JP6350877B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus.

  Generation copy often causes image quality deterioration such as density change, color turbidity, and gradation skip.

  An image forming apparatus (hereinafter, referred to as a first apparatus) has a plurality of pixels in which the color of each pixel of the image data is determined in accordance with the background color of the image represented by the image data in order to suppress image quality deterioration in the generation copy. Convert to one of the representative colors (that is, perform the limited color processing), and then convert each of the representative colors used in the limited color processing to a color corresponding to the color of the paper on which the image is formed Processing is performed (see, for example, Patent Document 1).

  Another image forming apparatus (hereinafter referred to as a second apparatus) converts input image data obtained by image reading from RGB data to CMY data, calculates an average value for each CMY color for each block, In the case of a generation copy, for each CMY color, the difference between the average value of the input image data in that block and the average value of the original document in that block is calculated for each block, and it is determined that the difference is greater than the threshold value. In this case, the correction value is calculated so that the mean square of each of the corrected CMY values and the average value of the original document is minimized, and correction processing is performed on the input image data based on the correction value (for example, Patent Document 2). reference).

JP 2006-094039 A JP 2007-194850 A

  However, in the limiting process in the first apparatus described above, in the case of a printer output product printed by a screen or error diffusion, a pixel area printed with halftone dots and a pixel area not printed with halftone dots May not be determined to belong to the same color range. For this reason, the color of an object that is recognized as a uniform color by the user's naked eye in the original document may not be converted to the same representative color in the printed matter by generation copy, and color unevenness and gradation skip are recognized. There is. Further, when the original is a copy output product, such a color shift at the time of representative color conversion becomes significant, and gradation skipping at the time of generation copying is more likely to occur.

  In the case of the second apparatus described above, the difference between the average values of the color values is calculated for each block, so that correction processing according to the types of various pixel areas is not performed. Since the same processing is executed for both a manuscript with many character objects and an intermediate manuscript, there is a possibility that appropriate correction according to the object type may not be performed for each object in the manuscript. Further, for each color of CMY of the original document, it is necessary to specify and hold an average value for each block in advance. However, depending on the format of the image data of the original document, an area for storing such data may not be secured. There is also sex. Furthermore, it is difficult to eliminate color misregistration at pixel level fineness when printed by a halftone screen, error diffusion, or the like.

  The present invention has been made in view of the above problems, and an object of the present invention is to obtain an image forming apparatus that forms an image while reducing image quality deterioration during generation copying.

An image forming apparatus according to the present invention performs an unsharp process on a non-character object and a region separation unit that identifies a non-character object in the input image based on image data of the input image in a generation copy job. A filter processing unit, an average color value specifying unit for specifying an average color value of the non-character object after the unsharp processing, and a color range from the average color value to a predetermined color range among pixel color values in the non-character object A color conversion unit that converts the color value into a single color value corresponding to the average color value.

  According to the present invention, image formation is performed while reducing image quality degradation during generation copying.

  These and other objects, features and advantages of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings.

FIG. 1 is a block diagram showing a configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a flowchart for explaining color conversion in the image forming apparatus shown in FIG. FIG. 3 is a diagram illustrating an example of an input image including a non-character object. FIG. 4 is a diagram showing a non-character object extracted from the input image shown in FIG. FIG. 5 is a flowchart for explaining correction of color conversion data for generation copy in the second embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

Embodiment 1 FIG.

  FIG. 1 is a block diagram showing a configuration of an image forming apparatus according to an embodiment of the present invention. An image forming apparatus 1 shown in FIG. 1 is a copying machine. However, the image forming apparatus 1 may be a multifunction machine.

  The image forming apparatus 1 includes a printing device 11, an image reading device 12, an image processing device 13, and a storage device 14.

  The printing apparatus 11 is an example of an output device, and an original image is electrophotographic using CMYK (cyan, magenta, yellow, black) toner based on image data after color conversion by the image processing apparatus 13. An internal device that prints in the process.

  The image reading device 12 is an internal device that optically reads a document image from a document and generates image data of the document image as RGB data.

  The image processing device 13 performs image processing such as color conversion on the image data generated by the image reading device 12 or the like.

  The storage device 14 is a rewritable nonvolatile storage device such as a flash memory, and stores various data.

  The image processing apparatus 13 is realized by an ASIC (Application Specific Integrated Circuit) or a microcomputer, and includes a control unit 21, a region separation unit 22, a filter processing unit 23, an average color value identification unit 24, and a color conversion unit 25. Further, the storage device 14 stores color conversion data 31. The color conversion data 31 includes a color conversion table (lookup table) corresponding to a plurality of color conversion characteristics. The color conversion table (lookup table) converts RGB data into CMY data.

  The control unit 21 controls the printing device 11 and the image reading device 12 to acquire image data of the input image, and causes the image processing device 13 to print the input image after the image processing.

  The region separation unit 22 specifies character objects and non-character objects in the input image based on the image data of the input image. Here, the input image is a document image read by the image reading device 12.

  For example, the region separation unit 22 extracts an edge in the input image, identifies a pixel region surrounded by the edge as an object, classifies an object having an area of the pixel region equal to or less than a predetermined value as a character object, An object whose pixel area is larger than a predetermined value is classified as a non-character object. In addition, the region separation unit 22 extracts, as a non-character object, a chromatic color or an achromatic pixel region having a larger area than a predetermined value and having an area larger than a predetermined value.

  When a document image including a single color and a solid (solid) region (graph, table, etc.) is printed, such a region becomes a halftone dot region by halftoning processing. Since such an area is detected as a non-character object, the non-character object of the copy print or the print print includes a halftone dot area. Therefore, in the case of generation copy, the non-character object includes a halftone dot area.

  The filter processing unit 23 performs unsharp processing on the specified non-character object with a predetermined filter.

  The filter size (number of pixels in the main scanning direction and sub-scanning direction) of this filter is set corresponding to the number of halftone screen lines or halftone dot density used for the input image. That is, the filter size is determined so that the halftone dot pattern is leveled by the unsharp process to obtain a substantially uniform density distribution. The filter processing unit 23 specifies a halftone screen line number or halftone dot density from the input image, and converts the filter having a filter size corresponding to the specified halftone screen line number or halftone dot density to the above-described unsharpness. You may make it use for a process.

  The average color value specifying unit 24 specifies the average color value (in this case, the RGB value) of the non-character object after the unsharp process.

  The color conversion unit 25 converts the RGB data into CMY data for each pixel of the input image using the color conversion data.

  The color conversion unit 25 uses color conversion data for normal copying during normal copying, and uses color conversion data for generation copying during generation copying. The color conversion data for generation copy performs color conversion for a predetermined basic color using a color near the basic color as a basic color. By doing so, the basic color deteriorated due to the generation copy is recovered.

  The color conversion data for generation copy includes color conversion data for character objects and color conversion data for non-character objects. Color conversion data for character objects is used for color conversion of character objects. Color conversion data for non-character objects is used for color conversion of non-character objects. Since the emphasis filter is applied to the character object, color conversion data that compensates for a hue shift caused by the emphasis filter is used.

  The color conversion unit 25 converts a color value (in this case, an RGB value) within a predetermined color range from the specified average color value to a single color corresponding to the average color value among the color values of the pixels in the non-character object. It converts to a value (here, CMY value).

  Next, color conversion in the image forming apparatus will be described. FIG. 2 is a flowchart for explaining color conversion in the image forming apparatus shown in FIG.

  First, the control unit 21 controls the image reading device 12 to acquire a document image read from a document as an input image. Here, the input image is an image of RGB color data.

  Next, the control unit 21 determines whether the current copy job or print job is a generation copy based on, for example, a user operation on an operation unit (not shown) (step S1).

  If it is determined that the current copy is a generation copy, the control unit 21 causes the region separation unit 22, the filter processing unit 23, the average color value specifying unit 24, and the color conversion unit 25 to perform the following processing (steps S2 to S10). Is executed.

  On the other hand, when it is determined that the current copy is not a generation copy, that is, a normal copy, the control unit 21 causes the color conversion unit 25 to perform color conversion during normal copy on the input image (step S11). . In this case, the color conversion unit 25 performs color conversion of the input image using a normal copy lookup table.

  If it is determined that the current copy is a generation copy, first, the region separation unit 22 extracts character objects and non-character objects in the input image (step S2).

  FIG. 3 is a diagram illustrating an example of an input image including a non-character object. FIG. 4 is a diagram showing a non-character object extracted from the input image shown in FIG. For example, the input image 101 shown in FIG. 3 includes a table and a graph, and a non-character object is detected as shown in FIG. Characters are not detected as non-character objects because of their small area. In addition, even if it is surrounded by the edge, if the inner color is the same as the paper color (background color), it is not detected as a non-character object but as a ruled line.

  Next, the control unit 21 sequentially selects a target object to be color-converted from the extracted character object and non-character object (step S3).

  The control unit 21 determines whether or not the object of interest is a character object (step S4).

  When it is determined that the object of interest is not a character object (that is, a non-character object), the control unit 21 performs the following processing (step S5) on the filter processing unit 23, the average color value specifying unit 24, and the color conversion unit 25. To S8).

  On the other hand, when determining that the target object is a character object, the control unit 21 causes the color conversion unit 25 to perform color conversion of the target object (step S9). In this case, the color conversion unit 25 performs color conversion of the target object using the lookup table for the character object among the lookup tables for generation copy.

  If the target object is a non-character object, first, the filter processing unit 23 performs unsharp processing on the target object (step S5).

  Next, the average color value specifying unit 24 specifies the average color value of the non-character object after the unsharp process (step S6). Here, the average color value of each color component of RGB is calculated based on the RGB data of the pixels in the non-character object.

  For example, as shown in FIG. 3, when the non-character object has a contour line of a color (for example, black) different from the inner region, the average color value of the inner region of the contour line is not included and the ruled line To do.

  Then, for each pixel in the object of interest, the color conversion unit 25, when the color value after unsharp processing of the pixel is a color value within a predetermined color range from the specified average color value, Is converted into a single color value corresponding to the average color value (step S7). In this case, the color conversion unit 25 performs color conversion of the object of interest using a lookup table for non-character objects in the generation copy lookup table.

  For example, the “color range” is a range in which a value of a predetermined color difference expression indicating a color difference from the average color value is equal to or less than a predetermined value.

  In addition, for each pixel in the object of interest, the color conversion unit 25 unsharps the color value after unsharp processing of the pixel that is outside the predetermined color range from the specified average color value. The color value of the pixel in the later or original input image is converted into a color value corresponding to the color value using a lookup table (step S8). In this case, the color conversion unit 25 performs color conversion of the object of interest using a lookup table for non-character objects in the generation copy lookup table.

  Then, after the color conversion of the object of interest is completed, the control unit 21 determines whether or not the color conversion of all the extracted objects has been completed (step S10). Returning to FIG. 2, the unprocessed object is selected as the next target object, and the color conversion process for the selected target object is executed in the same manner. On the other hand, when the color conversion of all the extracted objects is completed, the control unit 21 ends the color conversion process for the objects in the input image. It should be noted that color conversion may be performed on portions other than the above-described objects (photographs, ruled lines, backgrounds, and the like) in the same manner as normal color conversion (step S11).

  In addition, after color conversion to CMY data is performed in this way, black generation and UCR (Under Color Removal) processing are performed to generate CMYK data. Necessary for each color component of CMYK data. Accordingly, after the halftone processing or the like is executed, printing by the printing apparatus 11 is executed.

  As described above, according to the first embodiment, the region separation unit 22 identifies the non-character object in the input image based on the image data of the input image. The filter processing unit 23 performs unsharp processing on the non-character object, and the average color value specifying unit 24 specifies the average color value of the non-character object after the unsharp processing. The color conversion unit 25 converts a color value within a predetermined color range from the average color value to a single color value corresponding to the average color value among the color values of the pixels in the non-character object.

  As a result, the density change caused by the generation copy is compensated, so that image formation (printing or the like) can be performed while reducing the image quality deterioration during the generation copy.

  In other words, the dot density, jaggy, density fluctuation, etc. caused by halftone screen, error diffusion, etc., which are generated when a printed material containing uniform single color patches is generated, are reduced, and the overall density of the image is also reduced. Distribution can be maintained and color reproducibility is improved.

Embodiment 2. FIG.

  In the second embodiment, the color conversion unit 25 corrects the color conversion data (lookup table) for generation copy based on the input image, and uses the corrected color conversion data (lookup table) to perform color conversion. Perform conversion.

  Specifically, the color conversion unit 25 extracts a color within a predetermined color range from a predetermined basic color (red, green, blue, cyan, magenta, yellow, black, white, etc.) in the input image. For example, the color conversion unit 25 extracts a color within a predetermined hue range from a predetermined basic color. Alternatively, for example, the color conversion unit 25 extracts a color within a predetermined color difference range based on a predetermined color difference formula from a predetermined basic color.

  Then, the color conversion unit 25 specifies the maximum density and the minimum density of the extracted color, and when the maximum density is larger than a predetermined first threshold, the color of the maximum density among the extracted colors is the basic color. The color conversion data is corrected so that it is converted to the upper limit density (maximum value on the color value) and the density range of the basic color is expanded.

  In addition, when the minimum density is larger than the predetermined second threshold, the color conversion unit 25 selects a color having a density between the minimum density and the second threshold among the extracted colors that has a predetermined printable lower limit density. The color conversion data is corrected so that the density range of the basic color is expanded.

  Note that, in the image forming apparatus according to the second embodiment, the configuration other than the color conversion unit 25 is the same as that of the first embodiment, and a description thereof will be omitted.

  Here, details of correction of color conversion data for generation copy will be described. FIG. 5 is a flowchart for explaining correction of color conversion data for generation copy in the second embodiment.

  The color conversion unit 25 selects a basic color of interest from predetermined basic colors (step S21).

  Next, the color conversion unit 25 extracts a color within a specific color range from the selected target basic color from the input image, for example, converts the extracted color to gray scale, and generates a density histogram. Then, the color conversion unit 25 specifies the maximum value (that is, the maximum density) and the minimum value (that is, the minimum density) in the density histogram (step S22).

  The color conversion unit 25 determines whether or not the specified maximum density is greater than a predetermined first threshold (step S23). If the specified maximum density is greater than the predetermined first threshold, the color of the maximum density is focused. In the color conversion data, the color-converted value of the color is replaced with the data maximum value so that the data is converted into the maximum data value of the basic color (step S24).

  For example, when the color value (8-bit color) of the non-character object 111 in FIG. 3 is R = 240, G = 5, B = 250, and has the maximum density within the specific color range of the basic color red, the maximum The color-converted value corresponding to the density color is replaced with C = 0, M = 255, Y = 255 (that is, the CMY value corresponding to R = 255, G = 0, B = 0).

  In addition, the color conversion unit 25 converts the value after color conversion of the color into the paper color so that the specified minimum density color is converted into a predetermined paper color (background color such as white). (Step S25).

  Further, the color conversion unit 25 determines whether or not the specified minimum density is greater than a predetermined second threshold (step S26). If the specified minimum density is greater than the predetermined second threshold, In the color conversion data, a color having a density between the minimum density and the second threshold is converted so that a color having a density between the minimum density and the second threshold is converted into a color having a predetermined printable lower limit density. The value after color conversion is replaced with the predetermined color (step S27). This “printable lower limit density color” is preset for each basic color.

  For example, when the color value (8-bit color) of the non-character object 112 in FIG. 3 is R = 250, G = 230, B = 195 and has the minimum density within the specific color range of the basic color red, the minimum density The color-converted value corresponding to the color having the density from to the second threshold value is replaced with a predetermined color (R = 255, G = 220, B = 160) set for the basic color red.

  Then, the color conversion unit 25 determines whether or not the above-described processing has been executed for all the basic colors (step S28). If there is an unprocessed basic color, the process returns to step S21, and the unprocessed Is selected as the next target basic color, and the same processing is performed on the next target basic color. On the other hand, when the above-described processing is executed for all the basic colors, the color conversion unit 25 ends the correction of the color conversion data.

  As described above, according to the second embodiment, the color conversion data for generation copy is appropriately corrected according to the input image and used for color conversion of the input image. The concentration change is compensated more appropriately.

  Various changes and modifications to the above-described embodiment will be apparent to those skilled in the art. Such changes and modifications may be made without departing from the spirit and scope of the subject matter and without diminishing its intended advantages. That is, such changes and modifications are intended to be included within the scope of the claims.

  The present invention can be applied to an image forming apparatus such as a multifunction peripheral or a copier.

22 Region Separation Unit 23 Filter Processing Unit 24 Average Color Value Identification Unit 25 Color Conversion Unit

Claims (2)

An area separation unit for identifying a non-character object in the input image based on the image data of the input image in the generation copy job ;
A filter processing unit that performs unsharp processing on the non-character object;
An average color value specifying unit for specifying an average color value of the non-character object after the unsharp processing;
Among the color values of pixels in the non-character object, a color conversion unit that converts a color value within a predetermined color range from the average color value to a single color value corresponding to the average color value;
An image forming apparatus comprising: The non-character objects, an image forming apparatus according to claim 1 Symbol mounting, characterized in that it comprises a halftone dot region.