JP2009284407A - Background removing apparatus and program, and image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a background removing apparatus and a background removal program that prevent occurrence of a concentration step even if the background of an original changes for each compartment of a line, and to provide an image forming device. <P>SOLUTION: At an input gradation conversion section 310 of an input gradation correction section 32, input image data is converted according to the characteristics of an image read section 20 so that a prescribed gradation change is achieved. Further, at a color space conversion section 320, conversion to a brightness signal and a chromaticity signal is performed for internal image processing. The brightness signal in the converted signals is used to generate a histogram with prescribed image data width as one concentration region at a histogram generation section 330. At a background region determination section 340, a concentration region to which the background of an original 1 belongs is determined based on the histogram. At a background correction section 350, image data from the color space conversion section 320 is subjected to background removal by a threshold for background removal corresponding to a concentration region of background determined by the background region determination section 340 by converting a part thinner than background concentration to a while level. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a background removing device, a program, and an image forming apparatus.

  Conventionally, in an image forming apparatus that reads a background document and performs various image processing to generate a print image, by generating an image with the background removed, as a technique for improving the readability of the print image, What was disclosed by patent document 1 is known.

When the image forming apparatus described in Patent Document 1 reads an image and generates an output image, the frequency is maximized from the histogram of image data for several lines after shading correction stored in the buffer. The portion is determined to have a background density, and a background removal process is performed.
JP 2001-223898 A

  In the conventional technique described in Patent Document 1 described above, when this method is applied to the entire document, if an image close to the background density exists with a certain area, the maximum density region changes. As a result, the threshold value for removing the background also changes, causing a problem that a partial density step occurs on the output image.

  In addition, when the image other than the density range that is the detection target of the background has a large area, the frequency of the original background is relatively decreased and falls below the threshold for determination. The problem that it cannot be detected as a background occurs.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a background removing apparatus, a program, and an image forming apparatus that prevent a density step from occurring even if the background of an original changes for each line section.

  In order to achieve the above object, the background removing apparatus according to the first aspect of the present invention is a histogram generating means for dividing a document into a plurality of sections each having a predetermined number of lines and generating a histogram having a predetermined density width from image data of each section. A background area determination means for determining a background area to which the background belongs from the frequency of each density area of the histogram generated by the histogram generation means, and image data of each section corresponding to the background area determined by the background area determination means Threshold calculating means for calculating a threshold for removing the background from the image, and background removal for removing the background from the image data of each section of the document based on the threshold calculated by the threshold calculating means Means.

  Further, according to a second aspect of the present invention, in the first aspect, the background area determination means examines the frequency of each density area from a predetermined density area on the low density side toward the high density side of the histogram. A density area having a frequency maximum and exceeding a preset first value is determined as the background area.

  According to a third aspect of the present invention, in the second aspect of the present invention, the background area determination means is configured to set a predetermined density area when the frequency does not exceed the first value in all density areas of the histogram. Is determined as the background area.

  According to a fourth aspect of the present invention, in the second aspect of the present invention, the background area determination means determines that the background area exceeds the first value by the histogram of the immediately preceding section created by the histogram creation means. When the frequency of the determined density area is lower than the first value and larger than the preset second value, the density area is continuously determined as the background area.

  According to a fifth aspect of the present invention, in the second aspect of the invention, when the density region determined as the background region is continuous in a predetermined section, the density region is the background region of the entire document. It is determined that there is, and is fixed, and the determination of the background in the subsequent sections is stopped.

  According to a sixth aspect of the present invention, in the second aspect of the present invention, the background region determining means has predetermined sections that do not exceed the first value in all density regions of the histogram created by the histogram creating means. If the sections continue, it is determined that the document is a pattern document, the current background area is fixed as the background area of the entire document, and background determination in the subsequent sections is stopped.

  In the invention of claim 7, in the invention of claim 1, when the density area determined as the background area by the histogram is different from the immediately preceding section, the background area determining means changes the background area from the immediately preceding section. Limit the amount to less than a preset amount of change.

  Further, in the invention of claim 8, in the invention of claim 1, when the background area determined by the calculation histogram is different from the immediately preceding section, the threshold value corresponding to each background area is Sequentially change line by line at the boundary of the section.

  According to a ninth aspect of the present invention, there is provided a histogram removing means for dividing a computer into a plurality of sections each having a predetermined number of lines and creating a histogram having a predetermined density width from image data of each section, A background area determination means for determining the background area to which the background belongs from the frequency of each density area of the histogram generated by the histogram generation means, and the background is removed from the image data of each section corresponding to the background area determined by the background area determination means. A threshold value calculating means for calculating a threshold value for performing the processing, and a background removing means for removing a background portion from the image data of each section of the document based on the threshold value calculated by the threshold value calculating means.

  According to a tenth aspect of the present invention, there is provided an image forming apparatus that forms an image of a document based on image data obtained by removing the background from the image data of the document using a background removal device, and the background removal device includes: A histogram generating means for dividing a document into a plurality of sections each having a predetermined number of lines, creating a histogram having a predetermined density width from image data of each section, and the frequency of each density area of the histogram generated by the histogram generating means. A skin area determination means for determining a skin area to which the skin belongs, and a threshold value calculation for calculating a threshold value for removing the skin from the image data of each section corresponding to the skin area determined by the skin area determination means And background removal means for removing a background portion from the image data of each section of the document based on the threshold value calculated by the threshold value calculation means.

  According to the first aspect of the present invention, it is possible to prevent a density step from occurring even if the background of the document changes for each line section.

  According to the second aspect of the present invention, it is possible to determine the optimum background area corresponding to the background even if the background of the document changes for each section of the line.

  According to the invention of claim 3, the background area can be determined even when the first threshold value is not exceeded in all density areas of the histogram.

  According to the invention of claim 4, it is possible to prevent a large density step from occurring even if the background of the document changes for each line section.

  According to the invention of claim 5, the optimum background area can be determined without determining the density area of the entire document.

  According to the invention of claim 6, it is possible to determine the background area even when the first threshold value is not exceeded in all density areas of the histogram, and to determine the density area of the entire document. And the optimum background area can be determined.

  According to the seventh aspect of the present invention, it is possible to prevent an abrupt density step from occurring even if the background of the document changes for each line section.

  According to the invention of claim 8, it is possible to obtain an image in which a density step is gradually generated even if the background of the document changes for each section of the line.

  According to the ninth aspect of the present invention, it is possible to provide a background removal program that prevents a density step from occurring even if the background of a document changes for each line section.

  According to the tenth aspect of the present invention, it is possible to provide an image forming apparatus that prevents a density step from occurring even if the background of the document changes for each line section.

  Embodiments of a background removal apparatus, a program, and an image forming apparatus according to the present invention will be described below in detail with reference to the accompanying drawings.

  FIG. 1 is a diagram showing the overall configuration of an embodiment of an image forming apparatus according to the present invention.

  An image forming apparatus 100 shown in FIG. 1 constitutes an electrophotographic copying machine. The image forming apparatus 100 includes an image reading unit 20, an image processing unit 30, and an image forming unit 40.

  The image reading unit 20 reads an image from the document 1 placed on the document table 2, and guides the light source 3 and the reflector 4 that irradiates the document 1 with light and the reflected light from the document 1 to the photoelectric conversion unit 21. The optical system 5 which consists of the reflective mirrors 5a, 5b, 5c and the light converging device 5d, the photoelectric conversion unit 21, and the A / D conversion unit 22 are provided.

  Here, the photoelectric conversion unit 21 generates an electrical signal corresponding to the image on the document by taking out the accumulated electric charge according to the amount of light guided by the optical system 5.

  The A / D conversion unit 22 performs analog / digital conversion on the electrical signal output from the photoelectric conversion unit 21 and outputs image data to the image processing unit 30.

  The image processing unit 30 processes image data corresponding to the image read by the image reading unit 20 under the control of the image processing control unit 31, and includes an input gradation correction unit 32, a sharpness correction unit 33, and a color conversion unit. 34, an output tone correction unit 35, and a halftone processing unit 36.

  Here, the input tone correction unit 32 corrects the tone of the image data output from the A / D conversion unit 22 in accordance with the characteristics specific to the image reading unit 20, and the image data from the image reading unit 20 is also corrected. Conversion to a color space signal for image processing is performed to perform background removal processing for removing the background from the image data.

  The sharpness correction unit 33 corrects the image data converted by the input tone correction unit 32 so that the character portion has a high degree of sharpness and the photograph and the background portion become weak.

  The color conversion unit 34 converts the image data corrected by the sharpness correction unit 33 from the color space signal of the image processing unit 30 to the color space signal of the image forming unit 40.

  The output tone correction unit 35 corrects the tone of the image data converted by the color conversion unit 34 in accordance with characteristics unique to the image forming unit 40.

  The halftone processing unit 36 performs a halftone processing of the number of lines suitable for the characteristics of the image forming unit 40 on the image data subjected to the gradation correction by the output gradation correction unit 35.

  Under the control of the image formation control unit 41, the image forming unit 40 forms an image corresponding to the image data processed by the image processing unit 30 on a sheet and discharges it to the outside. The image forming unit 40 includes a pulse generation unit 42, a laser driving unit 43, a photosensitive member 6, a charger 7, a developing unit 8, a toner supply device 9, a density sensor 10, a cleaning unit 11, an intermediate transfer member 12, and a paper conveyance path. 13, a fixing device 14, a temperature sensor 15, and a humidity sensor 16, and further, a laser light amount control unit 44, a toner supply control unit 45, a development bias control unit 46, and a charging control unit 47 controlled by the image formation control unit 41. It comprises.

  Here, the pulse generator 42 generates a pulse signal having a pulse width corresponding to the image data subjected to the halftone processing by the halftone processing unit 36.

  The laser driving unit 43 is driven by a pulse signal generated from the pulse generating unit 42 and irradiates a laser beam for forming an electrostatic latent image corresponding to the image of the document on the photosensitive member 6.

  The image formation control unit 41 receives detection outputs from the density sensor 10, the temperature sensor 15, and the humidity sensor 16, controls the amount of laser light emitted from the laser drive unit 43 by the laser light amount control unit 46, and supplies toner. The controller 45 controls the amount of toner supplied from the toner supply device 9, the developing bias controller 46 controls the bias of the developing device 9, and the charging controller 47 controls the charger 8 that charges the photoreceptor 6. .

  The schematic operation of the image forming apparatus 100 having the above configuration will be described as follows.

  Prior to the copying operation, the image forming unit 40 of the image forming apparatus 100 forms a patch for calibration on the photosensitive member 6, irradiates light on the patch, and measures the reflection amount by the density sensor 10. The amount of toner adhering to the photosensitive member 6 is measured, and the parameters of each part of the image forming unit 40 are determined so as to obtain a target density based on this value.

  In an actual copying operation, the image reading unit 20 irradiates the document 1 placed on the document table 2 with the light source 3 and guides the reflected light to the photoelectric conversion unit 21 via the optical system 5. An electric signal corresponding to the image on the original 1 is generated by taking out the electric charge accumulated according to the amount of received light from the photoelectric conversion unit 21, and converted into digital data (image data) by the A / D conversion unit 22. And output to the image processing unit 30.

  The image processing unit 30 corrects the gradation of the image data output from the image reading unit 20 in accordance with the characteristics specific to the image reading unit 20 by the input gradation correction unit 32, and the color from the image reading unit 20. The space signal is converted into a color space signal for image processing, and a background removal process for removing the background from the image data is performed. The sharpness correction unit 33 corrects the character portion so that the sharpness degree is strong and the photograph and the background portion are weak. The color conversion unit 34 converts the color space signal for image processing from the image reading unit into a color space signal for the image forming unit, and the output gradation correction unit 35 adjusts the gradation in accordance with the characteristics specific to the image forming unit 40. Then, the halftone dot processing unit 36 performs a halftone dot conversion process suitable for the characteristics of the image forming unit 40.

  In the image forming unit 40, under the control of the image forming control unit 41, the charger 7 is charged with the potential determined by the charging control unit 48, whereby a predetermined potential is applied to the surface of the photoreceptor 6. On the other hand, the bias potential determined by the development bias controller 47 is applied to the toner in the developing device 8 supplied from the toner supply device 9.

  Under such a state, a pulse signal having a pulse width corresponding to the data after halftone dot processing output from the image processing unit 30 is generated by the pulse generating unit 42, and this is supplied to the laser driving unit 43 to provide a laser signal. Is generated. This scans the surface of the photosensitive member 1 to generate an electrostatic latent image of image data, and a toner to which a developing bias is applied adheres to this portion, and yellow, magenta, cyan, and black are deposited on the intermediate transfer member 12 in this order. Transferred toner images with four colors overlapped are generated. This is transferred onto the paper transported on the paper transport path 13 and heated by the fixing device 14 so that the toner is fixed on the paper and discharged outside the apparatus.

  Next, the background removal constituting the main part of the present invention will be described.

  The background removal process of the present invention is performed by the input tone correction unit 32 of the image processing unit 30 shown in FIG.

  FIG. 2 is a diagram showing an outline of the background removal process performed by the input tone correction unit 32 shown in FIG.

  As shown in FIG. 2A, the document 1 is divided into a plurality of sections 1-1 to 1-n for each predetermined number of read lines. Then, in each of the sections 1-1 to 1-n, a histogram having a predetermined image data width as one density region (1 to 9) as shown in FIG. 2B is generated.

  In the histogram shown in FIG. 2B, the vertical axis indicates the frequency corresponding to the number of appearances of the pixels in each density region (1-9), and the horizontal axis indicates the density region (1-9). The region to which the background of the document 1 belongs is specified from the shape of the histogram shown in FIG.

  That is, the histogram shown in FIG. 2B corresponds to the section 1-1 of the document 1, and, for example, each density region (1 to 9) of the histogram is determined from the histogram corresponding to the section 1-1. 2), a search is performed from a predetermined density region on the low density side of the histogram to a maximum area to be detected from the low density side toward the high density side. First, the frequency reaches a maximum and exceeds a predetermined value. The density area (4) of b) is determined as a background area corresponding to the background of the section 1-1 of the document 1. A background removal threshold for removing the background is calculated corresponding to the determined background area, and is smaller than this threshold in the input image data of the section 1-1 of the document 1 (light). The background is removed by converting the input image data to a white level.

  FIG. 3 is a block diagram showing an example of the internal configuration of the input tone correction unit 32 shown in FIG.

  The input tone correction unit 32 shown in FIG. 3 performs a background removal process for removing the background from the image data input from the image reading unit 20, and includes an input tone conversion unit 310, a color space conversion unit 320, and a histogram generation. Unit 330, background region determination unit 340, and background correction unit 350.

  In other words, in the input tone correction unit 32, the input image data is converted by the input tone conversion unit 310 using the conversion table so as to have a predetermined tone change in accordance with the characteristics of the image reading unit 20, Further, the color space conversion unit 320 converts it into a lightness signal and a chromaticity signal for internal image processing.

  Using the brightness signal in the signal converted by the color space conversion unit 320, the histogram generation unit 330 generates a histogram as shown in FIG. 2B with a predetermined image data width as one density region. Then, the background area determination unit 340 determines the density area to which the background of the document 1 belongs based on this histogram.

  Then, the background correction unit 350 converts the image data from the color space conversion unit 320 to a portion that is lighter than the background density with a threshold for background removal corresponding to the background density region determined by the background region determination unit 340. Remove background by converting to white level.

  FIG. 4 is a block diagram illustrating an example of an internal configuration of the histogram generation unit 330 illustrated in FIG.

  4 includes an adding unit 331, an added value holding unit 332, an average value calculating unit 333, a histogram frequency adding unit 334, a histogram holding unit 335, and a timing generating unit 336.

  That is, in the histogram generation unit 330 shown in FIG. 4, image data output from the color space conversion unit 320 shown in FIG. 3 is added by a predetermined number of pixels by the addition unit 331, and this is held by the addition value holding unit 332. To do. The timing generation unit 336 generates a timing signal once for each predetermined number of pixels, and each time this signal is input, a predetermined number of pixels is generated based on the value held in the added value holding unit 332 at that time. The average value of the minute is calculated by the average value calculation unit 333 and the addition value held by the addition value holding unit 332 is cleared.

  Then, the average value calculated by the average value calculation unit 333 is added by the histogram frequency addition unit 334 to add the frequency of the region to which the average value belongs to generate a histogram.

  The histogram holding unit 335 holds the histogram at the end portion of one section shown in FIG. 2A only during the next section and uses it for the background determination processing in the background area determination unit 340 shown in FIG. To do.

  FIG. 5 is a block diagram illustrating an example of an internal configuration of the background correction unit 350 illustrated in FIG. 3. The background correction unit 350 includes a threshold value calculation unit 351 and a background removal unit 352.

  The threshold calculation unit 351 calculates a threshold for background removal corresponding to the background density from a signal indicating the density region to which the background belongs, determined by the background region determination unit 340 in FIG. The calculation of the threshold value for removing the background is performed based on the density value of the density area to which the background belongs, determined by the background area determination unit 340.

  Then, the background removal unit 352 converts the density data of the input image data to a value lower than the background removal threshold (light) and a white level (output value 0), thereby removing the background.

  Here, the output value is also corrected for data slightly darker than the background removal threshold value that has not been converted to the white level, so that a pseudo contour does not occur on the output image.

  FIG. 6 is a diagram illustrating a background removal process for preventing a pseudo contour from being generated on an output image.

  In FIG. 6, the vertical axis represents the output density and the horizontal axis represents the input density. The background removal using the threshold value for removing the background is performed by setting a portion where the input density is smaller than the threshold value (portion indicated by a in FIG. 6) to an output value 0. In the portion shown, since the density suddenly changes from 0, a pseudo contour is generated on the output image. Therefore, the portion indicated by b in FIG. 6 is corrected as indicated by c in FIG. 6 so that a pseudo contour does not occur on the output image.

  FIG. 7 is a diagram for explaining a background area determination process in the background area determination unit 340 shown in FIG. 3.

  When the background area to which the background belongs is specified by the density areas (1 to 11) of the histogram shown in FIG. 7 by the background area determination unit 340 shown in FIG. 3, a predetermined density area (see FIG. 7 from the start region (1)) to the maximum region (the end region (8) in FIG. 7) to be detected toward the higher concentration side, and the density first reaches the maximum and exceeds the first value. The area, that is, the density area (4) is determined as the background area.

  If all the density areas (1 to 11) do not exceed the first value, the density area set in advance (the preset area (0) in FIG. 7) is determined as the background area.

  FIG. 8 is a flowchart showing the determination process of the background area in the background area determination unit 340 shown in FIG.

  In FIG. 8, first, the frequency on the higher density side than the end area is cleared (step 900), the evaluation area is set to the start area (1) (step 901), and the frequency of the evaluation area is 1 in the area on the higher density side. It is checked whether it is greater than the frequency (step 902). If it is determined that the frequency of the evaluation area is not greater than the frequency of the area on the high density side (NO in step 902), the evaluation area is changed to the area on the high density side (step 903). Is larger than the end area, that is, whether the end area is exceeded by a search toward the high density side (step 904). If the end area is not exceeded (NO in step 904), the process returns in step 902.

  If it is determined in step 902 that the frequency of the evaluation region is larger than the frequency of the region on the high density side (YES in step 902), it is next checked whether the frequency of the evaluation region is larger than the first value (step 902). 905).

  If it is determined that the frequency of the evaluation area is not greater than the first value (NO in step 905), the process proceeds to step 903, and the evaluation area is changed to an area on the high concentration side.

  If it is determined in step 905 that the frequency of the evaluation area is larger than the first value (YES in step 905), this evaluation area is an area where the frequency is first maximized. The current evaluation area is determined as a background area (step 906), and this background area determination is terminated.

  If it is determined in step 904 that the end area has been exceeded (YES in step 904), it is determined that all the areas from the start area to the end area do not exceed the first value. The set density area (preset area (0) in FIG. 7) is determined as a background area (step 907), and this background area determination is terminated.

  In the flowchart shown in FIG. 8, a search is performed from a predetermined density region on the low density side of the histogram to a maximum area to be detected toward the high density side, and the density first reaches a maximum and exceeds the first value. Although the region is determined as a background region, when such a background region determination is performed for each section, if an image close to the background density exists with a certain area, the maximum concentration region is determined. As a result, the threshold value for removing the background also changes, and a partial density step occurs on the output image.

  Therefore, in the background area determination processing according to the present invention, in the histogram of a certain section, the density area first determined as the background area having the maximum frequency and exceeding the first value is the first area in the histogram of the next section. If the frequency of the density area exceeds the second value smaller than the first value, the density area is continuously determined as the background area.

  FIG. 9 is a diagram for explaining a background area determination process for preventing the occurrence of a partial density step on the output image.

  In FIG. 9, the histogram of a certain section of the document is as shown in FIG. 9A. In this histogram, the frequency is first maximized by the search from the low density area to the high density area, and the first value is set. It is assumed that the density region that exceeds, that is, the density region (3) is determined as the background region.

  Here, it is assumed that the histogram of the next original section adjacent to the original section corresponding to the histogram of FIG. 9A is as shown in FIG.

  In this case, in the histogram of FIG. 9 (b), the frequency is first maximized by the search from the low density area to the high density area, and the density area exceeding the first value becomes the density area (2). Since the frequency of the density region (3) of the histogram of FIG. 9 (b) corresponding to the density region (3) determined as the background region by the histogram of FIG. 9 (a) exceeds the second value, FIG. In the histogram of (b), the density region (3) is continuously determined as the background region.

  In the background area determination processing according to the present invention, if the density area determined to be the background exceeding the first value in consecutive sections in the document continues for a preset number of sections, the density area is the entire document. The background area is determined and fixed, and detection of the background in subsequent sections is stopped, so that the background area determination process does not have to be performed on the entire document.

  FIG. 10 is a diagram for explaining the background area determination process.

  In FIG. 10, the histogram of a certain section of the document is as shown in FIG. 10. In this histogram, the density region first having the maximum frequency and exceeding the first value by the search from the low density region to the high density region. That is, it is assumed that the density region (3) is determined as the background region.

  And when the same density area (3) is determined as a background area in a continuous section from this section, the number of continuous sections is counted, and when this count value reaches a preset number, The background area of the entire document is determined and fixed, and the background detection in the subsequent sections is stopped. In addition, in FIG. 10, the several dotted line described in the part beyond the 1st value of the density | concentration area | region (3) shows the frequency of each density | concentration area | region (3) determined as a background area | region by a continuous division.

  However, if there is a section below the first value in the middle of the determination (indicated by a dotted line below the first value of the density region (3)), it is assumed that the continuous count has stopped at that time, and the count value is clear.

  Further, in the background area determination process of the present invention, when the number of sections that do not exceed the first value in all density areas continues for a preset number of sections, it is determined that the document is a pattern document and is currently determined. The background area is fixed as the background area of the entire document, and detection of the background in subsequent sections is stopped.

  FIG. 11 is a diagram for explaining the background area determination process.

  In FIG. 11, the histogram of a certain section of the document is as shown in FIG. 11, and in this histogram, it is determined by searching from the low density area to the high density area that all density areas do not exceed the first value. To do. If the state continues for a preset number of sections, the number of sections is counted, and when the count value reaches a preset number, it is determined that the document is a picture document and is currently determined. The background area, that is, the density area determined as the background area in the previous section is fixed as the background area of the entire document, and detection of the background in the subsequent sections is stopped.

  In FIG. 11, the density region (3) indicates the density region determined as the background region in the previous section, and a plurality of dotted lines exceeding the second threshold value of the density region (3) and the second region A dotted line below the threshold value indicates the frequency of the density region (3) when it is determined that the first threshold value is not exceeded in all density regions.

  However, when the frequency of the density region (3) exceeds the first value during the determination (indicated by a dotted line exceeding the first value of the density region (3)), the continuous count is interrupted at that time. As a thing, the count value is cleared.

  Further, in the background area determination processing of the present invention, when the density area determined as the background area in the histogram of the immediately preceding section is different from the density area determined as the background area in the histogram of the next section, a rapid change in the background area is performed. In order to prevent this, the amount of change in the background area is limited to a predetermined value.

  FIG. 12 is a diagram for explaining the background determination process.

  In FIG. 12, the density area (2) in the histogram of the immediately preceding section exceeds the first value as indicated by the dotted line and is determined as the background area, but in the histogram of the next section, the density area (6) is the first area. It is assumed that a background area exceeding 1 is determined.

  In this case, the change amount of the background region is “6-2 = 4”. Therefore, when the change amount of the background area is limited to, for example, “2”, the density area (6) is originally determined as the background area, but due to this limitation, the density area (4) is determined as the background area. .

  In the present invention, when the background area determined by the histogram of each section is different from the immediately preceding section, the threshold value corresponding to each background area is sequentially changed for each line at the boundary of the section.

  FIG. 13 is a diagram for explaining the process of changing the threshold value.

  In FIG. 13, it is assumed that the threshold value calculated in the immediately preceding section is S1, and the threshold value calculated in the next section is S2. In this case, the threshold value is sequentially changed for each line from S1 to S2 in several lines from the first line of the next section.

  Although the above is an example of typical embodiment of this invention, this invention is not limited to the Example shown in the said Example and drawing, It can implement suitably deform | transforming within the range which does not change the summary. It is.

  The background removal processing can also be performed by processing with a central processing unit based on the background removal program stored in the storage device.

  The background removal program can be provided not only by a communication means such as a network but also by recording it on an external recording medium such as a CD-ROM or DVD.

1 is a diagram illustrating an overall configuration of an embodiment of an image forming apparatus according to the present invention. It is a figure which shows the outline | summary of the background removal process performed in the input gradation correction | amendment part shown in FIG. FIG. 2 is a block diagram illustrating an example of an internal configuration of an input tone correction unit illustrated in FIG. 1. It is a block diagram which shows an example of an internal structure of the histogram production | generation part shown in FIG. It is a block diagram which shows an example of an internal structure of the background correction | amendment part shown in FIG. It is a figure explaining the background removal process for preventing a pseudo contour from generating on an output image. It is a figure explaining the determination process of the background area | region in the background area | region determination part shown in FIG. It is a flowchart which shows the determination process of the background area | region in the background area | region determination part shown in FIG. It is a figure explaining an example of the background area | region determination process in the background area | region determination part shown in FIG. It is a figure explaining the other example of the background area | region determination process in the background area | region determination part shown in FIG. It is a figure explaining the other example of the background area | region determination process in the background area | region determination part shown in FIG. It is a figure explaining the other example of the background area | region determination process in the background area | region determination part shown in FIG. It is a figure explaining an example of the background correction process in the background correction | amendment part shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Document 2 Document stand 3 Light source 4 Reflector 5 Optical system 6 Photoconductor 7 Charger 8 Developer 9 Toner supply device 10 Density sensor 11 Cleaner 12 Intermediate transfer body 13 Paper conveyance path 14 Fixing device 15 Temperature sensor 16 Humidity sensor 20 Image reading unit 21 Photoelectric conversion unit 22 A / D conversion unit 30 Image processing unit 31 Image processing control unit 32 Input gradation correction unit 33 Sharpness correction unit 34 Color conversion unit 35 Output gradation correction unit 36 Halftone processing unit 40 Image Formation unit 41 Image formation control unit 42 Pulse generation unit 43 Laser drive unit 44 Laser light quantity control unit 45 Toner supply control unit 46 Development bias control unit 47 Charge control unit 310 Input tone conversion unit 320 Color space conversion unit 330 Histogram generation unit 331 Addition unit 332 Addition value holding unit 333 Average value calculation unit 334 Histogram frequency addition unit 335 Hist Ram holder 336 timing generating unit 340 background area determining section 350 background correction unit 351 threshold calculation unit 352 background elimination unit

Claims (10)

Histogram creation means for dividing a document into a plurality of sections each having a predetermined number of lines, and creating a histogram having a predetermined density width from image data of each section;
A background area determination means for determining a background area to which the background belongs from the frequency of each density area of the histogram created by the histogram creation means;
Threshold calculation means for calculating a threshold for removing the background from the image data of each section corresponding to the background area determined by the background area determination means;
A background removing device comprising: a background removing means for removing a background portion from image data of each section of the document based on the threshold value calculated by the threshold value calculating means. The background region determination means includes
The frequency of each density region is examined from a predetermined density region on the low density side of the histogram toward the high density side, and a density region where the frequency first reaches a maximum and exceeds a preset first value is defined as the background region. The background removal apparatus according to claim 1 for determination. The background region determination means includes
The background removal apparatus according to claim 2, wherein when the frequency does not exceed the first value in all density areas of the histogram, a density area set in advance is determined as the background area. The background region determination means includes
The frequency of the density area determined to be the background area as exceeding the first value by the histogram of the immediately preceding section created by the histogram creating means is less than the first value and is set to a preset second value. The background removal apparatus according to claim 2, wherein, when the value is larger than the value, the density region is continuously determined as the background region. The background region determination means includes
3. When the density area determined to be the background area continues in a predetermined section, the density area is determined to be the background area of the entire document and fixed, and determination of the background in the subsequent sections is stopped. The background removal apparatus of description. The background region determination means includes
If all the density areas of the histogram created by the histogram creation means have a section that does not exceed the first value for a predetermined interval, it is determined that the original is a pattern original and the current background area is the entire original. The background removal apparatus according to claim 2, wherein the background is fixed as a background area and the determination of the background in subsequent sections is stopped. The background region determination means includes
The background removal device according to claim 1, wherein when the density area determined as the background area by the histogram is different from the immediately preceding section, a change amount of the background area from the immediately preceding section is limited to a predetermined change amount or less. The background removing means
The background removal apparatus according to claim 1, wherein when the background area determined by the calculated histogram is different from the immediately preceding section, the threshold value corresponding to each background area is sequentially changed for each line at the boundary of the section. Computer
A histogram creating means for dividing a document into a plurality of sections each having a predetermined number of lines and creating a histogram having a predetermined density width from image data of each section;
A background area determination means for determining a background area to which the background belongs from the frequency of each density area of the histogram created by the histogram creation means;
Threshold calculation means for calculating a threshold for removing the background from the image data of each section corresponding to the background area determined by the background area determination means;
A background removal program that functions as a background removal means for removing a background portion from image data of each section of the document based on the threshold value calculated by the threshold value calculation means. An image forming apparatus that forms an image of a document based on image data obtained by removing the background from the image data of the document using a background removal device,
The background removing device is
Histogram creation means for dividing a document into a plurality of sections each having a predetermined number of lines, and creating a histogram having a predetermined density width from image data of each section;
A background area determination means for determining a background area to which the background belongs from the frequency of each density area of the histogram created by the histogram creation means;
Threshold calculation means for calculating a threshold for removing the background from the image data of each section corresponding to the background area determined by the background area determination means;
An image forming apparatus comprising: a background removing unit that removes a background portion from the image data of each section of the document based on the threshold value calculated by the threshold value calculating unit.

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