JP2009055121A - Image processing device, image processing method, image forming apparatus and program, recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image processing device which can enhance the output image quality by enhancing the detection accuracy of characters existing in a dot area of non-white ground, and to provide an image processing method, an image forming apparatus and program, and a recording medium. <P>SOLUTION: A line width control section 24 controls the line width for character region detection, when a ground area or a dot area is determined by using the determination results of a ground judging section 22 and a dot judging section 23. As control content, detection width is made thin, regarding the detection of a character having ground density in the dot matrix. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image processing apparatus, an image processing method, an image forming apparatus, and a program for reading a document in which areas are mixed, discriminating areas using a plurality of feature amounts, and performing image quality optimization processing suitable for each area, The present invention relates to a recording medium.

  Image forming apparatuses such as copiers and printers using electrophotographic processes and ink jet systems can reproduce color images with high image quality as digital image processing technology advances. The machine has been commercialized.

  Document images copied using these image forming apparatuses include characters, halftone dots (printed photographs), line drawings, photographs (continuous tone areas such as photographic paper photographs), or originals in which they are mixed. In order to obtain a good reproducible image, it is necessary to perform image processing suitable for the configuration type of each document.

  In such a situation, in order to perform optimal processing according to the type of document configuration, information on a mask centered on the pixel of interest is used to create a character area, a dot area, and other areas (photo area, background area). There is an area separation process for separating character areas such as areas and areas not divided into halftone dot areas.

  In general, image data read from an image input device such as a scanner is divided into pixels or blocks composed of a plurality of pixels, and is identified as a character area, a halftone dot area, or another area. Furthermore, there is a case where the character area in the halftone dot is detected in order to clearly reproduce the character existing in the halftone dot area. Based on the identification result, optimum image processing for each region for improving image quality is performed. In particular, for black character areas, it is important to improve the output image quality by emphasizing resolution and reproducing in black. Similarly, it is desirable to detect the black character region existing in the background region as a black character region and perform adaptive processing for the black character region.

  However, since there is no white spot problem around the character edge and the detection accuracy does not increase in the character area detection in the background area having a high density, there is a conventional technique in which the following measures are taken.

  For example, the above-described problem exists in character detection on a background region having a high density. In order to improve the above problem, the image area separation device disclosed in Patent Document 1 is connected when performing character detection processing. When there are more than a certain number of non-halftone white pixels connected around a black pixel, it is detected as a character, so that no character detection is performed in a region with a high possibility of a picture region other than a white background. So that it is controlled.

  In addition to the above method, the digital image processing apparatus disclosed in Patent Document 2 detects the presence or absence of a background color separately from the detection of characters on a normal white background, and determines that a background color exists When the character edge exists, the character processing is performed. As a result, not only a character area can be detected for a character on a normal white background, but also a character edge can be detected for a predetermined density area determined to be detectable.

Japanese Patent No. 3118469 Japanese Patent No. 3725255

  However, in the image area separation device described in Patent Document 1, it is determined that a pattern area is present when a background having a predetermined density or more is present, and an edge in the pattern area is not erroneously detected as a character area. While it is possible to detect characters on a normal white background that can ensure accuracy, it is impossible to detect characters on a non-white background that exist at a certain density or more. In this case, image processing with an emphasis on resolution is not performed on characters on a non-white background so that the reproducibility is improved, and an output image quality with an increased black monochrome resolution cannot be obtained. In addition to not being able to perform high image quality processing, in general, halftone processing using a plurality of pixels is performed in order to improve gradation, which may further degrade the output image quality. Therefore, the sharpness of characters in the background area having density is inferior, and black characters are output as blurred characters.

  On the other hand, even in the method of detecting characters on a background with a density according to Patent Document 2, it is possible to ensure detection accuracy only by determining the presence of a background color and performing character detection with a specific background color. There is no consideration on how to improve the problem of white spots on difficult non-white backgrounds.

  An object of the present invention is to provide an image processing method, an image processing apparatus, an image forming apparatus, a program, and a recording medium capable of improving the accuracy of detecting a character existing in a halftone dot area of a non-white background and improving the output image quality. It is to be.

The present invention provides an image processing apparatus including an area separation processing unit that performs area determination on a pixel block including each pixel or a plurality of pixels of input image data.
The region separation processing unit
A character determination unit that determines whether each pixel or pixel block belongs to a character region;
A halftone dot determining unit that determines whether each pixel or pixel block belongs to a halftone dot region;
A background determination unit that determines whether or not each pixel or pixel block belongs to the background region,
In the character determination unit, the halftone dot determination unit determines that the region is a halftone dot region, and the background determination unit determines that the background region has a density higher than a predetermined density. An image processing apparatus comprising: a control unit that changes a range that is determined to be a character area.

  According to the present invention, when the control unit determines that the halftone dot region is a halftone dot region and the background determination unit determines that the background region has a density higher than a predetermined density, the character The range determined by the determination unit to be a character region is set to be narrower than when it is determined that the background region has a density lower than a predetermined density.

  Further, according to the present invention, the background determination unit determines whether the background region has a density higher than a predetermined density using surrounding pixel density information including the target pixel, and the control unit On the basis of the density value, a range determined by the character determination unit to be a character region is changed.

According to another aspect of the present invention, there is provided an image forming apparatus including the above-described image processing apparatus.
Further, the present invention provides an image processing method including an area separation process step of performing area determination on a pixel block including each pixel or a plurality of pixels of input image data.
The region separation processing step includes
A character determination step of determining whether each pixel or pixel block belongs to a character region;
A halftone dot determining step for determining whether each pixel or pixel block belongs to a halftone dot area;
And at least a background determination step for determining whether each pixel or pixel block belongs to the background area,
In the character determination step, the halftone dot determination step determines that the region is a halftone dot region, and the background determination step determines that the background region has a density higher than a predetermined density. An image processing method characterized by changing a range to be determined as a character area.

  According to the present invention, when the halftone dot determination step determines that the area is a halftone dot area, and the background determination step determines that the background area has a density higher than a predetermined density, the character determination step determines the character area. A range determined to be present is set to be narrower than a case where it is determined that the background region has a density lower than a predetermined density.

  The present invention is also an image processing program for causing a computer to function as the above-described image processing apparatus.

  Furthermore, the present invention is a computer-readable recording medium that records an image processing program for causing a computer to function as the above-described image processing apparatus.

  According to the present invention, in the region separation processing unit, the character determination unit determines whether each pixel or pixel block belongs to the character region, and the halftone dot determination unit determines whether each pixel or pixel block is a halftone dot region. The background determination unit determines whether each pixel or pixel block belongs to the background region.

  The control unit is determined by the halftone dot determination unit to be a halftone dot region, and when the background determination unit determines that the background region has a density higher than a predetermined density, and in other cases, The range that is determined to be a character area by the character determination unit is changed.

  For characters existing in a normal white background area, that is, an area determined to be a background area having a density lower than a predetermined density, output is performed by detecting a certain wide area including the character area as a character area. It is possible to improve the image quality. As an example, the black character area on the white background can be detected a little broadly and blacked out to suppress the color scattering around the character, or the emphasis filtering process can also remove a small density around the character (removal). It is possible to improve the sharpness of the character (can remove the roughness caused by a slight density remaining around the character).

  When the background area around the character is a background area with a density higher than a predetermined density, black characters are used for black color processing and emphasis filtering, especially when characters on a halftone dot are detected as a wide character area in the same way as characters on a normal white background. As a result, white spots appear as if the surroundings of the characters are white, resulting in image quality degradation. In general, detection of characters existing at halftone dots is more difficult than detection of normal characters, and thus detection accuracy may be inferior. In such a case, if the white spots detected as characters are conspicuous, the processing gap becomes abnormally conspicuous due to the interruption of the character detection result due to insufficient determination accuracy, and the image quality is significantly deteriorated.

  Therefore, when the halftone dot determination unit determines that the area is a halftone dot area, and the background determination section determines that the background area has a density higher than a predetermined density, the white background area is a character area. By changing the determination range, it is possible to improve the accuracy of detecting characters existing in the halftone dot area of the non-white background and to improve the output image quality.

  Further, according to the present invention, when the control unit determines that the halftone dot region is a halftone dot region and the background determination unit determines that the background region has a density higher than a predetermined density, The range determined by the character determination unit to be a character area is set narrower than when it is determined that the background area has a density lower than a predetermined density.

  The detection of characters existing in a halftone dot region of a non-white background may be inaccurate. In such a case, if the white spots detected as characters are conspicuous, the processing gap becomes abnormally conspicuous due to the interruption of the character detection result due to insufficient determination accuracy, and the image quality is significantly deteriorated.

  In contrast, according to the present invention, the detection range of character detection existing in the halftone dot region of the non-white background is narrowed to improve detection accuracy and prevent image quality deterioration.

  According to the invention, the background determination unit determines whether the background region has a density higher than a predetermined density using surrounding pixel density information including the target pixel, and the control unit Based on the density value of the background area, the range determined as the character area by the character determination unit is changed.

  Since the width of the determination range can be changed using density information around the pixel of interest, instead of actually calculating the line width of the character, a circuit reduction effect due to processing reduction can be expected. As an example, if the density of the background area is calculated based on the maximum value of the pixel mask around the pixel of interest, and the difference between the density and the density of the pixel to be processed is equal to or less than a predetermined threshold, the character is finally used as a character. Change the judgment range so that it is not detected.

  According to the invention, there is provided an image forming apparatus comprising the above-described image processing apparatus.

  Since white spots around characters existing in a halftone dot region of a non-white background can be suppressed, an image forming apparatus capable of outputting a high-quality image can be provided.

  According to the invention, in the region separation step, the character determination step determines whether or not each pixel or pixel block belongs to the character region, and the halftone dot determination step determines whether each pixel or pixel block is a halftone dot. It is determined whether or not it belongs to a region, and the background determination step determines whether or not each pixel or pixel block belongs to a background region.

  Therefore, the character determination is performed when the halftone dot determination step determines that the region is a halftone dot region, and when the background determination step determines that the background region has a density higher than a predetermined density, and otherwise. The range determined to be a character area in the process is changed.

  For characters existing in a normal white background area, that is, an area determined to be a background area having a density lower than a predetermined density, output is performed by detecting a certain wide area including the character area as a character area. It is possible to improve the image quality.

  If the halftone dot determination step determines that the region is a halftone dot region, and the background determination step determines that the background region has a density higher than a predetermined density, the white background region determines a character region. By changing the range, it is possible to improve the accuracy of detecting characters existing in the halftone dot area of the non-white background, and to improve the output image quality.

  According to the invention, when it is determined that the halftone dot region is a halftone dot region in the halftone dot determination step and the background determination step is a background region having a density higher than a predetermined density, the character determination step A range that is determined to be a character area is set to be narrower than that determined to be a background area having a density lower than a predetermined density.

  The detection of characters existing in a halftone dot region of a non-white background may be inaccurate. In such a case, if the white spots detected as characters are conspicuous, the processing gap becomes abnormally conspicuous due to the interruption of the character detection result due to insufficient determination accuracy, and the image quality is significantly deteriorated.

  In contrast, according to the present invention, the detection range of character detection existing in the halftone dot region of the non-white background is narrowed to improve detection accuracy and prevent image quality deterioration.

  According to the invention, the image processing apparatus can be realized by causing a computer to function as each unit of the image processing apparatus by an image processing program.

  According to the present invention, the image processing apparatus can be realized by causing a computer to function as each unit of the image processing apparatus by an image processing program read from a recording medium.

  FIG. 1 is a block diagram showing a configuration of an image processing apparatus 1 according to an embodiment of the present invention. In the present embodiment, a digital color copying machine will be described as an example of an image forming apparatus including the image processing apparatus 1.

  As shown in FIG. 1, the color image processing apparatus 1 includes an A / D (analog / digital) conversion unit 2, a shading correction unit 3, an input tone correction unit 4, and a region separation processing unit 5. Subsequently, the color correction unit 6, the black generation and under color removal unit 7, the spatial filter processing unit 8, the output gradation correction unit 9, the gradation reproduction processing unit 10, and the operation panel 11 are configured. In addition, a color image input device 12 and a color image output device 13 are connected to the color image processing device 1 to constitute a digital color copying machine as a whole.

The color image input device 12 (image reading means) is, for example, a CCD (Charge Coupled).
It is composed of a scanner unit equipped with (Device), and the reflected light image from the original is read by the CCD as RGB (R: red, G: green, B: blue) analog signals, and the RGB analog signals are subjected to color image processing. It is output to the device 1.

  The analog signal read by the color image input device 12 is subjected to A / D conversion processing, shading correction processing, input tone correction processing, and region separation processing in the color image processing device 1, followed by color correction processing. , Black generation and under color removal processing, spatial filter processing, output tone correction processing, tone reproduction processing in this order, and C (cyan), M (magenta), Y (yellow), K (black) digital color signals Is output to the color image output device 13.

  The A / D conversion unit 2 converts RGB analog signals into digital signals, and the shading correction unit 3 inputs a color image with respect to the digital RGB signals sent from the A / D conversion unit 2. Processing for removing various distortions generated in the illumination system, imaging system, and imaging system of the apparatus 12 is performed. The shading correction unit 3 converts RGB signals (RGB reflectance signals) into signals that are easy to handle in the image processing system employed in the color image processing apparatus 1, such as density signals, and performs processing for adjusting color balance. Do.

  The signal corrected by the shading correction unit 3 is input to the input tone correction unit 4. The input tone correction unit 4 removes the background from the input image signal input from the shading correction unit 3 and simultaneously performs image quality adjustment processing such as contrast. Further, the output density can be increased or decreased according to a user-specified density change instruction.

  Based on the RGB signal, the region separation processing unit 5 assigns each pixel in the input image to a black character region, a color character region, a halftone dot region, a halftone dot character region, and other regions if they do not belong to any region. Are to be separated. Further, the region separation processing unit 5 generates a region identification signal indicating which region the pixel belongs to based on the separation result, and generates a black generation and under color removal unit 7, a spatial filter processing unit 8, and a gradation reproduction processing unit 10. In addition, the RGB signal input from the input tone correction unit 4 is output to the subsequent stage as it is.

  The color correction unit 6 performs processing for removing color turbidity based on spectral characteristics of CMY color materials including unnecessary absorption components in order to realize faithful color reproduction, and the RGB signal is converted into a CMY signal. .

  The black generation and under color removal unit 7 generates black signals for generating K signals from the CMY three-color signals after color correction, and generates new CMY signals by subtracting the K signals obtained by black generation from the original CMY signals. Is to do. That is, the black generation and under color removal unit 7 changes the CMY three-color signal to the CMYK four-color signal.

  The spatial filter processing unit 8 performs spatial filter processing using a digital filter on the image data of the CMYK signal input from the black generation and under color removal unit 7 based on the region identification signal, and outputs by correcting the spatial frequency characteristics. Processing is performed to prevent image blurring and graininess deterioration.

  The output tone correction unit 9 performs output tone correction processing for converting a signal such as a density signal into a halftone dot area ratio that is a characteristic value of the color image output device 13.

  The gradation reproduction processing unit 10 performs gradation reproduction processing (processing for making it possible to reproduce each gradation by finally separating the image into pixels based on the region identification signal with respect to the image data of the CMYK signal. Halftone generation).

  The operation panel 11 is a setting button (for example, an image mode [character mode / character photo mode / photo mode, etc.] indicating a document type to be copied) that controls the operation of the display unit such as a liquid crystal display and the entire digital color copying machine. For example). Furthermore, it has a setting slide button for setting the density and background level.

An image processing method by the digital color copying machine having the above configuration will be described.
First, the color image input device 12 reads image data of a document as RGB analog signals and outputs them to the color image processing device 1. The color image processing apparatus 1 converts an input analog signal into an RGB digital signal by the A / D conversion unit 2 and outputs the RGB digital signal to the shading correction unit 3. The shading correction unit 3 removes various distortions generated in the illumination system, imaging system, and imaging system of the color image input device 12 from the input RGB digital signal and converts the RGB reflectance signal into a density signal. And output to the input tone correction unit 4. The input tone correction unit 4 adjusts the color balance and performs image quality adjustment processing such as contrast on the input image signal input from the shading correction unit 3, and then outputs it to the region separation processing unit 5.

  The region separation processing unit 5 applies each pixel in the input image to a character region (black character, color character), halftone dot region, halftone dot character region (black character, color character), or any region from the input RGB signal. When it does not belong, it is separated as other areas. Based on the separation result, the region separation processing unit 5 outputs a region identification signal indicating which region the pixel belongs to to the black generation and under color removal unit 7, the spatial filter processing unit 8, and the gradation reproduction processing unit 10. In addition, the input RGB signal is output to the color correction unit 6 as it is.

  The color correction unit 6 performs a process of removing color turbidity based on the spectral characteristics of the CMY color material including unnecessary absorption components from the input RGB signal, and then converts the CMY signal after color correction into a black generation and under color removal unit 7. Output to.

  The black generation and under color removal unit 7 performs black generation for generating a K signal from the input CMY signal and processing for generating a new CMY signal by subtracting the K signal from the input CMY signal. The CMY three-color signal is converted into a CMYK four-color signal and then output to the spatial filter processing unit 8.

As an example of the black generation processing, there is a method (general method) for generating black by UCR (under color removal processing). In this method, the input / output characteristic of the black generation curve is y = f (x), the input data is C, M, Y, the output data is C ′, M ′, Y ′, K ′, UCR (Under When the color removal rate is α (0 <α <1), the black generation and under color removal processing is expressed by the following equations (1) to (4).
K ′ = f {min (C, M, Y)} (1)
C ′ = C−αK ′ (2)
M ′ = M−αK ′ (3)
Y ′ = Y−αK ′ (4)

  The spatial filter processing unit 8 performs spatial filter processing using a digital filter on the input image data of the CMYK signal based on the region identification signal, and corrects the spatial frequency characteristics to reduce blur and graininess of the output image. Process to prevent. Further, similar to the spatial filter processing unit 8, the gradation reproduction processing unit 10 performs predetermined processing on the image data of the CMYK signal based on the region identification signal.

  For example, a region separated into characters (black characters, color characters) and halftone characters by the region separation processing unit 5 is used in a spatial filter by the spatial filter processing unit 8 in order to improve the reproducibility of black characters or color characters. Sharp enhancement processing is performed to increase the amount of enhancement at high frequencies. At the same time, the gradation reproduction processing unit 10 selects binarization or multi-value conversion on a high-resolution screen suitable for high-frequency reproduction.

  Further, with respect to the region separated into halftone dot regions by the region separation processing unit 5, the spatial filter processing unit 8 performs low-pass filter processing for removing the input halftone component. The output tone correction unit 9 performs output tone correction processing for converting a signal such as a density signal into a halftone dot area ratio that is a characteristic value of the color image output device 13, and then the tone reproduction processing unit 10. Then, gradation reproduction processing (halftone generation) is performed so that the image is finally separated into pixels and each gradation is reproduced.

  For the region separated into other regions by the region separation processing unit 5, the spatial filter processing unit 8 is subjected to a low-pass filter that does not reduce the sharpness for noise removal.

Here, the region separation processing unit 5 which is a feature of the present invention will be described.
FIG. 2 is a block diagram showing an electrical configuration of the region separation processing unit 5. The region separation processing unit 5 includes a character determination unit 20, an achromatic color determination unit 21, a background determination unit 22, a halftone dot determination unit 23, a line width control unit 24, a determination unit 25, and a final determination unit 26. In other words, the region separation processing unit 5 includes at least a character determination unit 20, a background determination unit 22, and a halftone determination unit 23.

  First, a general method of separating into a character region (divided into a black character region and a color character region), a halftone dot region, and other regions in the region separation processing unit 5 will be described with reference to FIG.

  As a method for separating input image data into a character area, a halftone dot area, and other areas, for example, a method described in “Image Electronics Society of Japan Proceedings 90-06-04” can be used. A general method for separating the separated character area into a black character area and a color character area will be described.

  Details will be described below. The following determination is performed within a block of M × N (M and N are natural numbers, for example, 7 × 7) pixels centered on the pixel of interest, and is used as a region identification signal of the pixel of interest.

  An average value (Dave) of signal levels is obtained for the pixels in the block, and each pixel in the block is binarized using the average value. Further, the maximum pixel signal level (Dmax), the minimum pixel signal level (Dmin), and the maximum density difference (Dsub) obtained by subtracting the minimum pixel level from the maximum pixel signal level are simultaneously obtained.

Since it is considered that the difference between the maximum signal level and the minimum signal level is large and the density is high in the character region, the character determination unit 20 belongs to the character region if the character region is identified by the following equation (5). Judge that it is.
Dsub> P _C or Dmin <P _B (5)

In order to determine whether or not the target pixel is an achromatic region, the achromatic color determination unit 21 first uses Daver, Daveg, and Daveb obtained by averaging the pixel of interest and neighboring pixels on each of the RGB planes ( 6) As shown in the equation, the maximum difference Ddiff between the average values is calculated.
Ddiff = MAX (Daver, Daveg, Daveb) -MIN (Daver, Daveg, Daveb) (6)

  MAX () and MIN () are functions that output the maximum value and the minimum value of the input Daver, Daveg, and Daveb, respectively.

When the value of Ddiff is equal to or greater than a predetermined value (for example, 20 or more), it can be determined as a chromatic pixel, and when it is smaller than the predetermined value (for example, smaller than 20), it can be determined as an achromatic pixel. In combination with the result of the character determination unit 20, the determination unit 25 can perform separation as an achromatic character or a chromatic character (color character). In other words, using the fact that the density is higher than the background, the halftone dot determination unit 23 identifies a halftone dot region. With respect to the binarized data, the number of change points from 0 to 1 in the main scanning and sub-scanning directions is obtained, and the number of change points from 1 to 0 is obtained as K _H and K _V , respectively, and the threshold values T _H and T _{V are obtained.} If both of them exceed the threshold, the halftone dot region is set. In order to prevent the erroneous determination of the background, comparing the previously determined Dmax, Dmin, threshold Dave B _1, B ₂ and.
Dmax−Dave> B ₁ , Dave−Dmin> B ₂ , and K _H > T _H ,
And K _V > T _V ... halftone dot area ... (7)

  Using the character detection result output from the determination unit 25 and the output result from the halftone dot determination unit 23, the final determination unit 26 performs final determination as described below and outputs the result from the region separation processing unit.

  By the above, it can be separated into a character region (black character, color character), a halftone region (halftone dot, black character in halftone dot, color character in halftone dot), and other regions.

  Subsequently, regarding the control of the line width, which is a feature of the present invention, the line width control unit 24 determines the background region or the halftone dot region using the determination result in the background determination unit 22 and the determination result in the halftone determination unit 23. It is assumed that the line width to be detected as a character area is controlled when it is done. Hereinafter, the processing content of the background determination unit 22 and the processing content of the line width control unit 24 will be described.

In the background determination unit 22, I × J (I and J are natural numbers, for example) different from the mask size centered on the pixel of interest, in order to determine a region having a certain density as a background region as a region with a background. , 7 × 7) pixel block maximum pixel level (Fmax) is used. This Fmax is compared with a threshold value K. When the enable signal corresponding to the background density is smaller than a predetermined threshold value, it is determined that the background area has a density. The value of K is calculated using various image samples. For example, 200 is set.
Fmax <K (8)

  The line width control unit 24 detects the line width as a character region when the background determination unit 22 determines that a background region having a predetermined density exists and when the halftone dot determination unit 23 determines that the background region is a halftone dot region. Control.

  The control method is to output an enable signal for the character edge detection area to the determination unit 25, and the determination unit 25 controls the line width by performing edge detection only in the area where the enable signal is ON. The enable signal is a permission signal that is detected as a character area, and even if this signal is ON, it is not determined as a character area if it is not detected as an edge.

  FIG. 3 is a diagram for explaining an example of generation of an enable signal for controlling the line width. In the normal white background area, the character area output from the determination unit 25 is output as it is as a character area, and therefore the entire area including the tail in the density distribution is detected as a character area as shown in FIG. On the other hand, when the background determination unit 22 determines that the background region has a high density and the halftone dot determination unit 23 determines that the region is a halftone dot region, the following enable signal is generated to control the line width of the character.

  As shown in FIG. 3B, when the maximum pixel level Fmax of the predetermined mask is the background density value, the enable signal is turned on when the density of the pixel to be processed does not fall within the range of the threshold density K from the background density (Fmax). And control to detect it as a character area. For other densities, the enable signal is turned off. This makes it possible to narrow the character detection width with the background density in the halftone dots.

  As described above, the method for narrowly controlling the character detection width of the background area where the predetermined density in the halftone dot exists may be the following method in addition to the simple method in which the calculation amount is reduced.

FIG. 4 is a diagram for explaining another method for controlling the line width.
As shown in FIG. 4A, an average value using the peripheral pixels for the input signal S is set as Save, and an area where the value obtained by subtracting the average value from the input pixel signal is 0 or more (equation (9)) is a high density area. And The threshold value can be set to other than 0.
S-Save ≧ 0 (9)

The range for calculating the average value may be about 7 × 7 pixel blocks, for example.
Subsequently, as shown in FIG. 2B, for example, a 3 × 3 pixel mask is used to count the pixels determined to be the high density region included in the mask for each pixel, and the count value is 0 Larger pixels (regions within the dotted line in FIG. 4B (including regions where S-Save ≧ 0)) where the enable signal output from the determination unit 25 is turned ON (in this 3 × 3 mask example) , S-Save ≧ 0 is an area in which one pixel is added outside the area).

  In other areas, even if an edge is detected, the line width can be controlled to be thin by turning off the enable signal.

FIG. 5 is a flowchart showing the region separation processing by the region separation processing unit 5.
In step S1, it is determined whether or not it is a halftone dot region. If it is a halftone dot region, the process proceeds to step S7, and if not a halftone dot region, the process proceeds to step S2.

  In step S2, it is determined whether or not the pixel is an edge pixel. If the pixel is an edge pixel, the process proceeds to step S3. If the pixel is not an edge pixel, the process proceeds to step S6 to determine the other region. In step S3, it is determined whether or not the color is an achromatic color, and if it is an achromatic color, it is determined in step S4 that it is a black character region, and if it is not an achromatic color, it is determined that it is a color character region.

  In step S7, it is determined whether the background density has a density equal to or higher than a predetermined density. If the density is higher than the predetermined density, the process proceeds to step S8. If the density is lower than the predetermined density, the halftone dot area is determined in step S12. It is determined that

  In step S8, it is determined whether the pixel is an edge pixel and the enable signal is ON. If the pixel is an edge pixel and the enable signal is ON, the process proceeds to step S9 to determine whether the pixel is an edge pixel and enable. If the signal does not satisfy any of the ON states, the process proceeds to step S12 and is determined to be a halftone dot region.

  In step S9, it is determined whether or not the color is an achromatic color. If it is an achromatic color, it is determined in step S10 that it is a black character area in a halftone dot. .

  As described above, the image processing method for narrowing the character detection width for the area where the background density is higher than the predetermined density in the halftone dot area may be realized as software (application program) according to another embodiment. Good. In this case, it is possible to provide a computer or scanner with a scanner driver incorporating software that realizes control of suitable image processing by determining a halftone dot region and a background region and switching the character detection width to a normal character.

  FIG. 6 is a block diagram showing a configuration of an image reading apparatus (flatbed scanner) according to another embodiment of the present invention.

  As shown in the figure, the color image processing device 30 includes an A / D conversion unit 2, a shading correction unit 3, an input tone correction unit 4, and a region separation processing unit 5. The apparatus 12 is connected to constitute an image reading apparatus as a whole.

The color image input device (image reading means) 12 is, for example, a CCD (Charge Coupled).
A reflected light image from a document is read by a CCD as an RGB (R: red, G: green, B: blue) analog signal and input to a color image processing apparatus. Is.

  The analog signal read by the color image input device 12 is sent through the color image processing device 30 in the order of the A / D conversion unit 2, the shading correction unit 3, the input tone correction unit 4, and the region separation processing unit 5. Then, it is output as an RGB digital color signal to a personal computer or a printer.

  The processing contents of the A / D (analog / digital) conversion unit 2, the shading correction unit 3, the input tone correction unit 4, and the region separation processing unit 5 are the same as those of the image processing apparatus 1 shown in FIG.

  The image data that has been subjected to each processing described above is input to a computer or a printer, and subjected to color correction processing, spatial filter processing, gradation reproduction processing, and the like. The above processing is controlled by a CPU (Central Processing Unit) (not shown).

  Further, according to the present invention, a background density is higher than a predetermined density in a halftone dot area on a computer-readable recording medium in which program code (executable program, intermediate code program, source program) for causing a computer to execute is recorded. It is also possible to record a method of narrowing the detection width of characters for an area.

  As a result, the output image quality can be improved when image processing is adaptively performed by changing the normal character detection width and the detection width of the character existing in the background area having a predetermined density or higher in the halftone dot area. A recording medium in which the processing program code is recorded can be provided in a portable manner.

  The recording medium may be a memory (not shown) such as a program medium such as a ROM because processing is performed by a microcomputer, and a program reading device as an external storage device (not shown) is provided, and the recording medium is stored therein. It may be a program medium that can be read by being inserted.

  In any case, the stored program code may be configured to be accessed and executed by the microprocessor, or the program code is read, and the read program code is a program (not shown) of the microcomputer. It may be downloaded to the code storage area and the program code may be executed. In this case, it is assumed that the download program is stored in the main device in advance.

Here, the program medium is a recording medium configured to be separable from the main body, such as a tape system such as a magnetic tape or a cassette tape, a magnetic disk such as a flexible disk or a hard disk, and a CD-ROM / MO / MD / DVD. Optical discs, card systems such as IC cards (including memory cards) / optical cards, mask ROM, EPROM (Erasable Programmable Read Only Memory), EEPROM (Electrically
Erasable Programmable Read Only Memory), a medium that carries a fixed program including a semiconductor memory such as a flash ROM may be used.

  In this case, since the system configuration is capable of connecting a communication network including the Internet, the medium may be a medium that dynamically carries the program code so as to download the program code from the communication network. When the program code is downloaded from the communication network in this way, the download program may be stored in the main device in advance or installed from another recording medium.

  The recording medium is read by a program reading device provided in a digital color image forming apparatus or a computer system, whereby the above-described image processing method is executed. The present invention can also be realized in the form of a computer data signal embedded in a carrier wave in which the program code is embodied by electronic transmission.

  The computer system includes an image input device such as a flatbed scanner, a film scanner, and a digital camera, a computer that performs various processes such as the image processing method by loading a predetermined program, and a CRT that displays the processing results of the computer. It is composed of an image display device such as a display and a liquid crystal display, and a printer that outputs the processing results of the computer to paper. Furthermore, a network card, a modem, and the like are provided as communication means for connecting to a server or the like via a network.

1 is a block diagram illustrating a configuration of an image processing apparatus 1 according to an embodiment of the present invention. 3 is a block diagram showing an electrical configuration of a region separation processing unit 5. FIG. It is a figure for demonstrating an example of the enable signal generation for controlling line | wire width. It is a figure for demonstrating the other method for controlling line | wire width. 5 is a flowchart showing region separation processing by a region separation processing unit 5; It is a block diagram which shows the structure of the image reading apparatus which is other embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Color image processing apparatus 2 A / D (analog / digital) conversion part 3 Shading correction part 4 Input gradation correction part 5 Area separation processing part 6 Color correction part 7 Black generation lower color removal part 8 Spatial filter processing part 9 Output floor Tone correction unit 10 Tone reproduction processing unit 11 Operation panel 12 Color image input device 13 Color image output device

Claims (8)

In an image processing apparatus including an area separation processing unit that performs area discrimination for a pixel block including each pixel or a plurality of pixels of input image data,
The region separation processing unit
A character determination unit that determines whether each pixel or pixel block belongs to a character region;
A halftone dot determining unit that determines whether each pixel or pixel block belongs to a halftone dot region;
A background determination unit that determines whether or not each pixel or pixel block belongs to the background region,
In the character determination unit, the halftone dot determination unit determines that the region is a halftone dot region, and the background determination unit determines that the background region has a density higher than a predetermined density. An image processing apparatus comprising: a control unit that changes a range determined to be a character area.   The control unit determines that the halftone dot region is a halftone dot region, and the character determination unit determines that the character region is a background region having a density higher than a predetermined density. 2. The image processing apparatus according to claim 1, wherein a range that is determined to be is set to be narrower than a range that is determined to be a background region having a density lower than a predetermined density.   The background determination unit determines whether or not the background region has a density higher than a predetermined density using surrounding pixel density information including the target pixel, and the control unit is based on the density value of the background region. The image processing apparatus according to claim 1, wherein a range that is determined to be a character area by the character determination unit is changed.   An image forming apparatus comprising the image processing apparatus according to claim 1. In an image processing method having a region separation processing step of performing region determination on a pixel block made up of each pixel or a plurality of pixels of input image data,
The region separation processing step includes
A character determination step of determining whether each pixel or pixel block belongs to a character region;
A halftone dot determining step for determining whether each pixel or pixel block belongs to a halftone dot area;
And at least a background determination step for determining whether each pixel or pixel block belongs to the background area,
In the character determination step, the halftone dot determination step determines that the region is a halftone dot region, and the background determination step determines that the background region has a density higher than a predetermined density. An image processing method characterized by changing a range determined to be a character area.   A range that is determined to be a character region in the character determination step when it is determined in the halftone dot determination step that the region is a halftone dot region, and the background determination step is determined to be a background region having a density higher than a predetermined density. The image processing method according to claim 5, wherein the image processing method is set to be narrower than a case where it is determined that the background region has a density lower than a predetermined density.   An image processing program for causing a computer to function as the image processing apparatus according to claim 1.   A computer-readable recording medium having recorded thereon an image processing program for causing the computer to function as the image processing apparatus according to claim 1.

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