed pixels in addition to the above-described second determination method, that is, divides an original image into small areas of, for example, 5 × 5 pixels. Then, the number of changed pixels in each of the divided areas is counted, and when the counted value is equal to or larger than a predetermined threshold, the area is determined as a halftone candidate block (high-density area). As shown in FIG. 3, when a predetermined number or more (for example, five) are present consecutively, it is determined that the image includes pseudo halftones.

Fourth determination method: In facsimile communication, MH (Modified)
Huffman) coding method or MR (Modif)
ied READ) A compression process of the code amount is performed by an encoding method or the like. Since these encoding methods use the continuity of black and white pixels as a basis for compression, the code amount increases in a pseudo halftone image in which black and white pixels are dispersed. Therefore,
When the code amount is equal to or more than a predetermined level determined based on the number of pixels after decoding, the pseudo halftone determination unit 1 of the present embodiment determines that the image includes pseudo halftones.

Fifth determination method: In the above-described fourth determination method, there is a possibility that a small pseudo halftone area included in a character image cannot be detected. Therefore, in the fifth determination method, the code amount of each predetermined line to be encoded is reduced by the fact that the code amount of each predetermined line is If the level is equal to or higher than the predetermined level determined based on the image, it is determined that the image includes pseudo halftones.

The magnification storage unit 2 according to the present embodiment stores a magnification for performing a scaling process. The magnification is, for example, in a facsimile apparatus, based on the size of a document and the paper size on the receiving side determined by a communication protocol. Determined and stored.

As the scaling method of the scaling unit 3 in this embodiment, a nearest neighbor method, a logical sum method, and a multivalued scaling method are used. For example, the scaling unit # 1 The scaling processing unit # 2 performs scaling processing by a logical sum method, and the scaling processing unit #n performs scaling processing by a multi-valued scaling processing method. Here, the nearest neighbor method is a method in which the value of a peripheral pixel closest to the point P whose brightness is unknown is set as the value of the point P. The logical sum method is a method of setting the value of the point P to black if at least one of the four pixels a, b, c, and d surrounding the point P of unknown brightness is black. In addition, according to this method, the processing is simple and the preservation of image data at the time of image reduction is good, so that there is an advantage that blurring of characters can be prevented.

Further, the multi-value quantization process includes low-pass filtering, interpolation scaling, and error diffusion binarization. In other words, the low-pass filter that converts the input binary data into multi-valued data having the same pixel density as the input binary data is formed of an anti-alias filter, and the required cutoff frequency varies depending on the magnification.
The coefficient matrices shown in FIGS. 4 and 5 are used for low magnification. The processing using the respective filters is referred to as a high-magnification multi-value scaling process and a low-magnification multi-value scaling process. After being converted into multi-valued data by a low-pass filter, in interpolation scaling processing, the data is converted into multi-valued data having different pixel densities by linearly interpolating using four or three pixels in the vicinity of the converted pixel. The applicant has already applied for an image scaling method in which linear interpolation is performed using three pixels as Japanese Patent Application No. 3-108728. Then, the multi-value data is binarized by an error diffusion method.

The scaling means selecting section 4 of the present embodiment, based on the determination result from the pseudo half tone determining section 1, executes the scaling processing section 3.
Select That is, as shown in FIG. 6, when the pseudo halftone determination unit 1 determines that the image type is only characters, the scaling unit 3 that performs the processing by the logical sum method is selected, and the entire image is logically processed. Since the scaling process is performed by the sum method, the process can be performed without causing sharpness in the black thin line. On the other hand,
For images containing pseudo halftones, the scaling unit 3 that performs multi-level scaling processing is selected and the entire image is subjected to multi-level scaling processing, so that scaling processing with preserved density is possible. Becomes

Further, using the magnification information from the magnification storage unit 2, the scaling unit 3 can be selected. That is,
For example, the scaling processing unit 3 is selected as shown in FIG. 7 depending on whether or not the magnification is 90% or more and whether or not a pseudo halftone is included. Therefore, at the time of high magnification, the image of only characters is scaled by the logical sum method, so that it is possible to obtain the same image quality as the original image which does not cause sharpness in the fine black line, and at the time of low magnification, the image quality becomes large. An image free from blurring and sharpness can be obtained by the binarization scaling method.

On the other hand, for an image containing a pseudo halftone,
After processing with a low-pass filter suitable for the magnification, the image is scaled and binarized, so that an image free from moiré and texture disturbance can be obtained.

[0024]

As described above, according to the first aspect of the present invention, the scaling processing means is switched based on the information on whether or not a pseudo halftone is included and the scaling factor. Therefore, it is possible to select an optimum scaling processing method for the type and magnification of an image, and to perform high quality scaling processing. According to the second aspect of the present invention, it is determined whether or not a pseudo halftone is included based on the density information of the changed pixels. It is possible to accurately determine even an image including a tonal region. According to the third aspect of the present invention, it is determined whether or not a pseudo halftone is included based on the code amount of the binary image. Therefore, without decoding the encoded image data again, Discrimination can be easily performed. According to the fourth aspect of the invention, when the scaling ratio is close to 100% and the binary image is a character, the scaling process is performed by the logical sum method, so that the edge of the character is not disturbed.
In addition, high-quality scaling processing can be performed without causing breakage of fine lines.

[Brief description of the drawings]

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

FIG. 2 is a diagram illustrating a changing pixel.

FIG. 3 is a diagram illustrating a third method of the present embodiment for determining whether pseudo halftones are mixed.

FIG. 4 is a diagram showing a low-pass filter for high magnification.

FIG. 5 is a diagram showing a low-magnification low-pass filter.

FIG. 6 is a diagram illustrating a method of selecting a scaling unit according to the present embodiment.

FIG. 7 is a diagram illustrating another selection method of the scaling unit according to the embodiment;

[Explanation of symbols]

 Reference Signs List 1 pseudo half tone determination unit 2 magnification storage unit 3 scaling unit 4 selection unit

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H04N 1/38-1/393 G06T 3/00-5/50 G09G 5/00-5/42

Claims (4)

(57) [Claims] 1. A binary image scaling device for scaling a first binary image into second binary images having different pixel densities based on different scaling processing methods. Perform scaling processing
A plurality of scaling processing means, and a determination means for determining whether or not a pseudo halftone area is included in the first binary image;
Means for storing a magnification of the variable magnification processing, the determination of the determination means
Of the scaling processing means according to the result and the stored magnification .
A binary image scaling device comprising a selection means for selecting one . 2. The variable magnification of a binary image according to claim 1, wherein the determination unit detects a changed pixel in the first binary image and makes a determination based on density information of the changed pixel. Equipment . 3. The binary image scaling device according to claim 1, wherein said determination means makes the determination based on the code amount of said first binary image. And in wherein said stored magnification is 90%, when said determination means determines not include pseudo halftone region in said first binary image, said selection means, the logical sum method 2. A binary image scaling device according to claim 1, wherein a scaling process means for performing a scaling process is selected based on the following.