JP4522978B2 - Image processing apparatus, image processing method, image forming apparatus, image processing program, and recording medium - Google Patents

Description

  The present invention relates to an image processing apparatus, an image processing method, an image forming apparatus, an image processing program, and a recording medium for performing background color removal processing and color correction processing on image data read from a document.

  In recent years, digitalization of office automation equipment has progressed, and demand for color image output has increased. For example, image formation such as electrophotographic digital color copiers / multifunction printers, inkjet or thermal transfer color printers, etc. The device is widespread. For example, image data input from an image input device such as a scanner is output using these image forming devices.

  In these image forming apparatuses, it is necessary to output an image in which image data input from an image input apparatus or the like is appropriately color-reproduced. Therefore, color correction processing using digital image processing technology plays an important role in the image processing apparatus provided in the image forming apparatus.

  However, it is very troublesome for the operator to set parameters for color correction processing for each document. In addition, when an inappropriate parameter is selected, it is necessary to reset the parameter and then perform image formation again, resulting in useless copying.

  In order to solve such problems, a configuration for automatically performing color correction processing has been proposed.

  For example, Patent Document 1 is provided with a lookup table in which color correction data is stored in advance, and image data including the first color system is referred to as the second color system with reference to the lookup table. A technique for converting to image data is disclosed.

Further, in Patent Document 2, a correction table is generated based on a background color of a document from which image data is read and a background color of a recording sheet on which image formation is performed based on the read image data, and based on the generated correction table. A technique for performing color correction processing is disclosed. Specifically, in Patent Document 2, color correction in a direction in which the background color of the document is visually recognized as an achromatic color, and color correction in a direction in which the background color of the recording paper is visually recognized as an achromatic color, A correction table is generated so as to perform color correction combining the above.
JP 2003-153022 (Publication date: May 23, 2003) JP 2004-23771 A (publication date: January 22, 2004)

  However, in the above conventional technique, the background removal processing (background color removal processing; processing for removing the density component (background density) of the background color from the input image data) is performed regardless of the document type. For this reason, appropriate background removal processing may not be performed.

  For example, the background removal amount (removal amount of the density component of the background color) becomes insufficient in the background removal processing for the character document, and the background color should remain, or the background removal processing for the photo document should not be performed. In some cases, the background was removed.

  Further, when it is desired to change the background removal amount according to the document type, the operator needs to specify the background removal amount or the document type, and the operator has to perform a very troublesome work.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an image processing apparatus, an image processing method, an image forming apparatus, an image processing program, and an image processing apparatus capable of performing appropriate background processing according to the document type. It is to provide a recording medium.

An image processing apparatus according to the present invention is an image processing apparatus that performs image processing according to a document type of the document on image data read from the document in order to solve the above-described problem.
A document type determining unit that determines a type of a region to which a block including a plurality of pixels including a target pixel belongs, and that determines a document type based on a determination result of the region type;
A background color removing means for removing the density component of the background color from the image data,
The background color removing unit adjusts the removal amount of the density component of the background color according to the document type determined by the document type determining unit.

  According to the above configuration, the document type determination unit determines the type of the region to which a block including a plurality of pixels including the target pixel belongs, and determines the document type based on the determination result of the region type. Then, the background color removal unit adjusts the removal amount of the background color density component (background removal amount) according to the document type determined by the document type determination unit. Accordingly, the background removal amount can be adjusted according to the document type, and appropriate background removal can be performed according to the document type. For example, for text originals that require high contrast and photo originals that require appropriate reproduction of gradation, the background removal amount can be set appropriately according to the type of each original. It is possible to remove the background.

  Further, the background color removing means is provided corresponding to each of the gradation levels and gradation determination means for classifying the image data into one of a plurality of gradation levels according to the gradation of the background of the document. A plurality of background color removal tables associated with the image data before and after the background color removal, and using the background color removal table corresponding to the gradation level classified by the gradation determination means, A configuration in which the background color is removed may be employed.

  According to the above configuration, the data of each background color removal table can be set according to each gradation level of the background color. Therefore, the gradation determination unit classifies the gradation level into one of a plurality of gradation levels according to the background gradation of the document, and the background color removal unit uses the background color removal table corresponding to the classified gradation level. By removing the background color, the background color removal process can be appropriately performed according to the gradation level of the background.

  The document type determining means determines at least whether the document is a character document or a document other than a character document, and the background color removing means determines the removal amount of the density component of the background color from the character document. It may be configured to be larger than the removal amount of the density component of the background color for the document other than the character document.

  According to the above configuration, the background color component is sufficiently removed from the character document to prevent the background color component from remaining, and the background of the portion where the background removal should not be performed on the document other than the character document. It is possible to prevent the removal.

  In addition to the above-described configuration, a background color determination unit that classifies the image data into any of a plurality of groups according to the background color of the document, and a background color corresponding to each group. Color correction processing for color-correcting the image data using the plurality of color correction tables associated with the image data before and after the color correction and the color correction table corresponding to the group classified by the background color discrimination means It is good also as a structure provided with a means.

  In the technique disclosed in Patent Document 1, color correction processing is performed using a single lookup table regardless of the background color of the document. For this reason, when the background color is removed, there is a problem that the color of the color to be left largely changes, and appropriate color reproduction cannot be performed. In particular, when processing an image in which a light color image is formed on the ground under a dark color, the color reproducibility is likely to deteriorate due to the influence of the background color removal process. Specifically, for example, a light pink image formed on a deep yellow ground has been reproduced in orange.

  In the technique of Patent Document 2, color correction in a direction in which the background color of the document is visually recognized as an achromatic color, and color correction in a direction in which the background color of the recording paper is visually recognized as an achromatic color, Therefore, depending on the combination of the background color of the original and the background color of the recording paper, it may not be possible to perform appropriate color reproduction as in Patent Document 1. Further, in the technique of Patent Document 2, it is necessary to perform an image reading operation of a document and a recording sheet every time image formation is performed, and to determine a base color of each and generate a correction table. Problems such as an increase in size, an increase in processing time, and an increase in power consumption have been caused.

  On the other hand, according to the above configuration, a plurality of color correction tables provided corresponding to the background colors corresponding to each group are provided. Thus, each color correction table can be set in consideration of the influence of the background color removal process on colors other than the background color for each group of background colors of the document. Therefore, the background color discrimination means classifies the image data into one of a plurality of groups according to the background color of the document, and the color correction processing means performs color correction using the color correction table corresponding to the classified group. Thus, it is possible to suppress a change in the color other than the base color due to the removal of the base color and improve the color reproducibility. Further, since it is not necessary to perform the image reading operation of the recording paper and the generation of the correction table every time image formation is performed, the apparatus configuration is simplified, the processing time is reduced, and the power consumption is reduced as compared with the technique of the above-mentioned Patent Document 2. Reduction can be achieved.

  The color correction tables may be set so that changes in colors other than the base color due to the base color removal are small.

  According to the above configuration, the data stored in each of the color correction tables is set so that the change in colors other than the background color due to the background color removal becomes small. That is, each color correction table is set so that the change in colors other than the base color due to the base color removal becomes small according to the base color to be removed. As a result, it is possible to reliably suppress changes in colors other than the base color due to the removal of the base color, and it is possible to perform the color correction process more appropriately according to the base color.

  Further, the color correction table may be set so as to convert image data having the first color system into image data having the second color system. That is, the color correction table includes color correction processing and color conversion processing for converting image data composed of a first color system (for example, RGB) into image data composed of a second color system (for example, CMY). It may be for performing simultaneously.

  According to the above configuration, since the color correction process and the color conversion process can be performed using a common table, the configuration of the image processing apparatus can be simplified.

  The document type determination unit determines whether a block including a plurality of pixels including the target pixel belongs to the background region, and the background color removal unit determines that the block is a background region by the document type determination unit. The background color may be removed for the block, and the color correction unit may perform the color correction for the block determined to be the background region by the document type determination unit.

  According to the above configuration, it is possible to determine whether or not each block of the image data belongs to the background area by the document type determination unit, and to perform the above background color removal and color correction on the block in the background area. Therefore, background color removal processing and color correction processing can be appropriately performed on each block in the background region, and processing corresponding to the type of each region can be performed on blocks in other regions.

  An image processing method of the present invention is an image processing method for performing image processing according to a document type of the document on image data read from the document in order to solve the above-described problem, and includes a target pixel. A document type determination step for determining the type of an area to which a block composed of a plurality of pixels belongs, and determining the document type based on the determination result of the area type, and a background color removal for removing the density component of the background color from the image data In the background color removal step, the removal amount of the density component of the background color is adjusted according to the document type determined in the document type determination step.

  According to the above method, in the document type determination step, the type of an area to which a block composed of a plurality of pixels including the target pixel belongs is determined, and the document type is determined based on the determination result of the area type. Then, in the background color removal step, the removal amount of the density component of the background color is adjusted according to the document type determined by the document type determination unit. Accordingly, the background removal amount can be adjusted according to the document type, and appropriate background removal can be performed according to the document type.

  In addition to the above method, a background color determining step for classifying the image data into one of a plurality of groups according to the background color of the document, and a background color corresponding to each group is provided. Color correction processing for color-correcting the image data using a color correction table corresponding to the group classified in the background color discrimination step among a plurality of color correction tables associated with the image data before and after color correction And a process.

  According to the above method, the image data is obtained using the color correction table corresponding to the group classified in the background color discrimination step among the plurality of color correction tables provided corresponding to the background color corresponding to each group. Correct the color. Accordingly, since the data of each color correction table can be set in consideration of the influence of the background color removal processing on the colors other than the background color for each group of background colors of the document, the color of the color other than the background color accompanying the removal of the background color can be set. The change can be suppressed and the color reproducibility can be improved.

  The image forming apparatus of the present invention includes any one of the image processing apparatuses described above.

  According to the above configuration, the background removal amount can be adjusted according to the document type, and appropriate background removal can be performed according to the document type.

  The image processing apparatus may be realized by a computer. In this case, an image processing program for causing the image processing apparatus to be realized by the computer by causing the computer to operate as the respective means, and recording the program. Such computer-readable recording media are also included in the scope of the present invention.

  As described above, in the image processing apparatus of the present invention, the background color removing unit adjusts the removal amount of the density component of the background color according to the document type determined by the document type determining unit. In the image processing method of the present invention, in the background color removal step, the removal amount of the density component of the background color is adjusted according to the document type determined in the document type determination step.

  Accordingly, the background removal amount can be adjusted according to the document type, and appropriate background removal can be performed according to the document type.

  An embodiment of the present invention will be described. In the present embodiment, a case where the image processing apparatus of the present invention is applied to a digital color copying machine (image forming apparatus) will be described.

(1-1. Color image processing apparatus 2)
FIG. 2 is a block diagram showing a schematic configuration of a digital color copying machine to which the color image processing apparatus (image processing apparatus) 2 of the present invention is applied. As shown in this figure, the digital color copying machine according to this embodiment includes a color image input device 1, a color image processing device 2, a color image output device 3, and an operation panel 4. The color image processing apparatus 2 includes an A / D conversion unit 11, a shading correction unit 12, a document type automatic determination unit (document type determination unit) 13, an input tone correction unit (background color removal unit) 14, and a region separation processing unit 15. A color correction unit 16, a black generation and under color removal unit 17, a spatial filter processing unit 18, an output gradation correction unit 19, and a gradation reproduction processing unit 20.

  A color image input device (image reading means) 1 is composed of, for example, a scanner unit (not shown) provided with a CCD (Charge Coupled Device), and a reflected light image from a document is converted into RGB (R: red, G: green). B: read as an analog signal of blue) by the CCD and input to the color image processing apparatus 2

  An analog signal read by the color image input device 1 is converted into an A / D conversion unit 11, a shading correction unit 12, a document type automatic discrimination unit 13, an input tone correction unit 14, and a region separation in the color image processing device 2. The processing unit 15, the color correction unit 16, the black generation and under color removal unit 17, the spatial filter processing unit 18, the output gradation correction unit 19, and the gradation reproduction processing unit 20 are sent in this order, and a color image is output as a CMYK digital color signal. It is output to the device 3.

  The A / D (analog / digital) conversion unit 11 converts RGB analog signals into digital signals, and the shading correction unit 12 applies the digital RGB signals sent from the A / D conversion unit 11. The color image input apparatus 1 is subjected to processing for removing various distortions generated in the illumination system, the imaging system, and the imaging system. The shading correction unit 12 adjusts the color balance.

  In the automatic document type discrimination unit 13, the RGB signal (RGB reflectance signal) from which various distortions have been removed by the shading correction unit 12 and the color balance has been adjusted is employed in the color image processing apparatus 2 such as a density signal. The signal is converted into an easy-to-handle signal for the image processing system, and the document type is determined. The document type determination signal generated by the automatic document type determination unit 13 is sent to the input tone correction unit 14, the color correction unit 16, the black generation and under color removal unit 17, the spatial filter processing unit 18, and the tone reproduction processing unit 20. Is output. Details of the automatic document type discrimination unit 13 will be described later.

  The input gradation correction unit 14 performs image quality adjustment processing such as removal of background colors (background color density components) and contrast. Although details of the input tone correction unit 14 will be described later, the input tone correction unit 14 adjusts the removal amount of the density component of the background color according to the document type determined by the document type automatic determination unit 13. It is like that. The input gradation correction unit 14 has a plurality of background color removal tables, and selects a background color removal table corresponding to the gradation level of the background color to remove the background color. ing.

  The region separation processing unit 15 separates each pixel in the input image into one of a character region, a halftone dot region, and a photograph (photographic paper photograph) region from the RGB signal. Based on the separation result, the region separation processing unit 15 generates a region identification signal indicating which region the pixel belongs to, the color correction unit 16, the black generation and under color removal unit 17, the spatial filter processing unit 18, and the gradation reproduction. The output signal is output to the processing unit 20, and the input signal output from the input tone correction unit 14 is output to the subsequent color correction unit 16 as it is.

  The color correction unit 16 performs a process of removing color turbidity based on spectral characteristics of CMY (C: cyan, M: magenta, Y: yellow) color materials including unnecessary absorption components in order to realize faithful color reproduction. Is. Although details of the color correction unit 16 will be described later, the color correction unit 16 uses a color correction table adjusted so that the color tone of the color remaining after the background color removal is not changed significantly by the influence of the background color removal process. There are several depending on the color. As a result, in this embodiment, even when color correction is performed on image data in which the density component of the background color has been removed by input tone correction, it is possible to prevent the color tone after color correction from changing extremely. The color of the original can be reproduced appropriately.

  The black generation and under color removal unit 17 generates black (K) signals from the CMY three-color signals after color correction, and subtracts the K signals obtained by black generation from the original CMY signals to generate new CMY signals. The CMY three-color signal is converted into a CMYK four-color signal.

  As an example of the black generation process, there is a method (general method) for generating black by skeleton black. In this method, the input / output characteristic of the skeleton curve is y = f (x), the input data is C, M, Y, the output data is C ′, M ′, Y ′, K ′, UCR (Under Color When the removal rate is α (0 <α <1), the black generation and under color removal processing is expressed by the following equation (1).

K ′ = f {min (C, M, Y)}
C ′ = C−αK ′
M ′ = M−αK ′
Y ′ = Y−αK ′ (1)
The spatial filter processing unit 18 performs spatial filter processing by a digital filter on the image data of the CMYK signal input from the black generation and under color removal unit 17 based on the region identification signal, thereby correcting the spatial frequency characteristics. Processing is performed to prevent blurring of the output image and deterioration of graininess. Similar to the spatial filter processing unit 18, the gradation reproduction processing unit 20 also performs predetermined processing on the image data of the CMYK signal based on the region identification signal.

  For example, a region separated into characters by the region separation processing unit 15 has a high frequency enhancement amount in the sharp enhancement processing in the spatial filter processing by the spatial filter processing unit 18 in order to improve the reproducibility of black characters or color characters in particular. Increased. At the same time, the tone reproduction processing unit 20 selects binarization or multi-value processing 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 15, the spatial filter processing unit 18 performs low-pass filter processing for removing the input halftone component. The output tone correction unit 19 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 3, and then the tone reproduction processing unit 20. 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 photographs by the region separation processing unit 15, binarization or multi-value processing is performed on the screen with an emphasis on gradation reproducibility.

  The operation panel 4 includes, for example, a display unit (not shown) such as a liquid crystal display, a setting button, and the like. Based on information input from the operation panel 4, the color image input device 1, the color image processing device 2, and the color The operation of the image output device 3 is controlled.

  The image data that has been subjected to the above-described processes is temporarily stored in a storage unit, read at a predetermined timing, and input to the color image output device 3. The color image output device 3 outputs image data onto a recording medium (for example, paper). Examples of the color image output device 3 include a color image output device using an electrophotographic method or an inkjet method, but are not particularly limited. It is not something. The above processing is controlled by a CPU (Central Processing Unit) not shown.

(1-2. Automatic Document Type Discrimination Unit 13)
Next, the configuration of the document type automatic discrimination unit 13 will be described. Here, an example of the configuration of the document type automatic discrimination unit 13 will be specifically described. However, the document type automatic discrimination unit 13 is not limited to this configuration, and at least discriminates between a text document and a document other than a text document. Anything is possible.

  FIG. 3 is a block diagram showing a configuration of the document type automatic discrimination unit 13 shown in FIG. As shown in FIG. 3, the automatic document type discrimination unit 13 includes a minimum density value calculation unit 21 (feature amount extraction unit), a maximum density value calculation unit 22 (feature amount extraction unit), and a maximum density difference calculation unit 23 (features). Amount extraction unit), total density busyness calculation unit 24 (feature amount extraction unit), determination region setting unit (first area gradation pixel detection unit, second area gradation pixel detection unit) 25, maximum density difference threshold setting unit (Determination reference setting unit) 26, total density busyness threshold setting unit (determination reference setting unit) 27, character / halftone determination unit (first area gradation pixel detection unit) 28, background / photographic paper determination unit 29, character A halftone dot threshold setting unit (determination criterion setting unit) 30, a background / photographic paper determination threshold setting unit 31, a second area gradation pixel extraction unit 32, a character pixel counting unit 33, and a first area gradation pixel counting unit 34. , Background pixel counting unit 35, photographic paper pixel counting unit 36, area gradation pixel determining unit (type determining unit) 37, halftone dot pixel determination threshold setting section (classification determination section) 38 and a document determination unit and a (type determination portion) 39.

  The minimum density value calculation unit 21 calculates a minimum density value of a block including a plurality of pixels and including one target pixel. The maximum density value calculation unit 22 calculates the maximum density value of the block. The maximum density difference calculation unit 23 calculates the maximum density difference of the block using the minimum density value and the maximum density value calculated by the minimum density value calculation unit 21 and the maximum density value calculation unit 22. The total density busyness calculation unit 24 calculates the sum of absolute values of density differences between adjacent pixels in the block.

  The determination area setting unit 25 compares the maximum density difference calculated by the maximum density difference calculation unit 23 with the first maximum density difference threshold THd1 given from the maximum density difference threshold setting unit 26, and calculates the total density busyness. By comparing the total density busyness calculated by the unit 24 with the first total density busyness threshold value THb1 given from the total density busyness threshold setting unit 27, the target pixel of the block becomes the background area / printing paper ( It is determined whether it belongs to the (photo) area or the character area / halftone dot area.

  Further, the determination area setting unit 25 compares the maximum density difference calculated by the maximum density difference calculation unit 23 with the second maximum density difference threshold THd2 (THd1> THd2) given from the maximum density difference threshold setting unit 26. Further, the total density busyness calculated by the total density busyness calculating unit 24 is compared with the second total density busyness threshold THb2 (THb1> THb2) given from the total density busyness threshold setting unit 27. As a result, it is determined whether or not the above block satisfies the condition that the maximum density difference is equal to or greater than the second maximum density difference threshold THd2 and the total density busyness is equal to or greater than the second total density busyness threshold THb2.

  The determination process using the first maximum density difference threshold THd1 and the first total density busyness threshold THb1 and the determination process using the second maximum density difference threshold THd2 and the second total density busyness threshold THb2 are performed on the target pixel. It is performed sequentially. In other words, the document type automatic determination unit 13 determines the determination process as to which region one pixel of interest belongs to using two types of threshold values, a maximum density difference threshold value and a total density busyness threshold value. Further, as the target pixel is sequentially shifted, the area of the block including the target pixel is also sequentially shifted. Various controls associated with these determination processes are performed by the CPU.

  The maximum density difference threshold setting unit 26, based on the maximum density difference calculated by the maximum density difference calculation unit 23, the pixel of interest belongs to any of the background area / printing paper (photo) area and the character area / halftone dot area. And a second maximum density difference threshold THd2 (THd1> THd2) for determining whether or not the target pixel is a second area gradation pixel. The first maximum density difference threshold THd1 and the second maximum density difference threshold THd2 are used in the determination area setting unit 25.

  The total density busyness threshold setting unit 27 includes a pixel of interest belonging to any one of the background area, the photographic paper area, the character area, and the halftone dot area based on the total density busyness calculated by the total density busyness calculation unit 24. The first total density busyness threshold THb1 for determining whether or not the target pixel is the second area gradation pixel, and the second total density busyness threshold THb2 (THb1> THb) are set. The first total density busyness threshold THb1 and the second total density busyness threshold THb2 are used in the determination area setting unit 25.

  The second maximum density difference threshold value THd2 and the second total density busyness threshold value THb2 have characteristics as area gradation pixel regions with reference to threshold values for detecting pixels belonging to, for example, a photographic paper photograph region. In other words, pixels that are reproduced not only by halftone dots (first area gradation pixels) used in halftone printing, but also by error diffusion, dither processing, lines, etc. It is set so that pixels in the area gradation image pixel region can be extracted in a wide range including (second area gradation pixel).

  The character / halftone determination unit 28 determines whether the pixel determined as belonging to the character / halftone region by the determination region setting unit 25 is a character region or a halftone region (first area gradation pixel). It is judged whether it belongs to. The character / halftone dot determination threshold setting unit 30 sets a character / halftone dot determination threshold for the character / halftone dot determination unit 28 to perform the above determination.

  The background / photographic paper determination unit 29, for the pixels determined by the determination region setting unit 25 as belonging to the background region / printing paper region, includes the background region and the photographic paper region (photographic paper photographic region, continuous tone region). ). The background / photographic paper determination threshold value setting unit 31 sets a background / photographic paper determination threshold value for the background / photographic paper determination unit 29 to perform the determination.

  The second area gradation pixel extraction unit 32 includes a pixel extraction unit (second area gradation pixel detection unit) 41, a correction unit 42, and a pixel counting unit 43.

  The pixel extraction unit 41 determines in the determination area setting unit 25 that the maximum density difference is equal to or greater than the second maximum density difference threshold THd2 and the total density busyness is equal to or greater than the second total density busyness threshold THb2. For the pixel of interest, the value obtained by multiplying the maximum density difference by the character / halftone determination threshold is compared with the total density busyness, and the total density busyness is equal to or greater than the maximum density difference × character / halftone determination threshold. The target pixel of the block that satisfies the condition is extracted as the second area gradation pixel.

  In the determination region setting unit 25, the correction unit 42 is determined not to belong to either the character region or the halftone dot region in the determination process using the second maximum density difference threshold THd2 and the second total density busyness threshold THb2. Pixels that can be regarded as the second area gradation pixel among the pixels (target pixels) that have not been extracted as the second area gradation pixel by the pixel extraction unit 41 are treated as the second gradation pixel. To correct. Whether or not this correction is possible is determined by referring to the determination result of the surrounding pixels with the target pixel as the target pixel.

  The pixel counting unit 43 counts the number of pixels determined to be the second area gradation pixel by the pixel extracting unit 41 and the correcting unit 42 (including the number of pixels considered).

  The character pixel counting unit 33 counts the number of pixels determined to belong to the character area by the character / halftone determination unit 28. The first area gradation pixel counting unit 34 counts the number of pixels determined by the character / halftone determination unit 28 to belong to the halftone area (first area gradation pixel). The background pixel counting unit 35 counts the number of pixels determined to belong to the background region by the background / photographic paper determination unit 29. The photographic paper pixel counting unit 36 counts the number of pixels determined to belong to the photographic paper photograph area by the background / photographic paper determination unit 29. These count values are total values for the entire document image.

  The area gradation pixel determination unit 37 counts the pixels belonging to the dot area (first area gradation pixel) in the first area gradation pixel counting unit 34 and the pixel count of the second area gradation pixel extraction unit 32. The count result of the second area gradation pixel in the unit 43 is compared with the area gradation pixel determination threshold given from the area gradation pixel determination threshold setting unit 38, and a halftone dot (first area gradation pixel) is added to the document image. Whether or not is included is determined. The area gradation pixel determination threshold setting unit 38 sets an area gradation pixel determination threshold used in the area gradation pixel determination unit 37.

  The document determination unit 39 determines the document type based on the count result and the determination result of each pixel number from the character pixel counting unit 33, the background pixel counting unit 35, the photographic paper pixel counting unit 36, and the area gradation pixel determining unit 37. To do.

  Here, an example of pixel density distribution in each region of characters, halftone dots, photographic paper photograph, and background will be described with reference to FIGS. 4 (a) to 4 (d). In addition, a distribution using the maximum density difference and the total density busyness in each area as an index will be described with reference to FIG. Note that the total density busyness never falls below the maximum density difference in the relationship between the total density busyness and the maximum density difference, and the area where the maximum density difference = the total density busyness in FIG. Is shown.

  As shown in FIG. 4A, the background area usually has a small change in density, so that both the maximum density difference and the total density busyness are very small and are distributed in the area A shown in FIG. Therefore, a pixel that has been determined to belong to the background / printing paper region and that has a smaller maximum density difference than the background / printing paper determination threshold can be determined to be a background pixel.

  As shown in FIG. 4B, the photographic paper photograph area usually has a smooth density change, and both the maximum density difference and the total density busyness are small and slightly larger than the background area. It is distributed in the region B shown in FIG. Therefore, a pixel (a pixel of interest) that is determined to belong to the background area / photographic paper area and has a maximum density difference larger than the background / print paper determination threshold value is determined to belong to the photographic paper area. Is possible.

  In the halftone dot area, as shown in FIG. 4C, although the maximum density difference varies depending on the halftone dots, there are density changes as many as the number of halftone dots, so the ratio of the total density busyness to the maximum density difference is growing. For this reason, it becomes distribution like the area | region D shown in FIG. Therefore, a pixel (a target pixel) of a block that is determined to belong to the character / halftone dot area and has a total density busyness larger than the product of the maximum density difference and the character / halftone dot determination threshold is the halftone dot area. It is possible to determine that it belongs to.

  As shown in FIG. 4D, the character area has a large maximum density difference and a corresponding increase in the total density busyness. However, since the density change is smaller than that in the halftone dot area, the total density busyness is lower than that in the halftone dot area. The degree becomes smaller. In particular, since the ratio of the total density busyness with respect to the maximum density difference is small, the distribution is as shown in a region C in FIG. Therefore, a pixel (a pixel of interest) of a block that is determined to belong to the character / halftone dot area and has a total density busyness smaller than the product of the maximum density difference and the character / halftone dot determination threshold is included in the character area. It can be determined that it belongs.

  As described above, the maximum density difference and the total density busyness are smaller in the background area and the photographic paper photograph area than in the character area and the dot area. Therefore, by comparing the maximum density difference with the maximum density difference threshold (first maximum density difference threshold THd1) and comparing the total density busyness with the total density busyness threshold (first total density busyness threshold THb1), The determination area setting unit 25 can determine whether the pixel of interest belongs to the background / printing paper area or the character / halftone area.

  Next, the first area gradation pixel and the second area gradation pixel will be described. FIG. 6A is an explanatory diagram showing density values of pixels near one halftone dot (one dot) in a region including the first area gradation pixel (halftone dot), and FIG. It is explanatory drawing which shows the density change in the area | region containing a tone pixel. Similarly, FIG. 7A is an explanatory diagram showing the density value of a pixel near one dot in a region including the second area gradation pixel, and FIG. 7B is a diagram in the region including the second area gradation pixel. It is explanatory drawing which shows a density | concentration change. In FIG. 6A and FIG. 7A, the dot density is represented by six values, “0” being the lowest density (white: background) and “5” being the highest density.

  A halftone dot (first area gradation pixel) used in halftone printing has clear shading, and the number of lines suitable for the printed material is used. Therefore, the halftone dot density is high in the halftone printed document, and the halftone dot interval is substantially constant (see FIGS. 6A and 6B).

  The operation of the document type determination process by the document type automatic determination unit 13 in the above configuration will be described with reference to the flowcharts shown in FIGS. In the following description, it is assumed that a block including a plurality of pixels and including one target pixel includes n × m (for example, 15 × 15) pixels.

  First, for a block of n × m pixels including the target pixel, the minimum density value calculation unit 21 calculates the minimum density value (S1), and the maximum density value calculation unit 22 calculates the maximum density value (S2). Next, the maximum density difference calculation unit 23 calculates the maximum density difference in the block using the calculated minimum density value and maximum density value (S3). On the other hand, the total density busyness calculation unit 24 calculates the sum of absolute values of density differences between adjacent pixels in the block, that is, the total density busyness (S4). The maximum density difference calculation process and the total density busyness calculation process may be performed sequentially or in parallel.

  Next, the determination area setting unit 25 compares the maximum density difference calculated by the maximum density difference calculation unit 23 with the first maximum density difference threshold value THd1 and the second maximum density difference threshold value THd2, and calculates the total density busyness. The total density busyness calculated in the unit 24 is compared with the first total density busyness threshold THb1 and the second total density busyness threshold THb2 (S5 and S6, S151 and S152 (see FIG. 9)).

  Then, in the determination area setting unit 25, when the maximum density difference is smaller than the first maximum density difference threshold THd1 and the total density busyness is smaller than the first total density busyness threshold THb1 (S6), the determination area setting unit 25 sets the block. The target pixel included is determined to be in the background / printing paper region (S7). On the other hand, if the above condition is not satisfied in S6, the pixel of interest is determined to be in the character / halftone area (S9).

  In this determination, when it is determined that the pixel of interest is in the background / photographic paper region, the background / photographic paper determination unit 29 compares the maximum density difference of the block including the pixel of interest with the background / photographic paper determination threshold value. (S8). As a result of the comparison, if the maximum density difference is smaller, the target pixel is determined to be in the background area (S11), and if the maximum density difference is larger, the target pixel is determined to be in the photographic paper area (S12). ).

  On the other hand, if it is determined in S9 that the pixel of interest is in the character / halftone area, the character / halftone determination unit 28 determines the character / halftone determination threshold to the maximum density difference of the block including the pixel of interest. The value multiplied by is compared with the total density busyness (S10). If the total density busyness is smaller as a result of this comparison, the target pixel is determined to be in the character region (S13), and if the total density busyness is higher, the target pixel is determined to be in the halftone dot region. (S14).

  Next, the document type automatic determination unit 13 determines whether or not the above determination has been completed for all the pixels of the document image (S16: FIG. 11). Repeat the process. On the other hand, if the process has been completed, the document determination unit 39 determines the document type after the processing of S17 to S19 (S20).

  The document type automatic discrimination unit 13 performs second area gradation pixel extraction processing (S15) by the second area gradation pixel extraction unit 32 in parallel with the processing of S5 to S14. Details of this processing are shown in the flowchart of FIG.

  The determination area setting unit 25 compares the maximum density difference calculated by the maximum density difference calculating unit 23 with the second maximum density difference threshold THd2, and the total density busyness calculated by the total density busyness calculating unit 24. And the second total density busyness threshold THb2 are compared (S151 and S152).

  In the pixel extraction unit 41 of the second area gradation pixel extraction unit 32, it is determined that the maximum density difference is greater than or equal to the second maximum density difference threshold THd2, and the total density busyness is greater than or equal to the second total density busyness threshold THb2. For the block obtained, the value obtained by multiplying the maximum density difference by the character / halftone dot determination threshold is compared with the total density busyness (S153). If the total density busyness is larger as a result of this comparison, the target pixel included in the block is determined to be in the second area gradation pixel region (S155).

  On the other hand, in S152, the target pixel of the block in which the maximum density difference is determined to be smaller than the second maximum density difference threshold THd2, or the total density busyness is smaller than the second total density busyness threshold THb2, and in S153, For the target pixel of the block for which the total density busyness is determined to be smaller than the maximum density difference × character / halftone determination threshold value, the correction unit 42 sets the pixel as a candidate pixel for correction processing, and performs correction processing as appropriate (S154). This correction process will be described below with reference to the flowchart of FIG. 10 and FIG.

  First, as shown in FIG. 12, it is determined whether or not the pixel adjacent to the left side of the target pixel is determined as the second area gradation pixel (S161). In FIG. 12, it is assumed that the process proceeds from the left pixel to the right pixel, and the process has already been completed for the pixel on the left side of the target pixel. The opposite is true when processing proceeds from the right pixel to the left pixel. Further, the processing proceeds from the upper line to the lower line.

  Next, the number of pixels determined to be the second area gradation pixel existing in the predetermined area of the previous line adjacent to the target pixel is counted (S162), and the count value and a predetermined threshold THs are counted. Are compared (S163). If the number of second area gradation pixels is equal to or greater than the threshold value THs as a result of this comparison, the determination result for the target pixel is changed to the second area gradation pixel (S164). On the other hand, if the number of second area gradation pixels is smaller than the threshold THbs, the determination result of the target pixel is not changed (S165).

  The predetermined area of the previous line is selected so as to include a pixel adjacent to the target pixel, and is set as an area of about 10 pixels, for example. This predetermined area shifts in the same direction as the pixel of interest is sequentially shifted. When the predetermined area is an area of about 10 pixels, the threshold value THs is set to 3, for example.

  As described above, the second area gradation pixel extraction unit 32 compares the maximum density difference with the second maximum density difference threshold, and further, the total density busyness, the second total density busyness threshold, and the maximum density difference × character. The halftone dot determination threshold is compared, and a pixel having a feature amount as an area gradation pixel is extracted as a second area gradation pixel. Furthermore, from among the pixels determined not to have the feature amount as the area gradation pixel, it can be regarded as the second area gradation pixel based on information on a predetermined region (determination result of the peripheral pixel with respect to the target pixel). Pixels are added as second area gradation pixels.

  In the determination of S153 in the second area gradation pixel extraction unit 32, the maximum density difference in S10 × the character / halftone determination threshold is used as it is, but the present invention is not limited to this, and a different value is set. Also good. For example, a value smaller than the value used in S10 may be set. Specifically, if the value used in S10 is 6, it may be set to 4 in S153.

  Next, the determination operation in the area gradation pixel determination unit 37 will be described based on the flowchart of FIG.

In the area gradation pixel determination unit 37, the count value of the first area gradation pixel by the first area gradation pixel counting unit 34 is Cs1, the count value of the second area gradation pixel by the pixel counting unit 43 is Cs2, and the area level When the area gradation pixel determination threshold value in the adjustment pixel determination threshold value setting unit 38 is THs,
Cs1 / Cs2> THs
If the condition is satisfied, it is determined that the original halftone dot is included in the original image (S17, S18), and the count value of the first area gradation pixel is set as the halftone dot count value. On the other hand, when the above equation is not satisfied, it is determined that the original halftone dot is not included in the document image (S17, S19). In this determination, the area gradation pixel determination threshold value THs is set to 0.15, for example. The area gradation pixel determination threshold value THs may be set to an appropriate value based on various image samples.

  Next, the document type determination operation in the document determination unit 39 will be described in detail. The document type determination unit 39 determines the document type when the area gradation pixel determination unit 37 determines that the document image includes a print halftone dot as described above (S18 in FIG. 11). Pixels are discriminated using image data obtained by pre-scanning the original, the number of discriminated pixels is counted, and threshold values for a preliminarily prepared background area, photographic paper area, halftone dot area, and character area are prepared. To determine the type of the entire document.

  Specifically, for example, when the ratio of the character area and the ratio of the halftone dot area are equal to or greater than the threshold values, respectively, it is determined that the character / halftone print original (character print photo original). In the case where the detection accuracy increases in the order of characters, halftone dots, and photographic paper photographs, if the ratio of the character area is 30% of the total number of pixels, the ratio of the character original and the halftone area is the total number of pixels. When the ratio is 20%, it is determined that the image is a halftone print original (printed photo original), and when the ratio of the photographic paper photographic area is 10% of the total number of pixels, it is a photographic paper photographic original.

  In the above description, the area gradation pixel determination unit 37 includes a print halftone dot in the document image using the ratio between the count result of the first area gradation pixel and the count result of the second area gradation pixel. However, instead of the above ratio, arithmetic processing is performed on the counting results of the first area gradation pixel and the second area gradation pixel, such as the result of adding the two and the difference between the two. It is possible to use the results performed.

  In the above description, correction processing is performed as S154, but this correction processing is not essential. When the correction process is not performed, the second maximum density difference threshold, the second total density busyness threshold, and the maximum density difference × character / network with respect to the maximum density difference and the total density busyness calculated as described above. When determining the second area gradation pixel using the point determination threshold value, the second area gradation pixel is a pixel having a feature amount as the area gradation pixel, and the area gradation used in the halftone determination processing. The area gradation pixel determination threshold value of the pixel determination threshold value setting unit 38 may be set as high as 0.30, for example.

  In addition, the method of performing processing using the maximum density difference and the total density busyness as the feature amount has been described by the document type automatic determination unit 13, but the feature amount is not limited to these, and run length and It may be the number of inversions. In the above description, the pixel of interest is identified as the background area / printing paper (photo) area and the character area / halftone dot area, and again determined as the background area / printing paper area. It may be a method of performing determination processing in parallel as to whether or not each region is included in the region, the photographic paper region, and the background region. In addition, the character area and the halftone dot area may be combined into other areas.

  The document type automatic discrimination unit 13 scans one page of the document and feeds the discrimination result to each process in the subsequent stage to buffer (temporarily store) data for at least one page of the document. (Not shown).

  Next, an example of processing in each processing unit in the subsequent stage based on the determination result of the document type automatic determination unit 13 when the document type is determined will be described.

  When it is determined that a plurality of areas are not mixed, the process is the same as the area separation process described above. On the other hand, if it is determined that a plurality of areas are mixed, the intermediate parameters of the respective area processes may be used, and the area process parameters that have not been determined in the document type determination process may not be used.

  For example, as will be described in detail later, when it is determined that the input image (original) is a character original, the background removal amount of highlight (high luminance portion) is set to be larger in the input gradation correction processing. A correction curve that increases contrast is used.

  In addition, color correction processing that emphasizes saturation is performed on color characters, while black generation and lower color removal processing is performed on black characters (a gray component formed by overlapping CMY three colors is reduced and replaced with a K (black) component). In the processing, the black generation amount is set to be large. In addition, for a character, switching of parameters such as setting a filter coefficient so as to enhance an edge by spatial filter processing and weaken smoothing processing is performed.

  When it is determined that the input image is a character photographic paper photographic document, processing using intermediate parameters between the character document processing and the photographic paper photographic document processing is performed in each process. Depending on whether the text manuscript or photographic paper photo manuscript is prioritized, the input tone correction processing uses the intermediate parameters between the photographic paper photo manuscript processing and the character manuscript processing to remove highlights and adjust the contrast. Also, color correction processing is performed so that the intensity of saturation and the balance of gradation are not extreme. Further, in the black generation and under color removal processing, the black generation amount may be adjusted to such an extent that the photographic paper photographic image is not affected.

  Next, the configurations of the input tone correction unit 14 and the color correction unit 16 and the color correction processing for the background region will be described. First, the configuration of the input tone correction unit 14 will be described.

(1-3. Input tone correction unit 14)
FIG. 13 is a block diagram showing the configuration of the input tone correction unit 14. As shown in this figure, the input tone correction unit 14 includes a tone level determination unit (tone determination unit) 51, a tone correction processing unit 52, and a tone correction table storage unit 53.

  A document type determination signal indicating the determination result of the document type automatic determination unit 13 is input to the gradation level determination unit 51. The gradation level determination unit 51 determines the gradation levels of a block (a block including a plurality of pixels and including one target pixel) determined to belong to the background area based on the document type determination signal in a plurality of stages (this In the embodiment, classification is performed in 17 stages (TS16 to TS32), and the classification result is output to the gradation correction processing unit 52.

  Here, a gradation level classification method in the gradation level determination unit 51 will be described. Tables 1 to 3 show the relationship between the gradation levels of the R, G, and B components in the background area image data input to the input gradation correction unit 14 and the classified stages.

  As shown in Table 1, when the signals of R, G, B in each pixel of the block satisfy the relationship of R ≧ 230, RG ≧ 20, and RB ≧ 20, the signal is classified as TS16. Similarly, if R ≧ 230, R−G ≧ 16, and R−B ≧ 16, classify as TS17, and if R ≧ 230, R−G ≧ 12, and R−B ≧ 12, classify as TS18. , R ≧ 230, R−G ≧ 8, and R−B ≧ 8, classify as TS19. Note that the base color classified into TS16 to TS19 is a pink color.

  Also, as shown in Table 2, when the R, G, B signals in each pixel of the block satisfy the relationship of Rmax ≧ 235, Gmin ≧ 231, RG <4, and RB <4 If it is classified as TS20 and the relationship of Rmax ≧ 243, Gmin ≧ 236, RG <4, and RB <4 is satisfied, it is classified as TS21, Rmax ≧ 247, Gmin ≧ 244, RG <4 and If the relationship of R−B <4 is satisfied, it is classified as TS22. The base color classified into TS20 to TS22 is a gray color.

  As shown in Table 3, if the R, G, B signals in each pixel of the block satisfy the relationship of B ≧ 230, RB ≧ 20, and GB ≧ 20, the signal is classified as TS23. , If B ≧ 230 and RB ≧ 16 and GB ≧ 16 are satisfied, classify as TS24, and if B ≧ 230, RB ≧ 12 and GB ≧ 12, If it is classified as TS25 and B ≧ 230, R−B ≧ 8, and G−B ≧ 8 are satisfied, it is classified as TS26. Note that the base color classified as TS23 to 26 is a yellow color.

  The background color that does not correspond to any of TS16 to TS27 is a white color, and the image data composed of these white background colors is at any level of TS28 to TS32 according to the R, G, and B gradation levels. being classified. What is necessary is just to set arbitrarily about the classification method of TS28-TS32.

  The gradation correction table storage unit 53 is provided corresponding to the gradation levels (TS16 to TS32) of the background color classified as described above for each of a plurality of document types (or groups of document types). A plurality of background color removal tables (input gradation-output gradation conversion tables) are stored correspondingly. That is, a plurality of sets (17 stages × number of document types (or number of groups of document types)) of 17-stage background color removal tables of TS16 to TS32 are stored. Each of the background color removal tables includes data in which input image data and output image data after removal of the background color are associated with each other according to the respective gradation levels.

  FIG. 18 is a graph showing an example of the density appearance frequency for one page in a character document, a photographic paper photographic document, and a character photographic paper photographic document (a document in which characters and photographs are mixed). FIG. 19 is a graph showing an example of a background color removal table (γ curve) for a character document and an example of a background color removal table for a photographic document. As shown in this figure, in a character document, it is easy to distinguish between the background portion and the character portion. Therefore, if the gradation level determination result is the same, the background color removal table for the character document is more than the background color removal table for the photo document. Also set the amount of highlight ground removal large. Thereby, it is possible to prevent the background color component from remaining due to insufficient background removal amount for the character document. On the other hand, the background color removal table for photographic originals has a lower background removal amount than the background color removal table for character originals. As a result, in the case of a photographic document, it is possible to prevent the occurrence of a problem such as removal of a background where a background should not be removed.

  In the present embodiment, the density appearance frequency in the halftone printed document and the photographic paper document is almost the same when viewed from the macro viewpoint (entire document) (however, the micro viewpoint (range of several pixels)). As for the background removal table, the same table is used for the halftone print original and the photographic paper original.

  In the present embodiment, a printed photo document (a document in which halftone expression is represented by area gradation such as halftone dots (a method of expressing gradation by an ON / OFF area)) and a photographic paper document (area floor) The same background removal table is used for originals (halftones expressed by changing dyes or pigments themselves, regardless of tone). However, a dedicated background removal table may be used according to the characteristics of the device (for example, the resolving power of the image reading apparatus).

  Further, in the present embodiment, as a background color removal table for a character photographic paper photographic document, a table having an intermediate background removal amount between a background color removal table for a character document and a background color removal table for a photographic paper photographic document. Is used. However, the present invention is not limited to this, and a background color removal table for a photographic paper photographic document may be used as a background color removal table for a character photographic paper photographic document. Therefore, in the case of a document in which characters and photographs are mixed, the background removal amount may be appropriately set (or the background color removal table is appropriately selected) depending on whether background removal or gradation reproduction should be given priority.

  FIG. 14 is a graph showing an example of the base color removal table (γ curve). In the present embodiment, a common table is used for each of R, G, and B data for each document type (or group of document types) and gradation level. However, the present invention is not limited to this. , B may be provided with separate tables.

  The gradation correction processing unit 52 is a background color removal table stored in the gradation correction table storage unit 53 based on the document type determined by the document type automatic determination unit 13 and the classification result of the gradation level determination unit 51. A table corresponding to the document type and the gradation level of the background color is selected from among the image data, and the image data (R, G, B) input from the document type automatic discrimination unit 13 with reference to the selected table is output image data. It is converted into (R ′, G ′, B ′) and output to the region separation processing unit 15. When a document type determination signal other than the background area is input to the gradation level determination unit 51, for example, the gradation level determination unit 51 outputs the document type determination signal to the gradation correction processing unit 52 as it is, The correction processing unit 52 may select the gradation correction table corresponding to the document type and perform the gradation correction process.

(1-4. Color Correction Unit 16)
FIG. 15 is a block diagram illustrating a configuration of the color correction unit 16. As shown in this figure, the color correction unit 16 includes a background color determination unit (background color determination unit) 61, a color correction processing unit (color correction processing unit) 62, and a color correction table storage unit 63.

  The background color determination unit 61 receives a document type determination signal indicating the determination result of the document type automatic determination unit 13 and, based on the document type determination signal, is a block (consisting of a plurality of pixels) determined to belong to the background region. A block including one pixel of interest) is classified into a plurality of groups according to the color system of the background color. In the present embodiment, the gradation level of the block is classified into 17 levels of TS16 to TS32 by the same method as the gradation level determination unit 51 provided in the input gradation correction unit 14, and TS23 to TS26 (yellow). Block classified as group A), blocks classified as TS20 to TS22 (gray background color) into group B, and blocks classified as TS16 to TS19 (pink background color) into group Blocks classified as C and TS27 to TS32 (white base colors) are classified into group D. Then, the classification result is output to the color correction processing unit 62.

  The color correction table storage unit 63 stores a plurality of color correction tables (color correction / color conversion tables) provided corresponding to the above groups. FIG. 16 is an explanatory diagram showing the concept of each color correction table stored in the color correction table storage unit 63. As shown in this figure, each color correction table can be expressed as a three-dimensional space with R ′, G ′, and B ′ as axes, and addresses specified by the values of R ′, G ′, and B ′ include: C, M, and Y values that are color data after conversion are stored. That is, by using these color correction tables, it is possible to convert the first color system image data composed of RGB into the second color system image data composed of CMY.

  In addition, the data of each color correction table is such that the color tone remaining after the background color removal does not change drastically, that is, the color correction other than the background color due to the background color removal is reduced. It is set for each group corresponding to the table. For example, this is a case where color correction is performed on image data obtained by removing density components of the background color by input gradation processing on image data read from a document in which a light color image is formed on a dark ground. However, the data of each color correction table is set according to the background color corresponding to each table so that the light color image in the original is faithfully reproduced.

(1-5. Background color removal processing and color correction processing)
Next, the background color removal process in the input tone correction unit 14 and the color correction process in the color correction unit 16 will be described with reference to FIG. FIG. 17 is a flowchart showing the flow of background color removal processing and color correction processing.

  When the image data (R, G, B) and the document type determination signal are input from the document type automatic determination unit 13 to the input gradation correction unit 14, as shown in FIG. It is determined which gradation level of TS16 to TS32 corresponds to the block belonging to (S201). Further, the gradation level determination unit 51 outputs a signal indicating the determination result, that is, a signal indicating which gradation level of the TS 16 to TS 32 corresponds to the target block to the gradation correction processing unit 52. .

  Next, the gradation correction processing unit 52 selects the background color removal table according to the document type indicated by the document type determination signal and the gradation level indicated by the determination result of the gradation level determination unit 51 (S202). The input image data (R, G, B) for the block is corrected to output image data (R ′, G ′, B ′) based on the selected background color removal table, and the background color is removed (S203). ). The output image data (R ′, G ′, B ′) is output to the region separation processing unit 15. Here, description of the processing of the region separation processing unit 15 is omitted.

  In the color correction unit 16 to which the image data (R ′, G ′, B ′) is input from the region separation processing unit 15, the background color determination unit 61 determines which of the groups A to D the block belongs to. The determination result is output to the color correction processing unit 62 (S204).

  The color correction processing unit 62 selects a color correction table corresponding to the group indicated by the determination result of the background color determination unit 61 (S205), and selects the input image data (R ′, G ′, B ′) as the selected color correction. The output image data (C, M, Y) is corrected based on the table (S206).

  FIG. 1 is an explanatory diagram illustrating a selection method of lookup tables (background color removal table and color correction table) in the background color removal process in the input tone correction unit 14 and the color correction process in the color correction unit 16. As shown in this figure, the background color removal process is performed using the background color removal tables (LUT16 to LUT32) corresponding to the gradation levels (TS16 to TS32) indicated by the determination result of the gradation level determination unit 51, Color correction is performed using color correction tables (LUT-A to LUTD) corresponding to groups (groups A to D) indicated by the determination result of the background color determination unit 61.

  As described above, in the color image processing apparatus 2 according to the present embodiment, the document type automatic determination unit 13 determines the type of an area to which a block composed of a plurality of pixels including the target pixel belongs, and the determination result of the area type The input gradation correction unit 14 selects the background color removal table in accordance with the document type determined by the document type determination means, thereby adjusting the background removal amount.

  In other words, the input gradation correction unit 14 stores a plurality of sets of background color removal tables provided corresponding to the gradation levels of the background color corresponding to the document type (or group of document types). Based on the document type determined by the tone correction table storage unit 53 and the document type automatic determination unit 13, a table corresponding to the document type is selected from the background color removal tables stored in the gradation correction table storage unit 53. And a gradation correction processing unit 52 that performs background color removal processing using the selected table.

  Accordingly, the background removal amount can be adjusted according to the document type, and appropriate background removal can be performed according to the document type. For example, for text originals that require high contrast and photo originals that require appropriate reproduction of gradation, the background removal amount can be set appropriately according to the type of each original. It is possible to remove the background.

  In the present embodiment, the gradation correction table storage unit 53 stores a plurality of background color removal tables corresponding to the gradation levels of the background colors for each of a plurality of document types (or document type groups). Yes. The input tone correction unit 14 sets the tone levels of the blocks (blocks including a plurality of pixels and including one pixel of interest) determined to belong to the background area by the document type automatic discrimination unit 13 in a plurality of stages. A gradation level determination unit 51 for classification is provided, and a gradation correction processing unit 52 selects and selects a background color removal table according to the document type and the gradation level classified by the gradation level determination unit 51. The background color removal processing is performed using the table.

  As a result, the amount of background removal can be adjusted according to the document type and the gradation level of the background color, and more appropriate background removal processing can be performed. However, the present invention is not limited to this, and one background color removal table may be provided for each of a plurality of document types (or groups of document types).

  Further, in the present embodiment, when the gradation level of the background color is the same, the background color removal table for character originals has a higher amount of highlight background removal than the background color removal table for photo originals. As a result, the background removal amount in the character original is sufficient, and it is possible to prevent a problem that the background removal is performed in a portion where the background removal should not be performed in other originals (for example, photographic originals).

  In addition, the color image processing apparatus 2 according to the present embodiment includes a color correction table storage unit 63 that stores a plurality of color correction tables, and a background color determination unit 61 that determines a background color based on image data. The color correction table used for the color correction process is selected based on the determination result of the background color determination unit 61. In addition, each color correction table is set according to the color system of the background color so that a change in color due to the background color removal with respect to the color remaining after the background color removal is reduced. Thereby, it is possible to suppress a change in the color other than the base color due to the removal of the base color and improve the color reproducibility.

  In the present embodiment, the gradation level determination unit 51 provided in the input gradation correction unit 14 determines the gradation level of the block belonging to the background region, and the background color determination unit 61 provided in the color correction unit 16 determines the background level. Although the color system (group) of the blocks belonging to the region is determined, the present invention is not limited to this, and for example, each of these processes may be performed in the gradation level determination unit 51.

  In the present embodiment, the configuration including the four color correction tables respectively corresponding to the groups A to D has been described. However, the configuration is not limited thereto, and at least two or more color correction tables may be provided. While the color reproducibility can be improved as the number of color correction tables is increased, the storage capacity required for the color correction table storage unit 63 is increased. Therefore, the number of color correction tables may be appropriately set in consideration of the required color reproduction performance and the cost of the memory used as the color correction table storage unit 63.

  Further, as the color correction table, a table storing output image data corresponding to all combinations of input image data may be used (direct conversion method), and an output corresponding to some selected combinations of input image data may be used. Image data may be stored, and output image data may be obtained by interpolation calculation when color correction is performed on unstored input image data (table interpolation method). When the table interpolation method is adopted, the capacity of the memory used as the color correction table storage unit 63 can be reduced, and the cost can be reduced.

  In this embodiment, a table for performing color correction and color conversion at the same time is used as the color correction table. However, the present invention is not limited to this, and color correction and color conversion may be performed using separate tables. Good.

  Also, each block of the color image processing apparatus 2 in the present embodiment is realized by software using a processor such as a CPU as described above.

  That is, the color image processing apparatus 2 includes a CPU (central processing unit) that executes instructions of a control program that realizes each function, a ROM (read only memory) that stores the program, and a RAM (random access memory) that expands the program. ), A storage device (recording medium) such as a memory for storing the program and various data. An object of the present invention is a recording medium in which a program code (execution format program, intermediate code program, source program) of a control program of the color image processing apparatus 2 which is software that realizes the above-described functions is recorded so as to be readable by a computer. Is achieved by the computer (or CPU or MPU) reading and executing the program code recorded on the recording medium.

  Examples of the recording medium include tapes such as magnetic tapes and cassette tapes, magnetic disks such as floppy (registered trademark) disks / hard disks, and disks including optical disks such as CD-ROM / MO / MD / DVD / CD-R. Card system such as IC card, IC card (including memory card) / optical card, or semiconductor memory system such as mask ROM / EPROM / EEPROM / flash ROM.

  The color image processing apparatus 2 may be configured to be connectable to a communication network, and the program code may be supplied via the communication network. The communication network is not particularly limited. For example, the Internet, intranet, extranet, LAN, ISDN, VAN, CATV communication network, virtual private network, telephone line network, mobile communication network, satellite communication. A net or the like is available. Further, the transmission medium constituting the communication network is not particularly limited. For example, even in the case of wired such as IEEE 1394, USB, power line carrier, cable TV line, telephone line, ADSL line, etc., infrared rays such as IrDA and remote control, Bluetooth ( (Registered trademark), 802.11 wireless, HDR, mobile phone network, satellite line, terrestrial digital network, and the like can also be used. 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.

  In addition, each block of the color image processing apparatus 2 in the present embodiment is not limited to being realized using software, but may be configured by hardware logic.

  The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope shown in the claims. That is, embodiments obtained by combining technical means appropriately modified within the scope of the claims are also included in the technical scope of the present invention.

  The present invention can also be applied to a device that needs to determine the type of document, such as a color copier, a flatbed scanner, a film scanner, a digital camera, or the like.

It is explanatory drawing which shows the selection method of the look-up table used for a background color removal process and a color correction process in the image processing apparatus concerning one Embodiment of this invention. 1 is a block diagram illustrating a schematic configuration of an image forming apparatus including an image processing apparatus according to an embodiment of the present invention. FIG. 3 is a block diagram illustrating a configuration of a document type automatic determination unit provided in the image processing apparatus according to the embodiment of the present invention. FIG. 4A is an explanatory diagram showing the maximum density difference of the background region and the distribution of the region having the density, FIG. 4B is the same explanatory diagram in the photographic paper region, and FIG. 4C is the same in the halftone dot region. FIG. 4D is an explanatory diagram of the character area. It is a graph which shows the relationship between the maximum density difference about each area | region shown to Fig.4 (a)-FIG.4 (d), and total density busyness. FIG. 6A is an explanatory diagram showing density values of pixels near one halftone dot (one dot) in a region including the first area gradation pixel (halftone dot), and FIG. 6B is a first area gradation pixel. It is explanatory drawing which shows the density | concentration change in the area | region containing. FIG. 7A is an explanatory diagram showing the density value of a pixel near one dot in the region including the second area gradation pixel, and FIG. 7B is an explanation showing the density change in the region including the second area gradation pixel. FIG. FIG. 4 is a flowchart showing a flow of a document type determination process in a document type automatic determination unit shown in FIG. 3. It is a flowchart which shows the flow of the 2nd area gradation pixel extraction process by the 2nd area gradation pixel extraction part shown to S15 of FIG. It is a flowchart which shows the flow of the correction process by the correction | amendment part shown to S154 of FIG. FIG. 9 is a flowchart illustrating a flow of document type determination processing in a document type automatic determination unit following the flowchart of FIG. 8. It is explanatory drawing of the correction process in the correction | amendment part shown in FIG. FIG. 3 is a block diagram illustrating a configuration of an input tone correction unit provided in the image processing apparatus illustrated in FIG. 2. It is a graph which shows an example of the base color removal table used in the input tone correction unit shown in FIG. FIG. 3 is a block diagram illustrating a configuration of a color correction unit provided in the image processing apparatus illustrated in FIG. 2. It is explanatory drawing which shows the color correction table memorize | stored in the color correction part shown in FIG. FIG. 3 is a flowchart showing the flow of background color removal processing and color correction processing in the image processing apparatus shown in FIG. 2. It is a graph showing an example of density appearance frequency in a character manuscript, a photographic paper photographic manuscript, and a character photographic paper photographic manuscript. 14 is a graph illustrating an example of a background color removal table for a character document and a background color removal table for a photographic document, which are used in the input tone correction unit illustrated in FIG. 13.

Explanation of symbols

2 Color image processing device (image processing device)
13 Document Type Automatic Discrimination Unit (Document Type Discrimination Unit)
14 Input tone correction unit (background color removal means)
16 color correction unit 51 gradation level determination unit (gradation determination means)
52 Gradation correction processing unit 53 Gradation correction table storage unit (background color removal table storage unit)
61 Background color determination unit (background color determination means)
62 Color correction processing unit (color correction processing means)
63 color correction table storage

Claims (8)

An image processing apparatus that performs image processing on image data read from a document according to the document type of the document,
A document type determining unit that determines a type of a region to which a block including a plurality of pixels including a target pixel belongs, and that determines a document type based on a determination result of the region type;
A background color removal means for performing a background color removal process for removing the density component of the background color from the image data ;
Based on a combination of gradation values of each color component in each pixel of the area of the image data determined as the background area by the document type determination means, the gradation level of the background area is set to a plurality of predetermined gradation levels. Gradation discrimination means for classifying into either,
A table storage unit for storing a plurality of background color removal tables associated with the image data before and after the background color removal processing, which are provided corresponding to the respective gradation levels, for each of the plurality of document types; ,
A background color determining means for classifying the image data into one of a plurality of groups according to the background color of the document;
A plurality of color correction tables associated with the image data before and after color correction, provided corresponding to the background color corresponding to each group,
Color correction processing means for performing color correction processing on the image data after the background color removal processing is performed using the color correction table corresponding to the group classified by the background color determination means ,
The background color removing means is
From the background color removal table stored in the table storage unit, the background color removal corresponding to the document type determination result by the document type determination unit and the gradation level classification result by the gradation determination unit Extract the table, perform the background color removal process using the extracted background color removal table,
Each of the color correction tables is set so that a change in a color other than the background color associated with the background color removal process is reduced . The document type determining means determines at least whether the document is a text document or a document other than a text document,
2. The image according to claim 1, wherein the background color removing unit makes the removal amount of the background color density component for the character document larger than the removal amount of the background color density component for the document other than the character document. Processing equipment. The above color correction table, the image data composed of the first color system, the image processing according to claim 1, characterized in that it is set to convert the image data of a second color system apparatus. The document type determination unit is configured to detect, for a block including a plurality of pixels including a target pixel, a maximum density difference that is a difference between a maximum value and a minimum value of each pixel in the block, and adjacent pixels in the block. A total density busyness that is a sum of absolute values of the density differences is calculated, the first maximum density difference is smaller than a preset first maximum density difference threshold value, and the total density busyness is a preset first value. A block that is smaller than the total density busyness threshold and the maximum density difference is smaller than a preset background / photographic paper determination threshold is determined as a background area ,
The background color removing unit removes the background color for the block determined to be a background region by the document type determining unit;
The image processing apparatus according to claim 1, wherein the color correction processing unit performs the color correction on a block that is determined to be a background area by the document type determination unit. An image processing method for performing image processing on image data read from a document according to the document type of the document,
A document type determination step of determining a type of an area to which a block including a plurality of pixels including a target pixel belongs, and determining a document type based on a determination result of the area type;
A background color removal step of performing a background color removal process for removing a background color density component from the image data ;
Based on a combination of gradation values of each color component in each pixel of the area determined as the background area in the document type determination step in the image data, the gradation level of the background area is set to a plurality of predetermined gradation levels. A gradation discrimination process classified into one of the following:
A background color determination step for classifying the image data into one of a plurality of groups according to the background color of the document;
Color correction corresponding to the group classified in the background color discrimination step among a plurality of color correction tables associated with the image data before and after color correction provided corresponding to the background color corresponding to each group. A color correction processing step for performing color correction processing on the image data after the background color removal processing is performed using a table ,
In the background color removal step,
For each of the plurality of document types, the document type is selected from a plurality of background color removal tables associated with the image data before and after the background color removal process, which are provided corresponding to the respective gradation levels. The background color removal table corresponding to the document type determination result in the determination step and the gradation level classification result in the gradation determination step is extracted, and the background color removal process is performed using the extracted background color removal table. Done
The image processing method according to claim 1, wherein each of the color correction tables is set so that a change in a color other than the background color associated with the background color removal process is reduced . An image forming apparatus characterized by comprising an image processing apparatus according to any one of claims 1 to 4. An image processing program for operating an image processing apparatus according to claim 1, any one of 4, an image processing program for causing a computer to function as each means described above. A computer-readable recording medium on which the image processing program according to claim 7 is recorded.

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