JP2005045373A - Color image processing apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a color image processing apparatus whereby wrong discrimination of the types of originals can more excellently be prevented. <P>SOLUTION: The color image processing apparatus recognizes tentative color pixels on the basis of the density value of each of pixels configuring the image of an original. When the number of the tentative color pixels within a prescribed region around a pixel recognized to belong to a dot region is a threshold value V2 or over (YES in a step T3), the image processing apparatus recognizes the pixel to be a color pixel (step T4). The image processing apparatus discriminates the original on the basis of the number of pixels recognized to be color pixels. The color image processing apparatus can discriminate originals by taking into account the recognition result as to whether or not each pixel is a pixel belonging to the dot region in addition to the density value data of each pixel. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a color image processing apparatus that performs image processing on input image data of a document.
[0002]
[Prior art]
In the color image processing apparatus, for the color image data (red (R), green (G), and blue (B) density value data) of the input document, the document type is color document or monochrome. Some image processing can be performed in a different manner depending on whether the document is a document. In this type of color image processing apparatus, processing (document discrimination) for determining whether a document is a color document or a monochrome document is performed based on input document image data.
[0003]
As a document discrimination method, for example, each row (main scanning direction) of a document image is defined as one line, and each line is classified as a color line (chromatic line) or a monochrome line (achromatic line). (For example, refer to Patent Document 1). That is, each pixel is recognized as a color pixel, intermediate pixel, or monochrome pixel based on image data (density value data) of each pixel constituting the original image, and the color pixel, intermediate pixel, and monochrome pixel included in each line. By identifying each line as a color line or a monochrome line based on the number of documents, the document type (color document or monochrome document) is determined based on the number of color lines included in the entire document image.
[0004]
[Patent Document 1]
Japanese Patent Laid-Open No. 11-146211
[Problems to be solved by the invention]
However, when the original image includes a halftone dot area composed of color pixels, the density (gradation) in the halftone dot area is not represented by the density value of each pixel, but the color in the halftone dot area. Since it is expressed by the ratio of pixels (area ratio), there are cases where there are many monochrome pixels in the halftone dot region.
Therefore, each line is recognized as a color line or a monochrome line based on the number of color pixels, intermediate pixels, and monochrome pixels included in each line as in the above prior art, and based on the number of color lines included in the entire original image. In the case of a method for discriminating the document type, there is a high possibility that a line including a halftone dot area composed of color pixels is recognized as a monochrome line, and as a result, the document to be identified as a color document is identified as a monochrome document ( May be misidentified). If the document type is erroneously determined, appropriate image processing according to the document type cannot be performed, and a desired output product (printed product) cannot be obtained.
[0006]
The present invention has been made under such a background, and an object of the present invention is to provide a color image processing apparatus that can prevent erroneous determination of a document type.
[0007]
[Means for Solving the Problems and Effects of the Invention]
In order to achieve the above object, according to the first aspect of the present invention, image processing is performed on the input image data in a different manner depending on whether the document type is a color document or a monochrome document. A color image processing apparatus (1) capable of identifying a pixel belonging to a halftone dot region from among pixels constituting an original image, and a recognition result obtained by the halftone pixel recognition unit. And document determination means (12) for determining whether the document type is a color document or a monochrome document based on the density value data of each pixel included in the image data. A color image processing apparatus.
[0008]
The alphanumeric characters in parentheses indicate corresponding components in the embodiments described later. The same applies hereinafter.
According to this configuration, it is possible to perform document determination in consideration of not only the density value data of each pixel but also the recognition result as to whether or not each pixel belongs to a halftone dot region. Therefore, even when a document image includes a halftone dot area composed of color pixels, it is possible to satisfactorily prevent a document to be determined as a color document from being erroneously determined as a monochrome document.
[0009]
According to a second aspect of the present invention, the document discrimination means (12) recognizes a temporary color pixel based on density value data of each pixel included in the image data (121, S4). ) And a predetermined area including pixels recognized as belonging to a halftone dot area by the halftone pixel recognition means (13) (for example, x rows × y columns centering on a pixel recognized as belonging to a halftone dot area) Color pixel recognition means (121, T4) for recognizing a color pixel (chromatic pixel) based on the number of provisional color pixels in the area of the color area), and the number of color pixels recognized by the color pixel recognition means Therefore, if the document type is configured to determine whether the document type is a color document or a monochrome document, the document can be determined with higher accuracy. Even if it does, can be more effectively prevented from being discriminated erroneously document to be determined that a color document and a monochrome document.
[0010]
The temporary color pixel recognition means (121, S4) detects the maximum value and the minimum value of each color density value (for example, the density value of each RGB color or the density value of each CMY color) based on the density value data of each pixel, The temporary color pixel may be certified based on the difference value between the maximum value and the minimum value.
Further, as in the invention described in claim 3, the document discriminating means (12) is configured so that each line constituting the document image is based on the number of color pixels recognized by the color pixel identifying means (121, T4). The number of color lines recognized by the color line recognition means, including color line recognition means (122, E3) for recognizing a color line (a chromatic line) from (for example, each row or each column of an original image) Therefore, if the document type is determined to be a color document or a monochrome document, document determination can be performed with higher accuracy, so that a halftone dot region including color pixels is included in the document image. Even if it is included, it is possible to better prevent a document to be determined as a color document from being erroneously determined as a monochrome document.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be specifically described below with reference to the drawings.
FIG. 1 is a block diagram showing a schematic configuration of an image forming apparatus including an image processing apparatus 1 according to an embodiment of the present invention.
This image forming apparatus uses cyan (C), magenta (based on color image data (red (R), green (G), and blue (B) density value data)) of a document read by the image reading unit 2. This is a digital color copying machine capable of forming a full-color image by a so-called electrophotographic system by superimposing monochromatic toners of M), yellow (Y) and black (Bk) on a recording sheet.
[0012]
The image reading unit 2 is provided with, for example, a scanner (not shown) for irradiating light toward the original, and the image data of the original is based on reflected light of light emitted from the scanner toward the original. Obtained as an electrical signal. More specifically, the scanner includes a light source for irradiating light toward the original and a CCD image sensor that receives reflected light from the original and outputs an electrical signal. The main scanning of the document is achieved by the electrical scanning in, and the sub scanning of the document is achieved by moving the light source in the sub scanning direction while irradiating light toward the document.
[0013]
The image processing apparatus 1 performs predetermined image processing on image data of a document read by the image reading unit 2. The image processing apparatus 1 includes a microcomputer, and functionally includes an image processing unit 11, a document discrimination unit 12, a region separation unit 13, and the like. The image data of the document read by the image reading unit 2 is input to the image processing unit 11, the document determination unit 12, and the region separation unit 13.
In the region separation unit 13, based on the image data of the document input from the image reading unit 2, a region (character region, halftone dot region, etc.) to which each pixel (m rows × n columns) constituting the document image belongs. Is detected (region separation). Data representing the result of region separation in the region separation unit 13, that is, data representing which region each pixel belongs to (region data) is input to both the document discrimination unit 12 and the image processing unit 11.
[0014]
As a method for detecting pixels belonging to the character area, for example, a well-known technique as disclosed in Japanese Patent Laid-Open No. 2-222074 can be employed. That is, image data (density value data) of each pixel constituting the document image is binarized, and edge pixels (pixels constituting the outline of the character) are recognized by detecting a steep density change, and binary data is detected. Pixels belonging to the character area can be detected based on the ratio between the number of pixels converted to black pixels and the number of edge pixels.
[0015]
As a technique for detecting pixels belonging to the halftone dot region, for example, a well-known technique as disclosed in Japanese Patent Laid-Open No. 63-109656 can be employed. That is, a pixel having a peak density value (peak pixel) is identified based on image data (density value data) of each pixel constituting the document image, and belongs to a halftone dot region based on the periodicity of these peak pixels. Pixels can be detected.
The document discrimination unit 12 determines whether the type of the document is a color document or a monochrome document based on the image data of the document input from the image reading unit 2 and the region data input from the region separation unit 13. Determined. Then, data of the discrimination result (original discrimination data) in the original discrimination unit 12 is input to the image processing unit 11. The processing in the document discrimination unit 12 will be described later.
[0016]
The image processing unit 11 responds to the image data of the document input from the image reading unit 2 with respect to the region data input from the region separating unit 13 and the document determination data input from the document determination unit 12. After the processing, the image data after the image processing is given to the image output unit 3. Then, in the image output unit 3, an image based on the image data after the image processing is transferred (output) to the recording paper, thereby achieving an image forming process.
[0017]
The configuration of the image output unit 3 is a known configuration including, for example, a photoconductor, a main charger, a developing device, a transfer device, and the like. That is, at the time of image formation, the surface of the substantially cylindrical photoconductor is uniformly charged by the main charger, and the surface of the photoconductor is irradiated with light based on image data, so that the surface of the photoconductor is so-called static. An electrostatic latent image is formed. A monochromatic toner is selectively attached to the surface of the photoconductor on which the electrostatic latent image is formed by a developing device to form a toner image. The toner image formed on the surface of the photoconductor is transferred to a recording sheet by the action of a transfer device.
[0018]
FIG. 2 is a block diagram showing the configuration of the document discrimination unit 12.
Referring to FIG. 2, document determination unit 12 functionally includes color pixel detection unit 121, color line detection unit 122, and document determination processing unit 123. Document image data from the image reading unit 2 and region data from the region separation unit 13 are input to the color pixel detection unit 121.
The color pixel detection unit 121 detects color pixels (chromatic pixels) included in the document image based on the document image data from the image reading unit 2 and the region data from the region separation unit 13. Further, the color line detection unit 121 detects a color line (a chromatic color row) based on the number of color pixels included in each row (main scanning direction) of the document image. Then, the document determination processing unit 123 determines the document type (color document or monochrome document) based on the number of color lines included in the entire document image.
[0019]
FIG. 3 is a flowchart showing the flow of processing in the color pixel detection unit 121.
Referring to FIG. 3, color pixel detection section 121 sequentially sets each pixel constituting the original image as a target pixel, and sets the maximum value and minimum value of the target pixel density value (the density value of each RGB color or the density value of each CMY color). A value is detected (step S1). Then, a difference value between the maximum value and the minimum value of the detected density value is calculated (step S2). If the difference value is equal to or greater than a predetermined threshold value V1 (YES in step S3), the target pixel is a temporary color pixel. (Step S4).
[0020]
On the other hand, when the difference value calculated in step S2 is less than the threshold value V1 (NO in step S3), the target pixel is not recognized as a temporary color pixel.
In this way, when the processing of steps S1 to S4 is completed for all the pixels constituting the document image (YES in step S5), the color pixel that certifies the color pixel based on the number of pixels that are recognized as temporary color pixels. An authorization process is executed (step S6).
[0021]
FIG. 4 is a flowchart showing the processing contents during the color pixel recognition processing.
Referring to FIG. 4, in the color pixel recognition process, each pixel constituting the original image is sequentially set as a target pixel, and the target pixel belongs to the halftone dot region based on the region data input from the region separation unit 13. Is determined (step T1). If the pixel of interest belongs to a halftone dot region (YES in step T1), it is included in a predetermined region (x rows × y columns (x <m, y <n)) centered on the pixel of interest. The number of temporary color pixels to be counted is counted (step T2). If the counted number of provisional color pixels is equal to or greater than a predetermined threshold value V2 (YES in step T3), the target pixel is recognized as a color pixel (step T4). If the number of temporary color pixels counted in step T2 is less than the threshold value V2 (NO in step T3), the target pixel is not recognized as a color pixel.
[0022]
On the other hand, when the target pixel is not a pixel belonging to the halftone dot region (NO in step T1), the target pixel is recognized as a color pixel as it is (step T4).
In this way, when the processing of steps T1 to T4 is completed for all the pixels constituting the document image (YES in step T5), the color pixel recognition processing is completed.
FIG. 5 is a flowchart showing the flow of processing in the color line detection unit 122.
[0023]
Referring to FIG. 5, the color line detection unit 122 counts the number of color pixels included in each line based on the processing result in the color pixel detection unit 121 with each row (main scanning direction) of the document image as one line. (Step E1). If the counted number of color pixels is equal to or greater than the predetermined threshold V3 (YES in step E2), the line is recognized as a color line (step E3).
On the other hand, when the number of color pixels counted in step E1 is less than the threshold value V3 (NO in step E2), the line is not recognized as a color line.
[0024]
However, the present invention is not limited to the configuration in which each row (main scanning direction) of the document image is defined as one line and the number of color pixels included in each line is counted, and each column (sub-scanning direction) of the document image is defined as one line. The configuration may be such that the number of color pixels included in each line is counted.
FIG. 6 is a flowchart showing the flow of processing in the document discrimination processing unit 123.
[0025]
Referring to FIG. 6, in document discrimination processing unit 123, first, the number of color lines included in the entire document image is counted based on the processing result in color line detection unit 122 (step P1). If the counted number of color lines is equal to or greater than a predetermined threshold value V4 (YES in step P2), the type of the original is determined to be a color original (step P3).
On the other hand, if the counted number of color lines is less than the threshold value V4 (NO in step P2), the type of the original is determined to be a monochrome original (step P4).
[0026]
In this embodiment, document discrimination can be performed in consideration of not only the density value data of each pixel but also the result of recognition as to whether or not each pixel belongs to a halftone dot region. Therefore, even when a document image includes a halftone dot area composed of color pixels, it is possible to satisfactorily prevent a document to be determined as a color document from being erroneously determined as a monochrome document.
In particular, the color pixel detection unit 121 recognizes the temporary color pixel based on the density value of each pixel, and then, based on the number of temporary color pixels in a predetermined area centered on the pixel that is recognized as belonging to the halftone dot area. Thus, the color pixels are recognized, and the document discrimination is performed based on the number of the color pixels, so that the document discrimination can be performed with higher accuracy. Therefore, even when a document image includes a halftone dot area composed of color pixels, it is possible to better prevent a document to be determined as a color document from being erroneously determined as a monochrome document.
[0027]
In addition, the color line detection unit 122 is configured to recognize a color line from each line constituting the document image based on the number of color pixels and perform document determination based on the number of color lines. Therefore, it is possible to perform document discrimination with higher accuracy. Therefore, even when the original image includes a halftone dot area composed of color pixels, it is possible to better prevent the original to be determined as a color original from being erroneously determined as a monochrome original.
[0028]
The present invention is not limited to the contents of the above embodiments, and various modifications can be made within the scope of the claims.
For example, in the above embodiment, a configuration has been described in which color pixels are identified based on the number of provisional color pixels included in a predetermined region centered on a pixel belonging to the halftone dot region. However, the present invention is not limited to this configuration. Alternatively, an average value of density values of pixels in a predetermined area centered on a pixel belonging to the halftone dot area may be calculated, and a color pixel may be recognized based on the average value.
[0029]
In the above-described embodiment, the digital color copying machine has been described as an example of the image forming apparatus. However, the present invention is not limited to the digital color copying machine, and is not limited to the digital color copying machine. It is also applicable to the device.
[Brief description of the drawings]
FIG. 1 is a block diagram illustrating a schematic configuration of an image forming apparatus including an image processing apparatus according to an embodiment of the present invention.
FIG. 2 is a block diagram illustrating a configuration of a document discrimination unit.
FIG. 3 is a flowchart showing a flow of processing in a color pixel detection unit.
FIG. 4 is a flowchart showing processing contents during color pixel recognition processing.
FIG. 5 is a flowchart illustrating a flow of processing in a color line detection unit.
FIG. 6 is a flowchart showing a flow of processing in a document discrimination processing unit.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Image processing apparatus 12 Document discrimination part 121 Color pixel detection part 122 Color line detection part 13 Area separation part

Claims (3)

A color image processing apparatus capable of performing image processing on input image data in different modes depending on whether the document type is a color document or a monochrome document,
Halftone pixel recognition means for recognizing pixels belonging to the halftone dot region from among the pixels constituting the document image;
Document identifying means for determining whether the document type is a color document or a monochrome document based on the recognition result by the halftone pixel recognition means and the density value data of each pixel included in the image data. A color image processing apparatus comprising: The document discrimination means is
Temporary color pixel recognition means for recognizing a temporary color pixel based on density value data of each pixel included in the image data;
Color pixel certifying means for certifying a color pixel based on the number of provisional color pixels in a predetermined area including pixels certified to belong to the halftone dot area by the halftone pixel certifying means,
2. A color image processing apparatus according to claim 1, wherein the color image processing apparatus determines whether the document type is a color document or a monochrome document based on the number of color pixels certified by the color pixel certification means. . The document discrimination means is
Based on the number of color pixels certified by the color pixel certification means, including a color line certification means for certifying a color line from each line constituting the document image,
3. The color image processing apparatus according to claim 2, wherein the color image processing apparatus determines whether the document type is a color document or a monochrome document based on the number of color lines recognized by the color line recognition means. .

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