JP2008092541A - Image processing method, image processing apparatus, image forming apparatus, computer program, and recording medium - Google Patents

Abstract

The present invention relates to a method for selectively reducing a consumption amount of a recording material such as toner or ink for an area where deterioration of image quality is not expected, and also causing deterioration of the entire image and loss of information included in the image. An image processing method, an image processing apparatus, an image forming apparatus, a computer program, and a recording medium that can be prevented are provided.
A gradation reproduction processing unit selects and inputs a density conversion table corresponding to a character region, a photographic region, a graphic region, or a background region based on a determination signal input from an region recognition processing unit. Density conversion processing for reducing the density is performed on the background area or the drawing area of the CMYK signals. Further, the gradation reproduction processing unit 28 binarizes or multi-values the CMYK signal after the density conversion by a dither process using a predetermined dither matrix, and outputs a halftone image that artificially represents a grayscale. Generate data.
[Selection] Figure 1

Description

  The present invention relates to an image processing method, an image processing apparatus, an image forming apparatus including the image processing apparatus, and a computer program for realizing the image processing apparatus, which can reduce the consumption of a recording material such as toner or ink. The present invention also relates to a recording medium on which the computer program is recorded.

  Image forming devices such as copiers and printers that use various recording methods such as thermal transfer, electrophotography, or ink jet can reproduce color images with high image quality as digital image processing technology advances. As a result, full-color digital copiers and multifunction devices have been commercialized.

  Full-color digital copiers, multifunction devices, etc., when printing output images on recording paper, have a limited number of gradation representations that can be displayed. By performing binarization processing or multi-value conversion processing that converts to a tone, a gradation image including a halftone is formed in a pseudo manner to generate an output image.

  On the other hand, digital copying machines and multifunction peripherals are being shared and printed by many users in the office as information processing represented by the Internet in recent years has increased in speed or the amount of information has increased. The amount of recording paper has become enormous, and there is an increasing demand for reducing the consumption of recording materials such as toner or ink used during printing.

  For example, as a method of reducing the consumption of a recording material such as toner or ink, when a mode for reducing the usage of the recording material is designated, the brightness component or luminance of the intermediate color space in which the color space of the input image is converted Proposed a color image processing device that can reduce the consumption of recording materials with a simple configuration while making the components brighter than the normal mode or performing correction processing to lower the saturation and suppressing deterioration in color reproducibility (See Patent Document 1).

  In addition, when a mode for reducing the amount of recording material used is specified, output is performed by performing white mask processing that replaces a predetermined position with white for the image data in the intermediate color space in which the color space of the input image is converted. There has been proposed a color image processing apparatus capable of reducing the amount of recording material used while reducing the area to minimize color conversion (see Patent Document 2).

Further, it is determined whether the manuscript is a monochrome manuscript, a business color manuscript including color characters or line drawings and not including a photographic image, or a color manuscript including a photographic image (a color manuscript other than a business color manuscript). When the type is a business color original, the density value of the color pixel that is not a color edge pixel is converted to a value of 1 / n (n is a positive number), and when the type of the original is a color original, the color pixel Is converted to a value of 1 / m (m is a positive number, and m <n), so that when the document type is a business color document, the density value of the color pixel is reduced and the toner is processed. Has been proposed (see Patent Document 3).
JP 2005-86289 A JP 2005-86719 A JP 2005-59444 A

  However, in the apparatuses disclosed in Patent Documents 1 to 3, in order to reduce consumption of a recording material such as toner or ink, predetermined processing is performed on the entire input image or color pixels other than the edge pixels. Therefore, the density value of the entire output image or the entire image composed of color pixels is uniformly reduced. However, the output image contains various attribute areas such as characters, photographs, drawings, and backgrounds, and depending on the image area, the density value decreases uniformly, which causes the image quality to deteriorate. There is a problem of inviting. In addition, when the output image includes an area in which the image quality is deteriorated by decreasing the density value of the image, the above-described apparatus cannot perform the process of reducing the recording material consumption, and the recording is performed. There is also a problem that the consumption of the material cannot be reduced at all.

  The present invention has been made in view of such circumstances. When one or a plurality of regions are extracted based on input image data, and the density difference of the extracted regions is smaller than a predetermined threshold value, By converting the density value of each pixel to a low density value and performing gradation reproduction processing, the consumption of a recording material such as toner or ink is selectively reduced in an area where deterioration of image quality is not expected. An image processing method, an image processing apparatus, an image forming apparatus including the image processing apparatus, and the image processing apparatus capable of preventing the deterioration of the entire image and the loss of information included in the image while performing the processing An object of the present invention is to provide a computer program and a recording medium on which the computer program is recorded.

  Another object of the present invention is to perform dither processing using a dither matrix having a large number of matrices on the extracted area when the density difference of the extracted area is smaller than a predetermined threshold value. When the difference is larger than a predetermined threshold, by performing dither processing using a dither matrix with a small number of matrices for the region and performing gradation reproduction processing, regions of various attributes are mixed in the image. The present invention provides an image processing method, an image processing apparatus, and an image forming apparatus including the image processing apparatus that can reproduce faithful image quality while reducing the consumption of recording material.

  Another object of the present invention is to extract one or a plurality of regions based on input image data, and when the density difference of the extracted regions is smaller than a predetermined threshold, a part of the pixels in the region is thinned out. In addition to performing the gradation reproduction process, the processing for reducing the consumption of the recording material such as toner or ink is selectively performed on the area where the deterioration of the image quality is not expected. Image processing method capable of preventing deterioration and loss of information included in image, image processing apparatus, image forming apparatus including the image processing apparatus, computer program for realizing the image processing apparatus, and computer program It is to provide a recorded recording medium.

  Another object of the present invention is to perform color correction with a low number of gradations on the extracted area when the density difference of the extracted area is smaller than a predetermined threshold value. If the area is larger than the threshold, color correction is performed on the area with a high number of gradations and gradation reproduction processing is performed, so that even if areas with various attributes are mixed in the image, the recording material The present invention provides an image processing method, an image processing apparatus, and an image forming apparatus including the image processing apparatus that can reproduce faithful image quality while reducing the consumption amount of the image processing apparatus.

  Another object of the present invention is to identify the area as a background area or a drawing area when the density difference of the extracted area is smaller than a predetermined threshold, and the density difference of the extracted area is larger than the predetermined threshold. In this case, by identifying the region as a character region or a photographic region, an image processing method and an image processing capable of performing gradation reproduction processing by distinguishing between a region where gradation is important and a region where resolution is important And an image forming apparatus including the image processing apparatus.

  Another object of the present invention is to provide a control means for controlling to perform a predetermined gradation reproduction process when an instruction for reducing the consumption amount of toner or ink is received. Accordingly, an object of the present invention is to provide an image processing apparatus capable of reducing the consumption of recording material and reproducing faithful image quality, and an image forming apparatus including the image processing apparatus.

  An image processing method according to the present invention is an image processing method for generating pseudo-halftone output image data by performing gradation reproduction processing on input image data, and is based on the pixel value of each pixel in the input image data. Alternatively, a plurality of areas are extracted, the density difference of the extracted areas is calculated, and when the calculated density difference is smaller than a predetermined threshold, the density value of each pixel in the area is converted to a low density value and converted. The tone reproduction process is performed on the input image data including the image data obtained in this way.

  In the image processing method according to the present invention, when the density difference of the extracted region is smaller than a predetermined threshold, the dither processing is performed on the region using a dither matrix having a large number of matrices, and the density difference of the extracted region is Is larger than a predetermined threshold value, the tone reproduction processing is performed by performing dither processing on the region using a dither matrix having a small number of matrices.

  An image processing method according to the present invention is an image processing method for generating pseudo-halftone output image data by performing gradation reproduction processing on input image data, and is based on the pixel value of each pixel in the input image data. Alternatively, a plurality of areas are extracted, the density difference of the extracted areas is calculated, and when the calculated density difference is smaller than a predetermined threshold, gradation reproduction processing is performed on the input image data including the image data of the area. Before or after application, a part of the pixels in the area is thinned out.

  In the image processing method according to the present invention, when the density difference of the extracted area is smaller than the predetermined threshold, the area is subjected to color correction with a low number of gradations, and the density difference of the extracted area is set to the predetermined threshold. If larger, the tone correction process is performed by performing color correction on the area with a high number of tones.

  An image processing method according to the present invention is an image processing method for generating pseudo-halftone output image data by performing gradation reproduction processing on input image data, and is based on the pixel value of each pixel in the input image data. Alternatively, a plurality of areas are extracted, the density difference of the extracted areas is calculated, and if the calculated density difference is smaller than a predetermined threshold, color correction is performed by performing color correction with a low number of gradations on the area. The tone reproduction process is performed on the input image data including the image data obtained in this way.

  In the image processing method according to the present invention, when the density difference of the extracted area is smaller than a predetermined threshold, the area is identified as a background area or a drawing area, and the density difference of the extracted area is larger than the predetermined threshold The region is identified as a character region or a photo region.

  An image processing apparatus according to the present invention is an image processing apparatus that performs gradation reproduction processing on input image data to generate pseudo-halftone output image data, based on the pixel value of each pixel in the input image data. Or an extracting means for extracting a plurality of areas, a calculating means for calculating a density difference of the areas extracted by the extracting means, and a density difference calculated by the calculating means is smaller than a predetermined threshold value, It comprises conversion means for converting the density value of a pixel to a low density value, and means for performing gradation reproduction processing on input image data including image data obtained by conversion by the conversion means.

  In the image processing apparatus according to the present invention, the means for performing the gradation reproduction process may be configured so that the density difference of the area extracted by the extraction means is smaller than a predetermined threshold, and the area is based on a dither matrix having a large number of matrices. And a dithering process performed on the area based on a dither matrix having a small number of matrices when the density difference of the area extracted by the extracting unit is larger than a predetermined threshold value. It is characterized by that.

  An image processing apparatus according to the present invention is an image processing apparatus that performs gradation reproduction processing on input image data to generate pseudo-halftone output image data, based on the pixel value of each pixel in the input image data. Alternatively, an extraction unit that extracts a plurality of regions, a calculation unit that calculates a density difference between the regions extracted by the extraction unit, and an image of the region when the density difference calculated by the calculation unit is smaller than a predetermined threshold value Means for thinning out part of the pixels in the region before or after the gradation reproduction process is performed on the input image data including the data.

  When the density difference of the extracted area is smaller than a predetermined threshold, the image processing apparatus according to the present invention performs color correction with a low number of gradations on the area, and the density difference of the extracted area is a predetermined threshold. If larger, color correction means for performing color correction on the area with a high number of gradations is provided, and gradation reproduction processing is performed on input image data including image data color-corrected by the color correction means. It is characterized by being.

  An image processing apparatus according to the present invention is an image processing apparatus that performs gradation reproduction processing on input image data to generate pseudo-halftone output image data, based on the pixel value of each pixel in the input image data. Alternatively, an extraction unit that extracts a plurality of regions, a calculation unit that calculates a density difference between the regions extracted by the extraction unit, and a density difference calculated by the calculation unit is smaller than a predetermined threshold, And color correction means for performing color correction with a low number of gradations, and means for performing gradation reproduction processing on input image data including image data color-corrected by the color correction means.

  When the density difference of the area extracted by the extraction means is smaller than a predetermined threshold, the image processing apparatus according to the present invention identifies the area as a background area or a drawing area, and the area extracted by the extraction means And a means for identifying the region as a character region or a photo region when the density difference is larger than a predetermined threshold value.

  An image processing apparatus according to the present invention includes an accepting unit that accepts an instruction to reduce toner or ink consumption, and when the accepting unit accepts an instruction, the extraction unit, the calculating unit, and the conversion unit Control means for controlling to perform the thinning-out process.

  An image forming apparatus according to the present invention includes the image processing apparatus according to any one of the above-described inventions, and an image forming unit that forms an output image based on output image data generated by the image processing apparatus. It is characterized by.

  A computer program according to the present invention is a computer program for causing a computer to perform tone reproduction processing on input image data to generate pseudo-halftone output image data. If the calculated density difference is smaller than a predetermined threshold, the means for extracting one or more areas based on the value, the computer, the means for calculating the density difference of the extracted area, and the computer The means for converting the density value of each pixel into a low density value and the computer function as means for performing gradation reproduction processing on the input image data including the image data obtained by the conversion.

  A computer program according to the present invention is a computer program for causing a computer to perform tone reproduction processing on input image data to generate pseudo-halftone output image data. If the calculated density difference is smaller than a predetermined threshold, the means for extracting one or more areas based on the value, the computer, the means for calculating the density difference of the extracted area, and the computer Before or after the gradation reproduction process is performed on the input image data including the image data, a part of the pixels in the region is made to function as a thinning process unit.

  A computer-readable recording medium according to the present invention records a computer program according to any of the above-described inventions.

  In the present invention, based on the pixel value of each pixel in the input image data, one or a plurality of regions for identifying image attributes are extracted. For example, a connected region is extracted by performing a labeling process on a binarized image obtained by binarizing input image data with a predetermined binarization threshold. A rectangular area circumscribing the extracted connected area is extracted. Based on the shape or size of the extracted area (rectangular area), a character area or a non-character area (non-character area) is identified. In this case, it can be used that the character area is a relatively elongated area. A density difference between pixels in an area identified as a non-character area is calculated. In this case, a histogram of the density value of each pixel in the region is created, and the density difference is calculated from the difference between the maximum density value and the minimum density value.

  It is determined whether or not the calculated density difference is smaller than a density threshold value. For example, a substantially uniform density and low density area can be determined as a base area, and an area having a higher density and a substantially uniform density than the low density area is a drawing area (for example, It is possible to determine that the image area is an image area such as a figure or a picture and is not a photographic image. Note that a non-character area that is not a background area or a drawing area is an area (for example, a photographic area) where the density difference is larger than a predetermined density threshold and the density change exists over a wide range.

  The density value of each pixel in the area where the density difference of the extracted area is smaller than the density threshold value is converted to a low density value, and tone reproduction processing is performed on the input image data including the image data obtained by the conversion. This reduces the consumption of a recording material such as toner or ink used when forming an image in an area where the density difference is smaller than the density threshold (for example, the background area or the graphic area). In addition, since an area having a density difference larger than the density threshold (for example, a character area or a photographic area) is not converted into a low density value, image quality deterioration or information contained in the image is not lost.

  In the present invention, when the density difference of the extracted area is smaller than the density threshold, dither processing is performed on the area using a dither matrix having a large number of matrices, and the density difference of the extracted area is determined. If it is larger than the density threshold value, the tone reproduction process is performed by performing a dither process on the area using a dither matrix having a small number of matrices. An area where the density difference is smaller than the density threshold is, for example, a background area or a graphic area, and since the density change in the area is small, dither processing is performed using a dither matrix having a large number of matrices (for example, 8 × 8). In this way, processing that places importance on gradation in the low density region is performed, and fluctuations in dot reproducibility or deterioration in color reproducibility due to the ambient temperature of the apparatus or changes over time are suppressed. If an area where the density difference is larger than the density threshold (for example, a character area or a photographic area) is a photographic area, dither processing is performed using a dither matrix with a small number of matrices (for example, 4 × 4) to emphasize gradation. However, the processing for increasing the resolution is performed. If the area where the density difference is greater than the density threshold is a character area, dither processing is performed using a dither matrix having a smaller number of matrices (for example, 2 × 2, 3 × 3), and processing that places importance on resolution is performed. As a result, even when areas with various attributes are mixed in the image, it is possible to reproduce faithful image quality while reducing the consumption of the recording material.

  In the present invention, one or more regions for identifying image attributes are extracted based on the pixel value of each pixel in the input image data. For example, a connected region is extracted by performing a labeling process on a binarized image obtained by binarizing input image data with a predetermined binarization threshold. A rectangular area circumscribing the extracted connected area is extracted. Based on the shape or size of the extracted area (rectangular area), a character area or a non-character area (non-character area) is identified. In this case, it can be used that the character area is a relatively elongated area. A density difference between pixels in an area identified as a non-character area is calculated. In this case, a histogram of the density value of each pixel in the region is created, and the density difference is calculated from the difference between the maximum density value and the minimum density value.

  It is determined whether or not the calculated density difference is smaller than a density threshold value. For example, a substantially uniform density and low density area can be determined as a base area, and an area having a higher density and a substantially uniform density than the low density area is a drawing area (for example, It is possible to determine that the image area is an image area such as a figure or a picture and is not a photographic image. Note that a non-character area that is not a background area or a drawing area is an area (for example, a photographic area) where the density difference is larger than a predetermined density threshold and the density change exists over a wide range.

  A part of the pixels in the area where the density difference of the extracted area is smaller than the density threshold is thinned out. For example, the pixel values of several adjacent pixels (for example, four pixels) are set to “0” every other pixel or plural pixels. Thereby, the pixel values of one or a plurality of pixels are left as they are, and the pixel values of four adjacent pixels are set to “0”. Further, the thinning process is performed before or after the gradation reproduction process (for example, error diffusion process). This lowers the density of areas where the density difference is smaller than the density threshold (for example, the background area and the graphic area), thereby reducing the consumption of recording material such as toner or ink used when forming an image in the area. To do. Further, since the density reduction by the thinning process is not performed on the area where the density difference is larger than the density threshold (for example, the character area or the photographic area), the image quality is not deteriorated or the information included in the image is not lost.

  In the present invention, when the density difference of the extracted area is smaller than the density threshold, the area is subjected to color correction with a low number of gradations, and the density difference of the extracted area is larger than the density threshold. In this case, tone reproduction processing is performed by performing color correction on the area with a high number of gradations. An area where the density difference is smaller than the density threshold is, for example, a background area or a graphic area, and since the density change in the area is small, color correction is performed with a low number of gradations. For example, when the number of gradations of RGB as the input signal is 256 gradations, the color correction table is used to reduce the number of colors so that the number of gradations of CMY becomes 64 gradations (or 128 gradations). to correct. This reduces the amount of recording agent used such as toner or ink. Further, if a region (for example, a character region or a photographic region) where the density difference is larger than the density threshold is a photographic region, color correction is performed with a high number of gradations. For example, when the number of gradations of RGB is 256 gradations, color correction is performed using a color correction table in which the number of gradations of CMY is 256 gradations. As a result, even when areas with various attributes are mixed in the image, the consumption of the recording material can be reduced without impairing the image quality of the character area or the photographic area.

  In the present invention, an area where the density difference is smaller than the density threshold is identified as a background area or a graphic area, and an area where the density difference is greater than the density threshold is identified as a character area or a photograph area. As a result, the gradation reproduction process is performed by distinguishing between the area where the gradation is important and the area where the resolution is important.

  In the present invention, when an instruction for reducing the consumption amount of toner or ink is received, the above-described extraction process, calculation process, conversion process, and thinning process are performed. Thereby, the consumption of the recording material can be reduced according to the user's preference, and faithful image quality can be reproduced.

  In the present invention, when one or a plurality of areas are extracted based on the input image data, and the density difference of the extracted areas is smaller than a predetermined threshold, the density value of each pixel in the area is set to a low density value. The entire image is processed while selectively reducing the consumption of the recording material such as toner or ink to an area where deterioration in image quality is not expected by performing gradation reproduction processing. Deterioration of the image and loss of information included in the image can be prevented.

  In the present invention, when the density difference of the extracted area is smaller than a predetermined threshold value, dither processing is performed on the area using a dither matrix having a large number of matrices, and the density difference of the extracted area is Is larger than a predetermined threshold value, dither processing is performed on the region using a dither matrix having a small number of matrices, and gradation reproduction processing is performed, so that regions of various attributes are mixed in the image. Even in this case, faithful image quality reproduction can be performed while reducing the consumption of the recording material.

  In the present invention, one or more regions are extracted based on the input image data, and when the density difference of the extracted regions is smaller than a predetermined threshold, a part of the pixels in the region is thinned out In addition, by performing gradation reproduction processing, degradation of the entire image is performed while performing processing for selectively reducing the consumption of recording material such as toner or ink for areas where degradation of image quality is not expected. Further, loss of information included in the image can be prevented.

  In the present invention, when the density difference of the extracted area is smaller than the density threshold, the area is subjected to color correction with a low number of gradations, and the density difference of the extracted area is larger than the density threshold. In this case, by performing color reproduction with a high gradation number on the area and performing gradation reproduction processing, even if areas with various attributes are mixed in the image, the character area or the photographic area The consumption of the recording material can be reduced without impairing the image quality.

  In the present invention, when the density difference of the extracted area is smaller than the predetermined threshold, the area is identified as a background area or a drawing area, and the density difference of the extracted area is larger than the predetermined threshold. By identifying the area as a character area or a photographic area, the gradation reproduction process can be performed by distinguishing the area where the gradation is important and the area where the resolution is important.

  In the present invention, when an instruction for reducing the consumption amount of toner or ink is received, the above-described extraction process, calculation process, conversion process, and thinning process are performed. Thereby, the consumption of the recording material can be reduced according to the user's preference, and faithful image quality can be reproduced.

Embodiment 1
Hereinafter, the present invention will be described with reference to the drawings illustrating embodiments. FIG. 1 is a block diagram illustrating a configuration of an image forming apparatus 100 including an image processing apparatus according to the present invention. The image forming apparatus 100 (for example, a digital color copier, a multi-function machine, a multi-function machine having a printer function, a fax function or an e-mail delivery function) includes a color image input device 1, a color image processing device 2 (image processing device), an image A color image output device 3 as a forming unit, an operation panel 4 for performing various operations (for example, a toner save mode selection operation for reducing the amount of toner used), and the like. Image data of RGB (R: red, G: green, B: blue) analog signals obtained by reading a document with the color image input device 1 is output to the color image processing device 2, and the color image processing device 2. Then, a predetermined process is performed and output to the color image output device 3 as a digital color signal of CMYK (C: cyan, M: magenta, Y: yellow, K: black).

  The color image input device 1 is, for example, a scanner including a CCD (Charged Coupled Device), reads a reflected light image from a document image as an RGB analog signal, and outputs the read RGB signal to the color image processing device 2. . The color image output device 3 is an image forming unit using an electrophotographic system or an inkjet system that outputs image data of a document image onto a recording sheet. The color image output device 3 may be a display device such as a display.

  The color image processing apparatus 2 includes a CPU, an application specific integrated circuit (ASIC), and the like.

  The A / D conversion unit 20 converts the RGB signal input from the color image input device 1 into, for example, a 10-bit digital signal, and outputs the converted RGB signal to the shading correction unit 21.

  The shading correction unit 21 performs correction processing for removing various distortions generated in the illumination system, imaging system, imaging system, and the like of the color image input apparatus 1 on the input RGB signal. The shading correction unit 21 adjusts the color balance and outputs the adjusted RGB signal to the input tone correction unit 22.

  The input tone correction unit 22 performs a process for adjusting the color balance on the RGB signal (RGB reflectance signal) input from the shading correction unit 21 and performs an image quality adjustment process such as removal of background density or contrast. The processed RGB signals are output to the region recognition processing unit 23 and the region separation processing unit 24.

  When the toner save mode is selected and operated on the operation panel 4, the region recognition processing unit 23 performs predetermined processing instead of the processing in the region separation processing unit 24. Based on the RGB signal (input image data) input from the input tone correction unit 22, the region recognition processing unit 23 recognizes a region such as a character region, a photographic region, a drawing region, or a background region (for example, extraction of a rectangular region). And the determination signal (region recognition result) is output to the color correction unit 25, the black generation and under color removal unit 26, the spatial filter processing unit 27, and the gradation reproduction processing unit 28. Further, the region recognition processing unit 23 outputs the region recognition result to the operation panel 4. As a result, a part or all of the region-recognized document image of the read document is displayed, and a predetermined process is performed to reduce the toner consumption by the user selecting each displayed region. Done. Details of the area recognition processing unit 23 will be described later.

  When the toner save mode is not selected and operated on the operation panel 4, the region separation processing unit 24 performs predetermined processing instead of the processing in the region recognition processing unit 23. The region separation processing unit 24 separates whether each pixel in the input image is a character region, a dot region, or a photographic region based on the RGB signal input from the input tone correction unit 22. Based on the separation result, the region separation processing unit 24 outputs a region identification signal indicating which region each pixel belongs to, a color correction unit 25, a black generation and under color removal unit 26, a spatial filter processing unit 27, a tone reproduction The data is output to the processing unit 28. The region separation processing unit 24 outputs the input RGB signal as it is to the subsequent color correction unit 25.

  In addition, it may replace with the structure which provides the area | region recognition process part 23 and the area | region separation process part 24 separately, and the structure which integrates both may be sufficient.

  The color correction unit 25 converts the input RGB signal into a CMY color space, performs color correction in accordance with the characteristics of the color image output device 3, and outputs the corrected CMY signal to the black generation and under color removal unit 26. To do. Specifically, the color correction unit 25 performs a process of removing color turbidity based on the spectral characteristics of CMY color materials including unnecessary absorption components in order to make color reproduction faithful.

  The black generation and under color removal unit 26 generates a K (black) signal based on the CMY signal input from the color correction unit 25 and generates a new CMY signal by subtracting the K signal from the input CMY signal. Then, the generated CMYK signal is output to the spatial filter processing unit 27.

  An example of processing in the black generation and under color removal unit 26 is shown. For example, in the process of generating black by skeleton black, the input / output characteristic of the skeleton curve is y = f (x), the input data is C, M, Y, and the output data is C ′, M ′. , Y ′, K ′, and the UCR (Under Color Removal) rate is α (0 <α <1), the data output by the black generation and under color removal processing is K ′ = f {min (C, M, Y)}, C ′ = C−αK ′, M ′ = M−αK ′, and Y ′ = Y−αK ′.

  The spatial filter processing unit 27 performs spatial filter processing on the CMYK signal input from the black generation and under color removal unit 26 using a digital filter based on the region identification signal. As a result, the spatial frequency characteristics of the image data are corrected, and blurring of the output image in the color image output device 3 or deterioration of graininess is prevented. For example, the spatial filter processing unit 27 performs sharp enhancement processing on the region separated into character regions by the region separation processing unit 24 to enhance the reproducibility of black characters or color characters, and emphasizes high frequency components. The spatial filter processing unit 27 performs low-pass filter processing for removing the input halftone component on the region separated into the halftone dot region by the region separation processing unit 24. The spatial filter processing unit 27 outputs the processed CMYK signal to the gradation reproduction processing unit 28.

  The gradation reproduction processing unit 28 stores a density conversion table considering density characteristics of image formation (recording) in the color image output device 3 as a LUT (Look Up Table), and the toner save mode is selected. Based on the determination signal input from the area recognition processing unit 23, a density conversion table corresponding to the character area, the photograph area, the graphic area, or the background area is selected, and the CMYK signal input from the spatial filter processing unit 27 is selected. To perform density conversion processing. Further, the gradation reproduction processing unit 28 performs binarization or multi-leveling by performing a dither process using a predetermined dither matrix (dither matrix) on the CMYK signal after the density conversion, thereby pseudo gray scales. Output halftone output image data (CMYK signal). The generated output image data is temporarily stored in a storage unit (not shown). Details of the gradation reproduction processing unit 28 will be described later.

  Further, when the toner save mode is not selected, the gradation reproduction processing unit 28 applies the CMYK signal input from the spatial filter processing unit 27 based on the region identification signal input from the region separation processing unit 24. Perform predetermined processing. For example, the gradation reproduction processing unit 28 performs binarization processing or processing so as to be suitable for reproduction of high-frequency components in the color image output device 3 in order to improve the reproducibility of the region separated into character regions, particularly black characters or color characters. Multilevel processing is performed. Further, the gradation reproduction processing unit 28 performs gradation reproduction processing so that the region separated into halftone dot regions in the region separation processing unit 24 can be finally separated into pixels and the respective gradations can be reproduced. (Generate halftone). Further, the gradation reproduction processing unit 28 performs binarization processing or multi-value processing so that the region separated into the photographic region by the region separation processing unit 24 is suitable for the gradation reproducibility in the color image output device 3. .

  The color image processing apparatus 2 temporarily stores the image data (CMYK signal) processed by the gradation reproduction processing unit 28 in a storage unit (not shown), and stores the image data in the storage unit at a predetermined timing for image formation. And the read image data is output to the color image output device 3. These controls are performed by a CPU (not shown), for example.

  The operation panel 4 includes, for example, a display unit such as a liquid crystal display and a setting button. The color image input device 1, the color image processing device 2, and the color image output device 3 are based on information input from the operation panel 4. Operation is controlled.

  FIG. 2 is a block diagram showing a configuration of the area recognition processing unit 23. The area recognition processing unit 23 includes a binarization processing unit 231, a run expansion processing unit 232, a labeling processing unit 233, a circumscribed rectangle extraction processing unit 234, a determination unit 235, and the like.

  The binarization processing unit 231 performs binarization processing on input image data (for example, a pixel value of 8 bits per pixel), and outputs the processed binarized image to the run expansion processing unit 232. More specifically, the binarization processing unit 231 binarizes the input image data based on a threshold value determined independently of the pixel value of the target pixel or a threshold value determined according to the pixel value of surrounding pixels. To do. As a binarization processing method, for example, a binarization process by an error diffusion method in which a binarization error is distributed to surrounding pixels and a gradation is stored, and a binarization error of a target pixel is processed next. Binarization processing for compensating gradation and storing gradation, binarization processing by random threshold, binarization processing by systematic dither method in which threshold changes regularly, (n × n) window including target pixel There is a binarization process using the average value of the values as a threshold. Note that the binarization processing method may be any of those described above, or may be another method.

  The run expansion processing unit 232 scans the target pixel (black pixel) of the input binarized image in the main scanning direction, and if there is a black pixel within a predetermined number of pixels in the main scanning direction, By replacing all the pixels up to the black pixel with black pixels, a black pixel portion (referred to as “run”) in which the black pixels are expanded is generated (run expansion processing), and a run expansion signal based on the generated image is labeled. The data is output to the processing unit 233.

  FIG. 3 is an explanatory diagram showing the contents of the run expansion process. FIG. 3 shows a binarized image, and pixels surrounded by a rectangle in the figure are black pixels. Also, the position in the direction parallel to the main scanning direction and the position in the direction perpendicular to the main scanning direction of the binarized image are represented by coordinates (X, Y). Also, a description will be given assuming that the predetermined pixel number range when replacing with black pixels is “4” pixels. FIG. 3A shows a binarized image before the run expansion process, and FIG. 3B shows an image after the run expansion process.

  As shown in FIG. 3A, black pixels continuously exist from the coordinates (2, 1) to the coordinates (5, 1) in the main scanning direction, and are separated from the coordinates (8, 1) by two pixels. Black pixels continue to the coordinates (12, 1) in the main scanning direction. In the next line, black pixels continuously exist from the coordinates (1, 2) to the coordinates (3, 2) in the main scanning direction, and are separated by 5 pixels, and the coordinates (9, 2) to the coordinates (11 2), there are continuous black pixels, and there is a continuous black pixel from coordinates (13, 2) to coordinates (15, 2) one pixel apart.

  As shown in FIG. 3B, when the run expansion process is performed, the coordinates (5, 1) and the coordinates (8, 1) are separated by only two pixels (the black pixels are within four pixels). Therefore, all pixels from coordinates (2, 1) to coordinates (12, 1) are replaced with black pixels. Thereby, a run (black pixel portion) L1 is obtained. Also, since the coordinates (3, 2) and the coordinates (9, 2) are separated by 5 pixels (there are no black pixels within 4 pixels), the coordinates (3, 2) Black pixels up to) are obtained as run L2. Also, since the coordinates (11, 2) and the coordinates (13, 2) are separated by only one pixel (there are black pixels within 4 pixels), the coordinates (9, 2) to the coordinates (15, All pixels up to 2) are replaced with black pixels. Thereby, a run (black pixel portion) L3 is obtained.

  As described above, the run expansion signal output based on the run (black pixel portion) extracted from the binarized image includes, for each extracted run, the run start coordinates, the run length, and the like. Contains information.

  FIG. 4 is an explanatory diagram showing an example of run information. FIG. 4A shows an example of the extracted run, and FIG. 4B shows the run information corresponding to FIG. The run information is composed of fields such as a run number for identifying the extracted run, the start point coordinates of the run, and the length of the run. In FIG. 4A, a run L10 with a run number “1”, a run L11 with a run number “2”, and a run L12 with a run number “3” are extracted. In this case, as shown in FIG. 4B, the coordinates of the start point of the run with the run number “1” are (4, 1), the run size (length) M is “4”, and the run number The coordinates of the start point of the run with “2” are (1, 2), the run size M is “5”, the coordinates of the start point of the run with the run number “3” are (7, 2), The size M is “4”.

  Based on the input run expansion signal, the labeling processing unit 233 connects adjacent runs and integrates (labels) them as one run (connected run), and connected run information indicating the characteristics of the integrated connected run Is output to the circumscribed rectangle extraction processing unit 234 as a labeling signal.

  FIG. 5 is an explanatory diagram showing an example of linked run information. As shown in the figure, the linked run information includes a label number for identifying the linked run, each run number column of each run constituting the linked run, and the like. For example, in the case of FIG. 4 described above, the run L10 with the run number “1” is adjacent to the run L11 with the run number “2”, and the run L10 is also adjacent to the run L12 with the run number “3”. is doing. In this case, when the labeling process is performed, the runs L10, L11, and L12 are connected, the label number indicating the connected run is “A”, and the run numbers of each run constituting the connected run are “1” and “2”. "," 3 ".

  The circumscribed rectangle extraction processing unit 234 extracts a rectangular area (circumscribed rectangular area) circumscribing the connected run based on the input labeling signal, and indicates the position and size of the extracted circumscribed rectangular area. Information is output to the determination unit 235 as an extraction signal.

  FIG. 6 is an explanatory diagram showing a method for extracting a circumscribed rectangular area. FIG. 6A is an example of extracted runs similar to FIG. 4A, and the runs L10, L11, and L12 are connected (see FIG. 5). When determining the size of a connected run, the start point, end point, and length of the run on the two lines from left to right (main scanning direction) in units of two lines, the target line and the previous line. Compare the etc.

  For example, in FIG. 6A, when attention is paid to the run L11 and the run L10 on the preceding line, the start point of the run L11 is located in front of the run L10 (in the direction in which the X coordinate value is small). Is located on the start point of the run L11, and the end point of the run L10 is located behind the end point of the run L11 (in the direction in which the X coordinate value is large). Therefore, the end point of the circumscribed rectangular area is the end point of the run L10. Will be on top. Accordingly, the rectangular area circumscribing the runs L10 and L11 has a shape (label number “A1”) indicated by a thick line in FIG. 6B.

  Next, in FIG. 6B, when attention is paid to the run L12 and the run L10, the start point of the run L10 is located in front of the run L12. Therefore, the start point of the rectangular area circumscribing them is on the start point of the run L10. Also, since the end point of the run L12 is located behind the end point of the run L10, the end point of the circumscribed rectangular area is on the end point of the run L12. Furthermore, by considering the shape A1 in FIG. 6B, the rectangular area circumscribing the runs L10, L11, and L12 has the shape indicated by the bold line in FIG. 6C (label number “A”). .

  In other words, the circumscribed rectangle extraction processing unit 234 obtains the minimum coordinate among the coordinates of the start point of each run constituting the connected run as the coordinates (Xs, Ys) of the start point of the circumscribed rectangular area. Therefore, if the coordinates of the start points of the n runs constituting the connected run are (X1, Y1), (X2, Y2),..., (Xn, Yn), the coordinates of the start points of the circumscribed rectangular area (Xs, Ys) ) Can be obtained as Xs = min (X1, X2,..., Xn) and Ys = min (Y1, Y2,..., Yn).

  Similarly to the calculation of the starting point, the coordinates (Xe, Ye) of the end point of the circumscribed rectangular area are obtained as Xe = max (X1, X2,..., Xn) and Ye = max (Y1, Y2,..., Yn). be able to. Furthermore, the size of the circumscribed rectangular region, that is, the sizes in the X direction and the Y direction (MX, MY) can be obtained as MX = Xe−Xs + 1 and MY = Ye−Ys + 1.

  FIG. 7 is an explanatory diagram showing an example of circumscribed rectangle information. The circumscribed rectangle information is composed of the following fields: a label number for identifying the extracted circumscribed rectangular area (corresponding to the label number of the connected run), the starting point coordinates of the circumscribed rectangular area, and the size (length) of the circumscribed rectangular area Has been. For example, the circumscribed rectangular area extracted in the example of FIG. 6 has the label number “A”, the coordinates (Xs, Ys) of the start point (1, 1), and the sizes (MX, MY) (10, 2). It is.

  The determination unit 235 obtains the size of each circumscribed rectangular area based on the input extraction signal (circumscribed rectangle information) and compares it with a predetermined threshold value to determine whether each circumscribed rectangular area is a character area or non-character. Determine if it is an area.

  FIG. 8 is an explanatory diagram showing determination conditions for determining the size (length) of the circumscribed rectangular area. In FIG. 8, as run information of the run L20 on the first line (upper line), the coordinates of the start point of the run are represented as (X0, Y0), the run length is represented as M0, and the second line (lower line). As the run information of the upper run L21, the coordinates of the start point of the run are represented as (X1, Y1), and the run length is represented as M1. The size of the circumscribed rectangular area is determined based on the positional relationship between the run L20 on the first line and the run L21 on the second line, and there are several cases as follows.

  FIG. 8A shows a case where the positional relationship between the run L20 and the run L21 is such that the run L21 on the second line is ahead of the run L20 on the first line and they are not connected to each other. is there. That is, when X0> X1 + M1, it is determined that the run L20 and the run L21 are not connected, and as a result, the starting point of the circumscribed rectangular area obtained is (X1, Y1) and the size is (M1, Y−Y1 + 1). It becomes. Here, Y represents the line number being processed, and Y = Y1.

  In FIG. 8B, the positional relationship between the run L20 and the run L21 is such that the start point of the run L21 on the second line is ahead of the start point of the run L20 on the first line, and on the second line. The end point of the run L21 is ahead of the end point of the run L20 on the first line, and both are connected to each other. That is, when X0> X1, X0 ≦ X1 + M1, and X0 + M0> X1 + M1, the starting point of the circumscribed rectangular area to be determined is (X1, Y0) and the size is (X0 + M0−X1 + 1, Y−Y0 + 1).

  In FIG. 8C, the positional relationship between the run L20 and the run L21 is such that the start point of the run L21 on the second line is ahead of the start point of the run L20 on the first line, and on the second line. The end point of the run L21 is behind the end point of the run L20 on the first line, and both are connected to each other. That is, when X0> X1, X0 ≦ X1 + M1, and X0 + M0 ≦ X1 + M1, the starting point of the circumscribed rectangular area to be determined is (X1, Y0) and the size is (M1, Y−Y0 + 1).

  In FIG. 8D, the positional relationship between the run L20 and the run L21 is such that the start point of the run L21 on the second line is behind the start point of the run L20 on the first line, and on the second line. The end point of the run L21 is ahead of the end point of the run L20 on the first line, and both are connected to each other. That is, in the case of X0 ≦ X1, X0 ≦ X1 + M1, and X0 + M0> X1 + M1, the starting point of the circumscribed rectangular area to be determined is (X0, Y0) and the size is (M0, Y−Y0 + 1).

  FIG. 8E shows that the positional relationship between the run L20 and the run L21 is such that the start point of the run L21 on the second line is behind the start point of the run L20 on the first line, and on the second line. The end point of the run L21 is behind the end point of the run L20 on the first line, and both are connected to each other. That is, when X0 ≦ X1, X0 ≦ X1 + M1, and X0 + M0 ≦ X1 + M1, the starting point of the circumscribed rectangle to be determined is (X0, Y0) and the size is (X1 + M1-X0 + 1, Y−Y0 + 1).

  FIG. 8F shows a case where the positional relationship between the run L20 and the run L21 is such that the run L21 on the second line is behind the run L20 on the first line and they are not connected to each other. is there. That is, in the case of X0 + M0 <X1, it is determined that the connection between the run L21 on the second line and the run L20 on the first line is finished, and as a result, the starting point of the circumscribed rectangular area obtained is (X0, Y0), which is large The length is (M0, Y−Y0 + 1). The determination unit 235 repeats the above processing for each line until the processing for one page of image data is completed.

  The determination of whether the circumscribed rectangular area is a character area or a non-character area can be performed using the feature that a character area formed of a character string has a long and narrow rectangular shape. For example, when the size of the circumscribed rectangular area is (MX, MY), an appropriate restriction is set on the size of the character string, and Ta <MX <Tb using appropriate threshold values Ta, Tb, Tc, Td. If Tc <MY <Td, the circumscribed rectangular area is determined to be a character area.

  For the circumscribed rectangular area determined to be a non-character area, the determination unit 235 determines whether the background area, the graphic area, or the photographic area is based on the pixel value (for example, the density value) of each pixel of the circumscribed rectangular area. It is determined whether it is a region. More specifically, the determination unit 235 creates a density histogram for each circumscribed rectangular area based on the density value of each pixel of the circumscribed rectangular area determined to be a non-character area, and determines the density histogram distribution status. The area is determined accordingly.

  FIG. 9 is an explanatory diagram showing an example of a density histogram. In the figure, the horizontal axis indicates the density value, and the vertical axis indicates the frequency. In the figure, when the distribution of the density values of the pixels in the circumscribed rectangular area is in the area H1, it can be determined that the area is nothing printed on the document.

  Further, when the density value distribution of the pixels in the circumscribed rectangular area is in the area H2, that is, the density value distribution of the pixels in the circumscribed rectangular area has a substantially uniform density and is on the low density side (for example, a density threshold value). If it belongs to THd or less), it can be determined that the background area is a light color on the document.

  Further, when the density value distribution of the pixels in the circumscribed rectangular area is in the area H3, that is, the density value distribution of the pixels in the circumscribed rectangular area is higher than that in the background area (for example, the density threshold value THd or more). If the density is substantially uniform, it can be determined that the area is a graphic area (for example, an image area such as a figure or a picture but not a photographic image).

  If the distribution of the density values of the pixels in the circumscribed rectangular area is in the area H4, that is, if the distribution of the density values of the pixels in the circumscribed rectangular area changes over a wide range, it is determined that the area is a photographic area. can do.

  When the distribution of the density values of the pixels in the circumscribed rectangular area is in the area H5, that is, when the density value distribution of the pixels in the circumscribed rectangular area has a substantially uniform density and belongs to the high density side, It can be determined that it is a character area.

  As described above, the determination unit 235 determines whether the circumscribed rectangular area is a character area or a non-character area based on the size of the circumscribed rectangular area. Further, the determination unit 235 determines that the circumscribed rectangular area is a background area, a graphic area, or a photograph for a circumscribed rectangular area determined to be a non-character area, based on a density histogram of pixels in the circumscribed rectangular area. It is determined which of the regions, and a determination signal is output to the gradation reproduction processing unit 28 and the like.

  Thereby, each area of an image having different characteristics (attributes) such as a character area, a photograph area, a drawing area, and a background area can be extracted with high accuracy, and each area can be easily identified. Further, when the binarization processing is performed by the above-described binarization processing unit 231, the gray area that is the background image of the photograph in which the input image is blurred is also subjected to gradation processing, so that the label expansion processing, labeling processing, circumscribed By performing expansion and rectangularization in the rectangular extraction process, the outline of the entire photographic image is not lost and is correctly extracted.

  Note that the region determination is not limited to the above-described method, and can be performed by other various methods. It is also possible to determine whether or not the circumscribed rectangular area is a photographic area based on the size of the circumscribed rectangular area. In this case, it is possible to use the feature that the area in which the photograph is printed has a relatively square shape. For example, when the size of the circumscribed rectangular area is (MX, MY), an appropriate limit is set on the size of the area to be determined, and appropriate thresholds Te, Tf, Tg, Th different from the determination of the character area are set. If Te <MX <Tf and Tg <MY <Th, the circumscribed rectangular area is determined to be a photographic area.

  FIG. 10 is a block diagram showing the configuration of the gradation reproduction processing unit 28. The gradation reproduction processing unit 28 includes a selector 281, a density conversion table 282, a density conversion unit 283, a dither processing unit 284, and the like.

  Based on the determination signal input from the area recognition processing unit 23, the selector 281 selects the optimum density conversion from the plurality of density conversion tables stored in the density conversion table 282 according to the determined area. The table is selected. Further, the selector 281 outputs the image data for each rectangular area in which the area determination has been performed among the image data (CMYK signal) input from the spatial filter processing unit 27 to the density conversion unit 283.

  The density conversion table 282 stores a plurality of density conversion tables as a LUT (Look Up Table). As the density conversion table, for example, a character / photo area table 282a, a graphic area table 282b, a background area table 282c, and the like are stored.

  FIG. 11 is an explanatory diagram showing an example of the density characteristics of the density conversion table 282. FIG. 11A shows the density (gamma) characteristics when not in the toner save mode (normal time), and FIG. 11B shows the density characteristics when the toner save mode is selected. As shown in FIG. 11A, normally, density conversion is performed by density characteristics (gamma characteristics) that maintain the gradation of the input image by using density characteristics Ga that shows output density linear with respect to input density. Do.

  As shown in FIG. 11B, in the toner save mode, density conversion is performed with different density characteristics (gamma characteristics) depending on the determined area. For example, by using the same density characteristic as the normal density characteristic Ga for a character / photo area, density conversion is performed using a density characteristic (gamma characteristic) that maintains the gradation of the input image.

  In addition, for the image area, the toner usage is reduced by using the density characteristic Gb having a lower density than the linear density characteristic Ga. Further, for the base region, the toner usage is further reduced by using the density characteristic Gc having a lower density than the density characteristic Gb. The character / photo area table 282a, the drawing area table 282b, or the background area table 282c corresponds to the density characteristics Ga, Gb, and Gc, respectively. The same density characteristic (for example, Gb or Gc) can also be used for the drawing area and the background area.

  The density conversion unit 283 uses the selected character / photo area table 282a, drawing area table 282b, or background area table 282c for each of the input image data for each rectangular area. The converted image data is output to the dither processing unit 284.

  The dither processing unit 284 divides the input image data into blocks of n × n pixels (for example, n = 4), and then each pixel for each block has a corresponding dither matrix (for example, 4 × 4 dither matrix). ) Is used to perform dither processing, and output pseudo halftone output image data (YMCK signal) after processing. The dither processing is not limited to binarization, and multi-value dither processing can also be used when the color image output device 3 has a display gradation of 2 to 3 bits / pixel. Also, error diffusion processing can be used instead of dither processing.

  12 and 13 are schematic views showing an example of the operation panel 4. As shown in FIG. 12, a “toner save” button 41 for accepting an instruction as to whether or not to select the toner save mode is displayed on the liquid crystal display. When the user operates the “toner save” button 41, the toner save mode is selected, and the instruction is output to a CPU (not shown) in the color image processing apparatus 2. It should be noted that the ink save mode may be selected instead of the toner according to the type of the color image output device 3.

  As shown in FIG. 13, the liquid crystal display displays a region recognition result that is a result of determining a region such as a character included in an image of a document. In the figure, as a result of area recognition, three rectangular areas (for example, a background area or a graphic area) of the original image are displayed, and the area selected by the user is highlighted. When the user selects an area, it is possible to reduce toner consumption for the selected area according to the user's preference.

  Next, the operation of the image forming apparatus 100 will be described. FIG. 14 is a flowchart showing the procedure of gradation reproduction processing in the toner save mode. The tone reproduction process is not only configured by a dedicated hardware circuit, but is also performed by loading a computer program that defines the procedure of the tone reproduction process into the RAM and executing it by a CPU (both not shown). You can also. In the following description, the color image processing apparatus 2 is referred to as a “processing unit”.

  The processing unit acquires input image data (S11), and performs region recognition processing (S12). Details of the area recognition process will be described later. The processing unit displays the region recognition result (S13), and determines whether there is a region selection by the user (S14).

  If there is an area selection (YES in S14), the processing unit determines whether the selected area is a background area (S15). If it is a background area (YES in S15), the background area table 282c. Then, density conversion is performed (S16), dither processing is performed on the converted image data (S17), pseudo halftone output image data is generated, and the process ends.

  If it is not a background area (NO in S15), the processing unit determines whether or not the selected area is a drawing area (S18). If it is a graphic area (YES in S18), the processing unit performs density conversion using the graphic area table 282b (S19), and performs the process of step S17. If it is not a graphic area (NO in S18), the processing unit performs density conversion using the character / photo area table 282a (S20), and performs the process of step S17. On the other hand, when there is no area selection (NO in S14), the processing unit performs the processes after step S20.

  FIG. 15 is a flowchart showing the procedure of region recognition processing. The processing unit performs binarization processing on the input image data (S121), and expands black pixels under a predetermined condition based on the binarized image that has been binarized (running the black pixel unit). Run expansion processing is performed to generate (S122).

  The processing unit performs a labeling process for connecting and integrating adjacent runs (S123), and performs circumscribed rectangle extraction for extracting a circumscribed rectangular region circumscribing the connected runs (S124). Based on the size of the extracted circumscribed rectangular area or the density distribution of pixels in the circumscribed rectangular area, the processing unit determines whether the area is a character area, a photographic area, a graphic area, or a background area ( S125), the process ends.

  As described above, according to the present invention, the consumption of the recording material such as toner or ink is selectively reduced in an area where deterioration in image quality is not expected, for example, a background area or a graphic area. For the character area or the photographic area, it is possible to prevent the deterioration of the entire image and the loss of information included in the image. Further, the gradation reproduction process can be performed by distinguishing between the area where the gradation is important and the area where the resolution is important. Furthermore, the consumption of the recording material can be reduced according to the user's preference, and faithful image quality can be reproduced.

Embodiment 2
In the first embodiment described above, the density characteristic for density conversion is changed according to the determined (recognized) area. However, the present invention is not limited to this, and the size of the dither matrix for dither processing Can also be changed.

  FIG. 16 is a block diagram illustrating a configuration of the gradation reproduction processing unit 28 according to the second embodiment. The gradation reproduction processing unit 28 includes a dither matrix unit 285 in addition to the selector 281, the density conversion table 282, the density conversion unit 283, and the dither processing unit 284.

  Based on the determination signal input from the area recognition processing unit 23, the selector 281 selects the optimum density conversion from the plurality of density conversion tables stored in the density conversion table 282 according to the determined area. A table is selected, and an optimum matrix is selected from a plurality of matrices stored in the dither matrix unit 285 according to the determined area. Similarly to the first embodiment, the selector 281 outputs, to the density conversion unit 283, image data for each rectangular region in which region determination has been performed among the image data (CMYK signal) input from the spatial filter processing unit 27. To do.

  The dither matrix unit 285 stores a character area matrix 285a, a photographic area matrix 285b, a graphic area matrix 285c, a background area matrix 285d, and the like.

  FIG. 17 is a schematic diagram illustrating an example of a dither matrix according to the second embodiment. As shown in the figure, the dither matrix for the character area used when the determined area is a character area has a size of 2 × 2, 3 × 3, for example, and performs dither processing with an emphasis on resolution. Can do.

  In addition, the dither matrix for the photographic area has a size of 4 × 4, for example, and uses a larger size than the dither matrix for the character area, so that processing with more emphasis on gradation than the case of the character area is used. I do. Further, instead of arranging the dither matrix elements in a square shape, a non-square dither matrix as shown in FIG. 17B may be used.

  In addition, the dither matrix for the base area and the graphic area is, for example, 8 × 8 in size, and a process larger in terms of gradation is performed by using a dither matrix having a size larger than that of the photographic area. It should be noted that a dither matrix for the base area and a dither matrix for the graphic area having different sizes may be used.

  The dither processing unit 284 performs dither processing using any of the selected character area matrix 285a, photo area matrix 285b, graphic area matrix 285c, and background area matrix 285d. Note that the processing contents of the density conversion unit 283 and the dither processing unit 284 are the same as those in the first embodiment, and a description thereof will be omitted.

  FIG. 18 and FIG. 19 are flowcharts showing the procedure of gradation reproduction processing in the toner save mode of the second embodiment. The processing unit acquires input image data (S31), and performs region recognition processing (S32). The region recognition process is the same as the process shown in FIG. The processing unit displays the region recognition result (S33), and determines whether there is a region selection by the user (S34).

  When there is an area selection (YES in S34), the processing unit determines whether or not the selected area is a character area (S35). If it is a character area (YES in S35), the processing unit performs density conversion using the character / photo area table 282a (S36), performs dither processing using the character area matrix 285a (S37), and outputs pseudo halftones. Image data is generated and the process ends.

  If it is not a character area (NO in S35), the processing unit determines whether or not the selected area is a background area (S38). If it is a background area (YES in S38), the processing unit performs density conversion using the background area table 282c (S39), performs dither processing using the background area matrix 285d (S40), and outputs pseudo halftone output image data. Is generated and the process is terminated.

  If it is not a background area (NO in S38), the processing unit determines whether or not the selected area is a graphic area (S41). If it is a graphic area (YES in S41), the processing unit performs density conversion in the graphic area table 282b (S42), performs dither processing in the graphic area matrix 285c (S43), and outputs pseudo halftone output image data. Is generated and the process is terminated.

  If it is not a graphic area (NO in S41), the processing unit performs density conversion using the character / photo area table 282a (S44), performs dither processing using the photo area matrix 285b (S45), and outputs a pseudo-halftone output image. Generate data and end the process. On the other hand, when there is no area selection (NO in S34), the processing unit performs the processes after step S36.

  As described above, in the present invention, processing that places importance on gradation in the low density region is performed, and fluctuations in dot reproducibility or color reproducibility due to the ambient temperature of the apparatus or changes over time are reduced. In addition, even when various attribute areas are mixed in the image, faithful image quality reproduction can be performed while reducing the consumption of the recording material.

  In the first and second embodiments described above, the density conversion unit 283 and the dither processing unit 284 are arranged after the selector 281, but the selector 281 is arranged after the density conversion unit 283 and the dither processing unit 284. You can also. In this case, the density conversion unit 283 and the dither processing unit 284 can perform the processing corresponding to each region in parallel, and the selector 281 can switch which image data after the processing is output.

Embodiment 3
In the first and second embodiments, the density conversion (reduction in density) is performed using the density conversion table 282. However, the present invention is not limited to this, and a part of the pixels of the image data is thinned out. It is also possible to reduce the concentration.

  FIG. 20 is a block diagram illustrating a configuration of the gradation reproduction processing unit 28 according to the third embodiment. The gradation reproduction processing unit 28 includes a selector 281, a thinning processing unit 286, error diffusion processing units 287 and 288, and the like.

  Based on the determination signal input from the region recognition processing unit 23, the selector 281 thins out image data for each rectangular region in which region determination has been performed among the image data (CMYK signal) input from the spatial filter processing unit 27. The data is output to either the processing unit 286 or the error diffusion processing unit 288. For example, the selector 281 outputs image data of an area determined to be a character area or a photographic area to the error diffusion processing unit 288, and thins out image data of an area determined to be a background area or a graphic area. Output to 286.

  The thinning processing unit 286 performs a thinning process on a part of the pixels of the input image data, and outputs the processed image data to the error diffusion processing unit 287. In the thinning-out process, for example, the pixel values of several pixels (for example, 4 pixels) that are continuously adjacent to each other are set to “0”. As a result, image data in which the pixel values of four adjacent pixels are “0” is output while the pixel value of one pixel remains unchanged. Note that the thinning-out process can be performed not for every other pixel but for every plurality of pixels such as two or three.

  The error diffusion processing unit 287 performs error diffusion processing on the input image data to generate and output pseudo halftone output image data. In the error diffusion processing, an error (hereinafter referred to as “quantization error”) generated when binarizing the pixel value (for example, density) of each pixel of the input image data is still binary around the pixel of interest. This is a method of performing binarization while allocating to pixels that have not been binarized. In this case, the quantization error of the pixel of interest to be binarized is the pixel value before the binarization processing positioned around the pixel of interest after weighting is performed according to the relative position from the pixel of interest. Is added to The error diffusion processing unit 288 performs the same process.

  FIG. 21 is a flowchart showing the procedure of gradation reproduction processing in the toner save mode of the third embodiment. The processing unit acquires input image data (S51), and performs region recognition processing (S52). The region recognition process is the same as the process shown in FIG. The processing unit displays the region recognition result (S53), and determines whether there is a region selection by the user (S54).

  When there is an area selection (YES in S54), the processing unit determines whether or not the selected area is a background area (S55). If it is not a background area (NO in S55), the processing unit determines whether or not the selected area is a drawing area (S56). If it is not a graphic area (NO in S56), the processing unit performs error diffusion processing on the image data in the selected area (S57), generates pseudo halftone output image data, and ends the process.

  If it is a background area (YES in S55), the processing unit performs a thinning process on the image data of the selected area (S58), and continues the process from step S57. If the image area is a graphic area (YES in S56), the processing unit performs a thinning process on the image data in the selected area (S58), and continues the processing from step S57. On the other hand, when there is no area selection (NO in S54), the processing unit continues the processing from step S57.

  In the third embodiment described above, the error diffusion process is used. However, the present invention is not limited to this, and other methods such as dithering can be used instead of the error diffusion process. In addition, the number of pixels to be thinned when performing the thinning process is an example, and is not limited, and the number of pixels can be set as appropriate. Further, although the thinning processing unit 286 and the error diffusion processing units 287 and 288 are arranged after the selector 281, the selector 281 may be arranged after the thinning processing unit 286 and the error diffusion processing units 287 and 288. it can. In this case, the thinning processing unit 286, the error diffusion processing unit 287, and the error diffusion processing unit 288 perform processing in parallel, and the selector 281 can switch which image data after processing is output.

  As described above, in the present invention, a toner is selectively applied to an area where deterioration of image quality is not expected or an area where particularly important information is not included, for example, a background area or a graphic area. Alternatively, it is possible to perform a process for reducing the consumption of a recording material such as ink, and at the same time, a process that does not completely delete information on the color of the area. In addition, for an area including important information, for example, a character area or a photograph area, it is possible to prevent deterioration of the entire image and loss of information included in the image.

Embodiment 4
In the first to third embodiments described above, in order to reduce the consumption of the recording agent such as toner or ink, the content of the gradation reproduction process is changed according to the determination signal. However, the present invention is not limited to this. However, the consumption of the recording material can be reduced by changing the content of the color correction processing according to the determination signal.

  FIG. 22 is a block diagram illustrating a configuration of the color correction unit 25 according to the fourth embodiment. The color correction unit 25 includes a selector 251, a color correction table 252, a color correction processing unit 253, and the like.

  Based on the determination signal input from the area recognition processing unit 23, the selector 251 selects an optimum color correction according to the determined area from among a plurality of color correction tables stored in the color correction table 252. Select a table. In addition, the selector 251 outputs image data for each rectangular area in which area determination has been performed among the image data (RGB signals) input from the area separation processing unit 24 to the color correction processing unit 253.

  The color correction table 252 stores a plurality of color correction tables as a LUT (Look Up Table). As the color correction table, for example, a character / photo area table 252a, a graphic area table 252b, a background area table 252c, and the like are stored.

  The color correction processing unit 253 uses the color correction table selected by the selector 251 to refer to the LUT using the input signal as an address signal, and determines the data stored in the LUT as data to be output, thereby determining the color space. Conversion processing and color correction processing are performed, and the color-corrected CMY signals are output to the black generation and under color removal unit 26.

  FIG. 23 is an explanatory diagram showing an example of a color correction table. FIG. 23A shows an example of the character / photo area table 252a used for the character / photo area when the toner save mode is not used (normal time) or when the toner save mode is selected. As shown in FIG. 23A, in the character / photo area table 252a, when the number of gradations of the RGB signal as the input signal is 256 gradations, the CMY signals after color conversion and color correction are each 256. It can represent gradation.

  FIG. 23B shows an example of the graphic area table 252b used for the graphic area when the toner save mode is selected. As shown in FIG. 23B, in the graphic area table 252b, when the number of gradations of the RGB signal is 256 gradations, each of the CMY signals can represent 128 gradations. This reduces the number of colors.

  FIG. 23C shows an example of the base area table 252c used for the base area when the toner save mode is selected. As shown in FIG. 23C, in the base area table 252c, when the number of gradations of the RGB signal is 256 gradations, each of the CMY signals can represent 64 gradations. In this way, the number of colors can be reduced by reducing the number of gradations in the color correction table in accordance with the character / photo area, which becomes a drawing area or background area, and recording of toner or ink, etc. The consumption of the agent can be reduced. Note that either the drawing area table 252b or the underlying area table 252c can be used for the drawing area and the underlying area. Thereby, the number of color correction tables to be stored can be reduced.

  FIG. 24 is a flowchart showing the procedure of color correction processing in the toner save mode. Note that the color correction process is not only configured by a dedicated hardware circuit, but can also be performed by loading a computer program that defines the procedure of the color correction process into the RAM and executing it by a CPU (both not shown). it can. In the following description, the color image processing apparatus 2 is referred to as a “processing unit”.

  The processing unit acquires input image data (S61), and performs area recognition processing (S62). The region recognition process is the same as the process shown in FIG. The processing unit displays the region recognition result (S63), and determines whether or not there is a region selection by the user (S64).

  If there is an area selection (YES in S64), the processing unit determines whether or not the selected area is a background area (S65). If it is a background area (YES in S65), the background area table 252c. Then, color correction processing is performed (S66), and the processing ends.

  If it is not a background area (NO in S65), the processing unit determines whether or not the selected area is a graphic area (S67). If it is a graphic area (YES in S67), the processing unit performs a color correction process on the graphic area table 252b (S68) and ends the process. If it is not a graphic region (NO in S67), the processing unit performs color correction processing on the character / photo region table 252a (S69), and ends the processing. On the other hand, when there is no area selection (NO in S64), the processing unit performs the processes after step S69.

  It is also possible to combine the above-described color correction processing and gradation difference dignity processing. FIG. 25 is a flowchart showing a processing procedure combining color correction processing and gradation reproduction processing in the toner save mode.

  The processing unit acquires input image data (S71), and performs area recognition processing (S72). The region recognition process is the same as the process shown in FIG. The processing unit displays the region recognition result (S73), and determines whether there is a region selection by the user (S74).

  If there is an area selection (YES in S74), the processing unit determines whether or not the selected area is a background area (S75). If it is a background area (YES in S75), the background area table 252c. The color correction process is performed (S76), the density conversion is performed using the background area table 282c (S77), the gradation reproduction process is performed on the converted image data (S78), and the pseudo halftone output image data is obtained. Is generated and the process is terminated.

  If it is not a background area (NO in S75), the processing unit determines whether or not the selected area is a graphic area (S79). If it is a graphic area (YES in S79), the processing unit performs color correction processing with the graphic area table 252b (S80), performs density conversion with the graphic area table 282b (S81), and performs the processing after step S78. Do.

  If it is not a graphic region (NO in S79), the processing unit performs color correction processing using the character / photo region table 252a (S82), performs density conversion using the character / photo region table 282a (S83), and subsequent steps S78 and thereafter. Perform the process. On the other hand, when there is no area selection (NO in S74), the processing unit performs the processes after step S82.

  By combining color correction processing and gradation reproduction processing, processing can be selected according to the type of document. For example, in the case of a manuscript that includes a photograph in a business document, color correction processing with a reduced number of colors is performed, and when the halftone (tone reproduction) is not changed, the resolution of the photograph is maintained and the image quality is relatively degraded. Can be reduced. In addition, in the case of a manuscript that does not include a photograph in a business document, halftone processing is performed, so that the influence on the image quality can be prevented even if the resolution is somewhat reduced. Also, in the case of a document that does not care about image quality, such as output in draft mode, the number of colors and the number of gradations are reduced. Such processing can be selected, for example, in advance as an image mode and can be selected from the operation panel of the digital multi-function peripheral, or can be selected on the printer driver setting screen of the host computer.

  As described above, in the present invention, an area in which deterioration in image quality is not expected or an area that does not include particularly important information, for example, a background area or a graphic area, is used for color correction. In addition to performing processing for selectively reducing the consumption of recording material such as toner or ink by reducing the number of colors in the image, processing that does not completely delete information regarding the color of the area is performed. it can. In addition, for an area including important information, for example, a character area or a photograph area, it is possible to prevent deterioration of the entire image and loss of information included in the image.

  In the third embodiment described above, the color correction processing unit 253 is arranged at the subsequent stage of the selector 251, but the selector 251 can also be arranged at the subsequent stage of the color correction processing unit 253. In this case, the color correction processing unit 253 performs color correction processing corresponding to each region (background region, drawing region, character / photo region) in parallel, and the selector 251 switches which image data is output after processing. be able to.

  In the third embodiment described above, the LUT is used for color correction for the background region. However, the present invention is not limited to this. For example, the calculation is performed using the calculation coefficient (1) using the matrix coefficient aij. You can also. Here, i = 0 to 8 and j = 0 to 2.

Embodiment 5
In the first to fourth embodiments, the example in which the present invention is applied to the image forming apparatus 100 including the color image processing apparatus 2 has been described. However, the scope of the present invention is not limited to the image forming apparatus, and a printer The present invention can also be realized by a personal computer incorporated in a driver.

  FIG. 26 is a block diagram showing a configuration of the image processing system according to the fifth embodiment. The image processing system according to the fifth embodiment includes a computer 5, for example, a color image input device 1 such as a scanner or a digital camera, and a color image output device 3 such as a printer. The computer 5 includes a printer driver 50. Are installed, and a communication port driver 51 and a communication port (for example, RS232C, LAN, etc.) 52 are provided.

  The printer driver 50 includes an area recognition processing unit 501, a color correction processing unit 502, a filter processing unit 503, a gradation reproduction processing unit 504, and a printer language translation unit 505 that translates output image data into a printer language (PJL: Printer Job Language). Etc. The region recognition processing unit 501, the color correction processing unit 502, the filter processing unit 503, and the gradation reproduction processing unit 504 are respectively the above-described region recognition processing unit 23, color correction unit 25, spatial filter processing unit 27, and gradation. It has the same function as the reproduction processing unit 28.

  The computer 5 processes the input image data acquired from the color image input device 1 at any time by the area recognition processing unit 501, the color correction processing unit 502, the filter processing unit 503, and the gradation reproduction processing unit 504. Areas such as characters, photographs, drawings and backgrounds printed on the original are determined, and pseudo-halftone output image data is generated in which the determined density conversion and gradation reproduction processing are performed for each determined area. The printer language translation unit 505 converts the generated output image data into a printer language, and the converted data is transmitted to the color image output device 3 (for example, an electrophotographic system or an inkjet via the communication port driver 51 and the communication port 52). Output to a printer of the type).

  Further, the toner save mode (or the ink save mode may be selected) can be selected. When the toner save mode is selected, the area recognition process is performed, and the toner save mode is not selected. In some cases, region separation processing may be performed.

  In the first to fifth embodiments described above, the case where the toner consumption is reduced has been described. However, the present invention is not limited to this, and the consumption of other recording materials such as ink can also be reduced.

  In the first to fifth embodiments described above, the user designates the selection of the toner save mode. However, the present invention is not limited to this, and the attributes of the document, that is, the determination is made regardless of the designation by the user. It is also possible to perform gradation reproduction processing that emphasizes density conversion for low density, resolution, or gradation, depending on the area. In addition, instead of a configuration in which the user selects an area to be subjected to gradation reproduction processing that emphasizes either density conversion for low density, resolution, or gradation, these processes are automatically performed regardless of whether or not the user selects. It can also be done automatically.

  In the above-described embodiment, as the color image input device 1, for example, a flat bed scanner, a film scanner, a digital camera, a mobile phone, or the like is used. Further, as the color image output device 3, for example, an image display device such as a CRT display or a liquid crystal display, an electrophotographic system or an ink jet system printer that outputs processing results to recording paper or the like is used. Further, the image forming apparatus 100 may include a modem as a communication unit for connecting to a server apparatus or the like via a network. Further, instead of acquiring the color image data from the color image input device 1, the color image data may be acquired from an external storage device, a server device, or the like via a network.

  In the present invention, a program code for performing gradation reproduction processing or the like can be recorded on a computer-readable recording medium on which a program code to be executed by a computer is recorded. As a result, it is possible to provide a portable recording medium on which the program code for performing the above processing is recorded. The recording medium may be a non-illustrated memory, for example, a program medium such as a ROM because processing is performed by a microcomputer, and a program reading device as an external storage device (not illustrated) is provided, and the recording medium is stored therein. It may be a program medium that can be read by being inserted.

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

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

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

1 is a block diagram illustrating a configuration of an image forming apparatus including an image processing apparatus according to the present invention. It is a block diagram which shows the structure of an area | region recognition process part. It is explanatory drawing which shows the content of a run expansion process. It is explanatory drawing which shows the example of run information. It is explanatory drawing which shows the example of connection run information. It is explanatory drawing which shows the extraction method of a circumscribed rectangle area | region. It is explanatory drawing which shows the example of circumscribed rectangle information. It is explanatory drawing which shows the determination conditions for determining the magnitude | size (length) of a circumscribed rectangular area. It is explanatory drawing which shows the example of a density histogram. It is a block diagram which shows the structure of a gradation reproduction process part. It is explanatory drawing which shows the example of the density | concentration characteristic of a density | concentration conversion table. It is a schematic diagram which shows an example of an operation panel. It is a schematic diagram which shows an example of an operation panel. 6 is a flowchart illustrating a procedure of gradation reproduction processing in a toner save mode. It is a flowchart which shows the procedure of an area | region recognition process. 6 is a block diagram illustrating a configuration of a gradation reproduction processing unit according to Embodiment 2. FIG. 6 is a schematic diagram illustrating an example of a dither matrix according to Embodiment 2. FIG. 10 is a flowchart illustrating a procedure of gradation reproduction processing in a toner save mode according to the second embodiment. 10 is a flowchart illustrating a procedure of gradation reproduction processing in a toner save mode according to the second embodiment. 10 is a block diagram illustrating a configuration of a gradation reproduction processing unit according to Embodiment 3. FIG. 14 is a flowchart illustrating a procedure of tone reproduction processing in a toner save mode according to a third embodiment. FIG. 10 is a block diagram illustrating a configuration of a color correction unit according to a fourth embodiment. It is explanatory drawing which shows the example of the table for color correction. 6 is a flowchart illustrating a procedure of color correction processing in a toner save mode. 6 is a flowchart illustrating a procedure of processing that combines color correction processing and gradation reproduction processing in a toner save mode. FIG. 10 is a block diagram illustrating a configuration of an image processing system according to a fifth embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Color image input device 2 Color image processing device 3 Color image output device 4 Operation panel 23,501 Area recognition processing unit 28,504 Tone reproduction processing unit 50 Printer driver 231 Binization processing unit 232 Run expansion processing unit 233 Labeling processing Unit 234 circumscribed rectangle extraction processing unit 235 determination unit 251, 281 selector 252 color correction table 253 color correction processing unit 282 density conversion table 283 density conversion unit 284 dither processing unit 285 dither matrix unit 286 decimation processing unit 287, 288 error diffusion processing unit

Claims (17)

In an image processing method for generating pseudo-halftone output image data by performing gradation reproduction processing on input image data,
Extract one or more regions based on the pixel value of each pixel in the input image data,
Calculate the density difference of the extracted area,
When the calculated density difference is smaller than a predetermined threshold, the density value of each pixel in the region is converted to a low density value,
An image processing method characterized by performing gradation reproduction processing on input image data including image data obtained by conversion. When the density difference of the extracted area is smaller than a predetermined threshold, dither processing is performed using a dither matrix having a large number of matrices for the area,
2. The tone reproduction process according to claim 1, wherein when the density difference of the extracted area is larger than a predetermined threshold, the area is subjected to a gradation reproduction process by performing a dither process using a dither matrix having a small number of matrices. Image processing method. In an image processing method for generating pseudo-halftone output image data by performing gradation reproduction processing on input image data,
Extract one or more regions based on the pixel value of each pixel in the input image data,
Calculate the density difference of the extracted area,
When the calculated density difference is smaller than a predetermined threshold value, a part of pixels in the area is thinned out before or after the gradation reproduction process is performed on the input image data including the image data of the area. An image processing method. When the density difference of the extracted area is smaller than a predetermined threshold, color correction is performed on the area with a low number of gradations,
4. The gradation reproduction process according to claim 1, wherein when the density difference of the extracted area is larger than a predetermined threshold, color correction is performed on the area with a high number of gradations to perform gradation reproduction processing. The image processing method as described in one. In an image processing method for generating pseudo-halftone output image data by performing gradation reproduction processing on input image data,
Extract one or more regions based on the pixel value of each pixel in the input image data,
Calculate the density difference of the extracted area,
When the calculated density difference is smaller than a predetermined threshold, color correction is performed on the area with a low number of gradations,
An image processing method characterized by applying gradation reproduction processing to input image data including image data obtained by color correction. If the density difference of the extracted area is smaller than a predetermined threshold, the area is identified as a background area or a drawing area,
6. The image processing method according to claim 1, wherein if the density difference of the extracted area is larger than a predetermined threshold, the area is identified as a character area or a photograph area. In an image processing apparatus that performs gradation reproduction processing on input image data to generate pseudo-halftone output image data,
Extraction means for extracting one or a plurality of regions based on the pixel value of each pixel in the input image data;
Calculating means for calculating a density difference of the region extracted by the extracting means;
Conversion means for converting the density value of each pixel in the region to a low density value when the density difference calculated by the calculation means is smaller than a predetermined threshold;
An image processing apparatus comprising: means for performing gradation reproduction processing on input image data including image data obtained by conversion by the conversion means. The means for performing the gradation reproduction process is:
When the density difference of the region extracted by the extracting means is smaller than a predetermined threshold, a dithering process applied to the region based on a dither matrix having a large number of matrices;
And a dithering process applied to the region based on a dither matrix having a small number of matrices when the density difference of the region extracted by the extracting unit is larger than a predetermined threshold. The image processing apparatus described. In an image processing apparatus that performs gradation reproduction processing on input image data to generate pseudo-halftone output image data,
Extraction means for extracting one or a plurality of regions based on the pixel value of each pixel in the input image data;
Calculating means for calculating a density difference of the region extracted by the extracting means;
If the density difference calculated by the calculation means is smaller than a predetermined threshold, a part of the pixels in the area is thinned out before or after the gradation reproduction process is performed on the input image data including the image data of the area. And an image processing apparatus. When the density difference of the extracted area is smaller than a predetermined threshold, color correction is performed on the area with a low gradation number, and when the density difference of the extracted area is larger than the predetermined threshold, Color correction means that performs color correction with a high number of gradations,
The image according to any one of claims 7 to 9, wherein gradation reproduction processing is performed on input image data including image data color-corrected by the color correction means. Processing equipment. In an image processing apparatus that performs gradation reproduction processing on input image data to generate pseudo-halftone output image data,
Extraction means for extracting one or a plurality of regions based on the pixel value of each pixel in the input image data;
Calculating means for calculating a density difference of the region extracted by the extracting means;
When the density difference calculated by the calculation means is smaller than a predetermined threshold, color correction means for performing color correction with a low number of gradations on the area;
An image processing apparatus comprising: means for performing gradation reproduction processing on input image data including image data color-corrected by the color correction means. Means for identifying the area as a background area or a graphic area when the density difference of the area extracted by the extracting means is smaller than a predetermined threshold;
12. The method according to claim 7, further comprising: a unit for identifying the region as a character region or a photo region when the density difference of the region extracted by the extracting unit is larger than a predetermined threshold value. The image processing apparatus described in one. Accepting means for accepting an instruction to reduce the consumption of toner or ink;
13. The control unit according to claim 7, further comprising: a control unit configured to perform control so as to perform the processing in the extraction unit, the calculation unit, and the conversion unit and the thinning-out process when an instruction is received by the reception unit. The image processing apparatus according to any one of the above.   An image processing apparatus according to claim 7, and an image forming unit that forms an output image based on output image data generated by the image processing apparatus. Image forming apparatus. In a computer program for causing a computer to generate gradation halftone output image data by performing gradation reproduction processing on input image data,
Means for extracting one or more regions based on the pixel value of each pixel in the input image data;
Means for calculating a density difference of the extracted area;
Means for converting the density value of each pixel in the region into a low density value when the calculated density difference is smaller than a predetermined threshold;
A computer program causing a computer to function as means for performing gradation reproduction processing on input image data including image data obtained by conversion. In a computer program for causing a computer to generate gradation halftone output image data by performing gradation reproduction processing on input image data,
Means for extracting one or more regions based on the pixel value of each pixel in the input image data;
Means for calculating a density difference of the extracted area;
When the calculated density difference is smaller than a predetermined threshold, the computer thins out a part of the pixels in the area before or after applying the gradation reproduction process to the input image data including the image data of the area. A computer program that functions as a means. 17. A computer-readable recording medium in which the computer program according to claim 15 or 16 is recorded.

Images