JP2008154115A - Image forming apparatus and correction method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To generate a color separation table so as not to discontinue gradations of a formed image even in the case an input signal is directly subjected to color-separation into the number of the color materials when performing image formation using the color materials, including deep and pale color materials having equal hue to one another with different brightness. <P>SOLUTION: The present invention relates to a correction method in an image forming apparatus, including the steps of: outputting a primary color gradation characteristic chart (S1302); reading the primary color gradation characteristic chart (S1303); comparing it with a target value to calculate a correction amount in the case the variable deep color materials and pale color materials are output individually, respectively (S1304); reading the output deep/pale mixed color patch chart using the correction amount, comparing it with a target value to calculate the correction amount of a color mixing ratio and then correcting the color separation table using the calculated correction amount of the color mixing ratio (S1306). <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a correction processing technique in an image forming apparatus that forms an image on an input image signal using a dark color material and a light color material having the same hue and different brightness.

  In recent years, in addition to four color materials that are process colors such as cyan (C), magenta (M), yellow (Y), and black (K), an electrophotographic image is formed using a special color material. Forming devices are emerging.

  In general, special color materials include light color materials such as light cyan (c) and light magenta (m) that have the same hue and low density (high brightness) as cyan and magenta, and metallic color materials such as gold and silver, There are fluorescent color materials containing a fluorescent agent, and transparent color materials for adjusting glossiness. By using such a special color material, the image forming apparatus can expand the color reproduction range, improve the gloss and texture, and improve the graininess and gradation.

  Here, among such a wide variety of special color materials, in this specification, the light colors c and m are added to the four color materials C, M, Y, and K, which are process colors. An image forming apparatus using six color materials (hereinafter referred to as “six color system”) will be described. In the following, the four color materials C, M, Y, and K, which are the process colors, are called dark color materials in the sense of low brightness (high density) color materials as opposed to light color materials. To do. Further, an image forming apparatus using four color materials of process colors C, M, Y, and K is referred to as a “four-color system”.

  In general, in the four-color system, correction (calibration) is periodically performed on various tables used when image formation is performed on an input image signal. This is because the color tone also changes due to the change in density over time (density change).

  The same applies to the six-color system, and similarly to the calibration in the four-color system, calibration is performed by individually adjusting the transfer voltage and creating a density correction table for each of the dark color material and the light color material. Specifically, it is performed in the following two stages.

  First, a test pattern is printed, and the transfer voltage is adjusted so that the maximum density becomes a specified density value by measuring the density of the printed test pattern using a sensor in the apparatus. Next, a test pattern including a halftone pattern is printed, the density of the test pattern is measured by an apparatus such as a scanner, and the density characteristic of the halftone pattern is obtained. The obtained density characteristic is a specified density characteristic (target value). ) To create a density correction table.

  Here, since the correction of the maximum density by adjusting the transfer voltage is an analog correction, an error is likely to occur, and the maximum density may be excessive or insufficient with respect to the specified density value. However, even in that case, in the four-color system, since the excess or deficiency of the maximum density is a problem in the high density part, the influence on the image quality is relatively small.

  On the other hand, in the case of the six-color system, only the light color material is used in the range where the density value of the input image signal is low, and the dark color material is used when the input image signal reaches the reference density value. Configured to start. For this reason, the maximum density of the light color material corresponds to an intermediate density region as a basic color (a color formed using a dark color material and a light color material having the same hue).

  In other words, the excess or deficiency of the maximum density of the light color material causes density fluctuations in the intermediate density area, and as a result, the gradation of the basic color becomes discontinuous in the density area where the use of the dark color material starts. Become. For this reason, it is required to create a density correction table so as to absorb fluctuations in the maximum density of the light color material.

  In order to meet such needs, the applicant of the present application has proposed to create a one-dimensional density correction table, for example, in the processing shown in FIG.

  FIG. 15 is a diagram showing a process of separating the RGB signals, which are input image signals, into six color materials and outputting them. According to the figure, first, an RGB signal that is an input image signal is color-separated into a primary color primary color material (C, M, Y, K) using a color separation table 1500. The After that, the color component signals (1501 and 1502) corresponding to the dark color materials (C and M) having the combination of the dark and light color materials are subjected to gradation correction using the one-dimensional density correction table (1503 and 1504).

  Here, the one-dimensional density correction table is, for example, a table having density characteristics as shown in FIG. 17, and density correction configured to compensate for the shortage of the maximum density of the light color material with the dark color material. It is a table. Specifically, in the case of White → Cyan gradation, when a dark cyan color material and a light cyan color material are used at a color mixture ratio as shown in FIGS. 17A and 17C, the light cyan color material is A → B. It is assumed that the concentration has changed.

  In this case, the density correction table for the primary color is created so that the characteristic of the dark cyan color material changes from C to D. By creating such a one-dimensional density correction table, it is possible to avoid the occurrence of discontinuous gradation.

  Here, in the process shown in FIG. 15, the advantage of using the one-dimensional density correction table is that the color separation of the basic color does not adversely affect the entire color gamut. That is, it is not necessary to consider other color gamuts that use a light color material for color separation of the basic color, and for other color gamuts, the color mixture ratio after color separation of the basic color can be used as it is.

  A specific example will be described. For example, it is assumed that the color mixture ratio of the basic color fluctuates as shown in B and D of FIG. Even in this case, in the case of the processing method shown in FIG. 15, cyan used for reproducing other colors, for example, White → Black gradation, may use the color mixture ratios shown in B and D of FIG. 17 as they are. it can.

  On the other hand, if the processing method is different, the color mixture ratio in the one-dimensional density correction table may not be used as it is in another color gamut. As an example, as shown in FIG. 16, a processing method for directly separating colors from RGB signals into six color materials of C, c, M, m, Y, and K using a color separation table 1600 will be considered.

  In the case of such a processing method, even if white-to-cyan gradation is color-separated into a dark cyan color material and a light cyan color material at a color mixture ratio as shown in FIG. Is not always done.

  Specifically, the dark cyan color material and the light cyan color material are color-separated as E and F in FIG. 18 in the White → Black gradation, and the color mixture ratios are completely different. For this reason, if the change in the color mixture ratio in the White → Cyan gradation is used as it is in the White → Black gradation, the gradation continuity of the entire color gamut is impaired.

  For example, as shown in FIG. 17, it is assumed that the maximum density of the light color material decreases and the light cyan color material characteristic changes from A to B in the White → Cyan gradation. In this case, the color separation table 1600 is corrected, and the dark cyan color material characteristic is changed from C to D in the White → Cyan gradation.

  If the color mixture ratio at this time is used as it is in the White → Black gradation, the dark cyan color material characteristic is corrected from F to G. However, originally, in the White → Black gradation, since the light cyan color material does not use the vicinity of the maximum density, if it is corrected from F → G, the tone variation in the halftone or the gradation discontinuity will be caused. An evil will occur.

  As described above, in the case of a processing method that performs color separation directly from RGB (or CMYK) into six colors, the color and tone characteristics of the color gamut other than the basic color may be impaired due to the influence of the color separation of the basic color. There is sex. For this reason, it is required to create a density correction table (color separation table) in consideration of the color tone and gradation of a color gamut other than the basic color.

  The present invention has been made in view of the above problems, and when performing image formation using color materials including light and dark color materials having similar colors and different brightness, the input signal is directly color-separated into the number of color materials. Even in such a case, the object is to correct the gradation of the image so as not to be discontinuous.

In order to achieve the above object, an image forming apparatus according to the present invention has the following configuration. That is,
An image forming apparatus that forms an image with respect to an input image signal using a dark color material and a light color material having different lightness and similar colors,
Storage means for storing a color separation table for extracting each color component signal corresponding to the dark color material and the light color material from the image signal;
A first output means for outputting a primary color gradation characteristic chart by recording a plurality of images having different color gradations on a recording medium using the dark color material and the light color material individually;
The density value of each of the plurality of images having different color gradations obtained by reading the primary color gradation characteristic chart output by the first output unit and the plurality of predetermined color gradations having different color gradations are obtained. A first calculation means for calculating a correction amount in the case of individually outputting the dark color material and the light color material by comparing the density target values of the respective images;
A plurality of images having different color mixing ratios of the dark color material and the light color material are recorded on a recording medium after correcting the output of the color mixture material and the light color material using the correction amount calculated by the first calculation unit. A second output means for outputting the light and shade mixed color patch chart;
Density values for each of the plurality of images with different color mixture ratios obtained by reading the grayscale color mixture patch chart output by the second output means are color-separated using the color separation table, and the darkness is obtained. A second calculation for calculating a correction amount of the color mixture ratio by obtaining a color mixture ratio of the color material and the light color material and comparing with a target value of a density value for each of a plurality of predetermined images having different color mixture ratios Means,
And a correction unit that corrects the color separation table stored in the storage unit using the correction amount calculated by the second calculation unit.

  According to the present invention, when an image is formed using color materials including light and dark color materials having similar colors and different brightnesses, even when the input signal is directly color-separated into the number of color materials, the gradation of the image is not good. Corrections can be made so that they are not continuous.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings as necessary.

[First Embodiment]
1. Configuration of Image Forming Apparatus FIG. 1 is a diagram showing a hardware configuration of an image forming apparatus (MFP (Multi Function Peripheral) having both a copying function, a printer function, and a FAX function) according to the first embodiment of the present invention. It is.

  As shown in the figure, the MFP 100 has a digital color image reader unit 101 at the top and a digital color image printer unit 102 at the bottom.

  The digital color image reader unit 101 obtains a reflected light image from the original 130 by placing the original 130 on the original table glass 131 and performing exposure scanning with the exposure lamp 132. The reflected light image is condensed on the full color CCD sensor 134 by the lens 133 to obtain a color image signal. The color image signal passes through an amplifier circuit (not shown), is processed by a video processing unit (not shown), and is sent to the digital color image printer unit 102 via an image memory (not shown).

  In addition to the color image signal from the digital color image reader unit 101, the color image signal transmitted from the computer and the color image signal transmitted from the FAX are similarly sent to the digital color image printer unit 102. Come.

  Here, as an example, the operation of the digital color image printer unit 102 based on a signal from the digital color image reader unit 101 will be described.

  Details of various image processes performed on the input color image signal will be described later. Here, the digital color image printer unit 102 for forming an image on recording paper using the data after image processing. Will be described.

  The digital color image printer unit 102 is roughly divided into two image forming units, that is, a first image forming unit Sa including a first photosensitive drum 101a and a second image forming unit including a second photosensitive drum 101b. Sb is arranged. The image forming portions Sa and Sb have substantially the same configuration (shape) for the purpose of cost reduction. For example, the configuration and shape of the developing unit described later are almost the same. As a result, even if the developing devices 141 to 146 are interchanged with each other, the configuration can be dealt with.

  Two drum-shaped photosensitive members (photosensitive drums) as image carriers, that is, a first photosensitive drum 101a and a second photosensitive drum 101b, are each rotatably supported in the direction of arrow A in the figure. Around each of the photosensitive drums 101a and 101b, pre-exposure lamps 111a and 111b and corona chargers (charging means) 102a and 102b are arranged.

  In addition, a first exposure unit 103a that is a laser exposure optical system, a second exposure unit 103b, potential sensors 112a and 112b, and movable bodies (development rotary) 104a and 104b that are rotary developing device holding units are arranged. . Furthermore, three developing devices 141 to 143 and 144 to 146 containing developers of different colors are disposed in each holding portion, primary transfer rollers 105a and 105b as primary transfer means, and cleaning devices 106a and 106b. .

  Further, the number of developing units may be five or more for improving the image quality. In this embodiment, six developing units 141 to 146 are used. The developing unit is loaded with magenta color material 141, cyan color material 142, light magenta color 143, yellow color material 144, black color material 145, and light cyan color material 146. Suppose that

  Here, the dark and light color developers are prepared by changing the amount of the pigment having the same spectral characteristics. Therefore, the light magenta color material contains the pigment having the same spectral characteristics as magenta but has a small content, and the light cyan color material contains the pigment having the same spectral characteristics as cyan but has a low content.

  In addition, although the two-component developer used by mixing the color material and the carrier is loaded in the developing device, there is no problem even with the one-component developer composed of only the color material.

  Here, the use of dark and light colors for magenta and cyan is aimed at dramatically improving the reproducibility of light images such as human skin (to achieve a reduction in graininess). Is the aim).

  In the first and second exposure means 103a and 103b, the color image signal from the digital color image reader unit 101 is converted into an optical signal by a laser output unit (not shown). Then, the laser beam E converted into the optical signal is reflected by the polygon mirror 135 and projected onto the exposure positions 138a and 138b on the surfaces of the photosensitive drums 101a and 101b through the lens 136 and the reflecting mirrors 137.

  In the digital color image printer unit 102, the photosensitive drums 101a and 101b are rotated in the direction of arrow A during image formation. Then, the photosensitive drums 101a and 101b after being neutralized by the pre-exposure lamps 111a and 111b are uniformly charged by the chargers 102a and 102b, and irradiated with the light image E for each separated color, respectively, on the photosensitive drums 101a and 101b. To form a latent image.

  Next, the rotary developing device holding portion, that is, the first developing rotary 104a and the second developing rotary 104b, which are moving bodies, are rotated. Then, development is performed after the predetermined developing devices 141 and 144 are moved to the common developing units 140a and 140b between the developing devices 141 to 143 on the photosensitive drums 101a and 101b or between the developing devices 144 to 146. Actuators 141 and 144 are activated. Then, the electrostatic latent images on the photosensitive drums 101a and 101b are reversed and developed to form a developer image (color material image) using a resin and a pigment as a base on the photosensitive drums 101a and 101b. At this time, a developing bias is applied to the developing device.

  Further, as shown in the drawing, the color materials in the developing devices 141 to 146 are replenished as needed at a predetermined timing. This is because the color material ratio (in the developing device) from the color material storage units (hoppers) 161 to 166 for each color arranged between and next to the first and second exposure means 103a and 103b which are laser exposure optical systems. Alternatively, the color material amount) is kept constant.

  The color material images formed on the respective photosensitive drums 101a and 101b are sequentially primary-transferred sequentially by primary transfer rollers 105a and 105b which are primary transfer units. As a result, a color material image is formed on the intermediate transfer member (intermediate transfer belt) 105 as a transfer medium in an overlapping manner. At this time, a primary transfer bias is applied to the primary transfer rollers 105a and 105b. As a result, the color material images are sequentially superimposed on the intermediate transfer belt 105 to form a full color color material image.

  Thereafter, the full-color color material image on the intermediate transfer belt 105, which is a transfer medium, is secondarily transferred onto the recording paper at once. At this time, a secondary transfer bias is applied to the secondary transfer roller 154.

  The intermediate transfer belt 105 is driven by a driving roller 151. A transfer cleaning device 150 is configured to be able to contact and separate from the driving roller 151 at a position facing the intermediate transfer belt 105.

  Photosensitive drums 101a and 101b are provided on a transfer surface t which is the same plane portion formed by stretching the intermediate transfer belt 105 by two drive rollers 151 and 152. In addition, primary transfer rollers 105a and 105b, which are primary transfer units, are provided at portions facing the photosensitive drums 101a and 101b with the intermediate transfer belt 105 interposed therebetween.

  In addition, a sensor 153 that detects the positional deviation and density of the images transferred from the respective photosensitive drums 101a and 101b is disposed opposite to the driven roller 152 that forms the transfer surface t. Then, control is performed to correct the image density, the color material replenishment amount, the image writing timing, the image writing start position, and the like at any time in the image forming units Sa and Sb.

  Further, the transfer cleaning device 150 facing the upstream drive roller 151 finishes superimposing the necessary color on the intermediate transfer belt 105, and then is pressed by the facing drive roller 151 and transferred to the recording paper. The remaining color material on the intermediate transfer belt 105 is cleaned. After the cleaning is completed, the transfer cleaning device 150 is separated from the intermediate transfer belt 105.

  On the other hand, the recording paper is conveyed one by one from the storage units 171, 172, 173 or the manual feed tray 174 by the paper feeding units 181, 182, 183, 184, and the skew is corrected by the registration rollers 185. Thereafter, the color material image on the intermediate transfer belt 105 is conveyed to a secondary transfer portion between the secondary transfer roller 154 and the intermediate transfer belt 105 which is a secondary transfer means for transferring the color material image on the intermediate transfer belt 105 to the recording paper at a desired timing. .

  The color material image is transferred onto the recording paper in the secondary transfer unit, the recording paper passes through the transport unit 186, the color material image is fixed by the heat roller fixing device 109, and the paper discharge tray 189 or the recording paper post-processing device ( The paper is discharged (not shown).

  On the other hand, the intermediate transfer belt 105 after the secondary transfer is cleaned with the transfer residual color material by the transfer cleaning device 150 as described above, and again used for the primary transfer process of the image forming portions Sa and Sb.

  Further, when forming images on both sides of the recording paper, the recording paper passes through the heat roller fixing device 109 and immediately after that, the conveyance path switching guide 191 is driven to move the recording paper from the conveyance vertical path 175 to the reverse path 176. Guide once. Thereafter, by reverse rotation of the reverse roller 187, the rear end at the time of feeding is set at the top, the sheet is withdrawn in the direction opposite to the fed-in direction, and is sent to the duplex conveyance path 177. After that, the paper passes through the double-sided conveyance path, is skew-corrected and timed by the double-sided conveyance roller 188, and is conveyed to the registration roller 185 at a desired timing. Transcript.

2. Functional Configuration of MFP 100 A functional configuration of the MFP 100 will be described with reference to FIG.

  In the figure, an input image processing unit 201 reads a document with a digital color image reader unit 101 and performs image processing on the read image data.

  A NIC (Network Interface Card) unit 202 passes image data (mainly PDL data) transmitted using the network to the RIP unit 202, and transmits image data and device information inside the MFP 100 to the outside via the network. To do. The RIP unit 202 is a part that decodes the input PDL (Page Description Language) data and develops the RIP (Raster Image Processor).

  The input image data is sent to the MFP control unit 204. The MFP control unit 204 plays a role of traffic control for controlling input image data and output image data.

  Further, the image data input to the MFP control unit 204 is temporarily stored in the memory unit 205. The stored image data is temporarily stored or called as necessary.

  The output image processing unit 206 performs image processing for printing on recording paper, and sends it to a printer unit 207 (corresponding to the digital color image printer unit 102).

  The printer unit 207 feeds recording paper and sequentially prints the image data created by the output image processing unit 206. The printed recording paper is sent to the post-processing unit 208, where sheet sorting processing and sheet finishing processing are performed.

  The operation unit 203 is for selecting the above-described various flows and functions and for instructing operations.

As described above, the MFP 100 can realize various functions and usage methods under the control of the MFP control unit 204, and an example is shown below.
・ Copy function:
Input image processing unit 201 → output image processing unit 206 → printer unit 207
・ Network scan:
Input image processing unit 201 → NIC unit 202
・ Network print:
NIC unit 202 → RIP unit 202 → output image processing unit 206 → printer unit 207
-Box scan function:
Input image processing unit 201 → output image processing unit 206 → memory unit 205
-Box print function:
Memory unit 205 → printer unit 207
-Box reception function:
NIC unit 202 → RIP unit 202 → output image processing unit 206 → memory unit 205
・ Box transmission function:
Memory unit 205 → NIC unit 202
・ Preview function:
Memory unit 205 → operation unit 203
Among these, details of the functional configuration of the output image processing unit 206 for realizing the copy function, the network print function, the box scan function, and the box reception function will be described below with reference to FIG.

3. Functional Configuration of Output Image Processing Unit 206 FIG. 3 is a block diagram showing a detailed functional configuration of the output image processing unit 206. In many cases, image data output from the input image processing unit 201 and input to the output image processing unit 206 via the MFP control unit 204 is RGB image data of 8 bits (256 gradations) per pixel.

  The shading correction unit 301 performs white reference correction on the input RGB image data. Also, the input color processing unit 302 performs input masking processing to remove color turbidity caused by the spectral characteristics of the CCD.

  Further, the spatial filter unit 303 corrects the frequency characteristics of the RGB image data. In the output image processing unit 206, the RGB image data obtained by the above processing or the RGB image data (each color 8 bits) generated and output by the RIP unit 202 and input to the output image processing unit 206 is converted into the RGB color. Color separation is performed by the separation unit 304 or 307.

  Specifically, when performing color separation into four colors, the RGB color separation unit 304 performs color separation into CMYK signals (10 bits for each color). In the case of separation into six colors, the RGB color separation unit 307 performs color separation into CcMmYK signals (10 bits for each color). In the color separation, a correction color separation table described later is used.

  Note that the RIP unit 202 may output CMYK image data. In this case, the CMYK image data is color-separated by the CMYK color separation unit 308 or 309.

  Specifically, when separating into four colors, the CMYK color separation unit 308 performs color separation into CMYK signals, and when separating into six colors, the CMYK color separation unit 309 performs color separation into CcMmYK signals. The The CMYK color signal is color-separated, and in addition to the CMYK color signal, a c signal that is a color material signal similar to C and a y signal that is a color material signal similar to Y are also obtained.

  The color-separated signal is input to the gamma correction unit 305. The gamma correction unit 305 performs output characteristic correction (gamma correction) on the CMYK signal or the CcMmYK signal using a primary color gradation correction LUT, which is an independent one-dimensional lookup table (1D LUT) for each color. Subsequently, the halftone processing unit 306 performs pseudo halftone processing corresponding to the number of gradations and the resolution that can be reproduced by the printer unit 207 on the CMYK signal or the CcMmYK signal. Then, the output image processing unit 206 outputs the CMYK signal or the CcMmYK signal subjected to pseudo halftone processing to the printer unit 207. Note that the number of gradations and the resolution of the printer unit 207 are, for example, 4 bits and 600 dpi, but are not particularly limited thereto. As the pseudo halftone process, a known screen line process or error diffusion process is used.

4). Calibration of Various Tables Used in Output Image Processing Unit 206 Next, calibration processing for various tables (corrected color separation table and primary color gradation correction LUT) used in image processing in the output image processing unit 206 will be described. .

4.1 Functions of MFP Control Unit 204 Related to Calibration First, the functional configuration of the MFP control unit 204 related to calibration regarding the correction color separation table and the primary color gradation correction LUT will be described.

  FIG. 4 is a diagram illustrating a functional configuration related to the calibration process in the MFP control unit 204. In the figure, reference numeral 401 denotes a primary color gradation correction unit for calibrating a primary color gradation correction LUT.

  The primary color gradation correction unit 401 reads a primary color gradation characteristic chart (described later) stored in the memory unit 205 and prints it through the output image processing unit 206. In the printed primary color gradation characteristic chart, the density value is measured by the user.

  The measured density value is input via the operation unit 203, and the primary color gradation correction unit 401 accepts it and creates a primary color gradation characteristic table for correction (described later). Then, it is compared with a reference primary color gradation characteristic table (described later) stored in the memory unit 205.

  In the primary color gradation correction unit 401, each density value (correction primary color gradation characteristic table) of the primary color gradation characteristic chart printed and measured by the user is made equal to the reference primary color gradation characteristic table. First, a primary color gradation correction LUT is generated. The generated primary color gradation characteristic LUT is stored in the memory unit 205.

  Reference numeral 402 denotes a color separation table correction unit for calibrating the color separation table. First, the color separation table correction unit 402 reads a dark / light mixed color patch chart (described later) stored in the memory unit 205, and outputs the dark color material and the light color material using the generated primary color gradation correction LUT. to correct. Then, the shaded color patch chart is printed via the output image processing unit 206. The printed light / dark mixed color patch chart is read by the digital color image reader unit 101 and input as a density value via the input image processing unit 201.

  The color separation table correction unit 402 performs color separation on the input density value using a reference color separation table (described later), and compares it with a reference gray-mixed color density characteristic table (described later) stored in the memory unit 205. Then, the density values of the dark color material and the light color material of the light and dark color mixture patch chart inputted through the input image processing unit 201 and color-separated using the reference color separation table become equal to the reference light and dark color mixture density characteristic table. As described above, the color separation table is corrected. Then, the corrected color separation table obtained by the correction is stored in the memory unit 205.

  Note that the processing in the primary color gradation correction unit 401 and the color separation table correction unit 402 is executed by receiving an instruction from the user via the operation unit 203.

4.2 UI of operation unit 203 related to calibration
Next, a user interface of the operation unit 203 for operating the primary color gradation correction unit 401 and the color separation table correction unit 402 will be described.

  FIG. 5 is a diagram illustrating an example of a user interface of the operation unit 203 for operating the primary color gradation correction unit 401 and the color separation table correction unit 402 in the MFP 100 according to the present embodiment.

  In FIG. 5A, reference numeral 501 denotes an “automatic gradation correction” start instruction button, and when the start instruction button 501 is pressed, the primary color gradation correction unit 401 operates. Reference numeral 502 denotes a status display field that displays the current status.

  A state display field 502 in FIG. 5A is a state before the “automatic gradation correction” start instruction button 501 is pressed. On the other hand, in the status display field 502 of FIG. 5B, when the “automatic gradation correction” start instruction button 501 is pressed, the primary color gradation correction unit 401 operates and the primary color gradation correction LUT is displayed. Indicates the state after being generated. Further, the state display column 502 in FIG. 5C indicates that the state after the color separation table correction unit 402 has been operated by agreeing to execute “high-accuracy gradation correction”.

  Note that after the automatic gradation correction is completed, a message for confirming to the user whether or not to operate the color separation table correction unit 402 is displayed (state display field 502 in FIG. 5B). reference). Therefore, when the “Yes” button 503 is pressed according to the message, the color separation table correction unit 402 starts operating. On the other hand, when the “No” button 504 is pressed, the color separation table correction unit 402 does not operate.

  In the above description, when the “automatic gradation correction” start instruction button 501 is pressed and the operation of the primary color gradation correction unit 401 is completed, the process is temporarily stopped, and high-precision gradation correction is performed on the user. However, the present invention is not limited to this. The color separation table correction unit 402 may be configured to automatically operate after the operation of the primary color gradation correction unit 401 is completed.

  Alternatively, it is possible to select a mode for confirming whether or not the user agrees to execute high-accuracy gradation correction, and a mode for automatically operating the color separation table correction unit 402 without confirmation. May be.

  FIG. 6 shows that a mode for confirming whether or not the user agrees to execute high-accuracy gradation correction and a mode for automatically operating the color separation table correction unit 402 without confirmation can be selected. It is an example of a user interface. The difference from FIG. 5A is that a check field 507 for confirming whether or not high-precision gradation correction is automatically performed is provided below the status display field 502. When a check is input in the check field 507, the color separation table correction unit 402 is automatically operated without confirming with the user whether or not to agree to the execution of the high precision gradation correction. On the other hand, if no check is entered in the check column 507, the color separation table correction unit 402 is operated after confirming whether or not the execution of the high-precision gradation correction is agreed.

4.3 Configuration of Memory Unit 205 Related to Calibration FIG. 7 is a diagram showing the storage locations in the memory unit 205 of various tables and data used for calibration processing of the correction color separation table and primary color gradation correction LUT. is there.

  Reference numeral 701 denotes a patch chart storage unit that stores images such as a primary color gradation characteristic chart and a light / dark color mixture patch chart. Reference numeral 702 denotes a reference primary color gradation characteristic table storage unit that stores a reference primary color gradation table (a table storing ideal density values for individual color materials).

  Reference numeral 703 denotes a reference dark / light mixed color density characteristic table storage unit, which stores a reference dark / light mixed color density characteristic table (a table storing ideal color mixture ratios of dark / light color materials). Reference color separation table storage unit 704 stores a default color separation table.

  A correction primary color gradation characteristic table storage unit 705 stores a correction primary color gradation characteristic table obtained by measuring the density value of the printed primary color gradation characteristic chart. A primary color gradation correction LUT storage unit 706 stores a primary color gradation correction LUT generated by calibration.

  Reference numeral 707 denotes a correction dark / light mixed color density characteristic table storage unit. A correction density mixed color density characteristic table obtained by reading the printed density mixed color patch chart and color-separating the density value input via the input image processing unit 201 using the reference color separation table is stored. A corrected color separation table storage unit 708 stores a corrected color separation table generated by calibration.

4.4 Explanation of various data used for calibration
(1) Primary color gradation characteristic chart FIG. 8 is a diagram showing an example of the primary color gradation characteristic chart. On the recording paper, there are C, M, Y, K, c, and m print areas, and in each color print area, a patch pattern having a halftone input density level in steps of 5% is formed.

(2) Dark / Mixed Color Patch Chart FIG. 9 is an example of a dark / light mixed color patch chart. The dark / light mixed color patch chart is obtained by extracting 17 density values of a light color material and a dark color material and printing the single color and a combination of the mixed colors on a recording sheet.

(3) Density Mixing Color Density Characteristic Table for Correction After measuring the density value of the shading mixed color patch chart using the digital color image reader unit 101 and performing color separation using the reference color separation table, the density of the dark color material and light color material By mapping values on a two-dimensional plane, a correction light / dark mixed color density characteristic table is obtained (FIG. 10). The light / dark color mixture density characteristic table has values at arbitrary intervals. For this reason, values that are not prepared are calculated by performing an interpolation operation by linear interpolation from the surrounding values.

  FIG. 11 is a diagram obtained by linearly interpolating between values in the correction light / dark color mixture density characteristic table and mapping the values on a two-dimensional plane. The solid line in the figure is an example in which an equal density curve is drawn for every density value 0.4.

  The correction dark / light mixed color density characteristic table needs to be created for each of cyan and magenta composed of a light color material and a dark color material.

(4) Reference Color Separation Table FIG. 12 is a diagram showing an example of the reference color separation table. The color separation table is a table in which RGB image data is associated with data corresponding to six kinds of color materials C, M, Y, K, c, and m. This table has values at regular intervals with respect to the input data, and values not prepared are obtained by interpolation calculation from their surrounding values.

4.5 Process flow for calibration (overall)
The flow of the color separation table and primary color gradation correction LUT calibration processing used in the color separation processing executed in the RGB color separation unit 307 and the gamma correction processing executed in the gamma correction unit 305 will be described. FIG. 13 is a flow of the color separation table and primary color gradation correction LUT calibration processing used in the color separation processing executed in the image forming apparatus according to the present embodiment and the gamma correction processing executed in the gamma correction unit 305. It is a flowchart which shows.

  Upon receiving an automatic gradation correction command via the operation unit 203 (FIG. 5A), the primary color gradation correction unit 401 starts processing. In step S1301, the color separation table is temporarily returned to the default one stored in the reference color separation table storage unit 703.

  In step S1302, the primary color gradation characteristic chart as shown in FIG. 8 stored in the patch chart storage unit 701 is output.

  In step S1303, the density of the output primary color gradation characteristic chart is measured. The measured density value is input via the operation unit 203 and is stored in the correction primary color gradation characteristic table storage unit 705 as a correction primary color gradation characteristic table.

  In step S1304, a primary color gradation correction LUT is created using the density value input in step S1303. Specifically, it is created by comparing the reference primary color gradation characteristic table and the correction primary color gradation characteristic table. The created primary color gradation correction LUT is stored in the primary color gradation correction LUT storage unit 1306.

  In step S1305, it is confirmed whether the maximum density values of light cyan and light magenta satisfy the target density value. If the target density value is not satisfied, the process proceeds to step S1306. If the target density value is satisfied, the process ends. As a comparison method with the target density value, a threshold value of the maximum density value of light cyan and light magenta is set in advance, and when it is out of the range, a confirmation screen as shown in FIG. 5B is displayed. Take the method. Alternatively, when a preset threshold value is exceeded, “High-definition gradation correction is performed” or the like may be displayed, and the process may automatically proceed to step S1306.

  In step S1306, a correction color separation table is created. Details thereof will be described later with reference to FIG.

  In step S1307, the created corrected color separation table is set in the corrected color separation table storage unit 708, and the process ends.

  Thereafter, color separation processing and gamma correction processing are performed using the correction color separation table and the primary color gradation correction LUT.

4.6 Process flow in calibration (Creation of correction color separation table)
FIG. 14 is a flowchart illustrating details of the correction color separation table creation process in step S1306.

  When the color separation table correction unit 402 starts to execute, in step S1401, the light / dark color mixture patch chart as shown in FIG. 9 stored in the patch chart storage unit 701 is printed.

  In step S1402, the density of the printed mixed color patch chart is measured. At this time, the digital color image reader unit 101 reads the image and converts the luminance density to obtain the density value. The measured density values are color-separated using a reference color separation table and stored in the correction light / dark mixed color density characteristic table storage unit 707 as a correction dark / light mixed color characteristic table.

  In step S1403, a grid counter for indicating an arbitrary grid in the reference color separation table is set to zero. Thereafter, the processing up to step S1407 is performed for both cyan and magenta colors, but only cyan will be briefly described here.

  In step S1404, the density value of cyan to be generated by the dark cyan color material and the light cyan color material is calculated in the corresponding grid. Specifically, first, the density value of the dark cyan color material and the density value of the light cyan color material in the corresponding grid of the reference color separation table are read. Then, the cyan density value generated by combining the read density values is read from the reference gray-mixed color density characteristic table.

  In step S1405, in order to obtain the density value of cyan to be generated, which is calculated in step S1403, the density value of the light cyan color material and the density value of the dark cyan color material that are actually necessary are calculated. Specifically, first, the density value corresponding to the density value of cyan to be generated, which is calculated in step S1403, is read from the correction light / dark color mixture density characteristic table. Then, the density value of the dark cyan color material and the density value of the light cyan color material corresponding to the density value are read out (the read density value of the dark cyan color material and the density value of the light cyan color material are This is the mixing ratio of the correction color separation table for obtaining the density value of cyan).

  In step S1406, the grid counter is advanced to the next, and the process proceeds to step S1407.

  In step S1407, it is determined whether or not the grid counter matches the total number of grids. If they match, the process proceeds to step S1408. On the other hand, if the grid counter is less than the total number of grids, the process returns to step S1404 and the above processing is repeated.

  In step S1408, a corrected color separation table describing the color mixture ratios of all grids is generated, and the process ends.

  In this embodiment, the case where the single-color maximum density value of the light color material does not satisfy the target density value has been described. However, the present invention can also be used when the target density value is exceeded. Further, although the primary color gradation characteristics of each color are ideal, it can also be used in the case where the density value of the light and shade color mixture has changed from that at the time of target creation due to a change in multiple transfer efficiency or the like.

  In the present embodiment, the light / dark mixed color patch chart is output after the primary color gradation correction, but the light / light mixed color patch chart may be output simultaneously with the primary color gradation characteristic chart.

  As is apparent from the above description, in the image forming apparatus according to the present embodiment, first, the primary color gradation characteristic chart is printed, and the density value of the printed primary color gradation characteristic chart is measured. Then, the primary color gradation correction LUT is generated by comparing the measurement result with the reference primary color gradation characteristic table. Thereby, the calibration for each color material is completed.

  Further, after correcting the density values of the dark color material and the light color material using the generated primary color gradation correction LUT, the dark / light mixed color patch chart is printed. The printed mixed color patch chart is read via the digital color image reader, and then color-separated by a reference color separation table to generate a mixed light / dark color density characteristic table. Then, the color mixture ratio in each color of the color separation table is calculated by comparing the light / dark color mixture density characteristic table with the reference color mixture density characteristic table. As a result, it is possible to calibrate the mixing ratio of all dark color materials and light color materials in the color separation table to an ideal ratio. As a result, the tone continuity of the entire color gamut is maintained.

[Second Embodiment]
In the first embodiment, the UI is displayed on the operation unit 203, but the present invention is not particularly limited to this. For example, it is possible to use an external input / output terminal connected via an interface instead of the operation unit 203 or to operate the UI via a network such as the Internet. At this time, it is also possible to perform correction remotely by setting a measuring device capable of automatically measuring the density, such as a color sensor, at the printer discharge port.

[Other Embodiments]
Note that the present invention can be applied to a system (for example, a copier, a facsimile machine, etc.) consisting of a single device even if it is applied to a system composed of a plurality of devices (for example, a host computer, interface device, reader, printer, etc.). You may apply.

  Needless to say, the object of the present invention can also be achieved by supplying a system or apparatus with a storage medium storing software program codes for realizing the functions of the above-described embodiments. In this case, the above functions are realized by the computer (or CPU or MPU) of the system or apparatus reading and executing the program code stored in the storage medium. In this case, the storage medium storing the program code constitutes the present invention.

  As a storage medium for supplying the program code, for example, a floppy (registered trademark) disk, hard disk, optical disk, magneto-optical disk, CD-ROM, CD-R, magnetic tape, nonvolatile memory card, ROM, or the like is used. be able to.

  Further, the present invention is not limited to the case where the functions of the above-described embodiments are realized by executing the program code read by the computer. For example, an OS (operating system) running on a computer performs part or all of actual processing based on an instruction of the program code, and the functions of the above-described embodiments may be realized by the processing. Needless to say, it is included.

  Furthermore, after the program code read from the storage medium is written in a memory provided in a function expansion board inserted into the computer or a function expansion unit connected to the computer, the functions of the above-described embodiments are realized. Is also included. That is, after the program code is written in the memory, the CPU or the like provided in the function expansion board or function expansion unit performs part or all of the actual processing based on the instruction of the program code, and is realized by the processing. This is also included.

1 is a schematic cross-sectional view of an image forming apparatus (MFP having both a copying function, a printer function, and a FAX function) according to a first embodiment of the present invention. 2 is a diagram showing a functional configuration of MFP 100. FIG. 3 is a block diagram illustrating an exemplary functional configuration of an output image processing unit 206. FIG. 3 is a diagram illustrating a functional configuration related to calibration of an MFP control unit 204. FIG. It is a figure which shows an example of the user interface of the operation part 203 for operating the primary color gradation correction | amendment part 401 and the color separation table correction | amendment part 402. A user interface that allows the user to select a mode for confirming whether or not to agree to the execution of high-accuracy gradation correction and a mode for automatically operating the color separation table correction unit 402 without confirmation. It is a figure which shows an example. FIG. 6 is a diagram illustrating a storage location in a memory unit 205 of various tables and data used for calibration processing of a correction color separation table and a primary color gradation correction LUT. It is a figure which shows an example of a primary color gradation characteristic chart. It is a figure which shows an example of a light / dark mixed color patch chart. It is an example of a light and shade mixed color patch chart. FIG. 5 is a diagram obtained by linearly interpolating between values in a correction light / dark mixed color density characteristic table and mapping on a two-dimensional plane. It is a figure which shows an example of a reference color separation table. 6 is a flowchart showing a flow of calibration processing of a color separation table and a primary color gradation correction LUT used in the gamma correction processing executed in the color separation processing and gamma correction unit 305. It is a flowchart explaining the detail of the preparation process of a correction | amendment color separation table. It is a figure which shows the process which color-separates the RGB signal which is the input image signal into 6 color materials, and outputs it. FIG. 10 is a diagram illustrating a processing method for directly performing color separation from RGB signals into six color materials of C, c, M, m, Y, and K using a color separation table 1600. It is a figure which shows the color mixture ratio of a dark cyan color material and a light cyan color material. It is a figure which shows the color mixture ratio of a dark cyan color material and a light cyan color material.

Claims (8)

An image forming apparatus that forms an image with respect to an input image signal using a dark color material and a light color material having different lightness and similar colors,
Storage means for storing a color separation table for extracting each color component signal corresponding to the dark color material and the light color material from the image signal;
A first output means for outputting a primary color gradation characteristic chart by recording a plurality of images having different color gradations on a recording medium using the dark color material and the light color material individually;
The density value of each of the plurality of images having different color gradations obtained by reading the primary color gradation characteristic chart output by the first output unit and the plurality of predetermined color gradations having different color gradations are obtained. A first calculation means for calculating a correction amount in the case of individually outputting the dark color material and the light color material by comparing the density target values of the respective images;
A plurality of images having different color mixing ratios of the dark color material and the light color material are recorded on a recording medium after correcting the output of the color mixture material and the light color material using the correction amount calculated by the first calculation unit. A second output means for outputting the light and shade mixed color patch chart;
Density values for each of the plurality of images with different color mixture ratios obtained by reading the grayscale color mixture patch chart output by the second output means are color-separated using the color separation table, and the darkness is obtained. A second calculation for calculating a correction amount of the color mixture ratio by obtaining a color mixture ratio of the color material and the light color material and comparing with a target value of a density value for each of a plurality of predetermined images having different color mixture ratios Means,
An image forming apparatus comprising: a correction unit that corrects the color separation table stored in the storage unit using the correction amount calculated by the second calculation unit. The second output means includes
When the density value obtained by correcting the output of the light color material using the correction amount calculated by the first calculation means is lower than the corresponding density target value, the density mixed color patch chart can be output. The image forming apparatus according to claim 1, wherein: The correction means includes
When the density value obtained by correcting the output of the light color material using the correction amount calculated by the first calculating means matches the density target value, the color separation table is corrected. The image forming apparatus according to claim 1, wherein the image forming apparatus is not broken. The image forming apparatus according to claim 1, wherein each color component signal corresponding to the dark color material and the light color material is extracted from the image signal using the color separation table corrected by the correction unit. The dark color material includes a dark cyan color material, a magenta color material, a yellow color material, and a black color material, and the light color material includes a light cyan color material and a light magenta color material. The image forming apparatus according to claim 1. A correction method in an image forming apparatus that forms an image with respect to an input image signal using a dark color material and a light color material having different lightness and similar colors,
A storage step of storing a color separation table for extracting each color component signal corresponding to the dark color material and the light color material from the image signal;
A first output step of outputting a primary color gradation characteristic chart by recording a plurality of images having different color gradations on a recording medium using the dark color material and the light color material individually;
The density value of each of the plurality of images having different color gradations obtained by reading the primary color gradation characteristic chart output by the first output step and the plurality of predetermined color gradations having different color gradations are obtained. A first calculation step of calculating a correction amount in the case of individually outputting the dark color material and the light color material by comparing the density target value of each image;
A plurality of images having different color mixing ratios of the dark color material and the light color material are recorded on a recording medium after correcting the output of the color mixture material and the light color material using the correction amount calculated in the first calculation step. A second output step of outputting the light and shade mixed color patch chart,
Density values for each of the plurality of images having different color mixture ratios obtained by reading the grayscale color mixture patch chart output in the second output step are color-separated using the color separation table, and the darkness is obtained. A second calculation for calculating a correction amount of the color mixture ratio by obtaining a color mixture ratio of the color material and the light color material and comparing with a target value of a density value for each of a plurality of predetermined images having different color mixture ratios Process,
A correction method comprising: a correction step of correcting the color separation table stored in the storage step using the correction amount calculated in the second calculation step. A storage medium storing a control program for causing a computer to execute the information processing method according to claim 6. A control program for causing a computer to execute the information processing method according to claim 6.