JP3725255B2 - Digital image processing device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a digital image processing apparatus such as an electrophotographic copying machine, a scanner device, and a facsimile, and more particularly to a digital image processing apparatus that separates an image from a character area and a picture area and performs appropriate processing on each area. is there.
[0002]
[Prior art]
In a digital image processing apparatus such as a digital copying machine or a facsimile, an input image is separated into a character area and a picture area (photograph, halftone dot, etc.) with a small amount of hardware, and MTF correction is performed on the character area. The image area is processed with an emphasis on resolution, and the image area is processed with an emphasis on gradation such as dithering and error diffusion to perform image processing suitable for the separated character area and the image area. (JP-A-4-248766). Further, in the above-described method, a character area of a thick part of the character is detected as a picture area, and processing with an emphasis on gradation is performed, so that some problems have been improved (Japanese Patent Laid-Open No. Hei 4-248766). ).
[0003]
[Problems to be solved by the invention]
However, in the above-described conventional technology, the character area is processed with an emphasis on resolution, but the area where the character exists is limited to a white background. However, with the recent development of printing technology, color manuscripts have increased, and catalogs containing text and photographs (pictures) are naturally becoming more and more colored. Furthermore, not only color and black-and-white, but also a large number of text information posted with a background color by hatching or the like. The characters on the background color, the characters on the hatching area, etc. are determined as the picture area in the conventional technology, and processing with an emphasis on gradation is performed. There was a problem that character information was damaged.
Therefore, the present invention determines a character on the background color, a character on the hatching region, etc. as a character region by providing a background color edge detection means for detecting whether the image has a background color and is in the edge region. An object of the present invention is to provide a digital image processing apparatus that performs processing with an emphasis on resolution, thereby significantly improving the reproducibility of characters on the background color and preventing the loss of important character information. Yes.
[0004]
[Means for Solving the Problems]
In order to achieve the first claim, an image area separation processing means for processing by determining whether a pixel of interest in an input image is in a character area or a picture area, and the image area separation processing means In the digital image processing apparatus having selection means for selecting either resolution priority processing means for prioritizing resolution or gradation priority processing means for prioritizing gradation based on a detection result, the image area separation processing means Detects the presence or absence of a background color for the pixel of interest, detects whether or not the pixel of interest is in an edge region, and has a background color and detects an edge region, the resolution priority processing is performed by the selection unit This is achieved by selecting means .
In order to achieve the second claim, in the digital image processing apparatus for achieving the first claim, the image area separation processing unit detects the presence or absence of a white background with respect to the target pixel, and the target pixel. This is achieved by including a white background edge detecting means for detecting whether or not the pixel is in the edge area and detecting whether the pixel has a white background and is in the edge area, and the background color edge detecting means. The
In order to achieve the third claim, in the digital image processing apparatus for achieving the first claim or the second claim, the background color edge detection means includes a background color for the pixel of interest. This is achieved by providing a background color threshold value changing means capable of changing the threshold value for determining the presence or absence of the background color.
In order to achieve the fourth aspect, in the digital image processing apparatus for achieving the first aspect or the second aspect, the background color edge detecting means has the pixel of interest in the edge region. This is achieved by providing an edge region threshold value changing means capable of changing a threshold value for determining an edge region when detecting whether or not.
[0005]
With the above configuration, the invention according to claim 1 includes the background color edge detection means in the image area separation processing means, detects the background color, and can detect whether or not the pixel of interest on the background color is in the edge area. Then, it is determined correctly whether the pixel of interest on the background color should be processed as a character area or a pattern area.
According to a second aspect of the present invention, in the digital image processing apparatus configured as in the first aspect, the image area separation processing unit can detect whether or not the pixel of interest is in an edge area on a white background. Since the background edge detection means and the background color edge detection means capable of detecting whether or not the pixel of interest is in the edge region on the background color are provided, even if the pixel of interest is on a white background, Even in this case, it is determined correctly whether it should be processed as a character area or a pattern area.
According to a third aspect of the present invention, in addition to the invention of the digital image processing apparatus configured as in the first or second aspect, the background color threshold value changing means detects the background color when detecting the presence or absence of the background color. Since the threshold for determining the presence / absence can be changed, a threshold suitable for the original is determined to detect the presence / absence of the background color.
According to a fourth aspect of the invention, in addition to the invention of the digital image processing apparatus configured as in the first or second aspect, when detecting whether or not the target pixel is in an edge region on the background color. Since the threshold value for determining the edge area can be changed by the edge area threshold value changing means, a threshold value suitable for the document is determined to detect whether or not the edge area exists.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a block diagram showing the main part of the digital image processing apparatus of the present invention. In FIG. 1, a scanner device 20 has a reading unit having a photoelectric conversion element such as a CCD (not shown), reads a document, and outputs a grayscale signal corresponding to an image. The gray signal is converted into, for example, a 6-bit digital signal and output. The image area separation processing unit 1 includes a background color edge detection unit 5, a white background / edge detection unit 6, and a determination unit 9, and outputs a determination result for each pixel. The digital image processing apparatus according to the present invention further includes a resolution priority processing unit 2 including an MTF correction circuit 11 and a fixed threshold binarization circuit 12, and a tone priority processing unit 3 including a smoothing circuit 13 and a dither processing circuit 14. Is provided. The selection circuit 4 selects a pixel subjected to resolution priority processing or a pixel subjected to gradation priority processing according to the determination result of the image area separation processing unit 1 and outputs the selected pixel to the printer 21.
The white background / edge detection unit 6 of the image area separation processing unit 1 mainly includes a circuit for detecting the presence / absence of a white background for the target pixel and a circuit for detecting whether the target pixel is an edge region. It consists of When the presence of a white background is detected and an edge region is detected, the determination unit 9 outputs an output signal “1” to select resolution priority processing. In cases other than the above, the determination unit 9 outputs the output signal “0” to select the gradation priority processing. Since the detection of the edge region on the white background is already known, the description thereof is omitted.
Similarly, the background color edge detection unit 5 of the image area separation processing unit 1 includes a circuit that detects the presence or absence of a background color for the pixel of interest and a circuit that detects whether or not the pixel of interest is an edge region. When the presence of the background color is detected and the edge region is detected, the determination unit 9 outputs the output signal “1” and selects the resolution priority process. In cases other than the above, the determination unit 9 outputs the output signal “0” to select the gradation priority processing.
[0007]
FIG. 2 is a detailed circuit configuration of the background color edge detection unit 5 that achieves the above object. The image signal output from the scanner device 20 is subjected to a uniforming process by applying the filtering process shown in FIG. Thereafter, the comparison circuit 32 compares the density level of the image signal with a threshold of a predetermined density level. If the density level of the target pixel after the smoothing process is A, it is necessary to be larger than a predetermined value α in order to determine that the target pixel is on the background color. In reality, there is an upper limit to the density level of the pixel of interest, and when the density level is too high, it is not treated as a background color. That is, if the upper limit value is β,
β ≧ A ≧ α (1)
If the following relational expression is satisfied, it is determined that the pixel of interest is on the background color, and the output “1” is transmitted from the comparison circuit 32 to the edge determination circuit 35 on the background color. If the above relational expression (1) is not satisfied, the output “0” is transmitted to the background color upper edge determination circuit 35.
Further, in order to detect whether or not the target pixel is in the edge region, the edge active detection circuit 33 examines the relationship between the left and right pixels with respect to the target pixel. With the 3 × 1 spatial filter shown in FIG. 4, the density change amount between adjacent pixels of the target pixel is compared with a predetermined threshold value. If the density of the pixel of interest is B, the density of adjacent pixels on the left and right is A and C, and the density of the threshold is γ,
| A-C | ≧ γ (2)
If the following relational expression is satisfied, “1” is output to the expansion circuit 34 at the next stage with the target pixel as the edge active pixel. In cases other than (2), “0” is output to the expansion circuit 34.
[0008]
Next, in the expansion circuit 34, for example, as shown in FIG. 5, expansion processing using a 5 × 1 mask is performed. That is, if the pixel of interest is c, and there is even one edge active pixel in the mask from adjacent pixels a to e, “1” is input to the background color upper edge determination circuit 35 using the pixel of interest c as an edge pixel. Is output. When there is no edge active pixel, “0” is output. Such an expansion process is a correction process in which a line area around the entire outline of a character is used as an edge area.
Further, the background color upper edge determination circuit 35 receives the outputs from the comparison circuit 32 and the expansion circuit 34 described above, and performs the following processing.
(1) When the comparison circuit 32 outputs “1” and it is determined that the target pixel is on the background color, and the determination result “1” of the expansion circuit 34 is output, the target pixel is an edge pixel. If the target pixel is determined to be “1”, the background color edge determination circuit 35 outputs “1” as the edge region pixel on the background color.
{Circle around (2)} When the target pixel does not satisfy the above condition, the background color upper edge determination circuit 35 outputs “0” as not being an edge region pixel on the background color.
[0009]
Therefore, referring back to FIG. 1, the edge region pixels on the background color can be reliably captured by the background color edge detection unit 5 and the selection circuit 4 is determined to perform resolution priority processing as described above. Work from part 9. As a result, the target pixel having the background color is also processed as a character region and recognized as an easy-to-see character with sharp edges.
Further, as shown in FIG. 1, since the background color edge detection unit 5 and the white background / edge detection unit 6 are provided, the edge region of the character is correct regardless of whether the edge region is on the white background or the background color. Can be detected, and processing that prioritizes resolution can be performed.
6 has a configuration in which a background color threshold value changing unit 7 or an edge region threshold value changing unit 8 is added to FIG. Since operations and functions other than the added portion are the same as those shown in FIG. 1, description thereof will be omitted, and the added background color threshold value changing unit 7 and edge region threshold value changing unit 8 will be described. The background color threshold value changing unit 7 changes the threshold value for determining the presence or absence of the background color of the background color edge detecting unit 5 in response to an instruction from an operation unit or an external device (not shown). That is, the background color threshold value changing unit 7 can change the threshold value α in the equation (1) when the background color edge detecting unit 5 detects the presence or absence of the background color for the target pixel. Therefore, it is possible to detect the presence or absence of the background color more accurately by appropriately changing the threshold value α according to the background density, hatching, or the like.
[0010]
The edge region threshold value changing unit 8 can change the threshold value γ in the equation (2) in response to an instruction signal from an operation unit or an external device (not shown). Therefore, in general, when the density of the background color is high, the density change of the adjacent pixels on the left and right of the target pixel tends to decrease. Therefore, the threshold γ is changed to a lower direction, and when the background color density is high, the target pixel Therefore, by changing the threshold value γ in a higher direction, it is possible to detect the edge region with higher accuracy and perform a process that gives priority to the resolution.
[0011]
【The invention's effect】
According to the invention of claim 1, the edge region of the target pixel on the background color can be detected by the background color edge detection means, and the edge region of the character on the background color, the character on the hatching region, etc. is correctly determined, Since processing with an emphasis on resolution has been performed, it is possible to provide a digital image processing apparatus that significantly improves the reproducibility of characters on the background color and prevents the loss of important character information. Became.
[0012]
According to the second aspect of the present invention, in addition to the digital image processing apparatus of the first aspect, a white background / edge detection unit is also provided. Even if the edge region of the target pixel is on the white background, the background color Even if it is on the top, it is correctly judged and processing with an emphasis on resolution is performed, so that the reproducibility of characters is always remarkably improved regardless of the type of document, and important character information is prevented from being damaged. It has become possible to provide a digital image processing apparatus.
[0013]
According to the invention of claim 3, in addition to the invention of the digital image processing apparatus of claim 1 or 2, it is possible to change the threshold for determining the presence or absence of the background color by the background color threshold changing means. Thus, the threshold value can be selected in consideration of the background color shading, hatching, etc., so that a digital image processing apparatus that can correctly detect the presence or absence of the background color can be provided. Became.
[0014]
According to the fourth aspect of the invention, in addition to the digital image processing apparatus of the first or second aspect, the edge region threshold value changing means allows the left and right adjacent to the target pixel when the background color density is high. Since the density change of the pixel tends to decrease, the threshold value is changed to a lower direction, and when the density of the background color is high, the density change of the adjacent pixels on the left and right of the target pixel tends to increase. Therefore, it is possible to provide a digital image processing apparatus in which the edge region can be correctly detected.
[Brief description of the drawings]
FIG. 1 is a block diagram of a main part of a digital image processing apparatus according to the present invention.
FIG. 2 is a detailed block diagram of a background color edge detection unit of the present invention.
FIG. 3 is an explanatory diagram illustrating an example of a filter used for smoothing processing of a background color edge detection unit according to the present invention.
FIG. 4 is an explanatory diagram illustrating an example of a pixel of interest when a background color edge detection unit of the present invention detects an edge region.
FIG. 5 is an explanatory diagram illustrating an example of a mask used for expansion processing when the background color edge detection unit of the present invention detects an edge region;
FIG. 6 is a block diagram of a main part of a digital image processing apparatus including a threshold value changing unit according to the present invention.
[Explanation of symbols]
1 Image area separation processing unit (image area separation processing means)
2 Resolution priority processing unit (resolution priority processing means)
3 Gradation priority processing unit (gradation priority processing means)
4 selection part (selection means)
5. Background color edge detection unit (background color edge detection means)
6 White background background edge detector (white background edge detection means)
7 Background color threshold value changing unit (background color threshold value changing means)
8 Edge region threshold value changing unit

Claims (4)

A resolution that prioritizes resolution based on the image area separation processing means to be processed by determining whether the pixel of interest in the input image is in the character area or the pattern area, and the detection result of the image area separation processing means In a digital image processing apparatus having a selection means for selecting either a priority processing means or a gradation priority processing means for giving priority to gradation, the image area separation processing means detects the presence or absence of a background color for the pixel of interest. And detecting whether or not the pixel of interest is in an edge region, and having the background color and detecting the edge region , the selection unit selects the resolution priority processing unit. Processing equipment.   2. The digital image processing apparatus according to claim 1, wherein the image area separation processing unit detects the presence or absence of a white background with respect to the target pixel, detects whether or not the target pixel is in an edge region, and has a white background. And a background image edge detecting unit for detecting whether the pixel is in an edge region and the background color edge detecting unit.   3. The digital image processing apparatus according to claim 1, wherein when the background color edge detecting unit detects the presence / absence of a background color with respect to the pixel of interest, a threshold for determining the presence / absence of the background color can be changed. A digital image processing apparatus comprising color threshold value changing means.   3. The digital image processing apparatus according to claim 1, wherein when the background color edge detecting unit detects whether or not the target pixel is in the edge region, a threshold value for determining the edge region can be changed. A digital image processing apparatus comprising an edge region threshold value changing unit.

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