JP2005192152A - Image processing apparatus and image color conversion processing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a color image processing apparatus capable of adjusting a specific color with a simple method. <P>SOLUTION: An original including only the specific color to be inspected is read and stored (ST1), a mean value of the specific color is acquired (ST2), and the grid point of 3D-LUT near the mean value of the specific color is used as a representative point (ST3). A conversion value corresponding to the representative point is read, referring to a present table (ST4). A plurality of correction values are generated using the conversion value as a reference, and a plurality of output values are subjected to interpolation operation from this conversion value and correction value (ST5, ST6). A plurality of output images are generated on the basis of the output values, and each of the images are recorded and outputted together with identification numbers (ST10). Upon accepting the identification numbers inputted (ST11), the 3D-LUT is changed on the basis of the output value corresponding to the accepted identification number (ST12). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a color image processing apparatus and an image color conversion processing method such as a copying machine, a facsimile machine, a multifunction machine having multiple functions such as a copying function and a facsimile function.

In general, a scanned input color space (for example, RGB) is converted into a color space (for example, Lab or YCC) that includes a brightness component or a luminance component, and each component of the color space is subjected to correction processing, and then output color space There is known a color image processing apparatus that converts an image into (for example, CMYK) and forms an image. In this type of color image processing apparatus, converted values corresponding to representative points in the color space are stored as a table, and interpolation is performed based on converted values corresponding to a plurality of representative points close to the values before conversion. Because of the calculation, not all colors in the color space match between the original and the copy. At this time, usually, a function for adjusting each component by an adjustment function such as RGB, CMYK, brightness, saturation, and hue is installed. With such an adjustment function, adjustment is made with respect to a wide range in the color space, and adjustment for a narrow range cannot be performed. As an adjustment method, in the apparatus for converting RGB into Lab by the color conversion unit, the CPU compares the Lab value obtained by reading the reference document with a preset reference value, and based on the comparison result, the CPU Is disclosed to control input / output characteristics of an LUT (look-up table) in the subsequent stage of the color conversion unit (see, for example, Patent Document 1).
JP-A-7-322080

  When performing color copying, there is a demand that the user wants to adjust only for a specific color, such as a company image color, and the color should be exactly the same. In the method of correcting the data before conversion or the data after conversion, the reproduction accuracy of a color close to a specific color increases, but the reproduction accuracy of a color that is not close deteriorates. Further, when color conversion is performed on CMYK using a three-dimensional LUT, there is a problem that a high level of technology is required to recreate all the LUTs, which is troublesome.

  The present invention has been made paying attention to the above problems, and provides a color image processing apparatus capable of easily adjusting a specific color by adopting a simple method of correcting a part of an LUT. The purpose is that.

  The image processing apparatus of the present invention refers to a means for inputting a color to be adjusted, a determination means for determining a representative point in the multidimensional LUT based on the input color to be adjusted, and the multidimensional LUT, A conversion value calculation unit that calculates a conversion value (CMYK value) corresponding to the determined representative point, a correction value generation unit that generates a plurality of correction values based on the calculated conversion value, and the conversion value and the correction value are used. Output value calculating means for calculating a plurality of output values (CMYK values), output image generating means for generating an output image based on the calculated output values, and outputting the generated output image Output means for receiving, and receiving means for receiving a selection input of a desired output value from among the plurality of output values outputted.

  In the image processing apparatus of the present invention, when the output unit outputs an output image, the output unit also outputs identification information, and the receiving unit can receive a selection input of the output image by inputting the identification information.

  The image processing apparatus according to the present invention may further include a storage unit that holds the output image generated by the output image generation unit until a one-page output image is generated.

  The image color conversion processing method according to the present invention includes a step of accepting a color to be adjusted as an input, a step of determining a representative point in the multidimensional LUT based on the input color to be adjusted, and a multidimensional LUT. Referring to the step of calculating a conversion value corresponding to the determined representative point, a step of generating a plurality of correction values based on the calculated conversion value, and performing an interpolation operation using the conversion value and the correction value A step of calculating a plurality of output values, a step of generating an output image based on the calculated output values, a step of outputting the generated output image, and a desired output value from among the plurality of output values output Receiving a selection input.

  According to the present invention, a part for color conversion can be corrected by a simple method, and a specific color can be easily adjusted.

  Hereinafter, the present invention will be described in more detail with reference to embodiments.

  FIG. 1 is a block diagram showing the configuration of a color copier according to an embodiment of the present invention. The color copier of this embodiment includes a printer (image recording unit) 11, an image reading unit 12, a main control unit (CPU) 13, a display unit 14, an operation unit 15, a ROM 16, a RAM 17, and an image memory. 18, CODEC 19, and LAN I / F 20.

  The printer 11 is an electrophotographic color printer, and color-records a read image or image data transferred from a PC or the like through the LAN I / F 19 on a recording sheet. This printer 11 uses CMYK four color recording agents (toners), and in addition to monochrome printing using only the K (black) component recording agent, printing using all CMYK four color recording agents is also possible. It is.

  The image reading unit 12 optically scans a document to read image data when copying. A color image can also be read. Details will be described later. A main control unit (CPU) 13 is connected to each unit via a bus 21 and executes reading processing, printing processing, and other various controls according to a program stored in the ROM 16. The display unit 14 displays icons, key buttons, message contents necessary for operation, and the like. As the display unit 14, an LCD (Liquid Crystal Display) is mainly used, but a CRT or other display may be used.

  The operation unit 15 includes a mode switching key, a start key, a numeric keypad, a clear key, a stop key, and the like. When the user selects and inputs a desired color conversion value (output image) from among a plurality of color conversion values printed out, the operation unit 15 inputs an identification number indicating the color conversion value ( To accept. The ROM 16 stores a program for controlling the operation of the entire apparatus. The RAM 18 stores data necessary for control by the main control unit 13 and data that needs to be temporarily stored during the control operation. The image memory 18 stores the image data read by the image reading unit 12 in a compressed state. Further, the image memory 18 stores image data received from an external device such as a personal computer via a network or image data read from a recording medium in a compressed state.

  The CODEC 19 encodes (encodes) the read image data by the MH, MR, MMR method or the like. Also, the CODEC 19 decodes (decodes) the received image data to be recorded by the printer 11 in a compressed and encoded state. The LAN I / F 20 is used to exchange data with an external device via a LAN (local area network). From the external PC (personal computer) via the LAN I / F 20, a network print and a network scanner are provided. Receive requests such as.

  As shown in FIG. 2, the image reading unit (color image processing circuit) 12 of the color copier of this embodiment includes a CCD 1 as a color image data input unit for inputting color image data, and an analog front end (AFE) circuit. An A / D converter 2, a first image processor 3, a second image processor 4, an image memory 5, a color space converter 6, a binarizer 7, and a binary memory 8 are provided. Each unit of the image reading unit 12 is controlled by the CPU 13. The processed image data is printed by the printer 11.

  The CCD 1 separates and reads one scanning line of the original into R, G, and B, and sequentially reads the next scanning line image at predetermined intervals. The A / D converter 2 analog-amplifies the output of the CCD 1 with an AFE circuit. This analog value is converted into digital data and output in multi-value. The first image processing unit 3 performs processing such as shading correction and gamma correction.

  The second image processing unit 4 receives image data in the RGB color space and uses the image memory 5 to perform ground color correction, color correction such as saturation and hue.

  The color space conversion unit 6 receives image data in the RGB color space and converts the RGB image data into CMYK image data by interpolation using the 3D-LUT 6a. The binarization unit 7 binarizes the input CMYK multilevel data and outputs it while storing it in the binary memory 8.

  In the image reading unit 12 shown in FIG. 2, the second image processing unit 4 performs ground color correction, saturation and hue color correction of RGB image data, and the color space conversion unit 6 converts the RGB image data into CMYK. However, instead of this, a color space conversion unit is provided between the first image processing unit 3 and the second image processing unit 4, and this color space conversion unit uses RGB image data. Is converted into L, a, b image data, the second image processing unit 5 performs ground color correction, color correction of saturation and hue, and the next color space conversion unit 6 further converts L, a, b. It is also possible to convert the image data into CMYK data. The present invention can also be applied to such a configuration.

  This embodiment apparatus has a rewriting function of a three-dimensional lookup table for color space conversion. In particular, it has a function of automatically changing some conversion values (conversion destination values) in the table.

  Further, in the present embodiment, the processing described below determines a plurality of representative points (grid points close to the input value) in the three-dimensional LUT based on the input pixel value (conversion source value). It is assumed that an output value is calculated by performing an interpolation operation using data of a converted value (converted value) corresponding to the representative point.

  Next, the processing operation at the time of calibration in the color copier of this embodiment will be described with reference to the flowchart shown in FIG. When this job is entered, the document is read and stored in step ST1. The document read here is a document including only a specific color prepared in advance, and is read by the image reading unit 12. The background color of the document includes only a specific color and a top plate color, the top plate color and the background color are white, and a color other than white is extracted as the specific color. The document reading in this step is a process of inputting the color to be adjusted. Instead, the chromaticity value (LCH) may be manually input from the operation unit 15. Subsequently, the process proceeds to step ST2.

  In step ST2, an average value of the input specific color (RGB) is acquired. That is, the average pixel value of the area other than white is calculated. Next, the process proceeds to step ST3. In step ST3, the lattice point of the three-dimensional lookup table (3D-LUT) 6a closest to the acquired average value of the specific color is used as a representative point. Not only the single lattice point closest to the input value (average value of the specific color) can be used as a representative, but also a plurality of lattice points close to the input value can be used as the representative point. An example of the 3D-LUT used here is shown in FIG. In FIG. 4, a correspondence relationship between addresses and CMYK values is stored as a 3D-LUT. For example, an address is obtained based on RGB values obtained by scanning, and CMYK values corresponding to the addresses are read out. . As shown in FIG. 4, when converting from RGB to CMYK, when the average value acquired as the specific color is (116), (124, 170) as (RGB), for example, the closest lattice point is (128, 128, 160), and this point is a representative point. When a chromaticity value (LCH value) is input, the input LCH value is converted into an RGB value, and a lattice point close to the converted RGB value is used as a representative point. Next, the process proceeds to step ST4.

  In step 4, the conversion value corresponding to the representative point is read with reference to the current table (for example, FIG. 4). For the representative points (128, 128, 160), (147, 131, 29, 24) are read as CMYK conversion values. Subsequently, the process proceeds to step ST5.

  In step ST5, a plurality of correction values are generated based on the calculated conversion values (CMYK). For example, as the correction value for the C component, a small value +5, 0, -5 is added to the conversion value (C) before correction to generate a plurality of correction values C + 5, C, C-5, and the correction value for the M component As a result, a small value +5, 0, -5 is added to the conversion value (M) before correction to generate a plurality of correction values M + 5, M, M-5. Next, the process proceeds to step ST6. In step ST6, a plurality of output values (CMYK) are interpolated based on the converted value (CMYK) and the correction value. This interpolation calculation will be described with reference to FIG. The description of FIG. 5 will be described later. For example, in the case of the upper left (number “1”) in FIG. 5, the conversion value is +5 for C, the conversion value is +5 for M, and a correction value is obtained. The output value (the color of the image output to the color display area) is calculated. In the middle of FIG. 5 (number “5”), the conversion values corresponding to the representative points for C and M are used as they are (without correction), and the output values are calculated by interpolation. For example, the number of correction values in all cases where the CMYK conversion value is added with any one of three small values of +5, 0, and −5 is the fourth power of 3 and is 81. Next, the process proceeds to step ST7.

  In step ST7, an output image is generated based on the output value obtained by the interpolation calculation. Here, assuming that an image obtained by scanning the document image of FIG. 6 is stored (stored), an image (an image corresponding to the scanned image) is generated in each color display area of each output value. Subsequently, the process proceeds to step ST8. In step ST8, the generated output image is stored in the binary memory 8. Subsequently, the process proceeds to step ST9.

  In step ST9, it is determined whether or not an output image for one page (for example, the image shown in FIG. 5) has been generated. If an output image for one page has not been generated, the process returns to step ST7 to continue generating the output image. On the other hand, when an output image for one page is generated, the process proceeds to step ST10. In step ST10, the printer 11 records and outputs the output image. Thereby, for example, the image shown in FIG. 5 is stored on the recording paper. FIG. 5 shows a case where a plurality of color display regions (scanned images) that have been color-corrected using correction values are formed together into one sheet. Here, each image when the correction value of C in the horizontal direction is displayed as minute values +5, 0, and −5 from the left and the correction value of M is displayed in the vertical direction as minute values +5, 0, and −5 from the top. Is shown. Each image is given an identification number “1”, “2”,..., “9”. The color-corrected image pattern is based on the scanned image shown in FIG. The color image may be a solid image corresponding to chromaticity value input instead of the scan image. The color display area of each image has a slightly different color depending on the correction value. This output image may be displayed on the display unit 14 instead of being recorded and output by the printer 11. Subsequently, the process proceeds to step ST11.

  In step ST11, it is determined whether an input selection of output value is accepted. This determination is made based on whether the user has selected the number (1 to 9) closest to the favorite color by looking at the printed matter of FIG. If there is a selection input acceptance of the output value by the user, the process proceeds to step ST12.

  In step ST12, the content of the 3D-LUT 6a is changed based on the received output value. That is, the conversion value (CMYK) corresponding to the representative point is rewritten to the correction value corresponding to the selected input value. For example, when the number “1” in FIG. 5 is selected and input, a correction value (CMYK) in which C is +5 and M is +5 with respect to the conversion value (CMYK) is set as a new conversion value in the 3D-LUT 6a. Remembered. Next, the process proceeds to step ST13. In step ST13, it is determined whether or not the calibration is OK. If the user inputs calibration OK, the process ends. On the other hand, if further calibration is required, the user does not input calibration OK and continues the calibration process. In other words, if the selected number is closest to the favorite color but is not yet completely desired, the calibration process is continued again. That is, the process proceeds to step ST4 and proceeds to the next process.

  When the calibration process is continued, since the 3D-LUT has already been changed, the correction value corresponding to the selection in step ST11 becomes the reference (middle of FIG. 5), and the same process as described above is performed as shown in FIG. Generate multiple images. Specifically, when the change information is changed to the next time, for example, when the selected change information is -5, 0, +5, 0, a value obtained by adding this value is used as a new conversion value (142, 131, 34, 24). ) And repeat the same process.

  In this case, since it is considered that the color is already close to the favorite color, the minute value (+5, -5) can be made smaller (for example, +2, -2) than the previous time.

  In this embodiment, as described above, the user can select and specify which component to be corrected among C, M, Y, and K components, that is, which component value is increased or decreased to generate a correction value. For example, when the user increases the C component value by +5 to generate a correction value, the user selects and inputs the number “4” shown in FIG.

  Here, the number of correction values generated for each component is three, but this number can be designated and selected by the user. Furthermore, as a method for specifying a correction value, the user may be allowed to specify words that assume a color change such as “red” or “blue”. In the case of “red”, correction for increasing C and M is performed. For example, the correction amount for C is 0, +5, +10, and the correction amount for M is 0, +5, +10. In the case of “blue”, correction for increasing M and Y is performed. Also, in the above, the calibration process is performed again, so that the color to be changed can be selected instead of the previous time, and the number of changes per color may be increased.

  In the above embodiment, the output output (or display output) of the output image is printed by arranging a plurality of output images on one sheet as shown in FIG. 5, or outputting an output image having a plurality of color conversion values. Although arranged side by side and displayed on one screen, each output image may be recorded and output (or displayed and output) as a different page.

1 is a block diagram showing a configuration of a color copier as an embodiment of the present invention. 2 is a block diagram illustrating a configuration of an image reading unit of the color copier according to the first embodiment. FIG. It is a flowchart explaining the calibration processing operation | movement of the color copier of the embodiment. It is a figure which shows the example of a table of 3D-LUT of the color copier of the embodiment. 5 is a diagram illustrating a print example of color conversion values at the time of calibration of the color copier according to the embodiment. FIG. FIG. 6 is a diagram showing a document pattern at the time of copying of the print example shown in FIG. 5.

Explanation of symbols

1 CCD
2 A / D conversion section 3 First image processing section 4 Second image processing section 5 Image memory 6 Color space conversion section 6a 3D-LUT
7 Binary Unit 8 Binary Memory 11 Printer 12 Image Reading Unit 13 CPU
14 Display unit 15 Operation unit 16 ROM
17 RAM
18 Image memory 19 CODEC
20 LAN I / F
21 Bus

Claims (4)

Means for inputting the color to be adjusted;
Determining means for determining a representative point in the multi-dimensional lookup table based on the input color to be adjusted;
Conversion value calculation means for calculating a conversion value corresponding to the determined representative point with reference to the multidimensional lookup table;
Correction value generation means for generating a plurality of correction values based on the calculated conversion values;
An output value calculating means for calculating a plurality of output values by performing an interpolation operation using the conversion value and the correction value;
Output image generation means for generating an output image based on the calculated output value;
An output means for outputting the generated output image;
Receiving means for receiving a selection input of a desired output value from the plurality of output values output;
An image processing apparatus comprising:   The image processing apparatus according to claim 1, wherein when outputting the output image, the output unit outputs identification information together, and the receiving unit receives a selection input of the output image by inputting the identification information. .   The image processing apparatus according to claim 1, further comprising a storage unit that holds the output image generated by the output image generation unit until an output image for one page is generated. Receiving a color to be adjusted as an input;
Determining a representative point in the multi-dimensional lookup table based on the input color to be adjusted;
Calculating a conversion value corresponding to the determined representative point with reference to the multi-dimensional lookup table;
Generating a plurality of correction values based on the calculated conversion values;
Calculating a plurality of output values by performing an interpolation operation using the converted value and the correction value;
Generating an output image based on the calculated output value;
Outputting the generated output image; and
Receiving a selection input of a desired output value from a plurality of output values output;
An image color conversion processing method comprising:

Images