JP2005086719A - Color image processor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To attain toner saving with a simple structure while suppressing changes in color to the minimum. <P>SOLUTION: RGB image data acquired by scanning an original (step ST1) are converted from an RGB color space to a Lab color space (step ST4), image processing such as ground color correction is performed (step ST5), and after that, the image data are converted from the Lab color space to a CMYK color space (step ST6). Next, it is determined whether or not an apparatus is set in a toner saving mode. If it is not in the toner saving mode (in a normal mode), a first dither matrix is selected (step ST8). If it is in the toner saving mode, a second dither matrix is selected in order to perform white mask processing (step ST9). The CMYK multivalued data are binarized with the selected dither matrix (step ST10), and the binarized data are outputted to a printer (step ST11). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

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

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, in order to reduce wasteful consumption of toner (toner), color system data representing hue, brightness, and luminance is generated from RGB data, and at most two types of CMYK toners are used. A technique is disclosed in which approximate hue data that can be expressed by using, and at least three types of density data of CMYK are generated, and an electrophotographic process is executed using the maximum of three types of density data (for example, , See Patent Document 1).
JP-A-9-163169

  In the technique described in Patent Document 1 described above, color system data is generated from RGB data, and approximate hue data that can be expressed using at most two types of CMYK toners is generated. In addition, there is a problem that the processing becomes complicated because at most three types of density data of CMYK are generated and the electrophotographic process is executed using the maximum of three types of density data in order.

  The present invention has been made paying attention to the above problems, and provides a color image processing apparatus capable of realizing toner saving (toner saving) with a simple configuration and minimizing color change. The purpose is that.

  A color image processing apparatus according to the present invention is a color image processing apparatus that performs gradation number reduction processing on color multivalued data in an output color space and outputs color image data having the number of gradations to be printed. When a mode for reducing the amount is designated, a control unit is provided for performing control to reduce the output area by performing mask processing for replacing a predetermined position of the output color image data with white.

  The color image processing apparatus of the present invention outputs the multi-value data in the output color space after the gradation number reduction process, and the control means outputs the data after the gradation number reduction process in the output color space. On the other hand, mask processing can be performed.

  The color image processing apparatus of the present invention outputs multi-valued data in the output color space after processing the number of gradations using a dither matrix, and the control means reduces the amount of recording material used. When the mode is designated, the gradation number reduction process can be performed using a dither matrix for reducing the recording material. However, in the present invention, the gradation value reduction processing of the multi-value data may be not only binarization processing but also ternarization processing and quaternary processing.

  The color image processing apparatus according to the present invention also performs mask processing (all pixels) on pixel components (for example, 4 × 4) at the same position and the same size among the pixels in the page for each component of the output color space. To replace with white). In this color image processing apparatus, since it is possible to suppress the occurrence of a region in which only a part of each component is lost, it is possible to prevent a decrease in color reproducibility due to mask processing.

  According to the present invention, when a mode for reducing the amount of recording material used is specified, the output area is reduced by performing mask processing for replacing a predetermined position of output image data with white. Printing with reduced toner consumption while minimizing color conversion is possible.

  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) 8, an image reading unit 9, a main control unit (CPU) 10, a display unit 11, an operation unit 12, a ROM 13, a RAM 14, and an image memory. 15, CODEC 16, and LAN I / F 17.

  The printer 8 is an electrophotographic color printer, and performs color recording on a read image and image data transferred from a PC or the like through the LAN I / F 17. This printer 8 uses CMYK four-color recording agents (toners), and in addition to monochrome printing using only the K (black) component recording agent, it is possible to print using all CMYK four-color recording agents. It is.

  The image reading unit 9 optically scans a document and reads image data when copying. A color image can also be read. Details will be described later. A main control unit (CPU) 10 is connected to each unit via a bus 18 and executes reading processing, printing processing, and other various controls according to a program stored in the ROM 13. The display unit 11 displays icons, key buttons, message contents necessary for operation, and the like. As the display unit 11, an LCD (Liquid Crystal Display) is mainly used, but a CRT or other display may be used.

  The operation unit 12 includes a numeric keypad, a clear key, a stop key, and the like in addition to the mode switching key 12a and the start key 12b. The mode switching key 12a can switch between the normal mode and the toner saving mode. The toner saving mode is selected when it is desired to reduce and save the color toner consumed compared to the normal mode. The ROM 13 stores a program for controlling the operation of the entire apparatus. The RAM 14 stores data necessary for control by the main control unit 10 and data that needs to be temporarily stored during the control operation. The image memory 15 stores the image data read by the image reading unit 9 in a compressed state. Further, the image memory 15 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 16 encodes (encodes) the read image data by the MH, MR, MMR method or the like. Further, the CODEC 16 decodes (decodes) the received image data to be recorded by the printer 8 in a compression-coded state. The LAN I / F 17 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 17, 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) 9 includes a CCD 1 as a color image data input unit for inputting color image data, an A / D conversion unit 2 including an analog front-end circuit, a first An image processing unit 3, a first color space conversion unit 4, a second image processing unit 5, a second color conversion unit 6, and a binarization unit 7 are provided. Each unit of the image reading unit 9 is controlled by the CPU 10, and the processed image data is printed by the printer 8. The normal mode / toner saving mode is set by inputting an instruction from the operation unit 12.

  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 first color space conversion unit 4 converts the RGB image data output from the first image processing unit 3 into L, a, and b image data that can represent the brightness components separately. The second image processing unit 5 receives the image data in the Lab color space, and performs ground color correction, color correction such as saturation and hue.

  The second color space conversion unit 6 receives the image data in the Lab color space, and converts the Lab 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.

  In this embodiment, the second color space conversion unit 6 or the binarization unit 7 performs gradation reduction processing on the color multivalued data in the output color space (CMYK) in the toner saving mode, and the number of gradations to be printed. Is provided with a functional circuit for outputting to the printer 8 as color image data. As this functional circuit, for example, the circuit shown in FIG. 6 or FIG. 7 is used. The circuit shown in FIG. 7 uses a dither matrix of exactly the same size for each component of CMYK, or has a specific relationship (one is an integral multiple of the other) even when the sizes are different. Applicable circuit.

This circuit receives a dither matrix of each color of CMYK from each of the C, M, Y, and K tables and generates threshold _values , 20 _-1 , 20 _-2 , 20 _-3 , 20 _-4 , and CMYK Comparison circuits 21 _-1 , 21 _-2 , 21 _-3 for comparing each input multi-value data with each threshold value input from the threshold value generation circuits 20 _-1 , 20 _-2 , 20 _-3 , 20 _-4 , respectively. _21-4 .

In this circuit, in the normal mode, the 8 × 8 dither matrix shown in FIG. 4A is used for all the pixels in the same page, and in the toner saving mode, all the pixels in the same page are shown in FIG. The dither matrix shown in (a) is used. In FIG. 4 and FIG. 5 (b) the (a), when each multi-valued input data, the input multi-value data and FIG. 4 (b), comparing the threshold indicated by (a) in FIG. 5 circuit 21 _{- 1} , 21 ₋₂ , 21 ₋₃ , and 21 ₋₄ , and the data shown in FIG. 4C in the normal mode and the data shown in FIG. 5C in the toner saving mode are output.

  In this case, compared to the dither matrix in the normal mode shown in FIG. 4A, the dither matrix in the toner saving mode shown in FIG. 5A has threshold values of 4 × 4 at the upper right and 4 × 4 at the lower left. 63, these areas are mask areas (areas to be replaced with white in the output image data).

  As shown in FIG. 4C, the halftone dots in the normal mode are compared to the case where one halftone dot is 2 × 2 and the number is eight when the density is 32 at 64 gradations. However, the white mask in the toner saving mode has a 4 × 4 area and two white masks, so that the toner consumption can be reduced.

  The circuit shown in FIG. 6 is applicable when the matrix sizes of the CMYK components are not the same and are not in the specific relationship (the relationship in FIG. 7).

This circuit is similar to the circuit of FIG. 7 except for the threshold generation circuits 20 _-1 , 20 _-2 , 20 _-3 , 20 _-4 , and the comparison circuits 21 _-1 , 21 _-2 , 21 _-3 , 21 _-4 . Are provided with a mask generation circuit 22 and a mask processing circuit 23 that receives the mask signal from the mask generation circuit 22 and masks the outputs of the comparison circuits 21 _-1 , 21 _-2 , 21 _-3 , 21 _-4. Yes.

In this circuit, in the normal mode, for example, the dither matrix shown in FIG. 4A is input to the threshold value generation circuits 20 _-1 , 20 _-2 , 20 _-3 , and 20 _-4 for each color. 4 of the comparator circuit input data illustrated in (b) 21 _-1, 21 _-2, 21 _-3, type 21 _-4, the comparator circuit 21 _-1, 21 _-2, 21 _-3, each with 21 _-4 The threshold value and each input data are compared to obtain binarized data shown in FIG. Although this binarized data is input to the mask processing circuit 23, since the mask data is not input from the mask generating circuit 22 in the normal mode, the binarized data shown in FIG. 4C is output as it is. . On the other hand, in the toner saving mode, since the mask data is input from the mask generation circuit 22 to the mask processing circuit 23, the binarized data shown in FIG. 4C is masked by the mask data and output. The For example, when the mask is applied to the upper right 4 × 4 and the lower left 4 × 4, the mask processing circuit 23 outputs binary data shown in FIG. In order to further prevent deterioration in color reproducibility, the size of one mask area (4 × 4 in the example) is larger than the size of one halftone dot (2 × 2 in the example of FIG. 4C). It is preferable to increase the size. That is, it is desirable that one mask region has a size including a plurality of halftone dots.

  Thus, in this circuit, mask processing is performed on the output data after binarization. The mask process is performed for pixels corresponding to a predetermined area (mask area) in the page. In this circuit, since the masking process is performed independently of the binarization process, even when the matrix size of each component of CMYK is not equal, the pixel region of the same size is masked for the same size for each component. Processing can be performed. In this case, there is only one matrix for each of CMYK shown in FIG. 4A, and the toner saving mode matrix as shown in FIG. 5A is not necessary. In this example, since mask processing is performed on the result of reducing the number of gradations, the method for reducing the number of gradations is not limited to the dither method using the dither matrix as described above, and an error diffusion method is used. You can also.

  As a modification of the circuit shown in FIG. 6, the mask processing circuit 23 may be eliminated and the output from the mask generation block may be input to the threshold generation unit. For the pixels corresponding to the mask region, all the threshold values read from the table are replaced with those for masks (63 in FIG. 5A). Also in this modified example, since the mask generation processing is performed independently of the mask size, even if the matrix of each component is not equal, the mask processing is performed on the same size pixel region at the same position for each component. It can be performed. In this example, since mask processing (threshold replacement) is performed on the threshold value, the method for reducing the number of gradations is not limited to the dither method using the dither matrix as described above, and an error diffusion method may be used. it can. Regardless of which method is used, the threshold value may be set to a value at which the result of the gradation number reduction process is all white when the mask process is to be performed (for the pixel to be masked).

  Next, the processing operation at the time of image formation in this embodiment image processing circuit will be described with reference to the flowchart shown in FIG.

  When the start key 12b of the operation unit 12 is pressed, this processing routine is started, and the RGB scan of the document is executed by the CCD 1 in step ST1. The RGB image data read by this process is A / D converted by the A / D converter 2 in step ST2, and converted into multi-value digital data. Next, the process proceeds to step ST 3, where the first image processing unit performs shading correction and gamma correction on the RGB image data, and inputs them to the first color conversion unit 4. Subsequently, the process proceeds to step ST4.

  In step ST <b> 4, the RGB image data is converted into image data in the Lab color space and input to the second image processing unit 5. Next, the process proceeds to step ST5. In step ST5, the second image processing unit 5 performs an image such as ground color correction on the input Lab image data, and inputs the corrected Lab image data to the second color space conversion unit 6. To do. Next, the process proceeds to step ST6.

  In step ST6, the Lab image data input by the second color conversion unit 6 is interpolated by a 3D-LUT (three-dimensional lookup table) 6a to convert the image data into CMYK color space image data. Next, the process proceeds to step ST7. In step ST7, the mode setting device in the operation unit 12 is referred to and it is determined whether or not the toner saving mode is set. If it is not the toner saving mode but the normal mode, the process proceeds to step ST8. On the other hand, in the toner saving mode, the process proceeds to step ST9.

  In step ST8, the first dither matrix (see FIG. 4A) used in the binarization unit 7 is selected. On the other hand, in step ST9, the second dither matrix (see FIG. 5A) is selected. With the second dither matrix, a white mask is applied at a predetermined position (upper left 4 × 4 pixels, lower left 4 × 4 pixels) of the output data of the binarization unit 7. Subsequent to step ST8 or step ST9, the process proceeds to step ST10. In step ST 10, the multi-value YMCK data is binarized using the first dither matrix or the second dither matrix selected by the binarization unit 7 and output to the printer 8. Subsequently, the process proceeds to step ST11. In step ST11, print processing is executed with the binarized data input by the printer 8.

  In the above embodiment, the toner saving mode is set by the operation unit 12, but may be automatically set by detecting the remaining amount of toner.

  In the above embodiment, one of the normal mode and the toner saving mode is selected. However, a plurality of toner saving modes may be provided. In this case, a different dither matrix is provided in each mode.

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. FIG. 6 is a flowchart illustrating an image forming process operation of the color copier. It is a figure which shows an example of the matrix for demonstrating the dither process in the normal mode at the time of the image formation process. FIG. 10 is a diagram illustrating an example of a matrix for explaining dither processing in a toner saving mode during the image forming processing. It is a block diagram which shows an example of the specific circuit of the binarization part of the said embodiment color copier. It is a block diagram which shows the other example of the specific circuit of the binarization part of the same color copier.

Explanation of symbols

1 CCD
2 A / D converter 3 First image processing unit 4 First color space conversion unit 5 Second image processing unit 6 Second color space conversion unit 6a 3D-LUT
7 Binarization unit 8 Printer 10 CPU
11 Display Unit 12 Operation Unit 12a Mode Switch Key 12b Start Key 13 ROM
14 RAM
15 Image memory 16 CODEC
17 LAN I / F

Claims (4)

A color image processing device that performs gradation number reduction processing on color multivalued data in an output color space and outputs color image data of the number of gradations to be printed,
When a mode for reducing the amount of recording material used is specified, a control unit is provided for performing control to reduce the output area by performing mask processing for replacing a predetermined position of the output color image data with white. A color image processing apparatus.   The multi-valued data in the output color space is output after the gradation number reduction process, and the control means performs a mask process on the data after the gradation number reduction process in the output color space. The color image processing apparatus according to claim 1.   Outputs color multivalued data in the output color space after reducing the number of gradations using a dither matrix, and the control means reduces the recording material when a mode for reducing the amount of recording material used is designated. The color image processing apparatus according to claim 1, wherein the tone number reduction process is performed using a dither matrix.   4. The mask processing is performed on pixel components of the same size at the same position among the pixels in the page for each component of the output color space. Color image processing device.

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