JP4155290B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image processing apparatus that corrects each pixel value of image data composed of a plurality of pixels, and an image forming apparatus including the image processing apparatus.

An image processing apparatus that includes a scanner and corrects each pixel value of image data composed of a plurality of pixels (for example, performs gamma correction) sets a corrected pixel value for each pixel value before correction. Each pixel value of the image data is corrected according to the corrected data. Here, a case where the correction is gamma correction will be described. In a conventional image processing apparatus that performs gamma correction, gamma correction data generated based on the characteristics of the apparatus in advance is stored in all apparatuses of the same model. In some cases, the accuracy of gamma correction is not sufficient due to mounting errors of lenses. For this reason, Patent Document 1 discloses an image processing apparatus that generates gamma correction data suitable for the apparatus and gamma-corrects each pixel value of the image data according to the generated gamma correction data. The gamma correction data is stored in a nonvolatile storage device such as an EEPROM (Electrically Erasable and Programmable ROM) so that it will not be erased even if the power supply of the device is turned off, and read from the nonvolatile storage device. Used for gamma correction. Thus, by performing gamma correction using the gamma correction data generated for each image processing apparatus, the accuracy of gamma correction can be improved.
JP-A-6-22140

  However, if correction data in which pixel values after correction are set for each pixel value before correction, such as gamma correction data, is stored in a non-volatile storage device such as an EEPROM so that it is not erased even when the power of the device is turned off. However, there is a problem that the storage capacity of the nonvolatile storage device becomes large.

  The RGB color system color image data read by the scanner is subjected to corrections such as gamma correction, and then, for example, printing on paper or the like, depending on the intended use of the color image data, Lab color system, YCrCb The color space is converted to a color system or the like. Therefore, in consideration of color reproducibility of color image data after color space conversion, it is preferable to perform correction using correction data suitable for each color system, but the RGB color system, Lab color system, and YCrCb table. When correction data suitable for each color system such as a color system is stored in the nonvolatile storage device, there is a problem that the storage capacity of the nonvolatile storage device further increases.

  The present invention has been made in view of the above problems, and an image processing apparatus and an image forming apparatus that correct each pixel value of image data composed of a plurality of pixels according to correction data. An object of the present invention is to provide an image processing apparatus and an image forming apparatus capable of reducing the storage capacity.

The image forming apparatus according to claim 1 includes a nonvolatile storage device and a volatile storage device, and each pixel value of image data composed of a plurality of pixels is corrected for each pixel value before correction. An image processing apparatus that performs correction according to correction data for which a value has been set, wherein the first predetermined number of reference values of the pixel value and a corrected value of the first predetermined number of reference values are defined respectively. A first storage means for storing the predetermined number of target values in association with each other in the nonvolatile storage device, a first predetermined number of reference values and a first predetermined value stored in the first storage means Generating means for generating correction data defining a corrected value for each second predetermined number of pixel values larger than the first predetermined number that can be taken by the pixels constituting the image data, based on the target value of the number; The second case storing the correction data generated by the generating means. Comprising means, an image processing apparatus and a correcting means for correcting each pixel value of the image data according to the correction data stored in said second storage means, a scanner, a printer, a copier, and a facsimile of at least 2 An image forming apparatus having the above functions, wherein a receiving unit that accepts one of the plurality of functions from the outside, and a color system of image data based on the function that has received the selection by the receiving unit Selecting means, and the generating means generates correction data suitable for a plurality of color systems for each color system and stores them in the second storage means, respectively, characterized in that corrects each pixel value of the image data of the correction data stored in said second storing means, according to the correction data suitable for the color system selected by said selection means It is.

According to the above configuration, correction data suitable for a plurality of color systems is generated for each color system by the generation unit and stored in the second storage unit. Then, each pixel of the image data according to the correction data suitable for the color system selected by the selection unit based on the function of the selection received from the correction data stored in the second storage unit by the correction unit The value is corrected.

Therefore, the image data is color space converted into various color systems based on the function, but is corrected according to the correction data suitable for the color system selected based on the function for which the selection is accepted. Good color reproducibility after conversion. Further, since correction data suitable for a plurality of color systems is generated for each color system, the amount of data increases, but correction data suitable for a plurality of color systems is stored in the second storage means. Therefore, there is no need to increase the storage capacity of the nonvolatile storage device.

The image forming apparatus according to claim 2, wherein, in the image forming apparatus according to claim 1, wherein, when the power supply of the own device is turned on, and outputs the information for instructing the generation of the correction data to said generating means Instructing means, and the generating means generates the correction data when information indicating the generation of correction data is received from the instructing means, and the second storing means is provided by the generating means. The generated correction data is stored in the volatile storage device.

  According to the above configuration, when the image processing apparatus is turned on, the instruction unit outputs information indicating that the generation unit is instructed to generate correction data. Then, when information indicating the generation of correction data is received from the instruction unit, the generation unit generates correction data, and the generated correction data is stored in the second storage unit.

  Accordingly, the correction data is deleted when the image processing apparatus is turned off. However, since the correction data is generated when the image processing apparatus is turned on, the image processing apparatus is turned on. The correction data can be held while the image is being displayed.

According to a third aspect of the present invention, there is provided the image forming apparatus according to the first or second aspect, further comprising reading means for reading an image of a document and generating image data, wherein the first predetermined number of reference values is The reading means is obtained by reading a first predetermined number of reference images having different gradations formed on the original, and the correction means calculates each pixel value of the image data generated by the reading means. It is characterized by correction.

According to the above configuration, the first storage unit stores the first predetermined number of reference values obtained by reading the first predetermined number of reference images by the reading unit, and the first predetermined number of reference values. A first predetermined number of target values each defining a corrected value are stored in association with each other, and a first predetermined number of reference values stored in the first storage means by the generating means; The correction data is generated based on the first predetermined number of target values. The generated correction data is stored in the second storage means, and each pixel value of the image data generated by the reading means is corrected by the correction means according to the correction data stored in the second storage means. Is done.

Therefore, it is generated based on the first predetermined number of reference values obtained by reading the first predetermined number (for example, 13) of reference images by the reading means, and the first predetermined number of target values corresponding thereto. According to the corrected data, each pixel value of the image data generated by the reading unit is corrected, so that correction according to the characteristics of the reading unit can be performed. That is, accurate correction can be performed regardless of machine differences.

5. The image forming apparatus according to claim 4, wherein the image forming apparatus has at least two functions of a scanner, a printer, a copy, and a facsimile, and includes a non-volatile storage device and a volatile storage device, and a plurality of pixels. An image processing apparatus that corrects each pixel value of image data configured according to correction data in which a pixel value after correction is set for each pixel value before correction, and a first predetermined number of the pixel values A first storage means for associating a reference value with a first predetermined number of target values each defining a corrected value of the first predetermined number of reference values, and storing them in the nonvolatile storage device; Based on the first predetermined number of reference values and the first predetermined number of target values stored in the first storage means, the second larger than the first predetermined number that can be taken by the pixels constituting the image data. Value after correction for every predetermined number of pixel values A generation unit that generates correction data to be defined, a second storage unit that stores the correction data generated by the generation unit, and each pixel value of the image data according to the correction data stored in the second storage unit A correction unit that corrects the image, a reading unit that reads an image of a document and generates image data, a reception unit that receives an external selection of any one of the plurality of functions, and A selection unit that selects a color system of image data based on a function that has been selected by the reception unit, and when the color system selected by the selection unit is different from the previously selected color system, the reading unit And an instruction unit that outputs information indicating that the generation unit generates correction data when an image of a document is read, and the first predetermined number of reference values is: The reading means obtains a first predetermined number of reference images having different gradations formed on the original, and the generation means instructs the generation of correction data from the instruction means. When the information is received, the correction data suitable for the color system selected by the selection unit is generated, the generated correction data is overwritten on the correction data stored in the second storage unit, The correcting means corrects each pixel value of the image data generated by the reading means.

According to the above configuration, in the first storage means, the reading means first and a predetermined number of reference values obtained by reading a first predetermined number of the reference image, these first predetermined number of reference value The first predetermined number of target values that define the corrected values are stored in association with each other, and when the color system selected by the selection unit is different from the color system selected last time, the reading unit When the image of the original is read by this, the instruction means outputs information for instructing the generation means to generate correction data. Then, when the information for instructing the generation of correction data is received from the instruction unit, the generation unit generates correction data suitable for the color system selected by the selection unit, and the generated correction data is The correction data stored in the second storage means is overwritten. Then, each pixel value of the image data generated by the reading unit is corrected by the correction unit according to the correction data stored in the second storage unit.

Therefore, it is not necessary to store correction data suitable for each color system in which image data is subjected to color space conversion in the second storage means, so that the storage capacity of the second storage means can be reduced. Further, the first predetermined number of reference values obtained by reading a first predetermined number (for example, 13) of reference images by the reading unit, and a first predetermined number of target values corresponding thereto are generated. According to the corrected data, each pixel value of the image data generated by the reading unit is corrected, so that correction according to the characteristics of the reading unit can be performed. That is, accurate correction can be performed regardless of machine differences.

According to the image forming apparatus of the first aspect, it is possible to perform correction according to the characteristics of the reading unit. That is, accurate correction can be performed regardless of machine differences.

According to the image forming apparatus of the second aspect, for example, when the second storage unit is a volatile storage device, the correction data is erased when the power of the image processing apparatus is turned off. Since correction data is generated when the apparatus is turned on, the correction data can be held while the image processing apparatus is turned on.

According to the image forming apparatus of claim 3, since the image data is corrected according to the correction data suitable for the color system selected based on the function of accepting the selection, the color reproduction of the image data after the color space conversion is performed. Good properties. Further, since correction data suitable for a plurality of color systems is generated for each color system, the amount of data increases, but correction data suitable for a plurality of color systems is stored in the second storage means. Therefore, there is no need to increase the storage capacity of the nonvolatile storage device.

According to the image forming apparatus of the fourth aspect, it is not necessary to store correction data suitable for each color system in which the image data is color space converted in the second storage unit. The storage capacity can be reduced. Further, correction according to the characteristics of the reading means can be performed. That is, accurate correction can be performed regardless of machine differences.

  Embodiments according to the present invention will be described below with reference to the drawings. In this embodiment, a case where the image processing apparatus of the present invention is applied to an image forming apparatus having a scanner function, a printer function, a copy function, and a facsimile function will be described. FIG. 1 is a block diagram illustrating an example of an image forming apparatus 1 according to the present embodiment. As shown in the figure, an image forming apparatus 1 includes a control unit (MPU: Microprocessing Unit) 2, a ROM (Read Only Memory) 3, a RAM (Random Access Memory) 4, a CCD (Charge Coupled Device) 5, an AFE (Analog Front End). 6) A / D converter 7, scanner image processing circuit 8, page memory 9, scanner codec 10, printer codec 11, printer image processing circuit 12, printer 13, communication codec 14, modem 15, NCU (Network Control Unit) 16 , An I / F (Interface) unit 17, an operation panel 18, and an EEPROM 19. The image processing apparatus of the present invention provided in the image forming apparatus 1 includes a control unit 2, a ROM 3, a RAM 4, an AFE 6, an A / D converter 7, a scanner image processing circuit 8, a page memory 9, a scanner codec 10, a printer codec 11, and a printer. The image processing circuit 12, the communication codec 14, and the EEPROM 19 are included. In the present embodiment, each pixel value of image data composed of a plurality of pixels is gamma-corrected according to gamma correction data in which a pixel value after gamma correction is set for each pixel value before gamma correction. explain.

  The control unit 2 controls each part of the image forming apparatus 1 according to a control program stored in the ROM 3 and functions as an averaging processing unit 24 (see FIG. 4) described later. The RAM 4 is a volatile storage device in which stored contents are erased when power supply is stopped, that is, when the power of the image forming apparatus 1 is turned off. The RAM 4 includes a work memory area 20 (corresponding to a second storage unit) that functions as a work area of the control unit 2 and a code memory area 21 that stores encoded image data. The work memory area 20 stores gamma correction data.

  The CCD 5 (corresponding to a reading unit) reads an image of a document and generates image data. Here, the color image of the original is read to generate RGB color system analog color image data and output to the AFE 6. The CCD 5 can naturally read a monochrome image of a document, but in the present embodiment, a case where a color image is read will be described. The AFE 6 amplifies the analog color image data output from the CCD 5 and outputs it to the A / D converter 7. The A / D converter 7 performs A / D conversion on the analog color image data output from the AFE 6. Here, the digital color image data subjected to A / D conversion is output to the scanner image processing circuit 8. Note that each pixel value of the digital color image data subjected to A / D conversion is represented by 8 bits, that is, an integer of 0 to 255.

  A scanner image processing circuit 8 (corresponding to a correction unit) performs gamma correction, color space conversion, and the like on RGB color system color image data output from the A / D converter 7. Specifically, each pixel value of the color image data composed of a plurality of pixels output from the A / D converter 7 is gamma-corrected, and the color image data of the RGB color system that has been gamma-corrected is used for the color image data. In accordance with the color space conversion, the data is output to a predetermined output destination. For example, when color image data generated by the CCD 5 is printed on a sheet (copy function), the scanner image processing circuit 8 performs color space conversion of RGB color system color image data to the Lab color system. In this case, gamma correction is performed according to gamma correction data for the Lab color system (suitable for the Lab color system) stored in the work memory area 20. Further, for example, when the color image data generated by the CCD 5 is transmitted by facsimile (facsimile function), the scanner image processing circuit 8 converts the color image data of the RGB color system to the YCrCb color system. In this case, the gamma correction is performed according to gamma correction data for the YCrCb color system (suitable for the YCrCb color system). Further, for example, when color image data generated by the CCD 5 is transmitted to a personal computer (hereinafter referred to as “PC”) 22 (scanner function), the scanner image processing circuit 8 converts RGB color system color image data. Output directly without color space conversion. In this case, the gamma correction is performed according to gamma correction data for the RGB color system (suitable for the RGB color system). The color image data output from the scanner image processing circuit 8 is temporarily stored in the page memory 9.

  The scanner codec 10 reads and encodes the color image data stored in the page memory 9 when printing the color image data on a sheet or facsimile transmission, and the encoded color image data is stored in the code memory area of the RAM 4. 21 is written. Here, the scanner codec 10 encodes color image data by JPEG (Joint Photographic Experts Group).

  The printer codec 11 reads out and decodes the encoded color image data stored in the code memory area 21 when printing the color image data on a sheet, and outputs it to the printer image processing circuit 12. The printer image processing circuit 12 performs color space conversion, binarization processing, and the like on Lab color system color image data. Here, the output color specification represented by, for example, four components of C (cyan), M (magenta), Y (yellow), and K (black) of 1 bit for each component for color image data of the Lab color system. After color space conversion to system color image data, error diffusion processing or the like is performed to binarize and output to the printer 13. The printer 13 prints the color image data output from the printer image processing circuit 12 on paper. As a printing method in the printer 13, for example, an electrophotographic method can be used.

  When the color code data is transmitted by facsimile, the communication codec 14 reads the color image data encoded from the code memory area 21 and decodes it, and encodes the color image data by an encoding method suitable for facsimile transmission. It is. Examples of encoding methods suitable for facsimile transmission include MH (Modified Huffman), MR (Modified Read), and MMR (Modified Modified Read). Note that color image data encoded by the JPEG method may be transmitted by facsimile, but in this case, it is not necessary to perform the decoding and encoding processes as described above.

  The modem 15 is, for example, a ITU-T (International Telecommunication Union Telecommunication Standardization Sector) recommendation V.3. Modulation and demodulation of transmission / reception data according to the 30 standard or the like. The NCU 16 is a line network control device that controls a telephone line to place or disconnect a call, and is connected to the PSTN 23. The control unit 2 can control the modem 15 and the NCU 16 to perform facsimile transmission / reception of color image data.

  The I / F unit 17 is an interface that connects the PC 22 and the image forming apparatus 1 in a communicable manner. Color image data is transmitted from the image forming apparatus 1 to the PC 22 via the I / F unit 17.

  An operation panel 18 (corresponding to a part of the accepting unit) includes an operation unit including a start key for instructing start of reading of a document, a numeric keypad for inputting a facsimile number, the number of copies, and the like, and various setting states. And a liquid crystal display device (LCD: Liquid Crystal Display) that displays the operation state of the image forming apparatus 1 with characters, graphics, and the like, and a display unit that includes an LED lamp that is turned on or off. Note that the liquid crystal display device is a so-called touch panel type, and various operations can be performed by a user touching the screen of the liquid crystal display device with a finger or the like instead of the operation unit. The user uses the operation panel 18 to use color image data generated by the CCD 5, that is, a copy function for printing the color image data generated by the CCD 5 on paper, a facsimile function for facsimile transmission, and a scanner function for transmission to the PC 22. Any one of these can be selected. The gamma correction data setting unit 30 (see FIG. 4) of the control unit 2 receives a function selected by the user from the operation panel 18.

  The EEPROM (corresponding to the first storage means) 19 is a non-volatile storage device in which stored contents are not lost even when there is no power supply, that is, when the power of the image forming apparatus 1 is turned off. The EEPROM 19 stores the first predetermined number of reference values obtained by reading the first predetermined number of reference images with different gradations by the CCD 5 and the gamma-corrected values of the first predetermined number of reference values. A first predetermined number of target values defined respectively are stored in association with each other.

  FIG. 2 is a diagram showing an example of a document T (hereinafter referred to as “test chart”) T on which a first predetermined number of reference images A1 to A13 having different gradations are formed (printed). The reference image A1 is an image (black image) with the darkest gradation, the gradation becomes lighter in the order of the reference image A2, the reference image A3,..., And the reference image A13 is an image with the lightest gradation. (White image). The first predetermined number of reference values are obtained by reading the reference images A1 to A13 with the CCD 5. In the present embodiment, a case where 13 reference images are read by the CCD 5 to obtain 13 reference values, that is, a case where the first predetermined number is “13” will be described. The reference images A1 to A13 are achromatic grayscale images.

  FIG. 3 is a diagram showing a first predetermined number of reference values and a first predetermined number of target values stored in the EEPROM 19. The first predetermined number of reference values and the first predetermined number of target values are stored in the EEPROM 19 for each of the R component, the G component, and the B component. Here, the reference value “19” for the R component is a value obtained by reading the reference image A1 with the CCD 5 and averaging the pixel values constituting the image data of the reference image A1. The target value “0” of the R component is a value generated based on the reference image A1 of the test chart T. The R component reference value “19” obtained by reading the reference image A1 is associated with the R component target value “0” generated based on the reference image A1, and is generated by the CCD 5, for example. When “19” is included in the R component pixel value constituting the color image data, the scanner image processing circuit 8 corrects the pixel value to “0”.

  Incidentally, the reference value and the target value stored in the EEPROM 19 are 13 each, but the pixels constituting the color image data generated by the CCD 5 can take 256 pixel values from 0 to 255. Therefore, a color image is generated based on a first predetermined number of reference values and a first predetermined number of target values stored in the EEPROM 19 by a gamma correction data generation unit 28 (see FIG. 4) of the control unit 2 described later. Gamma correction data defining a value after gamma correction for each second predetermined number of pixel values larger than the first predetermined number that can be taken by the pixels constituting the data is generated. In the present embodiment, when the pixels constituting the color image data can take 256 pixel values (an integer from 0 to 255), that is, the second predetermined number is “256” which is larger than the first predetermined number “13”. Will be described.

  Note that FIG. 3 illustrates target values used when generating gamma correction data for the RGB color system. Further, the target value is generated in advance based on the reference images A1 to A13 of the test chart T and stored in the EEPROM 19, but the reference value is a test chart reading mode for reading the reference images A1 to 13 of the test chart T. When instructed from the operation panel 18, the reference images A 1 to A 13 are read by the CCD 5 and stored in the EEPROM 19.

  Next, a functional configuration of the control unit 2 that generates gamma correction data and the like will be described. The control unit 2 includes an averaging processing unit 24, a determination processing unit 25, an EEPROM management unit 26, a gamma correction data generation instruction output unit 27, a gamma correction data generation unit 28, a work memory area management unit 29, and a gamma correction data setting unit. 30.

  The averaging processing unit 24 configures image data of each reference image when a test chart reading mode is instructed by the user or the like from the operation panel 18 and the reference images A1 to A13 of the test chart T are read by the CCD 5. The pixel values are averaged to calculate a first predetermined number of reference values. As described above, when the test chart reading mode is instructed from the operation panel 18, the image data of the reference images A1 to A13 read by the CCD 5 are subjected to analog amplification by the AFE 6 and A / D conversion by the A / D converter 7. After being performed, it is output to the averaging processing unit 24.

  The determination processing unit 25 determines whether or not the reference images A1 to A13 of the test chart T are normally read by the CCD 5. Specifically, it is determined whether or not the first predetermined number of reference values are in ascending order or descending order. If it is determined that the first predetermined number of reference values are in ascending order or descending order, the CCD 5 uses the reference of the test chart T It is determined that the images A1 to A13 have been read normally. If it is determined that the order is not ascending or descending, it is determined that the reference images A1 to A13 of the test chart T are not normally read.

  The EEPROM management unit 26 writes data to the EEPROM 19 and reads data from the EEPROM 19. Here, the EEPROM management unit 26 writes the first predetermined number of reference values calculated by the averaging processing unit 24 in the EEPROM 19. At this time, as shown in FIG. 3, the EEPROM management unit 26 performs the first operation so that, for example, the reference value obtained by reading the reference image A1 corresponds to the target value generated based on the reference image A1. A predetermined number of reference values are written in the EEPROM 19, and the EEPROM 19 stores the first predetermined number of reference values and the first predetermined number of target values in association with each other. Information indicating that the gamma correction data generation instruction output unit 27 (corresponding to the instruction unit) instructs the gamma correction data generation unit 28 to generate gamma correction data when the image forming apparatus 1 is powered on. (Hereinafter referred to as “generation instruction”).

  The gamma correction data generation unit 28 (corresponding to a part of the generation unit) receives a first gamma correction data generation instruction output from the gamma correction data generation instruction output unit 27 and receives a first predetermined data stored in the EEPROM 19. The gamma correction data is generated based on the reference value of the number and the first predetermined number of target values. In other words, when the gamma correction data generation instruction is received from the gamma correction data generation instruction output unit 27, the gamma correction data generation unit 28 causes the EEPROM management unit 26 to send the first predetermined number of reference values and the first reference value. Information indicating that a predetermined number of target values are to be read (hereinafter referred to as “reading instructions”) is output, and the first predetermined number of reference values and the first predetermined number read by the EEPROM management unit 26. The gamma correction data is generated based on the target value.

  FIG. 5A is a diagram in which the first predetermined number of reference values and the first predetermined number of target values of the R component shown in FIG. 3 are plotted on a graph. The X axis of the graph indicates a reference value, and the Y axis of the graph indicates a target value. Point R0 indicates the origin ((X, Y) = (0, 0)), and points R1 to R13 are based on the reference values obtained by reading the reference images A1 to A13 and the reference images A1 to A13. The target value generated is shown. For example, a point R1 = (X, Y) = (19, 0) indicates a reference value obtained by reading the reference image A1, and a target value generated based on the reference image A1, and the point R2 = ( X, Y) = (26, 40) indicates a reference value obtained by reading the reference image A2, and a target value generated based on the reference image A2. The gamma correction data generation unit 28 acquires a reference value and a target value for interpolating between two adjacent points R0 to R13 shown in FIG. 5A, and generates gamma correction data. For example, when the reference value and target value for interpolating between the points R1 and R2 are acquired, the straight line connecting the points R1 and R2 (see FIG. 5B) is Y = (40-0) / (26-19) * (X-19) = (40/7) * (X-19), but the gamma correction data generation unit 28 sets Y obtained by sequentially substituting an integer from 20 to 26 to X in the above equation. While acquiring as a value, the value substituted for X is acquired as a reference value. That is, when X = 20 is substituted into the above equation, Y = 5.71..., And “20” is acquired as the reference value and “6” is acquired as the target value corresponding to the reference value “20”. When X = 21 is substituted into the above equation, Y = 11.42..., And “21” is acquired as a reference value and “11” is acquired as a target value corresponding to the reference value “21”. And the gamma correction data which matched the acquired reference value and target value are produced | generated.

  As described above, the gamma correction data generation unit 28 acquires the reference value and the target value for interpolating between two adjacent points R0 to R13, and the gamma correction data in which the acquired reference value and the target value are associated with each other. Generate. FIG. 5C shows a part of the gamma correction data generated by the gamma correction data generation unit 28 (from the reference value “19” to the reference value “19” based on the reference value and target value of the R component shown in FIG. 26 "). The scanner image processing circuit 8 corrects each pixel value of the color image data according to such gamma correction data. For example, when the R component pixel constituting the color image data includes a pixel having a pixel value “21”, the pixel value of the pixel is corrected to “11”. Further, for example, when the pixel of the pixel value “25” is included in the R component pixels constituting the color image data, the pixel value of the pixel is corrected to “34”. Here, the case where the gamma correction data (R component) for the RGB color system is generated has been described, but the same applies to the case where the gamma correction data for the YCrCb color system and the Lab color system are generated. The gamma correction data generation unit 28 generates gamma correction data for the RGB color system, the YCrCb color system, and the Lab color system.

  The work memory area management unit 29 (corresponding to a part of the generation unit) writes data into the work memory area 20 and reads data from the work memory area 20. Here, the work memory area management unit 29 writes the gamma correction data for the RGB color system, the YCrCb color system, and the Lab color system generated by the gamma correction data generation unit 28 in the work memory area 20. The work memory area 20 stores gamma correction data for RGB color system, YCrCb color system, and Lab color system, respectively.

  A gamma correction data setting unit 30 (corresponding to a part of the accepting unit and corresponding to the selecting unit) sets gamma correction data in the register 31 of the scanner image processing circuit 8. Specifically, the function selected from the operation panel 18 by the user is received, and the color system of the color image data is selected based on the function that has received the selection. For example, when the scanner function selection is accepted, the RGB color system is selected as the color system for color space conversion of color image data (in this case, color space conversion is not performed), and the facsimile function selection is accepted. In this case, if the YCrCb color system is selected as the color system for color space conversion of the color image data, and the copy function is selected, the Lab color system is used as the color system for color space conversion of the color image data. Select the system. Next, an instruction to read gamma correction data suitable for the selected color system is output to the work memory area management unit 29. That is, when the RGB color system is selected, an instruction to read out gamma correction data for the RGB color system is output, and when the YCrCb color system is selected, an instruction to read out gamma correction data for the YCrCb color system. When the Lab color system is selected, an instruction for reading gamma correction data for the Lab color system is output. Then, the gamma correction data read by the work memory area management unit 29 is set in the register 31 of the scanner image processing circuit 8. The scanner image processing circuit 8 performs gamma correction on each pixel value of the color image data according to the gamma correction data set in the register 31.

  Next, the processing operation of the control unit 2 when the test chart reading mode is designated from the operation panel 18 will be described based on the flowchart shown in FIG. First, the control unit 2 outputs information (reading instruction) to instruct the CCD 5 to read the test chart T (S1). Subsequently, the averaging processing unit 24 averages the pixel values constituting the image data of the respective reference images A1 to A13 of the test chart T read by the CCD 5, and calculates a first predetermined number of reference values (S2). ).

  Next, the determination processing unit 25 determines whether or not the reference images A1 to A13 of the test chart T are normally read by the CCD 5 (S3). If the determination processing unit 25 determines that the test chart T has not been read normally (S3: NO), the process returns to S1 until S1 to S1 until it is determined that the test chart T has been read normally. The process of S3 is repeatedly executed. When the determination processing unit 25 determines that the test chart T has been normally read (S3: YES), the EEPROM management unit 26 uses the first predetermined number of reference values calculated by the averaging processing unit 24 as the EEPROM 19. (S4).

  Next, the processing operation of the control unit 2 when the power of the image forming apparatus 1 is turned on will be described based on the flowchart shown in FIG. First, the gamma correction data generation instruction output unit 27 outputs a gamma correction data generation instruction to the gamma correction data generation unit 28 (S11). The gamma correction data generation unit 28 receives a gamma correction data generation instruction from the gamma correction data generation instruction output unit 27, and sends a first predetermined number of reference values and a first predetermined number to the EEPROM management unit 26. A target value reading instruction is output (S12). The EEPROM management unit 26 receives an instruction to read the first predetermined number of reference values and the first predetermined number of target values, and receives the first predetermined number of reference values and the first predetermined number of target values from the EEPROM 19. Is read (S13). The gamma correction data generation unit 28 generates gamma correction data based on the first predetermined number of reference values and the first predetermined number of target values read by the EEPROM management unit 26 (S14). At this time, the gamma correction data generation unit 28 sequentially generates gamma correction data for the RGB color system, the YCrCb color system, and the Lab color system. The work memory area management unit 29 writes gamma correction data for each color system sequentially generated by the gamma correction data generation unit 28 in the work memory area 20 (S15).

  As described above, the pixels constituting the color image data are determined based on the first predetermined number (13 in the present embodiment) of reference values stored in the EEPROM 19 and the first predetermined number of target values. Gamma correction data that defines a value after gamma correction for each of the second predetermined number (in this embodiment, 256 from 0 to 255) of pixel values that is greater than the first predetermined number is generated and generated Since the gamma correction data is stored in the work memory area 20, the storage capacity of the EEPROM 19 can be reduced.

  Also, when the power of the image forming apparatus 1 is turned off, the gamma correction data stored in the work memory area 20 is erased. However, when the power of the image forming apparatus 1 is turned on, the gamma correction data is deleted. Thus, the gamma correction data can be held while the image forming apparatus 1 is powered on.

  Also, the color image data is color space converted based on the function selected by the user, but is gamma corrected according to the gamma correction data suitable for the color system selected based on the function that received the selection. Good color reproducibility after color space conversion. Further, since gamma correction data suitable for a plurality of color systems is generated for each color system, the amount of data increases, but gamma correction data suitable for a plurality of color systems is stored in the work memory area 20. Therefore, it is not necessary to increase the storage capacity of the EEPROM 19.

  Further, the gamma correction generated based on the first predetermined number of reference values obtained by reading the first predetermined number of reference images A1 to A13 by the CCD 5 and the first predetermined number of target values corresponding thereto. Since each pixel value of the color image data generated by the CCD 5 is gamma-corrected according to the data, gamma correction according to the characteristics of the CCD 5 can be performed. That is, accurate gamma correction can be performed regardless of machine differences.

In addition, this invention can take the following aspects.
(A) In this embodiment, the gamma correction data is generated when the power of the image forming apparatus 1 is turned on. However, when the document reading start command is issued, the gamma correction data is generated. You may make it produce | generate.

  Specifically, as shown in the flowchart of FIG. 8, the gamma correction data generation instruction output unit 27 repeatedly determines whether or not a document reading start command has been issued, for example, by operating the start key of the operation panel 18. (S21). When it is determined by the gamma correction data generation instruction output unit 27 that a document reading start command has been issued (S21: YES), the gamma correction data setting unit 30 is based on the function selected from the operation panel 18 by the user. A color system for color space conversion of color image data is selected (S22). Subsequently, the gamma correction data generation instruction output unit 27 determines whether or not the color system selected by the gamma correction data setting unit 30 is different from the previously selected color system (S23). For example, if the color system selected in S22 is the RGB color system and the color system selected last time is the Lab color system, it is determined that the color system is different from the color system selected last time. If the gamma correction data generation instruction output unit 27 determines that the color system is different from the previously selected color system (S23: YES), the gamma correction data generation instruction output unit 27 outputs a gamma correction data generation instruction to the gamma correction data generation unit 28 (S24). ). The gamma correction data generation unit 28 receives an instruction to generate gamma correction data and outputs an instruction to read out the first predetermined number of reference values and the first predetermined number of target values to the EEPROM management unit 26 ( S25). The EEPROM management unit 26 receives an instruction to read the first predetermined number of reference values and the first predetermined number of target values, and receives the first predetermined number of reference values and the first predetermined number of target values from the EEPROM 19. Is read (S26). The gamma correction data generation unit 28 generates gamma correction data based on the first predetermined number of reference values read by the EEPROM management unit 26 and the first predetermined number of target values (S27). At this time, the gamma correction data generation unit 28 generates gamma correction data suitable for the color system selected by the gamma correction data setting unit 30. The work memory area management unit 29 writes the gamma correction data generated by the gamma correction data generation unit 28 in the work memory area 20 (S28). At this time, if gamma correction data is stored in the work memory area 20, the work memory area management unit 29 adds the gamma correction generated by the gamma correction data generation unit 28 in S27 to the stored gamma correction data. Overwrite the data.

  On the other hand, when the gamma correction data generation instruction output unit 27 determines that the color system selected by the gamma correction data setting unit 30 is the same as the color system selected last time (S23: NO), S25. It waits without performing the process of thru | or S28. Thereafter, the scanner image processing circuit 8 corrects each pixel value of the color image data of the original read by the CCD 5 in accordance with the gamma correction data stored in the work memory area 20.

  As described above, when the gamma correction data generation instruction output unit 27 determines that the color system selected by the gamma correction data setting unit 30 is different from the color system selected last time, the gamma correction data generation instruction output unit 27 notifies the gamma correction data generation unit 28. On the other hand, an instruction to generate gamma correction data is output. The gamma correction data generation unit 28 generates gamma correction data suitable for the color system selected by the gamma correction data setting unit 30 when a gamma correction data generation instruction is received. The work memory area manager 29 overwrites the gamma correction data generated by the gamma correction data generator 28 on the gamma correction data stored in the work memory area 20. Then, the scanner image processing circuit 8 performs gamma correction on each pixel value of the color image data generated by the CCD 5 in accordance with the gamma correction data stored in the work memory area 20. Therefore, since it is not necessary to store gamma correction data suitable for each color system in which color image data is color space converted in the work memory area 20, the storage capacity of the work memory area 20 can be reduced.

  (B) In the present embodiment, the case where the EEPROM 19 is used as the nonvolatile storage device has been described. However, the present invention is not limited to this. For example, a hard disk may be used.

  (C) In this embodiment, when the image forming apparatus 1 is turned on, the gamma correction data is generated. However, the main board (see FIG. 1) on which the RAM 4 is mounted is new. Gamma correction data may be generated when the main board is replaced.

  (D) In this embodiment, as shown in FIGS. 5A and 5B, a reference value and a target value for linear interpolation between two adjacent points R0 to R13 are acquired, and gamma is obtained. The correction data is generated. However, the present invention is not limited to this. For example, reference values and target values for polynomial interpolation and spline interpolation between points R0 to R13 are acquired, and gamma correction data is generated. Also good.

  (E) In the present embodiment, when the first predetermined number is “13” (generated based on 13 reference values obtained by reading 13 reference images and 13 reference images). However, the present invention is not limited to this, and the first predetermined number may be a number equal to or greater than “2”. For example, 15 gamma correction data is generated based on 13 target values. The gamma correction data may be generated based on the 15 reference values obtained by reading the reference images and the 15 reference images generated based on the 15 reference images.

  (F) In this embodiment, when the color image data generated by the CCD 5 can take 256 pixel values from 0 to 255, that is, as a reading unit, a CCD that outputs a pixel value from 0 to 255 is used. However, the present invention is not limited to this. For example, a high-performance CCD that outputs pixel values of 0 to 512 may be used. In this case, the second predetermined number is “512”, unlike “256” in the present embodiment.

  (G) In the present embodiment, the case where each pixel value of the color image data generated by the CCD 5 is gamma-corrected has been described. However, the monochrome image is read by the CCD 5 and each pixel value of the generated monochrome image data is converted to gamma. It is also possible to correct. In this case, gamma correction data for gray scale is generated, and each pixel value of the monochrome image data is gamma corrected in accordance with the gamma correction data for gray scale.

  (H) In the present embodiment, the case where the image processing apparatus of the present invention is applied to an image forming apparatus having a copy function, a facsimile function, and a scanner function has been described. However, an image processing apparatus that performs gamma correction is provided. The device is not limited to this as long as it is a device.

  (I) In this embodiment, a case has been described in which each pixel value of image data composed of a plurality of pixels is gamma-corrected according to gamma correction data. However, a pixel value after correction is set for each pixel value before correction. The correction is not limited to the gamma correction as long as the correction is performed according to the correction data (correction using a table in which the pixel values before correction and the pixel values after correction are correlated one-to-one). For example, white balance correction for correcting white balance of color image data of the RGB color system may be used. In this case, each pixel value of RGB color system color image data may be corrected in accordance with white balance correction data in which a pixel value after white balance correction is set for each pixel value before white balance correction.

  (J) In this embodiment, the case where each pixel value of RGB color system color image data is gamma-corrected has been described. However, the present invention is not limited to correction for RGB color system color image data. It is also possible to correct image data of the color system. For example, contrast correction for correcting the contrast of Y (or L) that is a lightness (luminance) component after the RGB color system color image data is converted to the YCrCb (or Lab) color system may be used.

1 is a block diagram illustrating an example of an image forming apparatus according to an embodiment of the present invention. It is the figure which showed an example of the test chart. It is the figure which showed an example of the 1st predetermined number of reference values and the 1st predetermined number of target values. It is the block diagram which showed an example of the function structure of the control part. (A) is the figure which plotted the 1st predetermined number of reference values and the 1st predetermined number of target values on a graph, (b) connects between R1 and R2 in Fig.5 (a). It is the figure which showed the straight line, (c) is the figure which illustrated a part of gamma correction data. It is the figure which showed an example of the processing operation of the control part when test chart reading mode was instruct | indicated. 3 is a flowchart illustrating an example of processing operation of a control unit when the image forming apparatus is powered on. 5 is a flowchart illustrating an example of processing operation of a control unit when a document reading start command is issued.

Explanation of symbols

1 Image forming device (image processing device)
2 Control unit 3 ROM
4 RAM
5 CCD (reading means)
8 Scanner image processing circuit (correction means)
18 Operation panel (part of acceptance means)
19 EEPROM (first storage means)
20 Work memory area (second storage means)
27 Gamma correction data generation instruction output unit (instruction means)
28 Gamma correction data generation unit (part of generation means)
29 Work memory area management part (part of generation means)
30 Gamma correction data setting section (selection means, part of reception means)

Claims (4)

A non-volatile storage device and a volatile storage device are provided, and each pixel value of image data composed of a plurality of pixels is corrected according to correction data in which a corrected pixel value is set for each pixel value before correction. An image processing apparatus, wherein a first predetermined number of reference values of the pixel values are associated with a first predetermined number of target values that respectively define corrected values of the first predetermined number of reference values Image data based on a first storage means stored in the non-volatile storage device, a first predetermined number of reference values and a first predetermined number of target values stored in the first storage means Generating means for generating correction data defining a corrected value for each of a second predetermined number of pixel values larger than the first predetermined number that can be taken by the pixels constituting the correction data, and correction data generated by the generating means The second storage means for storing the data and the second storage means Comprising a correction means for correcting each pixel value of the image data, the image processing apparatus comprising according to the correction data being paid,
An image forming apparatus having at least two functions of a scanner, a printer, a copy, and a facsimile, wherein a receiving unit that accepts one of the plurality of functions is received from outside, and the selection is received by the receiving unit Selecting means for selecting the color system of the image data based on the function,
The generating means generates correction data suitable for a plurality of color systems for each color system and stores them in the second storage means,
The correction means corrects each pixel value of the image data according to correction data suitable for the color system selected by the selection means among the correction data stored in the second storage means. An image forming apparatus. An instruction unit that outputs information to instruct the generation unit to generate correction data when the power of the device is turned on;
The generation unit generates the correction data when information indicating the generation of correction data is received from the instruction unit;
It said second storage means, the image forming apparatus according to claim 1, wherein the storing the correction data generated by said generating means to said volatile storage. A reading unit that reads an image of a document and generates image data;
The first predetermined number of reference values are obtained by reading the first predetermined number of reference images having different gradations formed on the original by the reading unit;
The image forming apparatus according to claim 1, wherein the correction unit corrects each pixel value of the image data generated by the reading unit. An image forming apparatus having at least two functions of a scanner, a printer, a copy, and a facsimile,
A non-volatile storage device and a volatile storage device are provided, and each pixel value of image data composed of a plurality of pixels is corrected according to correction data in which a corrected pixel value is set for each pixel value before correction. An image processing apparatus, wherein a first predetermined number of reference values of the pixel values are associated with a first predetermined number of target values that respectively define corrected values of the first predetermined number of reference values Image data based on a first storage means stored in the non-volatile storage device, a first predetermined number of reference values and a first predetermined number of target values stored in the first storage means Generating means for generating correction data defining a corrected value for each of a second predetermined number of pixel values larger than the first predetermined number that can be taken by the pixels constituting the correction data, and correction data generated by the generating means The second storage means for storing the data and the second storage means And correction means for correcting each pixel value of the image data according to the correction data being paid, and the image processing apparatus comprising,
A reading unit that reads an image of a document and generates image data, a receiving unit that accepts a selection of any one of the plurality of functions, and a function that receives the selection by the receiving unit. When the color image system selected by the selection unit and the color system selected by the selection unit are different from the color system selected last time, when the image of the original is read by the reading unit, Output means for instructing the generation of correction data, and
The first predetermined number of reference values are obtained by reading the first predetermined number of reference images having different gradations formed on the original by the reading unit;
The generation unit generates correction data suitable for the color system selected by the selection unit when information indicating that generation of correction data is instructed from the instruction unit, and generates the generated correction data. Overwriting the correction data stored in the second storage means,
  The image forming apparatus, wherein the correction unit corrects each pixel value of the image data generated by the reading unit.

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