JP2007329662A - Image processor, image processing method, image forming apparatus, and computer program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image processor and an image processing method that can improve reproducibility of characters by improving precision of color decision making by employing different color decision systems according to whether the characters are wide or narrow in line width, to provide an image forming apparatus equipped with the image processor, and to provide a computer program for achieving the image processor. <P>SOLUTION: Based upon an input RGB signal, a mask which includes a pixel of interest and its peripheral pixels is set for each pixel. When the line width is decided to be narrow, a first color deciding unit 43 makes a color decision based upon a mean value of pixel information in the mask as a feature quantity and when the line width is decided to be wide, a second color deciding unit 44 decides a color decision based upon the difference between color components having a maximum value of the pixel information in the mask as a feature quantity. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  In the present invention, when determining which pixel of interest in an input image belongs to among a plurality of region classifications based on neighboring pixel information, the color determination means is selected depending on the width of the line width, thereby selecting the region classification. The present invention relates to an image processing apparatus that performs suitable image processing, an image processing method, an image forming apparatus including the image processing apparatus, and a computer program for realizing the image processing apparatus.

  With the recent development of digital image processing technology, image forming apparatuses such as digital color copying machines or color digital multifunction peripherals that reproduce color images with high image quality have been commercialized. An image forming apparatus such as a copying machine using an electrophotographic process or an ink jet method is designed to output input after digitizing input image information and performing various processing instead of a conventional analog method. Such products tend to become popular.

  Document images copied using these image forming apparatuses may be characters, line drawings or photographs, or a document in which they are mixed. In order to obtain a good reproducible image, it is required to perform image processing suitable for each type, such as sharpening processing for character portions or smoothing processing for photo portions.

  In order to perform optimum processing according to the document configuration type, it is necessary to determine the configuration type of the entire document image or each region in the document image. In order to make this determination, the document image is divided into a predetermined area consisting of the pixel of interest and its neighboring pixels, and a character area, halftone dot area, or other area (based on the pixel value included in the predetermined area) There is an area discrimination process for discriminating to “photo area: photographic paper photograph”.

  In general, image information read by a color image input device such as a scanner is divided into blocks each including a pixel of interest and its neighboring pixels, and a character area, a halftone dot area, or other area is divided for each pixel of interest or for each block. Which one belongs to each other is determined, and the determination results are combined to determine the region type. Further, when determining whether or not it belongs to the character area, it is not only detected whether or not there is an edge area, but it is also determined whether the character belongs to an achromatic area or a chromatic area. The If it is determined that the block to be determined belongs to the character area and belongs to the achromatic area, the block is determined to be a black character area, and the black generation amount is increased for the block and enhancement processing is performed. On the other hand, if it is determined that it belongs to the character area and belongs to the chromatic color area, the block to be determined is determined to be a color character area, and the block is simply subjected to enhancement processing without increasing the black generation amount. By performing image processing suitable for the character color in the character area as described above, the sharpness of the character and the reproducibility of the image quality can be improved when outputting the read original.

  Whether the image belongs to the achromatic color region or the chromatic color region is determined.If the pixel information belongs to the achromatic color region, the pixel information such as the density between the respective color components of the target pixel is equal or almost the same, and there is almost no difference. In the case of belonging, the pixel information between the color components of the pixel of interest is performed using the feature that it differs according to the color characteristics. Specifically, when the difference between the maximum value and the minimum value of the pixel information between each color component in the target pixel is equal to or greater than a predetermined threshold value, it is determined that the pixel belongs to the chromatic color region.

  However, depending on the reading accuracy of the original of the scanner, a phenomenon that pixel information of each color component at the same position is detected as pixel information of a color component at a different position when reading a black character or a black line, that is, the pixel information is a color component. A pixel shift detected by shifting the position between them may occur. When a pixel shift occurs, there is a difference between the color components in the pixel information of the target pixel located at the edge portion. In addition, the steepest rising or falling gradient of the edge of the character is, the greater the difference in pixel information between the color components of the pixel of interest located at the edge when a pixel shift occurs. However, in the determination based on the difference between the maximum value and the minimum value of the pixel information between the color components described above with respect to the target pixel in the edge portion, the difference in the pixel information between the color components is actually the chromatic color region It is not possible to distinguish between the difference between the color components due to belonging to the color difference or the difference between the color components due to pixel shift. Therefore, in actuality, a pixel belonging to the black character region is erroneously determined as a pixel belonging to the chromatic color region, and image processing suitable for the black character cannot be performed, resulting in image quality degradation.

Therefore, even if it is determined that the target pixel belongs to the chromatic color area, if a predetermined number or more of pixels belonging to the achromatic color area are included in the predetermined area including the target pixel and its neighboring pixels, A technique for re-determining that the image belongs to an achromatic region is disclosed (Patent Document 1). Thereby, it is possible to avoid erroneously determining that a pixel belonging to a black character area in which a pixel shift occurs during reading belongs to a color character area.
Japanese Patent No. 3048158

  By the way, the pixel information of each color component of the pixel of interest may be out of color balance due to a difference in MTF (Modulation Transfer Function) of an image input device such as a scanner in addition to pixel shift. In this case, even when the target pixel actually belongs to the black character region, the pixel information of the edge portion is detected with the balance being lost among the color components. When the line width of the black character area is narrow, the width of the rising edge of the edge from the background area to the black character area and the falling edge of the edge from the black character area to the background area is narrow, and therefore, due to the difference in MTF at the edge area. The effect of the loss of balance among the color components becomes significant. When the line width is narrow, the number of pixels belonging to the black character area other than the edge part is originally small. For this reason, the number of pixels that are determined to be pixels that belong to the achromatic color region in which the pixel information between the respective color components is equal in the vicinity of the target pixel does not reach a predetermined number.

  Therefore, in the technique disclosed in Patent Document 1, when there is a loss of balance in pixel information between each color component due to the difference in MTF, it is determined as a chromatic color region without being determined again as belonging to the achromatic region, It is determined as a color character area. For this reason, it should be emphasized by increasing the amount of ink generated and sharpening the characters, so that the emphasis processing is performed without increasing the amount of ink generated. In some cases, it is formed in a turbid color and is expressed with blurred characters.

  Also, the difference in pixel information between color components at the pixel of interest at the edge portion differs in characteristics depending on the line width between the difference due to pixel shift and the difference due to the difference in MTF. If the determination based on the difference between the color components due to the pixel shift and MTF difference when the line width is narrow is applied to the case where the line width is wide, the target pixel belonging to the black character area is erroneously determined to belong to the chromatic color area. May end up.

  The present invention has been made in view of such circumstances, and image processing capable of improving the accuracy of color determination and improving the reproducibility of characters by using different color determination methods depending on the line width of the characters. An apparatus, an image processing method, an image forming apparatus including the image processing apparatus, and a computer program for realizing the image processing apparatus are provided.

  Another object of the present invention is to absorb the loss of balance even when the balance of each color component is lost due to the difference in MTF between the color components, which is noticeable when the line width of the character is narrow. Provided are an image processing apparatus, an image processing method, an image forming apparatus provided with the image processing apparatus, and a computer program for realizing the image processing apparatus capable of improving the accuracy of color determination and improving the reproducibility of characters. There is.

  Another object of the present invention is to improve the accuracy of color determination by absorbing the pixel shift even when a pixel shift that causes a significant shift when the line width of the character is wide is achieved, and the character reproducibility is improved. An image processing apparatus, an image processing method, an image forming apparatus including the image processing apparatus, and a computer program for realizing the image processing apparatus.

  The image processing apparatus according to the present invention uses any one pixel in an input image composed of a plurality of pixels represented by a plurality of color components as a target pixel, and determines whether the target pixel belongs to a character area or not. In the image processing apparatus that includes a region determination unit that determines based on information and determines an input image into a plurality of region classifications, and performs processing suitable for the region classification for each determined region on the input image, the region determination unit includes: Means for detecting the line width of the character; means for determining the width of the detected line width; a plurality of color determining means for determining whether the pixel of interest belongs to the achromatic region or the chromatic region; and the line width And means for selecting one of the plurality of color determination means.

  In the image processing apparatus according to the present invention, one of the color determination means is a means for calculating an average value of the densities of the target pixel and neighboring pixels for each color component, and a maximum difference between the calculated average values of the color components. Means for calculating as a feature amount, and determining whether the target pixel belongs to an achromatic region or a chromatic region from the feature amount.

  In the image processing apparatus according to the present invention, one of the color determination means includes a means for calculating the minimum value or the maximum value of the density of the target pixel and the neighboring pixel for each color component, and the calculated minimum or maximum color component. Means for calculating a maximum difference between them as a feature amount, and determining whether the target pixel belongs to an achromatic color region or a chromatic color region from the feature amount.

  The image processing method according to the present invention uses any one pixel in an input image composed of a plurality of pixels represented by a plurality of color components as a target pixel, and determines whether the target pixel belongs to a character area or not. In an image processing method for determining based on information, determining an input image into a plurality of region classifications, and performing processing suitable for the region classification on the input image for each of the determined regions, the line width of the character is detected, and the detected line Determine whether the width is wide or narrow, select one of multiple color determination methods to determine whether the pixel of interest belongs to the achromatic color region or the chromatic color region, and select the selected color determination method. In this determination, it is determined whether the target pixel belongs to an achromatic character region or a chromatic character region.

  In the image processing method according to the present invention, according to one of the color determination methods, the average value of the density of the target pixel and the neighboring pixel is calculated for each color component, and the maximum difference between the color components of the calculated average value is a feature amount. And determining whether the pixel of interest belongs to the achromatic color region or the chromatic color region based on the calculated feature amount.

  In the image processing method according to the present invention, one of the color determination methods is to calculate the minimum value or the maximum value of the density of the target pixel and neighboring pixels for each color component, and between the calculated minimum value or maximum value color components. Is calculated as a feature amount, and it is determined based on the calculated feature amount whether the target pixel belongs to an achromatic color region or a chromatic color region.

  An image forming apparatus according to the present invention includes any one of the above-described image processing apparatuses according to the present invention and an image forming unit that forms an image based on an input image processed by the image processing apparatus. And

  The computer program according to the present invention uses any one pixel in an input image composed of a plurality of pixels represented by a plurality of color components as a target pixel, and determines whether or not the target pixel belongs to a character area. In the computer program for causing a computer to execute the step of determining based on the step and the step of determining the input image into a plurality of region classifications, the computer detects the line width of the character and the width of the detected line width. A step of determining, a plurality of color determination steps for determining whether the target pixel belongs to an achromatic color region or a chromatic color region, and a step of selecting one of the plurality of color determination steps according to the line width Are executed.

  The computer program according to the present invention is characterized in that one of the color determination steps is a step of calculating an average value of densities of a target pixel and a neighboring pixel for each color component and a maximum difference between the calculated average values of the color components. And a step of determining whether the pixel of interest belongs to an achromatic color region or a chromatic color region based on the calculated feature amount.

  In the computer program according to the present invention, one of the color determination steps is to calculate a minimum value or a maximum value of the density of the target pixel and neighboring pixels for each color component, and between the calculated minimum value or maximum value color components. And a step of determining whether the target pixel belongs to an achromatic color region or a chromatic color region based on the calculated feature amount.

  In the present invention, when the pixel of interest belongs to the character area among the pixels constituting the input image information, the line width of the character is determined, and each color varies depending on the width of the character line width. A color determination method is selected that suits how pixel information is shifted between components.

  In the present invention, even when the image information between the originally equal color components is shifted due to occurrence of pixel shift and MTF difference in the target pixel, if the line width of the character is narrow, the entire line width is reduced. The average value of the density in the predetermined area to be covered is calculated, and it is determined whether it belongs to the chromatic color area or the achromatic color area by the color determination method that absorbs the shift between the color components of the pixel information of the target pixel. .

  In the present invention, even if the pixel information between each color component that is essentially equal is shifted due to the occurrence of pixel shift and the MTF difference in the target pixel, if the line width of the character is wide, The density difference at the position where the influence of the shift is small is calculated, and it is determined whether it belongs to the chromatic color area or the achromatic color area by the color determination method that absorbs the shift between the color components of the pixel information of the target pixel. To do.

  In the case of the present invention, a color determination unit that is suitable for the shift of pixel information between color components when reading a document image, which varies depending on the line width of a black character, is selected, and the target pixel belongs to the achromatic region Therefore, it is possible to improve the accuracy of color determination as to whether the color belongs to a chromatic color region and to improve the reproducibility of characters.

  In the case of the present invention, when the line width of the black character is narrow, the color determination means suitable for how to lose the balance due to the difference in MTF between the color components when reading the original image is selected, and the line width is narrow To improve the accuracy of color determination whether the pixel of interest belongs to the achromatic region or the chromatic region by absorbing the way the balance of each color component is lost due to the MTF difference that becomes noticeable. Can be increased.

  According to the present invention, when the line width of black characters is wide, a color determination means suitable for pixel shift between each color component when reading an original image is selected, and pixel shift that becomes noticeable when the line width is wide By absorbing the image information shift between each color component, the accuracy of color determination as to whether the target pixel belongs to the achromatic color area or the chromatic color area can be improved, and the reproducibility of the characters can be improved. .

(Embodiment 1)
Hereinafter, the present invention will be specifically described with reference to the drawings showing embodiments thereof.

  FIG. 1 is a block diagram illustrating a configuration of an image forming apparatus including an image processing apparatus according to the present invention. The image forming apparatus includes a color image input device 11 that reads a document image, an image processing device 10 that performs predetermined processing on the input image information, and a color image output device 12 that forms the processed image information on a sheet. And an operation panel 13 for receiving user operations.

  The color image input device 11 is a scanner having, for example, a CCD (Charge Coupled Device), projects white light onto a document, and reflects reflected light images from the document to R (red), G (green), and B (blue). Light is received by the CCD through the filter, read as analog signals of RGB color components, and output to the image processing apparatus 10. The image processing apparatus 10 performs predetermined processing described below on each analog signal of RGB, and converts it into a digital color signal of C (cyan) M (magenta) Y (yellow) K (black) to produce a color image. Output to the output device 12. The color image output device 12 is an electrophotographic or inkjet printer that forms an image on a sheet based on CMYK digital color signals input from the image processing device 10. The color image output device 12 may be a display device such as a display.

  The operation panel 13 includes, for example, a touch panel type liquid crystal display device and various keys such as a numeric keypad and various setting buttons. The user can control the operation of the image forming apparatus via the operation panel 13. The user determines the type of sheet on which an image is to be formed and the processing in the image processing apparatus 10 depending on whether the type of the read original is a text original, an original composed of characters and photos, or a photo original. And can be selected. The operation panel 13 displays an operation state of the image forming apparatus or a message to the user.

  The image processing apparatus 10 includes an A / D (analog / digital) conversion unit 1, a shading correction unit 2, an input tone correction unit 3, an area determination processing unit 4, a color correction unit 5, and a black generation lower color. Consists of, for example, an ASIC (Application Specific Integrated Circuit) having a removal unit 6, a spatial filter processing unit 7, an output tone correction unit 8, a tone reproduction processing unit 9, and a CPU 101 that controls each unit. Is done. The CPU 101 sequentially inputs / outputs image information obtained and input every time the line is scanned by the color image input device 11 to each of the components in synchronization with a horizontal synchronization signal, and sequentially processes by pipeline control. I do.

  RGB analog signals input to the image processing apparatus 10 are first input to the A / D converter 1 and converted into digital signals. The RGB signal converted into the digital signal is input to the shading correction unit 2. The shading correction unit 2 performs processing for removing various distortions generated in the illumination system, the imaging system, and the imaging system of the color image input device 11 from the input RGB digital signal. Input to the correction unit 3.

  The input tone correction unit 3 converts the input RGB signal (RGB reflectance signal) into a signal that can be easily handled by the image processing method employed in the image processing apparatus 10, adjusts the color balance, and adjusts the background density. Image quality adjustment processing such as removal or contrast adjustment is performed. The processed RGB signal is input to the region discrimination processing unit 4.

  The area discrimination processing unit 4 discriminates each pixel in the input image from a black character area, a color character area, a halftone dot area, or another area that does not belong to any area based on the input RGB signal. An area identification signal indicating which area the pixel belongs to is output from the area discrimination processing unit 4 based on the discrimination result to the color correction unit 5, the black generation and under color removal unit 6, the spatial filter processing unit 7, and the gradation. Input to the reproduction processing unit 9. In the region discrimination processing unit 4, the input RGB signal is output as it is and input to the color correction unit 5.

  The color correction unit 5 converts the input RGB signal into an additive color mixing CMY signal for printing. At the same time, processing for removing color turbidity based on the spectral characteristics of the CMY color materials including unnecessary absorption components is performed to faithfully reproduce the color based on the region identification signal input from the region determination processing unit 4. The processed CMY signal is input to the black generation and under color removal unit 6.

  The black generation and under color removal unit 6 performs a process of replacing the color at the position where all of the CMY signals overlap with the K signal (black) from the CMY signal after color correction, and newly converting it to a CMYK signal. If the density of each CMY of the CMY signals is equal and corresponds to black, or if the area identification signal input from the area determination processing unit 4 determines that the area is a black character area, a K signal is generated and the original CMY signal is generated. The processing corresponding to the K signal generated from the above is subtracted. The processed CMYK signal is input to the spatial filter processing unit 7.

  A UCR (Under Color Removal) process which is an example of a process in the black generation and under color removal unit 6 will be described. The input 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 ′, and the UCR rate is α ( If 0 <α <1), the data output by the black generation and under color removal processing are K ′ = f {min (C, M, Y)}, C ′ = C−αK ′, and M ′ = M. −αK ′, Y ′ = Y−αK ′.

  The spatial filter processing unit 7 performs spatial filter processing using a digital filter on the input CMYK signal simultaneously based on the region identification signal input from the region discrimination processing unit 4, and corrects the spatial frequency characteristics to obtain color. Blur or graininess deterioration of the output image in the image output device 12 is prevented. The region determined to be a black character region or a color character region by the region determination processing unit 4 is subjected to sharp emphasis processing to emphasize high frequency components. A low-pass filter process is performed on the area determined as the halftone dot area by the area determination processing unit 4 to remove the input halftone dot component. Further, the region discriminated by the region discriminating unit 4 is subjected to low-pass filter processing that does not reduce the sharpness, and noise is removed. The processed CMYK signal is input to the output tone correction unit 8.

  The output tone correction unit 8 performs output tone correction processing for converting the input CMYK signal into a halftone dot area ratio that is a characteristic value of the color image output device 12. The processed CMYK signal is input to the gradation reproduction processing unit 9.

  The gradation reproduction processing unit 9 performs gradation reproduction processing (halftone processing) for processing the input CMYK signal so that each gradation can be reproduced based on the region identification signal input from the region determination processing unit 4 at the same time. Generation) is performed for each pixel. For example, binarization processing is performed on an area determined as a black character area by the area identification signal so as to be suitable for the gradation reproducibility of the color image output device 12.

  The image information of the CMYK signal that has been subjected to the above-described processes and is finally output from the gradation reproduction processing unit 9 is temporarily stored in an image buffer memory (not shown), and is read out at a predetermined timing to be read out by the color image output device 12. Is input.

  Next, the area determination process in the area determination processing unit 4 will be described. FIG. 2 is a block diagram illustrating a configuration of the area determination processing unit 4 of the image processing apparatus 10 according to the first embodiment. The area determination processing unit 4 includes at least a character determination unit 41, a line width determination unit 42, a first color determination unit 43, a second color determination unit 44, a comprehensive character determination unit 45, and a halftone dot determination unit 46. And a comprehensive determination unit 47.

  The character determination unit 41 determines whether or not the character area belongs to the character area by utilizing the feature that the difference between the maximum value and the minimum value of the pixel signal level is large and the density is high in the character area. The character determination unit 41 sets an M × N mask (for example, 3 × 3) including the target pixel and its neighboring pixels based on the input RGB signal, and performs the following for each RGB color component in the mask. Judgment is made.

An average pixel signal level Dave, a maximum pixel signal level Dmax, a minimum pixel signal level Dmin, and a difference Dsub between the maximum pixel signal level and the minimum pixel signal level are obtained for 9 pixels in a mask composed of 3 × 3 pixels. When P _A , P _B , and P _C are respectively compared with the values obtained as described above, such as the average pixel level, as predetermined threshold values, and any one of Dmax> P _A , Dmin <P _B , or Dsub> P _C is satisfied Is determined to belong to the character area. The character determination unit 41 outputs a determination signal indicating the determination result to the comprehensive character determination unit 45. For example, “1” is output when it is determined that it belongs to the character area, and “0” is output when it is determined that it does not belong to the character area.

  When the line width of the character or line drawing is narrow, the line width determination unit 42 uses the feature that both the rising edge and the falling edge of the large change in the pixel signal level exist in the small region, and thereby the line width is narrowed. judge. The line width determination unit 42 sets an M × N mask (for example, 5 × 5) including the target pixel and its neighboring pixels based on the input RGB signal, and the density of the G signal from the RGB signal in the mask. Is extracted and the following determination is made.

FIG. 3 is a schematic diagram illustrating an example of a mask set by the line width determination unit 42 of the image processing apparatus 10 according to the first embodiment. FIG. 3A shows a case where the mask matches the edge portion of the character area having a narrow line width, and FIG. 3B shows a case where the mask matches the character area having a wide line width. The line width determination unit 42 uses the pixel (i−2, j−2) at the upper left corner in the 5 × 5 mask including the target pixel (i, j) as a starting point, the five pixels (i−2, j) in the horizontal direction. -2), (i-1, j-2), (i, j-2), (i + 1, j-2), (i + 2, j-2) and the concentration sum sum _x (0) is calculated, Similarly, the density sum sum _x (l) is similarly calculated for l = 0, 1,..., 4 for each row in the mask (Equation 1). Similarly, the density sum sum _y (l) is calculated for each column for l = 0, 1,..., 4 starting from the pixel (i−2, j−2) at the upper left corner in the mask (Formula 2).

Next, the line width determination unit 42 calculates a difference in density sum for each adjacent row and a difference in density sum for each adjacent column based on the density sum of each row and each column. The difference of the density sum between the j-2 row and the j-1 row is calculated as diff _x (0) = sum _x (1) −sum _x (0), and similarly, the density is calculated for each adjacent row. The sum difference diff _x (m) is calculated for m = 0, 1, 2, 3, respectively (Equation 3). Similarly, each column is calculated. pixel density for each column difference density sum and the calculated _{diff y (0) = sum y} (1) -sum y (0), adjacent to the same between the i-2 column and i-1 column The sum difference diff _y (m) is calculated for m = 0, 1, 2, 3 respectively. (Formula 4)

The presence / absence of rise and fall of the change in the pixel signal level is determined as follows based on the above calculation result. If there are actually rising and falling edges of the character in the mask, the amount of change in density should be a certain amount or more. Therefore, by setting a threshold of variation as T _width, the difference diff _x (m) or diff _y (m), respectively 's absolute value respectively whether the threshold T _width greater than m = 0, 1, 2, 3 And the horizontal component and the vertical component, respectively, and the number of rising edges and falling edges in the mask are counted. Let cntUP _x (i, j), cntUP _y (i, j), cntDOWN _x (i, j), cntDOWN _y (i, j) be the number of rising and falling edges in the mask of the pixel of interest (i, j). The initial value 0 is substituted for each.

For example, when the threshold T _width is set to 75 and diff _x (m) ≧ 75 is satisfied, it is determined that there is a rising edge of the pixel signal level change in the mask, and 1 is set to the rising number cntUP _x (i, j). Addition is not performed when diff _x (m) ≧ 75 is not satisfied (Formula 5). When diff _x (m) ≦ −75 is satisfied, it is determined that there is a falling edge of the change in the pixel signal level in the mask, and 1 is added to the falling number cntDOWN _x (i, j), and diff _x (m ) ≦ −75 is not satisfied, it is not added (Formula 6). Similarly, the vertical direction diff _y is also determined, and the number of rising edges cntUP _y (i, j) and the number of falling edges cntDOWN _y (i, j) are counted (Equations 7 and 8).

In fact, when the rising and falling edges of the character edge are present in the mask, the edge of the character should be continuously changing because it exists continuously along the contour of the character. Therefore, after counting the number of rising edges and the number of falling edges, T _up-down is set as a threshold, and by judging whether the number of rising edges and the number of falling are equal to or greater than the threshold, Eliminate counting due to falling. Accordingly, the presence / absence of rising and falling is determined by flag_up _x and flag_down _x indicating the presence or absence of rising and falling in the horizontal direction, and flag_up _y and flag_down _y indicating the presence or absence of vertical rising and falling. Is determined as follows.

When the horizontal rising number cntUP _x (i, j) is greater than or equal to T _{up-down for the} pixel of interest (i, j), there is a rising edge in the mask of the pixel of interest (i, j). Flag_up _x is set to true. If it is less than T _up-down , flag_up _x is set to false (Formula 9). Similarly, when the number of falling edges cntDOWN _x (i, j) in the horizontal direction is equal to or greater than T _up-down, it is determined that there is a falling edge in the mask of the pixel of interest (i, j). , Flag_down _x is set to true. If it is less than T _up-down , flag_down _x is set to false (Formula 10). Similarly, the line width determination unit 42 determines flag_up _y and flag_down _y in the vertical direction (Equations 11 and 12).

Next, the line width determination unit 42 determines whether the line width is wide or narrow. When the line width is actually narrow, since the contours exist almost in parallel in the small region, both rising and falling are present in the same direction in the small region (FIG. 3A). On the other hand, when the line width is wide, only one of the rising edge and the falling edge appears in the image mask (FIG. 3B). Therefore, when the rising edge and falling edge in the horizontal direction component and / or the vertical direction component of the target pixel (i, j) are both present in the mask, the line width of the character or line drawing is narrow. Is determined. That is, when Flag_up _x and Flag_down _x are both true, then or if Flag_up _y and Flag_down _y are both true, the or Flag_up _x and Flag_down _x is any is true, and Flag_up _y and Flag_down _y is any Is true, it is determined that the line width is narrow. Line width determination unit 4
2 outputs a determination signal indicating the determination result to the comprehensive determination unit 47. For example, “0” is output when it is determined that the line width is narrow, and “1” is output when it is determined that the line width is wide.

  Next, color determination will be described. In the present invention, the color is determined by different processing depending on whether the line width of the character is narrow or wide. In the first embodiment, two different processes are performed in parallel for high-speed processing in the ASIC, and which of the two processing results is used is selected based on the determination result of the character line width. .

  First, the color determination process when the line width of a character is narrow will be described. FIG. 4 is a distribution diagram showing a shift that occurs between each color component in a black character with a narrow line width. Each horizontal axis represents an arbitrary position in the region, and the vertical axis represents the density between the color components as a value from 255 to 0. The density is the lightest when the numerical value is 255 and white, and the darkest when the numerical value is 0. FIG. 4A shows the actual density of each color component of a black character having a narrow line width. In the case of an achromatic color, the density is equal among the RGB color components at any position. Since the line width is narrow, both rising and falling of the density appear in the region. FIG. 4D shows the density of each color component of a color character having a narrow line width for comparison. In the case of a chromatic color, the density of each color component of RGB varies depending on the color characteristics of the character.

  FIG. 4B shows the density of each color component of the black character when a pixel shift occurs when the color image input apparatus 11 reads the document. Although the density of each RGB color component is equal, the peak position of the density of each color component that should be detected at the same position is detected by shifting the position of the R signal to the left and the B signal to the right. Therefore, an original black or gray pixel is determined to be a reddish pixel on the left side, and is determined to be a bluish pixel on the right side. Since the line width is narrow, the influence of pixel shift is large, the portion where the density is uniform is lost, and there is no pixel that can be determined as an achromatic color, so that it is erroneously determined to belong to the chromatic color region.

  FIG. 4C shows the density of each color component of the black character when there is a difference in the MTF of the color image input device 11. Although the peak of the density of each color component of RGB is detected at the same position, the peak value of the same density is originally detected as a different value. In the case illustrated in FIG. 4C, the R signal has a wider peak width and a lower peak value than the G signal. The B signal has a wider peak width and a lower peak value. Therefore, in actuality, black or gray pixels are detected with the color balance lost. Since there are almost no pixels detected as black pixels, it may be erroneously determined to belong to the chromatic color region.

  The first color determination unit 43 performs processing corresponding to the case where the line width is narrow as described above. The first color determination unit 43 sets a rectangular mask having a size of 7 × 7 with the target pixel (i, j) as the center (Equation 13), and uses the density of the pixels included in the mask. Perform color determination. When the line width is narrow, the actual RGB signal density peak value and peak width are the same in the achromatic region (FIG. 4A). Even when a pixel shift occurs, only the peak position is shifted (FIG. 4B), so the peak value and the peak width are equal. When there is a difference in MTF, the peak value becomes lower and the peak width becomes wider (FIG. 4C), so that the integrated amount of the density of the entire peak is substantially equal to the other color components.

Using this feature, the first color determination unit 43 first calculates the average value of each color component of the 49-pixel RGB signal included in the mask (Formula 14). In the case of belonging to the achromatic color region, the average value of the RGB signals in the mask should be equal between the respective color components, so the difference between the respective color components should be 0 or very small. On the other hand, when belonging to the chromatic color region, the average value of the RGB signals in the mask should be different depending on the color, so the difference between each color component should be a non-small value. Therefore, the first color determination unit 43 calculates the difference between the maximum value between the RGB components of the average value and the minimum value between the RGB components of the average value as the feature value Para ₁ (Formula 15). ).

The first color determination unit 43 sets a threshold value T _color1 for the calculated feature amount Para ₁ and determines that it belongs to a chromatic color region if Para ₁ is _{equal to} or greater than the threshold value T color _1. If it is less than _Tcolor1 , it is determined that it belongs to the achromatic region (Formula 16). The first color determination unit 43 outputs the determination result to the comprehensive character determination unit 45. For example, “1” is output when it is determined that it belongs to the chromatic color area, and “0” is output when it is determined that it belongs to the achromatic color area.

  When the determination is made using the difference between the maximum value and the minimum value between the color components locally with only the target pixel, the difference between the color components at the target pixel due to the pixel shift and the difference in MTF becomes large. In some cases, an area that is actually a black character area is mistakenly identified as a color character area. However, by making the determination based on the above-described feature amount, the displacement in the position direction due to the pixel displacement can be calculated so as to cover the entire line width as well, so that the pixel displacement can be absorbed. it can. Further, since the difference in MTF can be calculated including the broadening of the peak width of the concentration, the deviation due to the difference in MTF can be absorbed. Accordingly, it is possible to absorb the pixel shift and the difference between the MTFs and improve the accuracy of color determination.

  On the other hand, a color determination process when the line width of a character is wide will be described. FIG. 5 is a distribution diagram showing a shift that occurs between each color component in a black character having a wide line width. Each horizontal axis represents an arbitrary position in the region, and the vertical axis represents the density between the color components as a value from 255 to 0. A density of 255 is the lightest and represents white. The darkest case is 0. FIG. 5A shows the actual density of each color component at the edge of a black character having a wide line width. In the case of an achromatic color, the density of each color component of RGB is equal at any position. Since the line width is wide, only the rise of density appears in the region. FIG. 5D shows the density of each color component of a color character having a wide line width for comparison.

  FIG. 5B shows the density of each color component of the black character when a pixel shift occurs when the original is read by the color image input device 11. Originally, the rising position of each color component to be detected at the same position is detected by shifting the position of the R signal to the left side and the B signal to the right side. For this reason, an originally gray pixel may be determined to be a reddish pixel and erroneously determined to belong to a chromatic color region.

  FIG. 5C shows the density of each color component of the black character when there is a difference in the MTF of the color image input device 11. Since the peak width of the density is widened, at the rising portion, gray pixels that are actually equal in density are detected with the color balance lost over the entire mask. Since there are almost no pixels detected as achromatic pixels, it may be erroneously determined to belong to the chromatic color region.

  The second color determination unit 44 performs processing corresponding to the case where the line width is wide as described above. The second color determination unit 44 sets a rectangular mask having a size of 7 × 7 with the target pixel (i, j) as the center, and performs color determination using the density of the pixels included in the mask. . When the line width is wide, in the achromatic region, the actual RGB signal density is the same over the entire rising portion (FIG. 5A). When a pixel shift occurs, the position of the density rising curve is shifted as it is, and as the gradient of the density rising becomes steep as in the edge of a character, the shift in the position has a greater effect on the density ( FIG. 5B). However, since the peak values are equal in pixel shift, the difference in density is small in the portion where the slope of the rising curve close to the peak value is gentle (FIG. 5B). Similarly, since the slope at the beginning of the rising curve is gentle, there is little difference in density due to pixel shift. When there is a difference in MTF, the gradient of the rise and fall of the concentration is dull, so the deviation from the actual concentration is large depending on the position (FIG. 5 (c)), but the difference from the actual concentration becomes closer to the peak value. Deviation is reduced.

Using this feature, the second color determination unit 44 first extracts the minimum value of each color component of the RGB signal of 49 pixels included in the mask, that is, the maximum value of density (Equation 17). When belonging to the achromatic color region, the minimum value of the signal is equal between the color components, so the difference between the color components should be 0 or very small. On the other hand, when belonging to the chromatic color region, the minimum value of the RGB signal in the mask differs depending on the color, and therefore the difference between the color components is not a small value. Therefore, the second color determination unit 44 calculates a difference between the maximum value between the RGB color components having the minimum value and the minimum value between the RGB color components having the minimum value as the feature amount Para ₂ (Formula 18). ).

The second color determination unit 44 sets a threshold value T _color2 for the calculated feature amount Para ₂ , and determines that it belongs to a chromatic color region when Para ₂ is _{equal to} or greater than the threshold value T color ₂ , and Para ₂ is a threshold value If it is less than _Tcolor2 , it is determined that it belongs to the achromatic region (Formula 19). The second color determination unit 44 outputs the determination result to the comprehensive character determination unit 45. For example, “1” is output when it is determined that it belongs to the chromatic color area, and “0” is output when it is determined that it belongs to the achromatic color area.

  When the determination is made by using the difference between the maximum value and the minimum value between each color component locally only by the pixel of interest, the difference between the color components at the pixel of interest due to the pixel shift and the difference in MTF increases. In some cases, a black character area is erroneously determined to belong to a color character area. However, by performing the determination based on the above-described feature amount, it is possible to perform the determination without being affected by the pixel shift and the MTF difference in the achromatic color region, and to improve the accuracy of the color determination.

  The comprehensive character determination unit 45 determines whether or not the character area is input from the character determination unit 41, determines whether the line width input from the line width determination unit 42 is narrow or wide, and determines the first color. The target pixel belongs to the black character region, the color character region, or the character region based on the chromatic color or achromatic color determination result input from the unit 43 and the second color determination unit 44 It is determined whether it is other than. The comprehensive character determination unit 45 adopts the determination result from the first color determination unit 43 when the line width determination unit 42 determines that the line width is narrow, and the line width determination unit 42 determines that the line width is wide. In such a case, the determination result from the second color determination unit 44 is adopted.

  FIG. 6 is an explanatory diagram showing a determination example in the comprehensive character determination unit 45. When the character determination unit 41 determines that the region is not a character region (character determination unit result: “0”), regardless of the results of the line width determination unit 42, the first color determination unit 43, and the second color determination unit 44. It is determined that it belongs to an area other than the character area. When it is determined that the character area is a character area (character determination unit result: “1”) and the line width determination unit 42 determines that the line width of the character is narrow (line width determination unit result) : “0”), the result of the first color determination unit 43 is adopted, and when the result of the first color determination unit 43 is an achromatic color (first color determination unit result: “0”), it belongs to the black character region When the result of the first color determination unit 43 is a chromatic color (first color determination unit result: “1”), it is determined that it belongs to the color character area. Further, when the character determination unit 41 determines that the character area is included (character determination unit result: “1”), and the line width determination unit 42 determines that the line width of the character is wide (line width determination). Part result: “1”), when the result of the second color determination unit 44 is adopted and the result of the second color determination unit 44 is an achromatic color (second color determination unit result: “0”), the black character area When the result of the second color determination unit 44 is a chromatic color (second color determination unit result: “1”), it is determined that it belongs to the color character area. The determination result by the comprehensive character determination unit 45 is, for example, a binary number “010” when belonging to the black character region, “011” when belonging to the color character region, and “000” when other than the character region. A signal is generated and input to the comprehensive determination unit 47.

  The halftone dot determination unit 46 determines whether or not the halftone dot region belongs to the halftone dot region using the fact that the pixel signal variation in the small region is large or the density is higher than the background. Similar to the character determination unit 41, the halftone dot determination unit 46 sets an M × N mask (for example, 3 × 3) including the pixel of interest and its neighboring pixels based on the input RGB signal, and within the mask, RGB The following determination is performed for each color component.

  The average pixel signal level Dave, the maximum pixel signal level Dmax, and the minimum pixel signal level Dmin are obtained for 9 pixels in the mask composed of 3 × 3 pixels, and each pixel in the mask is set to 1 or by using the average pixel signal level Dave. Binarize to 0. With respect to the binarized data, the number of change points from 0 to 1 and the number of change points from 1 to 0 are counted in the main scanning direction (horizontal direction) and the sub-scanning direction (vertical direction), respectively, and obtained as Kh and Kv. . Th and Tv are compared with the obtained Kh and Kv as predetermined threshold values, respectively, and when both Kh and Kv exceed Th and Tv, respectively, it is determined that they belong to the halftone dot region. In order to prevent erroneous determination that the background is an image belonging to a halftone dot area, B1 and B2 are set as predetermined threshold values, and when Dmax and Dmin are separated from the average value Dave by more than the threshold values B1 and B2, respectively, It is determined that it belongs to a point area. That is, when Kh> Th, Kv> Tv, Dmax-Dave> B1 and Dave-Dmin> B2 are satisfied, it is determined to belong to the halftone dot region. The halftone dot determination unit 46 outputs a determination signal indicating the determination result to the comprehensive determination unit 47. For example, “1” is output when it is determined that it belongs to the halftone area, and “0” is output when it is determined that it does not belong to the halftone area.

  Based on the determination results input from the comprehensive character determination unit 45 and the halftone dot determination unit 46, the comprehensive determination unit 47 determines whether the target pixel belongs to the black character region, the color character region, or the halftone dot region, Alternatively, it is determined whether it belongs to another area. FIG. 7 is an explanatory diagram illustrating an example of determination by the comprehensive determination unit 47. The determination result is, for example, a binary number “010” if it belongs to a black character area, “011” if it belongs to a color character area, “100” if it belongs to a halftone area, and “000” if it belongs to another area. Are input to the color correction unit 5, the black generation and under color removal unit 6, the spatial filter processing unit 7, and the gradation reproduction processing unit 9 as 3-bit region identification signals.

  The image processing apparatus 10 according to the first embodiment performs the above processes on the entire document image. By adopting the above configuration, for the pixels belonging to the character area of the document, the result of the color determination method is appropriately adopted depending on the line width of the character, and varies depending on the line width in the local portion such as a mask. Color determination corresponding to the appearance of a color component distribution having characteristics can be performed. In the first embodiment, when the line width is narrow, it is easily affected by the balance of each color component being lost due to the difference in MTF, but the determination result of the color determination method that absorbs the influence due to the difference in MTF is adopted. It is possible to improve the accuracy of color determination. Also, the color determination method that absorbs the influence due to the difference in MTF adopted when the line width is narrow is not suitable when the line width is wide, and is greatly affected by pixel shift. Therefore, when the line width is wide, it is possible to adopt the determination result of the color determination method that can avoid the influence of pixel shift and improve the accuracy of color determination. In addition, a color determination method suitable for the feature depending on the line width may be adopted.

  In the first embodiment, the line width determination unit 42, the first color determination unit 43, and the second color determination unit 44 are provided in parallel for high-speed processing, and the comprehensive character determination unit is based on the respective determination results. In 45, it is determined whether the target pixel belongs to the black character region, the color character region, or a region other than the character region. Based on the determination result in the line width determination unit 42, the first color determination unit 43 is determined. Alternatively, the color determination process may be performed after selecting which of the second color determination units 44 performs the color determination.

(Embodiment 2)
The processing in the ASIC in the first embodiment can be configured as a computer program that can be executed by a computer, and the CPU of the computer can execute similar processing based on the computer program. FIG. 8 is a block diagram of a computer system according to the second embodiment.

  The computer system according to the second embodiment includes an image processing device 20, a color image input device 30, and a color image output device 50. The image processing apparatus 20 stores a printer driver 231 for controlling the color image output apparatus 50, receives image information read by the color image input apparatus 30, and outputs the image information based on the printer driver 231 as a color image output. The color image output device 50 forms an image on a sheet based on the input image information.

  The image processing apparatus 20 is a PC (Personal Computer), and stores at least a CPU 21 that performs various controls, an internal bus 22 that connects various hardware, and various drivers that control various hardware. 23, a temporary storage area 24 for storing information temporarily generated in the course of arithmetic processing by the CPU 21, an input unit 25 connected to the color image input device 30 and receiving input of image data, and a display unit 26 having a monitor And a communication port 27 that communicates with the color image output device 50.

  The color image input device 30 is a flatbed scanner including a CCD, and includes an A / D conversion unit, a shading correction unit, and an input tone correction unit, and reads the read image information based on the characteristics of the color image input device 30. The corrected RGB digital signal is output. The color image output device 50 is a printer such as an electrophotographic system or an inkjet system, and forms an image on a sheet based on a digital color signal input from the image processing apparatus 20.

  The printer driver 231 is a software program for the CPU 21 to control the color image output device 50. The CPU 21 can output to the color image output device 50 image information that has been subjected to processing suitable for the performance and gradation reproducibility of the color image output device 50 by performing processing based on the printer driver 231.

  The printer driver 231 includes an area determination processing unit 232, a color correction unit 233, a spatial filter processing unit 234, a gradation reproduction processing unit 235, and a printer language translation unit 236.

  Based on the RGB signal of the input image, the region determination processing unit 232 determines each pixel in the input image as a black character region, a color character region, a halftone dot region, or any other region that does not belong to any region. Based on the determination result obtained by the region determination processing unit 232, the CPU 21 stores region identification information indicating which region the pixel belongs to as a temporary storage, the color correction unit 233, the spatial filter processing unit 234, and the gradation reproduction. Input to the processing unit 235.

  Based on the RGB signal of the input image and the region identification information, the color correction unit 233 converts the color mixture into an additive color mixture CMY signal for printing, and faithfully reproduces the color. A process of removing color turbidity based on the spectral characteristics of the CMY color material including the component is performed. Further, the color correction unit 233 converts the converted CMY signal into a new CMYK signal that generates black. The CPU 21 obtains a processed CMYK signal by inputting the RGB signal and the region identification information to the color correction unit 233.

  The spatial filter processing unit 234 performs spatial filter processing using a digital filter based on the input CMYK signal and the region identification information, and corrects the spatial frequency characteristics to correct the output image of the color image output device 50. Prevent blurring or graininess degradation. The CPU 21 inputs the CMYK signal processed by the color correction unit 233 to the spatial filter processing unit 234 to obtain a processed CMYK signal.

  The gradation reproduction processing unit 235 performs gradation reproduction processing (intermediate processing) based on the input CMYK signal and the region identification information so as to be adapted to the color image output device 50 and reproduce each gradation. Key generation). The CPU 21 gives the processed CMYK signal by giving the CMYK signal processed by the spatial filter processing unit 234 to the gradation reproduction processing unit 235.

  The CPU 21 acquires image information read by the color image input device 30 via the input unit 25 and performs the above-described processes based on the printer driver 231. The image information processed by the printer driver 231 is converted into a printer language via the printer language translation unit 236 of the printer driver 231. The CPU 21 controls the communication port 27 via the communication port driver 237 and outputs the converted image information to the color image output device 50.

  Next, the area determination process in the area determination processing unit 232 will be described. The area discrimination processing unit 232 according to the second embodiment implements the processing in the area discrimination processing unit 4 according to the first embodiment with a computer program. Therefore, similarly to the first embodiment, the image forming apparatus includes a character determination unit, a line width determination unit, a first color determination unit, a second color determination unit, and a halftone determination unit that are not shown, and performs processing for each pixel. In the second embodiment, in order to be realized as a computer program, RGB signals are simultaneously input to each determination unit, and the determination result is not determined by the comprehensive character determination unit and the comprehensive determination unit. In order, the character area is determined. FIG. 9 is a flowchart illustrating a processing procedure in which the CPU 21 of the image processing apparatus 20 according to the second embodiment performs area determination based on the stored printer driver 231.

  The CPU 21 sets a 3 × 3 mask including the target pixel and neighboring pixels for each pixel in the input RGB signal of the image information, and whether the target pixel belongs to the halftone dot area based on the halftone dot determination unit. Is determined (step S11). If it belongs to the halftone dot area (S11: YES), whether or not the process has been completed for the entire image to set the area identification information as a 3-bit binary number “100” indicating the halftone dot area and to process the next pixel. Is determined (step S16). If it does not belong to the halftone dot region (S11: NO), it is determined based on the character determination unit whether or not the pixel of interest belongs to the character region (step S12). If it does not belong to the character area (S12: NO), the area identification information is set to “001” indicating the other area, and it is determined whether or not the process has been completed for the entire image to process the next pixel ( S16).

  If it belongs to the character area (S12: YES), it is determined based on the line width determination unit whether or not the line width of the character is narrow (step S13). If the line width is narrow (S13: YES), it is determined whether the color belongs to the chromatic color region or the achromatic color region based on the first color determination unit (step S14), and if the line width is wide ( S13: NO), based on the second color determination unit, color determination is made as to whether it belongs to the chromatic color region or the achromatic color region (step S15). If it is determined in step S14 or step S15 that the image belongs to an achromatic region, the CPU 21 sets the region identification information to “010” indicating a black character region, and if it is determined that the image belongs to a chromatic color region, the region The identification information is set to “011” indicating the color character area, and it is determined whether or not the processing has been completed for the entire image in order to process the next pixel (S16). If the process has not been completed for the entire image (S16: NO), the CPU 21 returns the process to step S11 and performs each determination process for the next pixel. If the process has been completed for the entire image (S16: YES), the process ends.

  Through the above-described processing based on the printer driver 231, the CPU 21 can appropriately select a color determination method for the pixels belonging to the character area of the input image according to the line width of the character, and the influence of pixel deviation and MTF difference. And the accuracy of color determination can be improved. Therefore, the CPU 21 can perform processing suitable for the gradation reproducibility of the color image output device 50 on the input image, and can obtain an output result with high character reproducibility. Since the detailed determination method in each determination unit of the region determination processing unit 232 in the second embodiment is the same as that in the first embodiment, the description thereof is omitted.

  In the second embodiment, the CPU executes a configuration based on a printer driver stored in advance in a storage unit. However, a microcomputer in which a program is stored in advance may be used, or a program medium such as a ROM may be used. There may be.

  Further, the printer driver may be recorded in an external storage device and acquired by the computer as the image processing device from the external storage device. In this case, the external storage device is a recording medium in which a printer driver is stored, a tape medium such as a magnetic tape or a cassette tape, a magnetic disk such as a flexible disk or a hard disk, or a CD-ROM, MO, MD, or It may be an optical disc such as a DVD, or a semiconductor memory such as a mask ROM, an EPROM (Erasable Programmable Read Only Memory), an EEPROM (Electrically Erasable Programmable Read Only Memory), or a flash ROM. Further, the printer driver may be configured to be acquired by a computer by downloading from a specific server via a communication network.

  In the second embodiment, the color image input device for reading an image is configured as a flat bed scanner, but may be configured as a film scanner or a digital camera. In addition, the color image output device that forms an image based on image information processed by a computer is configured as a printer, but may be configured as a digital multi-function peripheral having a copy function and a fax function in addition to the printer function. A display device such as a display may be used.

  In the second embodiment, the input image region determination process is performed by an image processing apparatus that is a PC. However, each process performed by the image processing apparatus may be performed by an image reading apparatus such as a scanner. In this case, the image reading device includes a color image input device, an A / D conversion unit, a shading correction unit, an input tone correction unit, and an area discrimination processing unit, and an RGB signal or the like of the read image information An area determination signal may be output and input to an image processing apparatus or a color image output apparatus including each component after the color correction unit.

  In the first and second embodiments, the mask size is set to 5 × 5 when determining the line width. However, it is possible to adjust the reference for determining the width of the line width by changing the size. is there. That is, when the size of the mask is smaller than 5 × 5, the case where the line width is narrower is determined to be narrow, and it is determined to be wider than the line width that has been determined to be narrow so far. When the line width is larger than 5 × 5, it is determined that the line width is wider, and it is determined to be narrower than the line width that has been previously determined to be wide.

  In the first and second embodiments, the size of the mask in each of the determination units is illustrated. However, it is of course possible to use masks having different sizes, and the mask is limited to an M × N rectangular mask. It is not a thing. Further, in the first or second embodiment, the width of the line width is detected by detecting the rising or falling of the pixel signal level change within a predetermined range, and both the rising and falling are present within the predetermined range. The determination method is not limited to this.

1 is a block diagram illustrating a configuration of an image forming apparatus including an image processing apparatus according to the present invention. 3 is a block diagram illustrating a configuration of an area determination processing unit of the image processing apparatus according to Embodiment 1. FIG. 6 is a schematic diagram illustrating an example of a mask set by a line width determination unit of the image processing apparatus according to Embodiment 1. FIG. It is a distribution diagram which shows the shift | offset | difference which arises between each color component in the black character with a narrow line | wire width. It is a distribution diagram which shows the shift | offset | difference which arises between each color component in a black character with a wide line width. It is explanatory drawing which shows the example of a determination in a comprehensive character determination part. It is explanatory drawing which shows the example of a determination in a comprehensive determination part. FIG. 10 is a block diagram of a computer system in a second embodiment. 10 is a flowchart illustrating a processing procedure in which the CPU of the image processing apparatus according to the second embodiment performs area determination based on a stored printer driver.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10,20 Image processing apparatus 4,232 Area | region discrimination | determination process part 41 Character determination part 42 Line width determination part 43 1st color determination part 44 2nd color determination part 45 Comprehensive character determination part 46 Halftone dot determination part 47 Comprehensive determination part 21 CPU
231 Printer Driver

Claims (10)

Using any one pixel in the input image composed of a plurality of pixels represented by a plurality of color components as the target pixel, it is determined whether the target pixel belongs to the character area based on neighboring pixel information, and the input image In an image processing apparatus that includes a region discriminating unit that discriminates a plurality of region classifications, and performs processing suitable for the region classification on the input image for each discriminated region,
The region discriminating means
Means for detecting the line width of the character;
Means for determining the width of the detected line width;
A plurality of color determination means for determining whether the target pixel belongs to an achromatic color region or a chromatic color region;
An image processing apparatus comprising: means for selecting one of the plurality of color determination means according to the line width. One of the color determination means is
Means for calculating an average value of the densities of the target pixel and the neighboring pixels for each color component;
Means for calculating, as a feature amount, a maximum difference between color components of the calculated average value,
The image processing apparatus according to claim 1, wherein it is determined whether the target pixel belongs to an achromatic color region or a chromatic color region from the feature amount. One of the color determination means is
Means for calculating the minimum value or the maximum value of the density of the target pixel and the neighboring pixels for each color component;
Means for calculating the maximum difference between the calculated minimum or maximum color components as a feature amount,
The image processing apparatus according to claim 1, wherein it is determined whether the target pixel belongs to an achromatic color region or a chromatic color region from the feature amount. Using any one pixel in the input image composed of a plurality of pixels represented by a plurality of color components as the target pixel, whether the target pixel belongs to the character area is determined based on neighboring pixel information, and the input image In an image processing method for determining a plurality of region classifications and performing processing suitable for the region classification on the input image for each of the determined regions,
Detect the line width of the text
Determine the width of the detected line width,
Select one of a plurality of color determination methods for determining whether the pixel of interest belongs to an achromatic color region or a chromatic color region depending on the line width.
An image processing method comprising: discriminating whether a pixel of interest belongs to an achromatic character region or a chromatic character region based on determination by a selected color determination method. One of the color determination methods is
Calculate the average density of the target pixel and neighboring pixels for each color component,
The maximum difference between the calculated average color components is calculated as a feature value.
The image processing method according to claim 4, wherein it is determined whether the target pixel belongs to an achromatic region or a chromatic region based on the calculated feature amount. One of the color determination methods is
Calculate the minimum value or maximum value of the density of the target pixel and neighboring pixels for each color component,
Calculate the maximum difference between the calculated minimum or maximum color components as the feature amount,
The image processing method according to claim 4, wherein it is determined whether the target pixel belongs to an achromatic region or a chromatic region based on the calculated feature amount. An image forming apparatus comprising: the image processing apparatus according to claim 1; and an image forming unit that forms an image based on an input image processed by the image processing apparatus. . Determining, based on neighboring pixel information, whether any one pixel in an input image composed of a plurality of pixels represented by a plurality of color components is the target pixel, and whether the target pixel belongs to the character region; In a computer program for causing a computer to execute a step of discriminating an input image into a plurality of region classifications,
In the computer,
Detecting the line width of the character;
Determining the width of the detected line width;
A plurality of color determination steps for determining whether the target pixel belongs to an achromatic color region or a chromatic color region;
And a step of selecting one of the plurality of color determination steps depending on whether the line width is wide or narrow. One of the color determination steps is
Calculating an average value of the densities of the target pixel and neighboring pixels for each color component;
Calculating a maximum difference between color components of the calculated average value as a feature amount;
The computer program according to claim 8, further comprising: determining whether the target pixel belongs to an achromatic color region or a chromatic color region based on the calculated feature amount. One of the color determination steps is
Calculating a minimum value or a maximum value of the density of the target pixel and neighboring pixels for each color component;
Calculating the maximum difference between the calculated minimum or maximum color components as a feature amount; and
The computer program according to claim 8, further comprising: determining whether the target pixel belongs to an achromatic color region or a chromatic color region based on the calculated feature amount.

Images