JP2006262374A - Image processing apparatus, image processing method, program making computer perform the method, and record medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image processing apparatus which can reproduce a high stable and high quality image by making ink processing in image formation proper. <P>SOLUTION: In a principal color transformation unit 107 of the image processing apparatus, an inputted image signal is converted to an image signal which corresponds to a plurality of color materials and a plurality of black materials of distinct richness. First, a color corrector 1071 generates a color image signal which corresponds to a plurality of the color materials from the inputted image signal. An ink formation 1072 generates a black image signal which corresponds to a gray image from the inputted image signal. An UCR 1073 removes the black image signal generated by the ink formation 1072 from the color image signal generated by the color corrector 1071. A Bk/Lk version 1074 decomposes the black image signal generated by the ink formation 1072 into an image signal which corresponds to a plurality of the black materials of distinct richness. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image processing apparatus, an image processing method, a program for causing a computer to execute the method, and a recording medium, and more particularly to an image processing apparatus, an image processing method, and a method for performing image formation by electrophotography. The present invention relates to a program to be executed and a recording medium.

  In recent years, in inkjet printers, a method using light ink is used as a method for reducing graininess such as photographic images as much as possible. In this case, an image is reproduced using two light and dark inks having the same color, such as light cyan and magenta ink as well as light magenta. In particular, it is trying to improve the graininess by using light ink in a low density region and realize a photographic image without roughness. Further, there is a demand for an image processing technique for an image forming apparatus that improves image quality and suppresses toner consumption.

  In order to meet such a demand, for example, in the technique of Patent Document 1, the lightness and dark toner are used to improve the gradation in the highlight portion and the excessive amount of toner attached in the high concentration portion. Aims to reduce Specifically, based on image data, image exposure and development with light toner, and image exposure and development with dark toner are performed. That is, image data for light toner and dark toner are generated from the image density data, and after tone correction is performed, image exposure for light toner and dark toner is to be performed.

  Further, the technique of Patent Document 2 decomposes the black color into individual image information of the highlight density area and the dark density area among four colors of yellow, cyan, magenta, and black, and the highlight density area has a low density. The toner and dark density areas are for image formation using high density toner.

  Further, the technique of Patent Document 3 has dot formation determination means for determining whether or not each color dot is formed in an image output apparatus that prints in yellow, cyan, magenta, dark black, and light black, and based on the determination result. Form dots. Further, the light black ink is capable of forming an image of the same brightness of an achromatic image expressed by a combination of chromatic color inks with an ink amount smaller than the total ink amount of the chromatic color inks.

JP 2001-290319 A JP-A-8-171252 JP 2001-277552 A

  However, in the technique of Patent Document 1, a configuration of a combination of processing for Lk (light black) and Bk (dark black) is disclosed. However, a combination with black generation processing such as full black processing and high black processing is not possible. It was not disclosed.

  In the technique of Patent Document 2, the method of generating a black color only describes extracting a black component by UCR processing, and does not describe a technique of extracting all gray signals as black components. It was.

  Also in Patent Document 3, it is said that generating black with a high black setting (high UCR rate) with a configuration of Lk + Bk is effective in terms of stability of gray balance, but complete full black processing The configuration is not disclosed. For example, if full black processing (UCR rate 100%) is not achieved even if the UCR rate is increased, the C, M, and Y color components remain when attempting to reproduce black characters, and the color components remain. When the misregistration occurs, the characters are colored, and there is a problem that visibility is deteriorated such as double appearance. Further, the relationship between the color material usage amounts of the chromatic color material and the light black color material when reproducing the same brightness is described, however, the relationship between the graininess is not described.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide an image processing apparatus and an image in an image forming apparatus that can reproduce a high-quality and highly stable image by making the black processing in the image processing apparatus appropriate. A processing method, a program for causing a computer to execute the method, and a recording medium are provided.

  Another object of the present invention is to perform an image processing apparatus, an image processing method, and a computer that can perform high-quality image processing by performing full black processing with a configuration using light black and dark black. It is to provide a program and a recording medium.

  Another object of the present invention is to provide a granularity of a chromatic color material and a light black color material when reproducing the same brightness in a C, M, Y, K, Bk, and Lk five-color image processing apparatus that performs full black processing. Image processing apparatus, image processing method and image processing method capable of high-quality image processing by performing image processing based on a preferable relationship between the color material usage amount in addition to the preferable relationship between the image quality and the graininess A program to be recorded, and a recording medium.

  In order to solve the above-described problems and achieve the object, the invention according to claim 1 is an image processing for converting an input image signal into image signals corresponding to a plurality of color materials and a plurality of black materials having different densities. In the apparatus, color image signal generation means for generating color image signals corresponding to a plurality of color materials from the input image signal, and an image corresponding to a plurality of black materials from which the gray component is input from the input image signal And a black image decomposition means for converting into a signal.

  According to a second aspect of the present invention, in the image processing apparatus according to the first aspect, the black image decomposition unit converts all of the gray components from the input image signal into image signals corresponding to the plurality of black materials. It is a thing to do.

  According to a third aspect of the present invention, in the image processing apparatus according to the first or second aspect, the black image decomposing means uses the input image signal as an image signal corresponding to two types of black materials of dark black and light black. It is characterized by being decomposed into

  According to a fourth aspect of the present invention, in the image processing apparatus according to the third aspect, the black image disassembling unit is configured to use an image signal corresponding to the light black material for all of the gray components for the highlight area. It is generated.

  According to a fifth aspect of the present invention, in the image processing apparatus according to the first aspect, the color image signal generation means is a color generated by the color image generation means for a part of the gray component for the shadow area. It is generated by an image signal.

  According to a sixth aspect of the present invention, in the image processing device according to any one of the third to fifth aspects, the black image decomposition means is based only on the light black black material corresponding to the light black image signal. The gray reproduction granularity generates an image signal corresponding to a light black color material that is superior to the gray reproduction granularity of the plurality of color color materials corresponding to the color image signal. It is characterized by.

  According to a seventh aspect of the present invention, in the image processing apparatus according to the sixth aspect, the black image decomposing means has an image signal in which the density of the light black black material corresponding to the light black image signal is the dark black. Are divided into image signals corresponding to a plurality of black materials having a density of 0.2 to 0.6 times the density of the black material of the dark black.

  According to an eighth aspect of the present invention, in the image processing device according to any one of the third to seventh aspects, the black image decomposing means is based only on the light black black material corresponding to the light black image signal. An image signal corresponding to a light black color material is generated in which a toner usage amount in gray reproduction is smaller than a toner usage amount in gray reproduction by the plurality of color color materials corresponding to the color image signal. It is characterized by that.

  The invention according to claim 9 is the image processing apparatus according to any one of claims 1 to 8, wherein a plurality of color image signals by the color image signal generation unit and a plurality of different densities by the black image decomposition unit are provided. A first reproduction mode for reproducing a gray component by an image signal corresponding to the black material, a plurality of color image signals by the color image signal generation unit, and a plurality of black materials having different densities by the black image decomposition unit A second reproduction mode in which a gray component is reproduced by an image signal corresponding to a black material having the highest density, and the black image decomposition means has a black generation rate for replacing the gray component with an image signal of a black material. The mode is set higher than the second mode.

  The invention according to claim 10 is an image processing method in an image processing apparatus for converting an input image signal into image signals corresponding to a plurality of color materials and a plurality of black materials having different densities. A color image signal generating step for generating color image signals corresponding to a plurality of color materials from the input image signal, and a black image decomposing unit that converts a gray component from the input image signal to the plurality of black materials. And a black image decomposition step of converting into a corresponding image signal.

  According to an eleventh aspect of the present invention, in the image processing method according to the tenth aspect, in the black image decomposing step, the black image decomposing means converts all gray components from the input image signal to the plurality of black materials. Is converted into an image signal corresponding to.

  According to a twelfth aspect of the present invention, in the image processing method according to the tenth or eleventh aspect, in the black image decomposition step, the input image signal is converted into two types of dark black and light black by the black image decomposition means. It is characterized by being decomposed into an image signal corresponding to a black material.

  According to a thirteenth aspect of the present invention, in the image processing method according to the twelfth aspect, in the black image decomposition step, the black image decomposition unit converts all of the gray components into the black of the light black for the highlight area. It is generated by an image signal corresponding to a material.

  According to a fourteenth aspect of the present invention, in the image processing method according to the tenth aspect, in the color image signal generation step, a part of the gray component is generated by the color image generation means for the shadow area. It is generated by an image signal.

  The invention according to claim 15 is the image processing method according to any one of claims 12 to 14, wherein the black image decomposition step corresponds to the light black image signal by the black image decomposition means. An image signal corresponding to a light black color material in which the granularity of gray reproduction using only a light black material is superior to the granularity of gray reproduction using the plurality of color color materials corresponding to the color image signal. It is characterized by generating.

  According to a sixteenth aspect of the present invention, in the image processing method according to the fifteenth aspect, in the black image decomposition step, the density of the light black black material corresponding to the light black image signal is determined by the black image decomposition means. Is decomposed into image signals corresponding to a plurality of black materials that are 0.2 to 0.6 times the density of the dark black black material corresponding to the dark black image signal.

  According to a seventeenth aspect of the present invention, in the image processing method according to the fifteenth or sixteenth aspect, in the black image decomposing step, the black image material of the light black corresponding to the light black image signal by the black image decomposing means. Generating an image signal corresponding to a light black color material in which the amount of toner used in gray reproduction by only the toner is less than the amount of toner used in gray reproduction by the plurality of color color materials corresponding to the color image signal It is characterized by being.

  According to an eighteenth aspect of the present invention, in the image processing method according to any one of the tenth to tenth aspects, a plurality of color image signals by the color image signal generation unit and a plurality of different densities by the black image decomposition unit. A first reproduction mode for reproducing a gray component by an image signal corresponding to the black material, a plurality of color image signals by the color image signal generation unit, and a plurality of black materials having different densities by the black image decomposition unit A second reproduction mode in which a gray component is reproduced by an image signal corresponding to a black material having the highest density, and the black image decomposing step replaces the gray component with an image signal of a black material by the black image decomposing means. The black generation rate is set higher in the first mode than in the second mode.

  The invention according to claim 19 is a program that causes a computer to execute the image processing method according to any one of claims 10 to 18.

  The invention according to claim 20 is a recording medium, wherein the program according to claim 19 is stored in a computer readable manner.

  According to the first aspect of the present invention, it is possible to perform image reproduction with five colors by adding light black (Lk) toner having a density lower than that of normal black toner, and to replace gray components with Bk and Lk signals. In addition, it is possible to provide an image processing apparatus that obtains excellent graininess and is excellent in gray balance and color stability.

  According to the second aspect of the present invention, image reproduction is performed in five colors by adding light black (Lk) toner having a density lower than that of normal black toner, and the UCR (background removal) rate is set to 100%. On the other hand, by replacing the gray component with the Bk and Lk signals, it is possible to provide an image processing apparatus with excellent graininess and excellent gray balance and color stability.

  According to the invention of claim 3, image reproduction is performed in five colors by adding normal black toner (Bk) and light black (Lk) toner having a low density, and the UCR (background removal) rate is 100%. Alternatively, by replacing the gray component with the Bk and Lk signals while setting the value close to 100%, it is possible to provide an image processing apparatus with excellent graininess and excellent gray balance and color stability.

  According to the fourth aspect of the present invention, it is possible to provide an image forming apparatus capable of achieving both granularity and gray balance stability by performing full black processing using Lk at least in a highlight region.

  According to the fifth aspect of the present invention, an image processing apparatus that realizes wide color reproduction can be provided by using a color color material in addition to Bk and Lk in the shadow area in image formation including Lk toner.

  According to the sixth aspect of the present invention, by using a color material that is superior in granularity when reproduced using Lk over the granularity of CMY reproduction, reproduction using Lk is more granular. An image processing apparatus capable of obtaining an output excellent in both stability and gray balance stability can be provided.

  According to the seventh aspect of the present invention, the black material density corresponding to the Lk image signal is 0.2 to 0.6 times the black material density corresponding to the Bk image signal. By decomposing the image signal into the image signal, it is possible to provide an image processing apparatus having a good granularity in the entire brightness range.

  According to the eighth aspect of the invention, by setting so that the granularity is better and the toner consumption is smaller when the gray component is reproduced using CMY than when the gray component is reproduced using CMY. It is possible to provide an image processing apparatus that can satisfy the graininess, the toner consumption amount, and the gray balance stability.

  According to the ninth aspect of the present invention, in image formation having both the four-color mode and the five-color mode, both modes are set by setting the UCR rate to be high in the 5-color mode and setting to be low in the 4-color mode. In contrast, an image processing apparatus capable of reproducing an image with excellent graininess can be provided.

  According to the invention of claim 10, it is possible to perform image reproduction with five colors by adding light black (Lk) toner having a density lower than that of normal black toner, and to replace the gray component with Bk and Lk signals. In addition, it is possible to provide an image processing method that obtains excellent graininess and is excellent in gray balance and color stability.

  According to the eleventh aspect of the present invention, image reproduction is performed in five colors by adding light black (Lk) toner having a density lower than that of normal black toner, and the UCR (background removal) rate is set to 100%. On the other hand, by replacing the gray component with the Bk and Lk signals, it is possible to provide an image processing method with excellent graininess and excellent gray balance and color stability.

  According to the twelfth aspect of the present invention, image reproduction is performed in five colors by adding normal black toner (Bk) and light black (Lk) toner having a low density, and the UCR (background removal) rate is 100%. Alternatively, by replacing the gray component with the Bk and Lk signals while setting the value close to 100%, it is possible to provide an image processing apparatus with excellent graininess and excellent gray balance and color stability.

  According to the thirteenth aspect of the present invention, it is possible to provide an image forming method capable of achieving both granularity and gray balance stability by performing full black processing using Lk at least in a highlight region.

  According to the fourteenth aspect of the present invention, an image processing method for realizing wide color reproduction can be provided by using a color color material in addition to Bk and Lk in the shadow area in image formation including Lk toner.

  According to the fifteenth aspect of the present invention, by using a color material that is superior in granularity when reproduced using Lk over the granularity of CMY reproduction, reproduction using Lk is more granular. An image processing method capable of obtaining an output excellent in both stability and gray balance stability can be provided.

  According to the sixteenth aspect of the present invention, it corresponds to a plurality of black materials in which the density of the black material corresponding to the Lk image signal is 0.2 to 0.6 times the density of the black material corresponding to the Bk image signal. By disassembling the image signal, it is possible to provide a good image processing method with granularity in the entire brightness range.

  According to the seventeenth aspect of the present invention, by setting so that the granularity is improved and the toner consumption is smaller when the gray component is reproduced using CMY than when the gray component is reproduced using CMY. It is possible to provide an image processing method capable of satisfying graininess, toner consumption, and gray balance stability.

  According to the eighteenth aspect of the present invention, in image formation having both the four-color mode and the five-color mode, both modes are set by setting a high UCR rate in the 5-color mode and a low UCR rate in the 4-color mode. In contrast, an image processing method capable of reproducing an image with excellent graininess can be provided.

  According to the invention of claim 19, it is possible to provide a program that causes a computer to execute the image processing method according to any one of claims 10 to 18.

  According to the invention of claim 20, it is possible to provide a recording medium that allows a computer to read the program of claim 19.

  Exemplary embodiments of the present invention will be described below in detail according to first to sixth embodiments with reference to the accompanying drawings.

(1. Embodiment 1)
(1.1. Image forming apparatus incorporating image processing unit according to Embodiment 1)
FIG. 1 is an overall configuration diagram of an image forming apparatus including an image processing unit according to the first embodiment. A basic image forming operation of the image forming apparatus will be described with reference to FIG.

  The image forming apparatus includes a paper feeding roller 2, a conveying roller pair 3, a registration roller pair 4, an image forming station 35, a photosensitive member 5, a charging charger 6, an exposure beam 7, a developing device 8, a cleaning blade 9, and a primary transfer charger 10. , 16, 22, 28, and 34, image forming stations 37, 38, and 39, an intermediate transfer belt 40, a secondary transfer charger 41, and a fixing device 43.

  The recording paper 1 is separated and called one by one by the paper feeding roller 2 and is conveyed to the conveying roller pair 3. Further, the conveyance roller pair 3 conveys the recording paper 1 and conveys it to the registration roller pair 4. The registration roller pair 4 is configured such that the rotation and stop of the roller can be freely controlled by a registration clutch (not shown). In order to wait for the completion of a series of image forming processes to be described later, the registration roller pair 4 once. The recording paper 1 is stopped.

  The image forming station 35 surrounded by the dotted line is a cyan image forming station. In the image forming station 35, a charging charger 6, an exposure beam 7, a developing device 8, a cleaning blade 9, and a primary transfer charger 10 are arranged around the photosensitive member 5, and perform a series of image forming operations. The surface of the photoconductor 5 uniformly charged by the charging charger 6 is irradiated with an exposure beam 7 from a writing unit (not shown), and a latent image is formed on the photoconductor 5.

  In the developing unit 8, cyan toner is developed on the latent image formed on the photoconductor 5, and visualized as a toner image. Further, the toner image is transferred to the intermediate transfer belt 40 by the primary transfer charger 10. The toner remaining on the photoreceptor 5 is scraped off by the cleaning blade 9. Further, the photosensitive member 5 is charged again by the charging charger 6, and thereafter, the above image forming operation is repeated.

  The image forming station 36 surrounded by the dotted line is a magenta image forming station. The magenta plate image forming station 36 has the same configuration as the cyan plate image forming station 35, forms a magenta plate by the same operation, and transfers the toner image to the intermediate transfer belt 40.

  Further, the image forming stations 37, 38, and 39 are image forming stations for yellow plate, dark black plate, and light black plate, respectively, and similarly transfer the respective toner images to the intermediate transfer belt 40.

  After the toner images of all colors are transferred to the transfer belt 40 by the respective primary transfer chargers 10, 16, 22, 28, and 34, the recording paper 4 once stopped by the registration roller pair 4 is The toners of all colors are transferred onto the recording paper in the secondary transfer charger 41 by re-conveying at the timing. Next, the toner is conveyed to the fixing device 43, and the unfixed toner is fixed on the recording paper by heat and pressure, and is output. The toner remaining on the intermediate transfer belt 40 is scraped off by bringing the intermediate transfer cleaner 42 into contact with the belt, and the intermediate transfer belt 40 is cleaned.

(1.2. Image processing unit according to Embodiment 1)
FIG. 2 is a functional block diagram of the image processing unit according to the first embodiment. The image processing unit 100 includes a scanner 101, a scanner γ correction unit 102, an input masking unit 103, a filter processing unit 104, a selector 105, a storage unit 106, a color conversion unit 107, a printer γ correction unit 108, a halftone processing unit 109, and an output. An engine 110 and a host I / F 111 are provided.

  An image processing unit 100 shown in FIG. 2 outputs a copy output that outputs an image signal input from an image capturing apparatus such as a scanner 101, and a print output that outputs image data input from a host computer via a host I / F 111. It is the structure corresponding to both.

  The digital color image signal input by the scanner 101 is converted from a linear reflectance signal into a linear density signal by the scanner γ correction unit 102. Further, the input masking unit 103 converts the signal dependent on the input device into a standard signal such as sRGB independent of the device.

  The filter processing unit 104 corrects the spatial frequency characteristics. Specifically, an image that requires sharpness such as characters is sharply corrected by an edge enhancement filter, and an image that requires smoothness such as a photograph is softly corrected by a smoothing filter. Do. The image signal corrected as described above is transmitted to the storage unit 106 via the selector 105 and temporarily stored. The image signal stored in the storage unit 106 is read again and input to the color conversion unit 107.

  The color conversion unit 107 converts the RGB signal, which is a standard signal, into a device-dependent signal corresponding to the color material of the output engine 110. Here, the output engine uses a total of five toners of cyan (c), magenta (m), yellow (y) color materials and dark black (bk), light black (lk) achromatic materials. The image is played back. The color conversion unit 107 performs color separation into five colors of C, M, Y, K, Bk, and Lk in order to cope with the reproduction of these five toner images. The operation of the color conversion unit 107 will be described in detail later.

  The output from the color conversion unit 107 is subjected to γ characteristic conversion by table conversion by the printer γ correction unit 108, and then subjected to predetermined dither processing by the halftone processing unit 109 and output to the output engine 110.

(1.3. Color conversion unit)
FIG. 3 is a functional block diagram of the color conversion unit. The color conversion unit 107 is a main part of the image processing unit 100 according to the first embodiment.

  The color conversion unit 107 includes a color correction unit 1071, a black generation unit 1072, a UCR (under color removal) unit 1073, and a Bk / Lk separation unit 1074. UCR is an abbreviation for under color removal processing (Under Color Removal).

  The standard signal RGB input to the color conversion unit 107 is converted into a device-dependent CMY image signal by the color correction unit 1071. Various methods can be considered for the color correction processing. Here, it is assumed that a masking operation such as the following Expression 1 is performed.

C = α11 × R + α12 × G + α13 × B + β1
M = α21 × R + α22 × G + α23 × B + β2
Y = α31 × R + α32 × G + α33 × B + β3 (Formula 1)

  Here, α11 to α33 and β1 to β3 are predetermined color correction coefficients, and CMY also outputs 8-bit signals for RGB 8-bit (0-255) image signals.

Next, the image signal from the color correction unit 1071 is input to the black generation unit 1072 to generate a K signal. The generation of the K signal is obtained by the following equation 2.
K = Min (C, M, Y) (Formula 2)

  FIG. 4 is a diagram expressing Expression 2 in a graph. Here, the minimum value among C, M, and Y is equal to the K signal, and K with respect to Min (C, M, Y) has a simple linear relationship, that is, a straight line.

Further, the UCR unit 1073 obtains a C ′, M ′, Y ′ signal obtained by subtracting the black component based on the C, M, Y signal and the K signal generated by the black generation unit 1072 by the following Expression 3.
C ′ = C−K
M ′ = M−K
Y ′ = Y−K (Formula 3)

  FIG. 5 is a diagram for explaining that the UCR unit performs background removal processing. The color component level 501 before the background processing is subjected to UCR processing to remove the gray component 501 ', and the color component level becomes 502 ". This is so-called full black processing.

  Further, a part of gray components 503 ′ are removed from the color component level 501 to generate a color component level 503 ″. This is the so-called skeleton black method. Here, the background removal is less than 100% and 50% in FIG.

  A series of black ink processings according to Equations 2 and 3 are performed by the full black method described above. The common component of C, M, and Y, that is, the gray component is extracted by Expression 2, and all the gray components are output as the K signal. Further, since the value of K is subtracted from C, M, and Y in Equation 3, it can be said that the processing is a full black method as indicated by 502 ″ in FIG. 5.

  FIG. 6 is a schematic diagram of a table that separates the removed base into a Bk component and an Lk component. Separation means that the plate is decomposed into a Bk component and a Lk component.

  Next, the K signal generated by the black generation unit 1072 is decomposed into a Bk signal and an Lk signal by the Bk / Lk separation unit 1074. The separation table is as shown in FIG. As shown in FIG. 6, when the value of K is 0 to 128, only Lk gradually increases, and at 128, Lk is saturated. In addition, when the value of K is 128 to 255, Bk gradually increases, and when K = 255, Lk = Bk = 255 is output. By using such a separation table, the K signal is decomposed into an Lk signal and a Bk signal.

  FIG. 7A is a cross-sectional view illustrating toner adhesion on the transfer paper. As the density gradually increases from the highlight gray to the shadow gray, toner is formed as the attached toners 601 to 606 shown in FIG. In the figure, the halftone processing method, which has been subjected to the most general dithering, is viewed from the cross section of the recording paper.

  With the most highlighted toner 601, image formation is performed with Lk toner at a low area ratio. In the case of reproducing a slightly darker density, the area ratio of Lk is increased like the adhered toner 602. Further, the area ratio becomes 100% like the adhering toner 603 and is filled with Lk toner. The adhering toner 603 is just in the state of the input value K = 128 in FIG. 6, Lk is 255 (max value at 8 bits, that is, the area ratio is 100%), and Bk is zero.

  When the density further increases, Bk begins to enter next. An image is formed in a state where the Bk layer is placed on the Lk layer like the adhered toner 604. Further, the area ratio of Bk increases like the adhered toner 605, and finally the Bk solid is formed on the Lk solid. This is the position of the arrow in FIG. 6F, that is, the state of K = 255, Lk is 255, and Bk is also 255.

(1.4. Image Processing Procedure According to Embodiment 1)
FIG. 7-2 is a flowchart for explaining an image processing procedure according to the first embodiment. The color correction unit 1071 detects whether or not the RGB signal of the pixel to be processed has been input (step S101). If it is detected (Yes in step S101), the color correction unit 1071 calculates C, Conversion into M and Y signals (step S102).

Subsequently, the black generation unit 1072 generates a K signal based on K = min (C, M, Y) of Expression 2 from the C, M, Y signal (step S103). The UCR unit 1073 applies the C, M, Y signal and the K signal to Expression 3 to perform undercolor removal processing, and generates a C ′, M ′, Y ′ signal (step S104).

  The Bk / Lk separation unit 1074 generates Bk and Lk signals from the K signal based on the separation table shown in FIG. 6 (step S105). As shown in FIG. 6, the gray component starts from 0 and continues to (c) in FIG. That is, the highlight portion uses the Lk signal. When the Lk signal comes to (c) in the figure and the Lk signal is saturated, the Bk signal is generated from that point. This indicates that when viewed in FIG. 7A, dark gray is formed in the order of the sections 602, 603, 604, 605, and 606, starting from the section 601. Cross sections 601 to 606 in FIG. 7A correspond to (a) to (f) in FIG. 6, respectively. In particular, the cross section 603 corresponds to (c) in FIG.

The UCR unit 1073 and the Bk / Lk separation unit 1074 have C ′, M ′, Y ′ signals and Bk,
The Lk signal is output (step S106). The output signal is transmitted to an apparatus that outputs an image using a color material such as a printer.

  The UCR unit 1073 and the Bk / Lk separation unit 1074 determine whether or not processing has been performed for all pixels (step S107). If not yet (No in step S107), the process returns to step S101 and processing is performed for all. When the process is over (Yes in step S107), the process ends.

(1.5. Effect)
Conventional electrophotographic image forming apparatuses using conventional four-color toners of cyan, magenta, yellow, and black have difficulty in achieving both graininess, gray balance and color stability, and toner consumption. there were. Therefore, even if processing is performed at a high UCR rate such as a UCR rate of 100%, the above-mentioned difficult problem can be solved if an image forming apparatus having excellent graininess can be realized. Therefore, the present invention performs image reproduction with five colors by adding light black (Lk) toner having a density lower than that of normal black toner, and sets the UCR rate to 100% or close to 100%, while By replacing the components with Bk and Lk signals, an attempt is made to provide an apparatus with excellent graininess and excellent gray balance and color stability. In other words, the above problem is sought to be solved by a combination of “gray reproduction using Lk toner in addition to Bk toner” and “full black processing”.

  By the way, regarding the processing method for black characters, it is necessary to set a high UCR rate in order to reproduce black characters without coloring. Conventionally, a color copying machine has generally performed processing called image area separation. The character area in the original image is distinguished from the other picture area, and different UCR processing is performed. Determine the character area, or further detect the chromatic / achromatic color and determine the black character area, apply a high UCR rate process such as UCR 100%, and apply a low UCR rate process to the pattern area. Therefore, a method has been taken to realize reproduction of character image quality with high visibility and reproduction of picture image quality with excellent graininess.

  However, if an image forming apparatus excellent in graininess can be realized even if processing is performed at a high UCR rate such as a UCR rate of 100%, high UCR processing can be performed on the entire image, that is, image region separation processing is unnecessary. Therefore, a high-quality image forming apparatus can be realized at low cost. Thus, there is a very great merit if the granularity is excellent by processing by the full black method regardless of the type of the image area. The present invention seeks to achieve this advantage by performing full black processing in an image forming apparatus having toners of two types of density Bk and Lk.

  The image forming apparatus incorporating the image processing unit according to the first embodiment can express gray without using C, M, and Y by performing so-called full black processing in which all gray components are replaced with Lk and Bk signals. In addition, image reproduction with excellent gray balance and color stability can be performed. In addition, since the gray component is expressed by two achromatic materials having different densities of Bk and Lk, it is possible to reproduce an image with excellent graininess.

(2. Embodiment 2)
The image processing unit according to the second embodiment performs processing by the full black method similar to the image processing unit according to the first embodiment at least in the highlight region. The functional block configuration of the image processing unit according to the second embodiment is the same as that described in the image processing unit according to the first embodiment, but the black generation parameters are different.

  FIG. 8 is a diagram for explaining black generation parameters used by the information processing unit according to the second embodiment. The image signal from the color correction unit 1071 is input to the black generation unit 1072 to generate a K signal.

When the generation of the K signal is expressed by an expression, Expression 4 is obtained.
When Min (C, M, Y) <T, K = Min (C, M, Y)
When Min (C, M, Y)> T, K = Min (C, M, Y) × β4 + γ1 (Formula 4)
Here, β4 is a predetermined coefficient and a number less than 1. γ1 is a constant of the intercept in FIG. T is a predetermined threshold value.

  Further, the processing in the UCR unit 1073 is the same as that in the above-described Expression 3. According to Equation 4, in the highlight area, all gray components can be replaced with K signals, and part of the gray components are replaced with K signals above a predetermined threshold T. That is, above the threshold value T in FIG. 8, the portion of the difference between the dotted line 802 and the solid line 801 having the slope B4 is reproduced by the C, M, and Y signals without being reproduced by Bk and Lk.

  With this configuration, at least in the highlight region, the image reproduction is performed by the full black method, and the gray component is reproduced by Lk and Bk, and the image reproduction excellent in granularity, gray balance, and color stability is achieved. Can be done.

  By the way, the stability of the gray balance has been improved as a demerit when performing three-color printing (a method of reproducing the gray component by C, M, and Y), which is particularly remarkable in the highlight region.

  In the information processing unit according to the second embodiment, the result of achieving both the graininess and the gray balance stability is obtained by performing full black processing using Lk at least in the highlight region.

(3. Embodiment 3)
In the image processing unit according to the third embodiment, an object of the image processing apparatus using Lk and Bk is to make the black point lower in brightness so that a wide color gamut can be obtained. For this reason, C, M, and Y are used in addition to Bk + Lk at the black point.

The equation used by the UCR unit 1072 that realizes this operation is as the following equation 5.
C ′ = C−K × β5
M ′ = M−K × β5
Y ′ = Y−K × β5 (Formula 5)
However, β5 is a predetermined coefficient and a number less than 1. Note that the operation of the black ink generation unit 1072 in the previous stage is the same as that in Expression 2.

  With this configuration, the amount of subtracting C, M, and Y is reduced by β5, which is a coefficient less than 1, on the shadow side, so that C, M, and Y remain. This is a so-called UCA process, but this uses C, M, and Y to express the gray component in addition to Bk and Lk in the shadow area near the black point, so that lower brightness can be expressed and a wide color reproduction range is realized. it can.

  In a conventional color copying machine, in order to express the black color (black point) with the lowest brightness, by using C, M, Y toner in addition to 100% Bk toner, brightness reproduction lower than the brightness of Bk 100% is achieved. It was realized. As a result, the color reproduction range of the low brightness area is expanded, and the image reproduction with rich expressiveness can be performed. Even in an image forming apparatus equipped with Lk toner, the brightness of the black point may be high with only Bk and Lk, and it is necessary to use C, M, and Y together in order to widen the color reproduction range.

  In the information processing unit according to Embodiment 3, in the image forming apparatus having Lk toner, wide color reproduction is realized by using a color color material in addition to Bk and Lk in the shadow area.

(4. Image processing unit according to Embodiment 4)
The image processing unit according to the fourth embodiment pays attention to the granularity so that the granularity when gray is reproduced using Lk is lower than the granularity when gray is reproduced with C, M, and Y. A full black process or a process almost similar to a full black process is performed using a simple color material.

  If the granularity is deteriorated when reproducing using Lk rather than reproducing gray components with C, M, and Y, the meaning of using Lk toner is diminished. The setting of the Lk toner is an important factor that determines the performance of the entire image processing apparatus.

  Examples of toner settings for lowering the granularity include Lk toner density and toner particle size. First, the toner density will be described. The Lk toner density value is closely related to the granularity in each brightness region.

  FIG. 9 is a diagram showing the relationship of the granularity with respect to the lightness due to the difference in the Lk density. FIG. 9 conceptually shows the granularity with respect to lightness when three types of Lk density are set when Bk toner and Lk toner are used in the usage method as shown in FIG. is there.

  Here, the curve 903 has the lowest Lk concentration, for example, about 0.2 times the Bk concentration. The curve 901 has the highest Lk concentration, for example, a concentration about 0.6 times the Bk concentration. When the Lk toner density is high, the granularity of the highlight area is high and the granularity of the shadow area is low. By setting the curve 902, which is an intermediate density between the curves 901 and 903, the granularity of the highlight area and the shadow area are substantially equal.

  In the graph of FIG. 9, the granularity once decreases in the middle region is the point (c) in FIG. 6, where Lk is just solid. This point corresponds to the cross section 603 in FIG. Thus, the granularity can be controlled to some extent by setting the Lk density value.

  FIG. 10 is a diagram for explaining a comparison between the relationship between the granularity with respect to the brightness due to the difference in the Lk density and the gray reproduction in CMY. A curve 904 in FIG. 10 shows the granularity when gray is reproduced by CMY. With the settings of the curves 902 and 903 described in FIG. 9, the granularity can be made lower than the CMY gray reproduction of the curve 904.

  FIG. 11 is a diagram illustrating the relationship between the Lk toner particle size and the granularity. Here, the toner particle size will be described. A curve 1101 is a case where the particle size of the Lk toner is relatively large, and as the curves 1102 and 1103 are reached, the particle size becomes smaller. In general, a toner having a small particle diameter has a lower granularity, and smooth image reproduction can be performed.

  FIG. 12 is a diagram comparing the relationship between the Lk toner particle size and granularity and the gray reproduction in CMY. As shown in FIG. 12, if the Lk toner particle diameters of the curves 1102 and 1103 are set, the granularity can be made lower than that of the curve 1104 by CMY gray reproduction.

  As described above, the Lk toner particle size, which is a parameter deeply related to the granularity, is controlled, and the granularity is greater when Lk is reproduced in gray using the full black method than at least when gray is reproduced with CMY. By using a toner that becomes smaller, it is possible to achieve both granularity, gray balance, and color stability. Specifically, a color material is used that has a granularity superior to that of CMY reproduction when reproduced using Lk.

(5. Embodiment 5)
In addition to the configuration according to the fourth embodiment, the image processing unit according to the fifth embodiment pays attention to the toner consumption amount and uses Lk rather than the toner consumption amount when gray is reproduced in C, M, and Y. Using a color material that reduces the amount of toner consumed when gray is reproduced, a full black process or a process almost similar to a full black process is performed.

  If the amount of toner consumption is greater when reconstructing using Lk than when regenerating gray components with C, M, and Y, gray regeneration with C, M, and Y is more economical. It will be. Therefore, the setting of Lk toner is an important factor that determines the economics of the image processing apparatus.

  By paying attention to the toner consumption and setting it so that the granularity is better and the toner consumption is lower when regenerating using Lk than when reproducing gray components with CMY, Aim to satisfy toner consumption and gray balance stability.

  FIG. 13 is a diagram comparing the relationship between Lk toner density and toner consumption and gray reproduction in CMY. FIG. 13 is a graph of Lk toner consumption against gray density. The solid line indicates that the amount of consumption decreases as the Lk toner concentration increases.

  The broken line indicates that the total toner consumption when reproducing gray with CMY is constant Mc. Here, considering Ds, which is the intersection of the solid line and the broken line, if the Lk toner density is set to be higher than Ds, the toner consumption can be reduced as compared to when gray is reproduced with CMY.

  In this way, the parameters deeply related to the toner consumption are controlled, and the toner consumption is set to be smaller when Lk is reproduced in gray by the full black method than at least when gray reproduction is performed by CMY. At the same time, by setting the Lk toner to reduce the granularity as described above, it is possible to satisfy all of the granularity, toner consumption reduction, and gray balance and color stability.

(6. Embodiment 6)
In the image processing unit according to the sixth embodiment, in an image forming apparatus having five colors of C, M, Y, Bk, and Lk, all toners of five color reproduction modes (C, M, Y, Bk, and Lk are used. Mode) and the conventional 4-color reproduction mode (mode using C, M, Y, Bk toner), the 5-color mode has a high UCR ratio setting, and the 4-color mode Set a low UCR rate. By enabling the setting in this manner, it is possible to provide image reproduction with excellent graininess in both modes.

  Here, in which mode the data is output can be set, for example, by receiving a signal input by an operator via an operation display unit (not shown). At this time, it is important to perform processing with excellent graininess regardless of which mode the user selects.

  Therefore, by setting a high UCR rate in the 5-color mode and setting a low UCR rate in the 4-color mode, it is possible to reproduce an image with excellent graininess in any mode.

(7. Modifications)
FIG. 14 is a functional block diagram of a color conversion unit according to a modification. In the color conversion unit described so far, as shown in FIG. 3, the black generation unit 1072 once generates black from the CMY signals obtained by the color correction processing unit 1071. However, like the color conversion unit 207 shown in FIG. 14, after the C ′, M ′, Y ′, K signals are directly output using the three-dimensional lookup table 2074, the Bk / Lk separation unit 2073 You may comprise so that it may be separated.

(8. Hardware configuration etc.)
FIG. 15 is a diagram illustrating a hardware configuration of an image forming apparatus incorporating the image processing unit according to the first embodiment. As shown in the figure, this image forming apparatus has a configuration in which a controller 1210 and an engine unit 1260 are connected via a PCI (Peripheral Component Interconnect) bus. A controller 1210 is a controller that controls the entire image forming apparatus, image reading, information processing, and input from an operation unit (not shown). The engine unit 1260 is an image information processing engine that can be connected to a PCI bus, and includes an image information processing part such as error diffusion and gamma conversion for acquired image data.

  The controller 1210 includes a CPU 1211, a North Bridge (NB) 1213, a system memory (MEM-P) 1212, a South Bridge (SB) 1214, a local memory (MEM-C) 1217, and an ASIC (Application Specific Integrated Circuit). 1216 and a hard disk drive 1218, and the North Bridge 1213 and the ASIC 1216 are connected by an AGP (Accelerated Graphics Port) bus 1215. The MEM-P 1212 further includes a ROM (Read Only Memory) 1212 a and a RAM (Random Access Memory) 1212 b.

  The CPU 1211 performs overall control of the image forming apparatus, has a chip set including the NB 1213, the MEM-P 1212, and the SB 1214, and is connected to other devices via the chip set.

  The NB 1213 is a bridge for connecting the CPU 1211 and the MEM-P 1212, SB 1214, and AGP 1215, and includes a memory controller that controls reading and writing to the MEM-P 1212, a PCI master, and an AGP target.

  The MEM-P 912 is a system memory used as a memory for storing programs and data, a memory for developing programs and data, and the like, and includes a ROM 1212a and a RAM 1212b. The ROM 1212a is a read-only memory used as a memory for storing programs and data, and the RAM 1212b is a writable and readable memory used as a program and data development memory, an image drawing memory at the time of image information processing, and the like.

  The SB 1214 is a bridge for connecting the NB 1213 to a PCI device and peripheral devices. The SB 1214 is connected to the NB 1213 via a PCI bus, and a network interface (I / F) unit and the like are also connected to the PCI bus.

  The ASIC 1216 is an IC (Integrated Circuit) for multimedia information management application having hardware elements for managing multimedia information, and has a role of a bridge for connecting the AGP 1215, the PCI bus, the HDD 1218, and the MEM-C 1217.

  The ASIC 1216 includes a PCI target and an AGP master, an arbiter (ARB) that forms the core of the ASIC 1216, a memory controller that controls the MEM-C 1217, and a plurality of DMACs (Direct Memory) that perform rotation of image data by hardware logic or the like. A Universal Serial Bus (USB) 1240 and an IEEE (The Institute of Electrical and Engineering Engineers 1394) interface 1250 are connected between the Access Controller and the engine unit 1260 via a PCI bus.

  The MEM-C 1217 is a local memory used as a transmission image buffer and a code buffer, and the HDD 1218 is a storage for storing image data, programs, font data, and forms.

  The AGP 1215 is a bus interface for a graphics accelerator card proposed for speeding up graphics processing. The AGP 1215 speeds up the graphics accelerator card by directly accessing the MEM-P 1212 with high throughput.

  The keyboard 1220 connected to the ASIC 1216 receives an operation input from the operator and transmits the operation input information received by the ASIC 1216.

  An image processing program executed by the image forming apparatus is a file in an installable format or an executable format, and is read by a computer such as a CD-ROM, a flexible disk (FD), a CD-R, or a DVD (Digital Versatile Disk). You may comprise so that it may record on a possible recording medium and provide.

  Further, the image processing program executed by the image forming apparatus may be provided by being stored on a computer connected to a network such as the Internet and downloaded via the network. You may comprise so that it may provide or distribute via a network.

  The image processing program executed by the image forming apparatus includes the above-described units (color correction unit, black generation unit, UCR unit, Bk / Lk color separation unit, scanner γ correction unit, input masking unit, filter processing unit, selector, The module configuration includes a storage unit, a printer γ correction unit, a halftone processing unit, an output engine, and the like. As actual hardware, a CPU (processor) reads and executes an image processing program from the ROM. Are loaded onto the main storage device, and the color correction unit, black generation unit, UCR unit, Bk / Lk separation unit, scanner γ correction unit, input masking unit, filter processing unit, selector, storage unit, printer γ A correction unit, a halftone processing unit, an output engine, and the like are generated on the main storage device.

  The embodiments of the present invention described above and the modifications thereof are examples for description, and the present invention is not limited to these examples described here.

  The present invention can be used for an image processing technique in image formation, and in particular, can be used for an image processing technique in image formation of a digital multifunction peripheral.

1 is an overall configuration diagram of an image forming apparatus including an image processing unit according to Embodiment 1. FIG. 2 is a functional block diagram of an image processing unit according to Embodiment 1. FIG. It is a functional block diagram of a color conversion unit. It is the figure which expressed Formula 2 with the graph. It is a figure explaining UCR part performing a background removal process. It is a schematic diagram of the table which separates the removed foundation | substrate into Bk component and Lk component. FIG. 6 is a cross-sectional view illustrating toner adhesion on transfer paper. 5 is a flowchart for explaining an image processing procedure according to the first embodiment. It is a figure explaining the parameter of the black generation which the information processing unit by Embodiment 2 uses. It is a figure which shows the relationship of the granularity with respect to the brightness by the difference in Lk density | concentration. It is a figure explaining the comparison of the relationship of the granularity with respect to the brightness by the difference in Lk density, and the gray reproduction | regeneration in CMY. It is a figure explaining the relationship between a Lk toner particle size and granularity. FIG. 6 is a diagram comparing the relationship between Lk toner particle size and granularity and gray reproduction in CMY. FIG. 10 is a diagram comparing the relationship between Lk toner density and toner consumption and gray reproduction in CMY. It is a functional block diagram of the color conversion unit by a modification. 2 is a diagram illustrating a hardware configuration of an image forming apparatus in which an image processing unit according to Embodiment 1 is incorporated. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Image processing unit 101 Scanner 102 Scanner gamma correction part 103 Input masking part 104 Filter processing part 105 Selector 106 Accumulation part 107 Color conversion unit 108 Printer gamma correction part 109 Halftone processing part 110 Output engine 111 Host I / F
1071 Color correction unit 1072 Black generation unit 1073 UCR unit 1074 Bk / Lk separation unit

Claims (20)

In an image processing apparatus for converting an input image signal into an image signal corresponding to a plurality of color materials and a plurality of black materials having different densities,
Color image signal generating means for generating color image signals corresponding to a plurality of color materials from the input image signal;
Black image decomposition means for converting a gray component into an image signal corresponding to the plurality of black materials from the input image signal;
An image processing apparatus comprising:   The image processing apparatus according to claim 1, wherein the black image decomposition unit converts all of the gray components from the input image signal into image signals corresponding to the plurality of black materials.   3. The image processing according to claim 1, wherein the black image decomposition means decomposes the inputted image signal into image signals corresponding to two types of black materials, dark black and light black. apparatus.   The image processing apparatus according to claim 3, wherein the black image decomposition unit generates all of the gray components based on an image signal corresponding to the light black black material for a highlight region. .   2. The color image signal generation unit according to claim 1, wherein a part of the gray component is generated by a color image signal generated by the color image generation unit for a shadow area. Image processing device.   The black image decomposition means has a gray reproduction granularity of only the light black black material corresponding to the light black image signal, and a gray reproduction granularity of the plurality of color color materials corresponding to the color image signal. The image processing apparatus according to claim 3, wherein the image processing apparatus generates an image signal corresponding to a light black color material that is superior to the light black color material.   The black image decomposing means is configured such that the density of the light black black material corresponding to the light black image signal is 0.2 to 0.6 of the density of the dark black black material corresponding to the dark black image signal. The image processing apparatus according to claim 6, wherein the image processing apparatus decomposes image signals corresponding to a plurality of double black materials.   The black image decomposing means uses toner in gray reproduction by the plurality of color color materials corresponding to the color image signal so that a toner usage amount in gray reproduction by only the light black black material corresponding to the light black image signal is The image processing apparatus according to claim 3, wherein the image processing apparatus generates an image signal corresponding to a light black color material that is less than a usage amount. A first reproduction mode for reproducing a gray component by a plurality of color image signals by the color image signal generation unit and an image signal corresponding to a plurality of black materials having different densities by the black image decomposition unit;
Second reproduction mode for reproducing gray components by a plurality of color image signals by the color image signal generation means and an image signal corresponding to the black material having the highest density among the plurality of black materials having different densities by the black image decomposition means. And
2. The black image decomposition means, wherein the black generation rate for replacing the gray component with an image signal of a black material is set higher in the first mode than in the second mode. The image processing apparatus as described in any one of -8. In an image processing method in an image processing apparatus for converting an input image signal into image signals corresponding to a plurality of color materials and a plurality of black materials having different densities,
A color image signal generating step for generating color image signals corresponding to a plurality of color materials from the input image signal by the image signal control means;
A black image decomposition step of converting a gray component into an image signal corresponding to the plurality of black materials from the input image signal by a black image decomposition means;
An image processing method comprising:   11. The black image decomposing step converts all gray components from the input image signal into image signals corresponding to the plurality of black materials by the black image decomposing means. An image processing method described in 1.   11. The black image decomposing step is characterized in that the input image signal is decomposed into image signals corresponding to two kinds of black materials of dark black and light black by the black image decomposing means. Or the image processing method of 11.   The black image decomposition step is characterized in that, for the highlight area, all of the gray components are generated by an image signal corresponding to the light black black material by the black image decomposition means. 12. The image processing method according to 12.   11. The color image signal generation step of generating a part of the gray component for a shadow area by using a color image signal generated by the color image generation means. Image processing method.   In the black image decomposition step, the plurality of color colors in which the granularity of gray reproduction by only the black material of the light black corresponding to the light black image signal corresponds to the color image signal by the black image decomposition means. The image processing according to any one of claims 12 to 14, wherein an image signal corresponding to a light black color material that is superior to the granularity of gray reproduction by the material is generated. Method.   In the black image decomposing step, the density of the black material of the dark black corresponding to the image signal of the dark black is adjusted by the black image decomposing means so that the density of the light black black material corresponding to the light black image signal is the same. The image processing method according to claim 15, wherein the image processing method is one that decomposes into image signals corresponding to a plurality of black materials of 0.2 to 0.6 times.   In the black image separation step, the black image separation means uses the plurality of colors corresponding to the color image signal in which toner usage in gray reproduction using only the light black black material corresponding to the light black image signal corresponds to the color image signal. The image processing method according to claim 15 or 16, wherein an image signal corresponding to a light black color material which is smaller than a toner usage amount in gray reproduction by the color material is generated. A first reproduction mode for reproducing a gray component by a plurality of color image signals by the color image signal generation unit and an image signal corresponding to a plurality of black materials having different densities by the black image decomposition unit;
Second reproduction mode for reproducing gray components by a plurality of color image signals by the color image signal generation means and an image signal corresponding to the black material having the highest density among the plurality of black materials having different densities by the black image decomposition means. And
In the black image decomposition step, a black generation rate for replacing the gray component with an image signal of a black material by the black image decomposition unit is set higher in the first mode than in the second mode. The image processing method according to claim 10, wherein:   A program causing a computer to execute the image processing method according to any one of claims 10 to 18.   A recording medium storing the program according to claim 19 in a computer-readable manner.

Images