JP2008072237A - Image processing method, image processor, image forming apparatus and computer program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image processing method for executing processing to an image wherein a plurality of regions coexist, an image processor, an image forming apparatus and a computer program. <P>SOLUTION: Region separating processing is performed for input image data (S11), and an input image is separated into a character region, the shadow region of shadowed characters and the other region. Then, whether or not the block of a judgement object is the character region is judged (S12), and in the case of judging that it is not the character region (S12:NO), dither processing of 7×7 is executed (S13). Also, in the case of judging that it is the character region (S12:YES), whether or not the character region is the shadow region of the shadowed characters is judged (S14), the dither processing of 1×1 is executed (S15) in the case that it is not the shadow region (S14:NO), and the dither processing of 5×5 is executed (S16) in the case that it is the shadow region (S14:YES). <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image processing method, an image processing apparatus, an image forming apparatus, and a computer program for performing processing on an image in which a plurality of areas are mixed.

  2. Description of the Related Art Conventional image processing apparatuses such as a copying machine or a digital multifunction machine having a copying function, a facsimile function, a printing function, and the like include image data to be processed (hereinafter referred to as an original) generated by reading from an original or input from an external device. When a character area is detected from image data) and image data obtained by performing image processing on the pixel data of the detected character area (hereinafter referred to as processed image data) is output, character reproducibility of the output image is improved. There is something you can do. As general image processing for reproducing characters vividly and darkly, a method of binarizing and outputting pixel data of a character region, or a method of increasing the contrast by adjusting the density by performing gamma correction and outputting the data Etc. are used (for example, refer to Patent Document 1).

Patent Document 1 discloses an example in which a character area is detected from original image data and binarized. Specifically, pixel data included in a predetermined area of the original image data is classified according to its RGB values, and when the number of pixel data that is the second largest among the classified pixel data is within a specified value range, the largest number is obtained. Identify the pixel data area as the background area, the second most pixel data area as the character area, and if the identified background area has high brightness, classify it as a background area and an area other than the background area (character area) On the contrary, when the brightness of the identified character region is high, binarization is performed by classifying the character region into a region other than the character region (background region).
Japanese Patent Laid-Open No. 11-213090

  However, when the method disclosed in Patent Document 1 is applied to image processing of original image data corresponding to an original image including a shadowed character, pixel data of a region corresponding to a shadow is also classified as a character region. It is binarized into a character area (= character part + shadow part) and a background area. In particular, in the case of an original image in which dark (low lightness) shadow characters overlap on a bright (high lightness) background, the background is replaced with white, and both the character part and the shadow part are replaced with black. Therefore, the output image has a problem that characters are crushed and cannot be read.

  The present invention has been made in view of such circumstances, and extracts a character region composed of pixels constituting a character and a shadow region composed of pixels constituting a shadow of the character from an image, and the extracted character region and shadow region Image processing method capable of expressing the gradation difference between the character part and the shadow part without causing the shadow part of the shaded character to be crushed by performing a process for generating a gradation difference between An object of the present invention is to provide an image processing apparatus, an image forming apparatus, and a computer program.

  An image processing method according to the present invention is a method of extracting a specific area from an image composed of a plurality of pixels and performing processing on the extracted area. The character area including pixels constituting a character, and the character The method includes a step of extracting a shadow area composed of pixels constituting the shadow of the image from the image, and a step of performing a process of generating a gradation difference between the extracted character area and the shadow area.

  In the present invention, a character area consisting of pixels constituting a character and a shadow area consisting of pixels constituting a character shadow are extracted from the image, and a gradation difference is extracted between the extracted character area and shadow area. Since the process to generate is performed, it is possible to prevent the shadow portion of the shaded character from being crushed, and the reproducibility of the shaded character is improved.

  An image processing method according to the present invention includes a step of calculating a luminance value distribution for pixels included in the image, a step of determining whether or not three peaks are included in the distribution calculated by the step, If it is determined that a peak is included, the step of classifying the image into three regions with respect to the luminance value based on the luminance value corresponding to the peak value, and the region with the lowest luminance value among the three classified regions is a character Extracting a region having an intermediate luminance value as a shadow region and a region having the highest luminance value as another region.

  In the present invention, when three peaks are included in the distribution of luminance values, the three regions are classified based on the luminance values corresponding to the peak values. The shaded character area is composed of three components, that is, a character portion, a shadow portion, and a background portion, and has a feature that the brightness of each can be roughly divided. Therefore, by using the peak information from the luminance value distribution, each region is extracted with high accuracy.

  In the image processing method according to the present invention, the process is a dither process, and a dither matrix having a different size is used between the process for the character area and the process for the shadow area.

  In the present invention, by using a dither matrix having a different size between the dither processing for the character region and the dither processing for the shadow region, for example, halftone processing that emphasizes resolution for the character region, On the other hand, halftone processing that emphasizes gradation can be performed, and a gradation difference is generated between the extracted character area and shadow area.

  An image processing apparatus according to the present invention extracts a specific region from an image composed of a plurality of pixels, and performs processing on the extracted region. In the image processing device, a character region composed of pixels constituting a character, and the character And a means for extracting a shadow area composed of pixels constituting the shadow from the image and a means for performing a process for generating a gradation difference between the extracted character area and the shadow area.

  In the present invention, a character area consisting of pixels constituting a character and a shadow area consisting of pixels constituting a character shadow are extracted from the image, and a gradation difference is extracted between the extracted character area and shadow area. Since the process to generate is performed, it is possible to prevent the shadow portion of the shaded character from being crushed, and the reproducibility of the shaded character is improved.

  The image processing apparatus according to the present invention includes a means for calculating a distribution of luminance values for the pixels included in the image, a means for determining whether or not three peaks are included in the distribution calculated by the means, and three When it is determined that a peak is included, a means for classifying the image into three regions with respect to the luminance value based on a luminance value corresponding to the peak value, and a region having the lowest luminance value among the three classified regions is a character And a means for extracting a region having an intermediate luminance value as a shadow region and a region having the highest luminance value as another region.

  In the present invention, when three peaks are included in the distribution of luminance values, the three regions are classified based on the luminance values corresponding to the peak values. The shaded character area is composed of three components, that is, a character portion, a shadow portion, and a background portion, and has a feature that the brightness of each can be roughly divided. Therefore, by using the peak information from the luminance value distribution, each region is extracted with high accuracy.

  In the image processing apparatus according to the present invention, the process is a dither process, and a dither matrix having a different size is used between the process for the character area and the process for the shadow area.

  In the present invention, by using a dither matrix having a different size between the dither processing for the character region and the dither processing for the shadow region, for example, halftone processing that emphasizes resolution for the character region, On the other hand, halftone processing that emphasizes gradation can be performed, and a gradation difference is generated between the extracted character area and shadow area.

  An image forming apparatus according to the present invention includes the image processing apparatus according to any one of the above-described inventions, and a unit that forms an image processed by the image processing apparatus on a sheet.

  In the present invention, since the image processed by the above-described image processing apparatus is formed on the sheet, the reproducibility of the shaded character can be expressed well.

  A computer program according to the present invention is a computer program that causes a computer to extract a specific area from an image composed of a plurality of pixels and to perform processing on the extracted area. The computer program includes pixels that constitute characters. A step of extracting a character region and a shadow region composed of pixels constituting the shadow of the character from the image, and a step of causing a computer to perform a process of generating a gradation difference between the extracted character region and the shadow region It is characterized by having.

  In the present invention, a character area consisting of pixels constituting a character and a shadow area consisting of pixels constituting a character shadow are extracted from the image, and a gradation difference is extracted between the extracted character area and shadow area. Since the process to generate is performed, it is possible to prevent the shadow portion of the shaded character from being crushed, and the reproducibility of the shaded character is improved.

  According to the present invention, a character area composed of pixels constituting a character and a shadow area composed of pixels constituting a character shadow are extracted from the image, and a gradation difference is generated between the extracted character area and shadow area. Apply the process to be. Therefore, it is possible to prevent the shadow portion of the shaded character from being crushed, and each region can be expressed with good reproducibility.

  According to the present invention, when three peaks are included in the luminance value distribution, the three regions are classified based on the luminance value corresponding to the peak value. The shaded character area is composed of three components, that is, a character portion, a shadow portion, and a background portion, and has a feature that the brightness of each can be roughly divided. Therefore, by using the peak information from the luminance value distribution, the structure of the shaded character can be extracted with high accuracy.

  According to the present invention, by using a dither matrix having a different size between the dither processing for the character region and the dither processing for the shadow region, for example, halftone processing that emphasizes resolution for the character region, Thus, halftone processing can be performed with emphasis on gradation, a gradation difference can be generated between the extracted character area and shadow area, and a shaded character can be expressed with good reproducibility.

  In the case of the present invention, since the image processed by the above-described image processing apparatus is formed on the sheet, the reproducibility of the shaded character can be expressed well.

Hereinafter, the present invention will be specifically described with reference to the drawings showing embodiments thereof.
Embodiment 1 FIG.
FIG. 1 is a block diagram showing an internal configuration of an image processing apparatus according to the present invention. The image processing apparatus according to the present invention includes an operation unit 1, an image input unit 3, an image processing unit 5, and an image output unit 7.

  The operation unit 1 includes a display device that displays information to be notified to the user, various switches that accept operation instructions and selection operations by the user, buttons, and the like.

  The image input unit 3 is a unit that optically reads an image of a document, and includes a light source that irradiates light to a document for reading, an image sensor such as a CCD (Charge Coupled Device), and the like. In the image input unit 3, a reflected light image from a document set at a predetermined reading position is formed on the image sensor, and RGB (R: Red, G: Green, B: Blue) analog electrical signals are output. . The analog electrical signal output from the image input unit 3 is input to the image processing unit 5.

  The image processing unit 5 converts the analog electrical signal output from the image input unit 3 into a digital electrical signal, and then performs image processing according to the document type to generate an output image signal. The generated image signal is output to the image output unit 7. In the present embodiment, CMYK signals (C: Cyan, M: Magenta, Y: Yellow, K: Black) are generated as image signals for output. The internal configuration and operation of the image processing unit 5 will be described in detail later.

  The image output unit 7 is a unit that forms an image on a sheet such as paper or an OHP film based on the image signal output from the image processing unit 5. Therefore, the image output unit 7 is a charger that charges the photosensitive drum to a predetermined potential, and laser writing that generates an electrostatic latent image on the photosensitive drum by emitting laser light in accordance with image data received from the outside. An apparatus, a developing device that supplies toner to the electrostatic latent image formed on the surface of the photosensitive drum to make it visible, a transfer device that transfers the toner image formed on the surface of the photosensitive drum onto paper (not shown), etc. And an image desired by the user is formed on a sheet by electrophotography. In addition to image formation by an electrophotographic method using a laser writing apparatus, an image formation may be performed by an inkjet method, a thermal transfer method, a sublimation method, or the like.

  Although the image input unit 3 is configured as an image reading unit and the image output unit 7 is configured as an image forming unit, the image input unit 3 is configured as a unit that receives image data from the outside and a unit that transmits image data to the outside. Alternatively, a configuration in which they are appropriately combined may be used. For example, when the image input unit 3 is an image reading unit and the image output unit 7 is an image data transmission unit, the present invention operates as a scanner device. The image input unit 3 is an image data receiving unit, When the output unit 7 is an image forming unit, the present invention operates as a printer device (image forming device). Needless to say, the present invention can also be applied to a digital multi-function peripheral including an image reading unit, an image forming unit, and an image data transmitting / receiving unit.

  Details of the internal configuration of the image processing unit 5 will be described below. The image processing unit 5 includes an AD conversion unit 51, a shading correction unit 52, an input processing unit 53, a region separation processing unit 54, a color correction unit 55, a black generation and under color removal unit 56, a spatial filter processing unit 57, and a halftone generation unit. 58.

  The AD conversion unit 51 converts the RGB analog signal input from the image input unit 3 into a digital signal. The shading correction unit 52 performs a process of removing various distortions generated in the illumination system, the imaging system, and the imaging system of the image input unit 3 on the digital RGB signal output from the AD conversion unit 51. The input processing unit 53 performs processing for correcting gamma for each of the RGB signals.

  The region separation processing unit 54 separates a region to which each pixel in the input image belongs. For example, the density change tends to be large in both the vertical direction (sub-scanning direction) and the horizontal direction (main scanning direction) in the halftone area, and the density change tends to increase only in one of the character areas. Using this, the unit 54 can separate the character area, the halftone dot area, and the photograph area. Based on the separation result, the region separation processing unit 54 outputs a region identification signal indicating to which region the pixel belongs to the subsequent black generation and under color removal unit 56, the spatial filter processing unit 57, and the halftone generation unit 58. In addition, the input signal from the input processing unit 53 is output to the subsequent color correction unit 55 as it is.

  The color correction unit 55 performs processing for removing color turbidity based on the spectral characteristics of the CMY color material including unnecessary absorption components in order to faithfully reproduce color reproduction. The black generation and under color removal unit 56 generates black (K) signals from the CMY three-color signals after color correction, and generates a new CMY signal obtained by subtracting the K signal obtained by black generation from the original CMY signals. Generate the process. By this processing, the CMY three-color signal is converted into a CMYK four-color signal.

  The spatial filter processing unit 57 performs spatial filter processing by a digital filter on the image data of the CMYK signal input from the black generation and under color removal unit 56 based on the region identification signal, thereby correcting the spatial frequency characteristics. Performs processing to prevent blurring and particulate deterioration of the output image.

  The halftone generation unit 58 performs appropriate process switching according to the region identification signal output from the region separation processing unit 54. In the present invention, in order to improve the readability of a shaded character in particular, a dither process is performed according to a normal character portion (character region), a shaded character shadow portion (shadow region), and other regions.

  Next, processing contents in the region separation processing unit 54 will be described. FIG. 2 is a block diagram illustrating the configuration of the region separation processing unit 54. The region separation processing unit 54 includes a signal conversion unit 541, a maximum value calculation unit 542, a minimum value calculation unit 543, a maximum density difference determination unit 544, an inversion number calculation unit 545, an inversion number determination unit 546, a determination unit 547, and a shaded area. A character area determination unit 548 is provided.

  The signal converter 541 converts an RGB signal into a Lab signal in a block (for example, a 7 × 7 block) composed of a plurality of M × N pixels in the input RGB image. The Lab signal is a signal that indicates one color by a signal that L represents luminance, a signal that represents a red / green balance, and b a signal that represents a yellow / blue balance. Conversion from RGB signals to Lab signals is expressed by the following equation.

  The maximum value calculation unit 542 and the minimum value calculation unit 543 calculate the maximum value Lmax and the minimum value Lmin of the signal L representing the luminance based on the Lab signal output from the signal conversion unit 541, respectively.

  The maximum density difference determination unit 544 calculates a difference between the maximum value Lmax and the minimum value Lmin, and compares the calculated difference Lmax−Lmin with a threshold TH1 (for example, TH1 = 150) stored in advance. When Lmax−Lmin> TH1, that is, when the change of the luminance value in the block is large, the output signal S1 (= 0) is output. Further, when Lmax−Lmin ≦ TH1, that is, when the change in luminance in the block is small, the output signal S1 (= 1) is output.

  The inversion number calculation unit 545 binarizes the average luminance signal level of each pixel in the M × N block (converts it to 0 or 1), and 0 or 1 between consecutive pixels in the main scanning direction or the sub-scanning direction. The total Kh and Kv in the block of the number of changes is obtained.

  The inversion number determination unit 546 compares each value of Kh and Kv with a threshold value TH2 (for example, TH2 = 15) for a block with Lmax−Lmin> TH1. When Kh ≧ TH2 and Kv ≧ TH2, that is, when the luminance change is significant in both the main scanning direction and the sub-scanning direction, an output signal S2 (= 0) is output. When Kh <TH2 or Kv <TH2, that is, when the luminance change is severe in either the main scanning direction or the sub-scanning direction, the output signal S2 (= 1) is output.

  Based on the value of the output signal S1 output from the maximum density difference determination unit 544 and the value of the output signal S2 output from the inversion number determination unit 546, the determination unit 547 determines a character region, a dot region, and other regions ( The first region identification signal SEG 1 is output to the shaded character region determination unit 548. FIG. 3 is a chart illustrating an example of a table used when the determination unit 547 performs region determination. In this table, the photographic area (continuous gradation area) has gradation, and the background area has a substantially uniform density, so the maximum density difference in the block is small, and in the halftone area, The feature is that halftone dots are arranged periodically and pixels with high density are spatially dispersed.

  When the determination unit 547 determines that the shaded character area is a character area, the shadowed character area determination unit 548 performs a process of separating the shaded character area from the distribution of the luminance values L. FIG. 4 is a block diagram showing the internal configuration of the shaded character area determination unit 548. The shadowed character area determination unit 548 includes a histogram creation unit 548A and an area determination unit 548B. The histogram creation unit 548A creates a histogram by summing up the luminance values L of each pixel, and the region determination unit 548B determines whether or not the created histogram includes three peaks, thereby determining the shaded character. It is determined whether or not the region includes.

  If it is determined that the three peaks are not included, the region determination unit 548B determines that the region is a normal character region that is not shaded, and uses SEG1 output from the determination unit 547 described above as the final region identification signal SEG. Output as. If it is determined that three peaks are included, it is determined as a shaded character region, and two threshold values TH_L1 and TH_L2 are set using the brightness values PeaK_L1, PeaK_L2, and PearK_L3 corresponding to the peaks. For example, the threshold value TH_L1 can be set as the median value of the two luminance values PeaK_L1 and PeaK_L2, and the threshold value TH_L2 can be set as the median value of the two luminance values PeaK_L2 and PeaK_L3. Then, it is divided into three regions using threshold values TH_L1 and TH_L2, and the character portion (character region) of the shaded character, the shadow portion (shadow region) of the shaded character, The determination result is output as a region identification signal SEG.

  FIG. 5 is a schematic diagram showing an example of a histogram created by the histogram creation unit 548A. When the histogram shown in FIG. 5 is obtained as a result of summing up the luminance values for each pixel of the determination target block, that is, three peaks having peak values at Peak_L1 = 30, Peak_L2 = 80, and Peak_L3 = 150 are included. When the distribution is obtained, the region determination unit 548B sets two threshold values as TH_L1 = 55 and TH_L2 = 115, a region where the luminance value L is 0 ≦ L <55, and a character region, and the luminance value L is 55 ≦ L. The region <115 is determined as a shadow region, and the region where the luminance value L is 115 ≦ L <255 is determined as another region.

  When the above determination result is represented by a 3-bit signal, “000” is a halftone dot area, “001” is a character area, “01 *” is another area (* is 0 or 1), and “101” is It can be expressed as a shadow area of a shadowed character.

  Next, processing contents in the halftone generation unit 58 will be described. The halftone generation unit 58 performs an optimal dither process on each region (block) based on the region identification signal SEG output from the region separation processing unit 54. For example, the halftone dot area or other areas are 7 × 7 dither processing that emphasizes color gradation, the character area is 1 × 1 dither processing that emphasizes resolution, and the shadow portion of a shaded character is a character portion. 5 × 5 dither processing is performed in order to obtain a gradation difference.

  The dither processing uses, for example, a concentrated dot type systematic dither. FIG. 6 is a schematic diagram showing an example of a concentrated dot type systematic dither. When the size of one dither matrix is 5 × 5 and the output pixel value taken by each pixel is a binary value of 0 and 1, the number of gradations is 26 gradations from 0 to 25. The RGB signals of the input image data are values from 0 to 255, respectively. Each of the 5 × 5 dither matrices has a threshold value (threshold matrix), and the input pixel value x and the threshold value y are compared. When x ≧ y, the output pixel value is “1”, x <y In this case, the output pixel value is “0”. A halftone is generated by the above processing.

Embodiment 2. FIG.
In the first embodiment, each processing is realized by hardware. However, the image processing according to the present invention may be realized by software processing.

  FIG. 7 is a block diagram illustrating the internal configuration of the image processing apparatus in which the computer program of the present invention is installed. In the figure, reference numeral 100 denotes an image processing apparatus according to the present embodiment, specifically a personal computer, a workstation, or the like. The image processing apparatus 100 includes a CPU 101, and hardware such as a ROM 103, a RAM 104, a hard disk 105, an external storage unit 106, an input unit 107, a display unit 108, and a communication port 109 is connected to the CPU 101 via a bus 102. Yes. The CPU 101 controls the above-described hardware units according to a control program stored in advance in the ROM 103.

  The RAM 104 is a volatile memory that temporarily stores various data generated during execution of the control program described above or the computer program according to the present invention. The hard disk 105 is a storage unit having a magnetic recording medium, and stores the computer program of the present invention, image data to be processed, and the like. The external storage unit 106 includes a reading device for reading the computer program from the recording medium M on which the computer program of the present invention is recorded. As the recording medium M, an FD (Flexible Disk), a CD-ROM, or the like can be used. The computer program read by the external storage unit 106 is stored in the hard disk 105. The CPU 101 loads the computer program according to the present invention stored in the hard disk 105 onto the RAM 104 and executes it, thereby realizing the image processing method according to the present invention as described in the first embodiment.

  The input unit 107 functions as an interface for acquiring image data from the outside. For example, a color scanner device or the like is connected to the input unit 107. The display unit 108 functions as an interface for displaying image data to be processed, image data during image processing, image data after image processing, and the like. The display unit 108 may be configured to display image data by connecting an external display device such as a liquid crystal display device, or the display unit 108 may include a display device and display image data. The communication port 109 is an interface for connecting the printer 150 to the outside. When printing image data that has undergone image processing by the printer 150, the image processing apparatus 100 generates print data that can be decoded by the printer 150 based on the image data, and transmits the generated print data to the printer 150. .

  FIG. 8 is a flowchart for explaining a procedure of processing executed by the image processing apparatus 100 according to the second embodiment. First, the CPU 101 of the image processing apparatus 100 performs a region separation process on the image data captured through the input unit 107 (step S11). At this time, by using a method similar to the method described in the first embodiment, the determination target region is separated into three regions: a character region, a shadow region of a shaded character, and other regions.

  Based on the processing result in the region separation processing, the CPU 101 determines whether or not the character target block is a character region (step S12). When it is determined that the area is not a character area (S12: NO), that is, when it is determined that the area is a halftone dot area or other area, the CPU 101 executes a 7 × 7 dither process that emphasizes color gradation (see FIG. Step S13).

  When determining that it is a character area (S12: YES), the CPU 101 determines whether or not the character area is a shadow area of a shaded character (step S14). When it is determined that the area is not a shadow area (S14: NO), that is, when it is determined that the area is a normal character area or a character area with a shadow, 1 × 1 dither processing is performed with emphasis on resolution (step S15). If it is determined that it is a shadow area of a shadowed character (S14: YES), a 5 × 5 dither process is performed in order to obtain a gradation difference between the shadow portion of the shadowed character and the character portion (step S16).

  In the present embodiment, the CPU 101 performs various calculations. However, a dedicated chip for performing calculations related to image processing may be separately provided and calculations may be performed according to instructions from the CPU 101.

  As the recording medium M for recording the computer program according to the present invention, in addition to the FD and CD-ROM described above, optical recording media such as MO, MD, DVD, magnetic recording media such as hard disks, IC cards, memory cards, It is also possible to use a semiconductor memory such as a card-type recording medium such as an optical card, mask ROM, EPROM (Erasable Programmable Read Only Memory), EEPROM (Electrically Erasable Programmable Read Only Memory), flash ROM, or the like. In addition, since the system configuration allows connection to a communication network including the Internet, the computer program according to the present invention may be downloaded from the communication network.

  In addition, the computer program of the present invention may be provided as a single application program or utility program, or may be incorporated into another application program or utility program and provided as a partial function of the program. May be. For example, as one form, a form provided by being incorporated in a printer driver is conceivable.

It is a block diagram which shows the internal structure of the image processing apparatus which concerns on this invention. It is a block diagram explaining the structure of an area | region separation process part. It is a graph which shows an example of the table used when a determination part performs area | region determination. It is a block diagram which shows the internal structure of a character area determination part with a shadow. It is a schematic diagram which shows an example of the histogram created by the histogram creation part. It is a schematic diagram which shows an example of a systematic dither of a concentrated dot type. It is a block diagram explaining the internal structure of the image processing apparatus in which the computer program of this invention was installed. 10 is a flowchart for describing a procedure of processing executed by the image processing apparatus according to the second embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Operation part 3 Image input part 5 Image processing part 7 Image output part 51 AD conversion part 52 Shading correction part 53 Input processing part 54 Area separation processing part 55 Color correction part 56 Black generation under color removal part 57 Spatial filter processing part 58 Intermediate Key generation unit 541 Signal conversion unit 542 Maximum value calculation unit 543 Minimum value calculation unit 544 Maximum density difference determination unit 545 Inversion number calculation unit 546 Inversion number determination unit 547 Determination unit 548 Shaded character area determination unit

Claims (8)

In an image processing method for extracting a specific area from an image composed of a plurality of pixels and processing the extracted area,
A step of extracting a character area composed of pixels constituting a character and a shadow area composed of pixels constituting a shadow of the character from the image, and a process for generating a gradation difference between the extracted character area and the shadow area And an image processing method.   When calculating the luminance value distribution for the pixels included in the image, determining whether the distribution calculated by the step includes three peaks, and determining that the three peaks are included, A step of classifying the image into three regions with respect to the luminance value based on a luminance value corresponding to the peak value, and a region having the lowest luminance value among the three classified regions is a character region and a region having an intermediate luminance value 2. The image processing method according to claim 1, further comprising: extracting as a shadow region and a region having the highest luminance value as another region.   The image processing method according to claim 1, wherein the process is a dither process, and a dither matrix having a different size is used between the process for the character area and the process for the shadow area. In an image processing apparatus that extracts a specific area from an image composed of a plurality of pixels and performs processing on the extracted area.
Means for extracting, from the image, a character area comprising pixels constituting a character and a shadow area comprising pixels constituting a shadow of the character, and processing for generating a gradation difference between the extracted character area and the shadow area And an image processing apparatus.   A means for calculating a distribution of luminance values for the pixels included in the image, a means for determining whether the distribution calculated by the means includes three peaks, and a case where it is determined that three peaks are included, Means for classifying the image into three regions with respect to the luminance value based on the luminance value corresponding to the peak value, and among the three classified regions, the region having the lowest luminance value is a character region and the region having an intermediate luminance value 5. The image processing apparatus according to claim 4, further comprising: means for extracting as a shadow region and a region having the highest luminance value as another region.   The image processing apparatus according to claim 4, wherein the process is a dither process, and a dither matrix having a different size is used between the process for the character area and the process for the shadow area.   An image forming apparatus comprising: the image processing apparatus according to claim 4; and a unit that forms an image processed by the image processing apparatus on a sheet. In a computer program that causes a computer to extract a specific area from an image composed of a plurality of pixels and to perform processing on the extracted area,
Causing the computer to extract from the image a character area composed of pixels constituting a character and a shadow area comprising pixels constituting the shadow of the character; and causing the computer to store a hierarchy between the extracted character area and the shadow area. A computer program comprising a step of performing a process for generating a tone difference.

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