JP2007189278A - Color tone correction method and color tone correction apparatus, image forming apparatus, and program - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a color copying machine capable of simply and appropriately carrying out color tone correction even if a characteristic change for causing a change in a color gamut takes place. <P>SOLUTION: A test chart generating section 242 generates a color patch with the maximum density of primary and secondary colors of a plurality of color materials and an image output section 30 outputs the color patch. A test chart read section 244 reads the outputted color path image, a read data discrimination section 255 discriminates a color gamut size from the read data, a standard gamut data correction section 256 corrects a standard gamut target value on the basis of the discriminated color gamut size, and an output value correction processing section 257 adjusts the color tone of an output characteristic on the basis of the discriminated color gamut target value. Since the color tone correction is executed not by taking into account only a gradation characteristic but taking into account also a change in the color gamut size, even if the characteristic change causing a change in the color gamut such as a change in a fixing characteristic takes place, the color tone correction can simply and properly be carried out. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a mechanism for color tone correction of a color image in, for example, a printer device, a facsimile device, or a multifunction device having these functions.

  Conventionally, in a color image forming apparatus using, for example, Y (yellow), M (magenta), C (cyan), and K (black) ink colors, the paper type used, process speed, environmental changes, changes over time, etc. Since characteristic changes such as development and transfer occur, it is difficult to maintain the optimum color image quality. In such a changed state, the gradation characteristics change, and the original cannot be reproduced faithfully. For this reason, various mechanisms have been considered as gradation correction methods for reducing gradation fluctuations due to changes over time (for example, see Patent Documents 1 to 3).

JP 2003-333333 A Japanese Patent Laid-Open No. 09-186891 Japanese Patent Laid-Open No. 2002-1112048

  For example, in the mechanism described in Patent Document 1, a test chart with CMYK coverage for each single color is read by a scanner, and the CMYK solid density (100%) is first corrected to the specified density value by adjusting the transfer voltage from the read data. Then, the CMYK halftone data is corrected for the adjustment of the transfer voltage, and the entire tone correction curve (one-dimensional lookup table) is created.

  In this mechanism, the halftone correction is performed after adjusting the solid density of the single color to the design value, that is, the single color gradation correction is performed, so that the primary color using only one color ink is equivalent to the design level. However, it is difficult to obtain a good gradation reproducibility at the same level as the design for the secondary color obtained by mixing two colors of ink.

  For example, when there is a change in the fixing characteristics, the change in the secondary color is larger than the change in the primary color, and only the one-dimensional lookup table for the primary color is used to correct the change in the color tone of the secondary color. It is insufficient.

  On the other hand, the mechanisms described in Patent Documents 2 and 3 use not only a single color but also a test patch that is a mixture of two colors, so that the gradation reproducibility equivalent to that at the time of design can be achieved for secondary colors. A mechanism to obtain is proposed.

  However, in the mechanisms described in Patent Documents 2 and 3, correction is performed exclusively from the viewpoint of gradation characteristics, and it has been found that a sufficient correction effect may not be obtained by that alone. For example, when a characteristic change that causes a change in the color gamut occurs, such as when there is a change in the fixing characteristic, a portion that cannot be corrected by the mechanism described in Patent Documents 2 and 3 appears. .

  In order to correct this condition, for example, using commercially available software, the user outputs a number of patches by himself, and the colorimetry of the output patch is performed by the colorimeter, and a color conversion table is created. By doing so, it can be considered to achieve color balance.

  However, such adjustment work such as color balance is difficult for a general operator, and has a drawback that it can be used only by a limited number of specialists because it requires specialized knowledge.

  The present invention has been made in view of the above circumstances, and proposes a mechanism that can easily and appropriately perform color tone correction even when a characteristic change that causes a change in the color gamut occurs. Objective.

  In the color tone correction method according to the present invention, first, a color patch having a maximum density of primary colors and secondary colors of a plurality of color materials used by the image forming apparatus is output from the image forming apparatus. Note that when outputting a color patch from the image forming apparatus, the same gradation correction as in the prior art may be added. Then, by reading the output color patch, the output characteristic is measured to determine the color gamut size, and the color tone of the output characteristic is adjusted based on the determined color gamut size. In other words, the present invention is characterized in that the color tone correction is performed in consideration of a change in the color gamut size instead of performing the correction exclusively in consideration of the gradation characteristics.

  A color tone correction apparatus and an image forming apparatus according to the present invention are apparatuses for performing the color tone correction method according to the present invention, and are output from the image forming apparatus and are one of a plurality of color materials used by the image forming apparatus. Color tone correction processing unit that determines the color gamut size by measuring the output characteristics by reading the color patch of the maximum density of the secondary color and the secondary color, and adjusts the color tone of the output characteristics based on the determined color gamut size It was supposed to be equipped with.

  The inventions described in the dependent claims define further advantageous specific examples of the mechanism according to the present invention.

  The color tone correction mechanism according to the present invention can also be realized by software using an electronic computer (computer), and a program for this and a recording medium storing this program can be extracted as an invention. . The program may be provided by being stored in a computer-readable storage medium, or may be provided by distribution via wired or wireless communication means.

  According to the present invention, since the color tone correction is performed in consideration of the change in the color reproduction gamut size instead of performing the correction exclusively considering the gradation characteristic, a change in the color reproduction gamut such as a change in the fixing characteristic is performed. Even when a characteristic change that causes color tone occurs, color tone correction can be performed easily and appropriately.

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

<Overall configuration of image forming apparatus>
FIG. 1 is a mechanism diagram of a color copying apparatus which is an example of an image forming apparatus equipped with an embodiment of an image processing apparatus (color tone correction processing apparatus) for executing a color tone correction method according to the present invention. The image processing apparatus may be provided as a single apparatus in addition to being used in the image forming apparatus.

  As shown in the figure, the color copying apparatus 1 controls an image acquisition unit (IIT; Image Input Terminal) 10 that reads an original image and converts it into an electrical signal, a hard disk (HD), etc. by controlling page rearrangement of the read original image. An internal controller unit 20 having an image processing (IPS) function for performing desired image processing on input image data or a control function for controlling the operation of the entire apparatus, And an image output terminal (IOT) 30 that converts an electrical signal into an optical signal and forms an image using xerography using an electrostatic latent image.

  Further, the color copying apparatus 1 includes a platen cover 116. Although not shown, near the platen cover 116 at the top of the housing is provided a user interface (UI) for performing user instructions such as selection of various functions and various reading / printing designations. Although not shown, a reversing mechanism for reversing the orientation of the output paper having an image printed on the front surface can be provided for duplex printing.

  The internal controller unit 20 is provided on a substrate disposed at a boundary portion between the image acquisition unit 10 and the image output unit 30. An external output unit (ESS; Electronic Subsystem) for transferring the output image data to another apparatus may be provided.

  The image acquisition unit 10 includes a housing 112 and a platen glass (original placement table) 11 having a substantially A3 size and made of transparent glass provided on the housing 112.

  The image acquisition unit 10 also has a light source 12 that emits light toward a surface (back surface) opposite to the document placement surface of the platen glass 11 in the housing 112, and the light emitted from the light source 12 is platen glass. And a full-rate carriage (F / R-CRG) 134 that reflects toward the 11th side. As the light source 12, a fluorescent lamp whose longitudinal direction is the main scanning direction (the direction orthogonal to the paper surface in the figure) is used.

  The image acquisition unit 10 also includes a half rate carriage (H / R-CRG) 138 that deflects the reflected light deflected by the full rate carriage 134 in the housing 112. The full rate carriage 134 and the half rate carriage 138 are configured to reciprocate in the sub-scanning direction (in the direction of arrow X in FIG. 1) and in the opposite direction in conjunction with a stepping motor (not shown).

  Furthermore, the image acquisition unit 10 includes a lens 140 that converges the reflected light deflected by the half-rate carriage 138 in the housing 112, and a main light that is substantially orthogonal to the sub-scanning direction by receiving the reflected light converged by the lens 140. And a light receiving unit 13 that reads an image in the scanning direction (the depth direction in FIG. 1) and sequentially outputs an image signal corresponding to the density. The light receiving unit 13 is disposed on the substrate together with a drive circuit such as a CCD driver for driving a line sensor (not shown), a read signal processing unit 14 and the like.

  Although not shown, the image acquisition unit 10 also includes a wire, a drive pulley, and the like for moving the reading optical system, the light receiving unit 13, and the like under the platen glass 11 in the housing 112. The driving pulley is reciprocally rotated by the driving force of the driving motor, and the reading optical system and the like are moved at a predetermined speed below the platen glass 11 by winding the wire around the driving pulley by the rotational driving.

  In the above configuration, at the time of reading, the document G is manually placed on the platen glass 11 serving as a document placing table and fixed (stop-locked) at an arbitrary position on the platen glass 11, and the fixed reading image destination is fixed. Using the position G as the leading edge reference, the reading optical system is moved and scanned at a constant speed in the direction of arrow X to expose the document and read the image.

  For example, in a state where the document G placed on the platen glass 11 is covered with the platen cover 116, the light from the light source 12 irradiates the document G placed on the platen glass 11, and the reflected light is the full rate carriage 134. The light is split into red, green, and blue colors via a reading optical system including a half-rate carriage 138 and a lens 140. Each color light enters a corresponding line sensor divided for each color light, and an input image is read at a predetermined resolution, thereby obtaining an analog captured image signal of each color component of red, green, and blue. It is done.

  The captured image signal obtained by this reading is converted into digital image data of each color component of red (R), green (G), and blue (B), and the digital image data of red, green, and blue is converted into the internal controller unit 20. Send to. At the time of reading, the reading optical system including the light source 12 is such that the light from the light source 12 irradiates the entire surface of the document and the light receiving unit 13 reads the entire surface of the input image via the reading optical system such as the lens 140. The system, the light receiving unit 13 and the like are relatively moved in the sub-scanning direction in FIG.

  The read original image is changed in optical path by the full-rate carriage 134 or the half-rate carriage 138 and reduced by the lens 140 to reach the light receiving unit 13. Then, after receiving processing by the read signal processing unit 14, it is sent to the internal controller unit 20.

  The internal controller unit 20 processes the image data received from the image acquisition unit 10 and converts it into image formation data such as an image format used when the image output unit 30 actually transfers an image to output paper (forms an image). Convert.

  In this case, for example, RGB color system image data is converted into YCrCb color system image data, and at least three (preferably four) from the YCrCb color system, for example, the CMY color system or the CMYK color system are used. Mapping to the system is performed and color-separated raster data is generated for print output.

  In such raster data conversion processing, under color removal (UCR) for reducing the CMY components of the color image or gray component replacement (GCR) for partially replacing the reduced CMY components with the K component is performed. Furthermore, in order to adjust the toner image of the output image created in response to the output data (CMYK or the like), color separation linearization or similar processing is performed.

  In this example, black (K), yellow (Y), magenta (M), and cyan (C) image formation data are obtained based on red, green, and blue image data R, G, and B.

  The internal controller unit 20 acquires image data from a client terminal via a communication network (not shown), performs predetermined image processing based on the image data, and then outputs a binarized signal for each print color. You may make it obtain (it is a structure of what is called a network printer).

  The image output unit 30 of the present embodiment includes an image forming unit (transfer unit) 31 corresponding to the color material colors K, Y, M, and C (K, Y, M, and C are assigned to each; the same applies to other members; In other words, the image forming unit 31 has a so-called tandem configuration in which the image forming units 31 are sequentially juxtaposed at a predetermined interval in the sheet conveyance direction.

  Each image forming unit 31 corresponding to the color material color considers, for example, the relationship between the dark attenuation and the characteristics of each toner, or the difference in the influence of the mixed color of the other color toner on the black toner. The arrangement order in the paper conveyance direction is determined, and the illustrated example is merely an example.

  A photosensitive drum 32 is disposed at the center of the image forming unit 31, and a primary charger 33, a developing unit 34, a transfer charger 35, and the like are disposed around the photosensitive drum 32. A writing scanning optical system (exposure device) including a semiconductor laser 38, a polygon mirror 39, and other mirrors for recording a latent image on the photosensitive drum 32 based on the formation data is provided.

  The image output unit 30 also includes a manual document cassette (hereinafter also referred to as a manual feed tray) 41 for transporting output paper to the image forming unit 31, a transport path 42 having a transfer belt 43, rollers, and the like, and a paper feed tray. 52. Although only one sheet feeding tray 52 is shown in the figure, a structure in which a plurality of stages are arranged can be used.

  In addition, the image output unit 30 includes a leading edge detector 44 in proximity to the output paper conveyance path 42 conveyed from the document cassette 41 and the paper feed tray 52 to each image forming unit 31. The leading edge detector 44 optically detects, for example, the leading edge of the output sheet sent onto the transfer belt 43 through the registration roller 42a to obtain a leading edge detection signal. In synchronization with this leading edge detection signal, image forming data of each color of K, Y, M, and C is sequentially input to the image output unit 30 at regular intervals.

  A fixing unit 45 for fixing the image on the transferred paper by heat treatment is provided on the paper discharge port side of the image forming unit 31 (in this example, the cyan image forming unit 31c) configured in tandem. It has been.

  In the image output unit 30 having such a configuration, first, the semiconductor laser 38K as a light source is driven by the black image formation data from the internal controller unit 20 to convert the black image formation data into an optical signal. The converted laser light is irradiated toward the polygon mirror 39.

  The laser beam further scans the photosensitive drum 32K charged by the primary charger 33K via the reflection mirrors 47K, 48K, and 49K, thereby forming an electrostatic latent image on the photosensitive drum 32K.

  The electrostatic latent image is converted into a toner image by the developing device 34K to which black toner is supplied. Further, while the output paper on the transfer belt 43 passes through the photosensitive drum 32K, the electrostatic charging image is transferred onto the output paper by the transfer charger 35K. The toner image is transferred. After the transfer, excess toner is removed from the photosensitive drum 32K by the cleaner 36K.

  Similarly, the semiconductor lasers 38Y, 38M, and 38C are driven by the corresponding Y, M, and C color image formation data obtained from the internal controller unit 20 sequentially with respect to the black image formation data at regular intervals. As a result, the image forming data of each color is converted into an optical signal, and the converted laser light is irradiated toward the polygon mirror 39.

  The laser light further scans the photosensitive drums 32Y, 32M, and 32C charged by the primary chargers 33Y, 33M, and 33C via the reflection mirrors 47Y to 49Y, 47M to 49M, and 47C to 49C, thereby exposing the photosensitive drums. Electrostatic latent images are sequentially formed on the body drums 32Y, 32M, and 32C.

  Each electrostatic latent image is sequentially converted into a toner image by developing units 34Y, 34M, and 34C to which each color toner is supplied. Each toner image is a photosensitive drum 32Y, 32M, and 32C corresponding to the original on the transfer belt 43. Are sequentially transferred onto the output paper by the corresponding transfer chargers 35Y, 35M, and 35C.

  The output paper on which the toner images of K, Y, M, and C are sequentially transferred in this manner is peeled off from the transfer belt 43, and the toner is fixed by the fixing unit 45. Discharged outside.

  The image output unit 30 causes the transfer belt 43 to function as an intermediate transfer belt, and transfers (primary transfer) the toner image on the photosensitive drum 32 to the transfer belt 43 by a primary transfer device, and then secondary. A secondary transfer method in which the toner image on the transfer belt 43 is transferred (secondary transfer) to the printing paper at the transfer portion can be used. In such a configuration, image formation is performed on each photoconductor drum 32 with each color toner of YMCK, and this toner image is multiplex-transferred to the transfer belt 43, and then transferred to a predetermined printing paper, thereby forming a color image. To get.

  Further, the image output unit 30 sequentially forms an electrostatic latent image of each color of K, Y, M, and C on one photosensitive drum by one laser light scanner, and the electrostatic latent image is formed on the photosensitive drum. Are sequentially formed into toner images by a developing device provided with toners of respective colors K, Y, M, and C, and the toner images are sequentially transferred onto a document adsorbed on a transfer drum. It may be configured.

<Circuit configuration>
FIG. 2 is a diagram illustrating an example of a circuit configuration of a color copying apparatus as an image forming apparatus focusing on the image quality correction (particularly color tone correction processing) function in the internal controller unit 20. The color copying apparatus 1 incorporates a color correction processing apparatus that performs the color correction processing according to the present invention.

The color copying apparatus 1 includes an input image data acquisition unit 210 that acquires processing target color data R, G, and B expressed in an RGB color space, and color data R, G, and B output from the input image data acquisition unit 210. A first color conversion processing unit 220 that converts B into color data L1, a1, and b1 expressed in a Lab (correctly L ^* a ^* b ^* ) color space, and a color output from the first color conversion processing unit 220 A color tone correction processing unit (hue conversion unit) 240 that performs color tone correction on the data L, a, and b in consideration of a gamut size change.

  The first color conversion processing unit 220 performs color space conversion to a signal in a color space independent of the device when the input color data is a signal in a color space other than the color space independent of the device used internally. is there. For example, when the input color data is a signal in the RGB color space, the first color conversion processing unit 220 performs color space conversion from the RGB color space to the CIE-Lab color space.

  For example, the input image data acquisition unit 210 may acquire the color data R, G, B using the image acquisition unit 10 at the time of a copy job, and the print received from an information processing terminal such as a personal computer at the time of a print job. Color data R, G, and B may be obtained by drawing and developing data (for example, data described in PDL (Page Description Language)).

  Further, the color copying apparatus 1 is a color represented by a color space (Y, M, C, K in this example) in which the image output unit 30 handles the color data L1, a1, b1 output from the color tone correction processing unit 240. A second color conversion processing unit 270 that converts data C1, M1, Y1, and K1 and a gradation that performs gradation correction on the color data C1, M1, Y1, and K1 output from the second color conversion processing unit 270 A correction processing unit 280.

  The color data C2, M2, Y2, and K2 output from the gradation correction processing unit 280 are transferred to the image output unit 30, and an image is formed on a predetermined output medium.

  The tone correction processing unit 240 that is a characteristic part of the present embodiment includes a test chart generation unit 242 that generates a test chart, a test chart reading unit 244 that reads a test chart, and a data storage that stores target data related to the test chart. Part 246.

  As in this embodiment, in the color copying apparatus 1 having a copying function, the test chart reading unit 244 reads the test chart using the image acquisition unit 10 that reads the color image on the document, and the color data R, G , B can be obtained. In the case of a printing apparatus that does not have a copying function, the test chart reading unit 244 may be separately configured using a color scanner apparatus.

  The tone correction processing unit 240 also includes a tone correction curve creating unit 254 that creates a tone correction curve, a read data determining unit 255 that determines read data read by the test chart reading unit 244, and a standard gamut target value. A standard gamut data correcting unit 256 that corrects the color data L1, a1, and b1 input from the first color conversion processing unit 220 based on the corrected standard gamut target value (output characteristics). Correction unit) 257.

  In the color tone correction processing unit 240, the test chart generated by the test chart generation unit 242 is printed by the image output unit 30, and the printed test chart image is read by the test chart reading unit 244, so that the gradation / Color tone correction is performed.

  The read data determination unit 255 determines a change characteristic of the gamut size, selects an appropriate gamut corresponding to the gamut change, and sets data corresponding to the selection in the standard gamut data correction unit 256. Here, the read data determination unit 255 of the present embodiment particularly includes a plurality of gamut primary color and secondary color data obtained in advance, and the primary color and secondary read by the test chart reading unit 244. It is characterized in that an appropriate gamut size is selected for each of the primary color and the secondary color by comparing with color data.

  The output value correction processing unit 257 refers to the gamut data obtained by correcting the input color data by the standard gamut data correction unit 256 and corrects the output characteristics. Here, the standard gamut data correction unit 256 of the present embodiment is particularly characterized in that the standard gamut target value is corrected based on the standard gamut output target value and target values corresponding to a plurality of gamut sizes. At this time, in particular, the output target value of the standard gamut and the target values corresponding to a plurality of gamut sizes are set on the gamut outline with respect to the hue planes of the primary color and the secondary color. The output correction processing unit 257 corrects the output characteristics based on the corrected target value from the standard gamut data correction unit 256. For the inside of the gamut outline, the data is corrected by the proportional distribution.

  In addition, at the time of color correction, the target values of all data points cannot always be held due to the relationship with the memory capacity. In this case, in particular, at least the gamut for each hue plane of the primary color and the secondary color. The target points on the outline are held, and the points inside the gamut may be corrected by interpolation processing.

<Process overview>
3 to 7 are diagrams for explaining the outline of the color tone correction process. Here, FIG. 3 is a diagram illustrating an example of a reference pattern used in the color tone correction process. FIG. 4 is a diagram for explaining a color space (Lab color space in this example) and gamut changes. FIG. 5 is a diagram for explaining changes in color tone characteristics. FIG. 6 is a flowchart illustrating an example of the processing procedure of the color tone correction process. FIG. 7 is a diagram illustrating an example of gamut size determination in the read data determination unit 255.

<About the reference pattern>
The reference pattern (test chart) for inspection used in the present embodiment is a color material color used by the image output unit 30 (in this example, four colors of Y, M, C, and K) as shown in FIG. ), A plurality of gradation test patches whose brightness and density change stepwise at a predetermined pitch within a range from high density (low brightness) to low density (high brightness) are output. Then, by measuring the reference pattern image output from the color copying apparatus 1, the gradation level of the color copying apparatus 1 (specifically, the image forming units 31 for Y, M, C, and K) is inspected. Data for gradations that are not actually output may be dealt with by obtaining interpolation data using the output gradation patches.

<About color reproduction range>
At this time, the input device (for example, the image acquisition unit 10) and the output device (the image output unit 30) have different color gamuts. For this reason, the first color conversion processing unit 220 first performs the correction within the standard gamut color reproduction range by moving the Lab value according to the color of the input image signal. In this case, the color reproduction area on the input side and the color reproduction area (gamut) on the output side are obtained in advance. At this time, it may be obtained in a device-independent color space, for example, a CIE-Lab color space. In the following description, it is assumed that internal processing is performed in the CIE-Lab color space.

  Here, in general, the color reproduction range is not uniform, and for example, in the CIE-Lab color space, as shown in FIG. 4A, it has a complicated three-dimensional shape. The inside of the solid shown in FIG. 4A is a region where color reproduction is possible, and the outside thereof is a region where color cannot be reproduced.

  Next, the color tone correction processing unit 240 performs correction according to the output characteristics. When a color image is output on a sheet, a change in color tone may occur depending on the type of sheet to be used, process speed and conditions, environmental changes, changes with time, and the like, and correction is necessary.

  For example, FIG. 4B is a diagram showing a state of gamut change when there is a change in the fixing characteristics in the plan view of FIG. 4A projected onto the ab plane. In the figure, the color tone for each primary color and secondary color (achromatic color at the center origin / paper white) of the large gamut (arrow X) indicated by the solid line on the outside and the small gamut (arrow Y) indicated by the dotted line on the inside FIG. 5 shows the change.

  For example, FIG. 5A is a hue cross-sectional view (LC plane; the same applies hereinafter) on a dotted line indicated by an arrow x in FIG. 4B regarding yellow which is an example of a primary color. FIG. 5B is a hue sectional view on a dotted line indicated by an arrow y in FIG. 4B regarding cyan, which is an example of a primary color, and FIG. 5C shows a secondary color. It is hue sectional drawing on the dotted line shown by the arrow z in FIG.4 (B) regarding Green (Green) which is an example.

  Although the relationship with FIG. 4B is not shown, FIG. 5D is a hue cross-sectional view of red, which is an example of a secondary color, and FIG. It is hue sectional drawing regarding blue (Blue) which is an example.

  As can be seen from FIG. 5, when there is a change in the fixing characteristics, the gamut change is small in the primary color regions (Y, C) shown in FIGS. 5 (A) and 5 (B). In the secondary color region (G, R, B) shown in (E), the gamut size changes greatly with the change in the fixing characteristics.

  For the gamut change (change in color tone characteristics) of the primary color area, for example, as described in Japanese Patent Application Laid-Open No. 2003-333333, the test chart reading unit 244 reads and reads the test chart with the CMYK coverage. First, the CMYK solid density (100%) is corrected to the specified density value by adjusting the transfer voltage from the data, then the transfer voltage adjustment is corrected to the CMYK halftone data, and the entire tone correction curve ( It can be considered that this can be dealt with by creating a one-dimensional lookup table. That is, it may be considered that the primary color can be adjusted to the same level as the design level by correcting the halftone after adjusting the solid density of the single color to the design value.

  However, such correction using only the one-dimensional lookup table for the primary color region is not sufficient for correcting the gamut change in the secondary color region, and another method must be taken.

  Here, when the gamut change in the secondary color area shown in FIGS. 5C to 5E is seen in more detail, the tendency of the gamut size change with the same toner / machine shows the maximum brightness and the maximum saturation. It was found that there is a tendency to extend on the extension line with (concentration) (downward and diagonally to the right in the figure).

<Outline of processing procedure>
The processing procedure described below pays attention to this point, and uses this tendency to adjust the gradation and gradation in response to changes in output characteristics without imposing a burden on the user and without significantly increasing the memory. A mechanism for correcting the color tone.

  As a flow, the test chart 1 is read by the test chart reading unit 244. The test chart reading unit 244 outputs the read result to the read data determination unit 255 and the gradation correction curve creation unit 254.

  The data to be output to the gradation correction curve creation unit 254 is only primary color data, and the gradation correction curve creation unit 254 creates a gradation correction curve from the input data and a target value (not shown) for the input data, The tone correction processing unit 280 is set.

  On the other hand, the read data determination unit 255 takes in the read data of 100% and 200% data (CUSP) of the primary color and the secondary color and compares them with the CUSP data of a plurality of gamuts stored in the data storage unit 246. As a result of the comparison, when it is determined that the standard gamut is not applicable, the test chart generation unit 242 is instructed to generate and output the test chart 2. The output test chart 2 is read again by the test chart reading unit 244, and the result is output to the read data determination unit 255.

  The read data determination unit 255 instructs the data storage unit 246 to specify data to be used for each hue (standard gamut data + large or small), and the test chart input to the standard gamut data correction unit 256. 2 read data is output to the standard gamut data correction unit 256.

  The data storage unit 246 outputs data (target value) used for each hue to the standard gamut data correction unit 256 in accordance with an instruction from the read data determination unit 255.

  The standard gamut data correction unit 256 receives the standard gamut target value input from the data storage unit 246, the target value of the output gamut size determined by the read data determination unit 255, and the test input from the read data determination unit 255. Based on the read value of the chart 2, the standard gamut target value is corrected and output to the output value correction processing unit 257.

  The output value correction processing unit 257 corrects the color data L1, a1, b1 input from the first color conversion processing unit 220 based on the corrected standard gamut target value.

  When the read data determination unit 255 determines that the output value correction is not necessary from the read data of the test chart 1, the standard gamut data correction unit 256 sets the target value of the standard gamut as it is in the output value correction processing unit 257. Alternatively, the processing is not performed (L1, a1, b1 = L2, a2, b2).

  Specifically, as shown in FIG. 6, first, in the test chart generation unit 242, primary colors (Y, M, C, K) and secondary colors (R) as shown in FIG. = M + Y, G = Y + C, B = C + M) is generated, input to the image output unit 30, and output to the paper by the image output unit 30 (S10). Then, the output image of the test chart 1 formed on the sheet is read by the test chart reading unit 244 (S12).

  Here, the test chart 1 is a chart for checking the characteristics (IOT characteristics) of the image output unit 30 itself, and no gradation correction processing is performed. For example, for primary colors Y, M, C, and K, test patches are formed for each coverage (in increments of 10% in the figure), but only 200% data is formed for secondary colors R, G, and B. It is a thing.

  Next, the gamut selection unit 252 determines the gamut size of each hue based on the image data acquired from the test chart 1 read by the test chart reading unit 244 (S14). Specifically, the 100% and 200% data of the primary color and secondary color of the test chart 1 and the 100% and 200% data of the primary color and secondary color stored in the data storage unit 246 are used. In comparison, for example, as shown in FIG. 7, the standard gamut is used to determine OK or NG (S20).

  When there is no problem with the standard gamut, that is, when the magnitude relationship between the primary color and the secondary color is large or small overall or the same as the standard gamut (S20-OK), Since there is no problem even if the same gradation correction method is applied, a gradation correction curve is created as usual, and the gradation correction curve is set in the gradation correction processing unit 280 (S22). The gradation correction processing unit 280 performs gradation correction of output characteristics using only the set gradation correction curve (S40).

  On the other hand, when the values of the primary color and the secondary color cannot be handled by the standard gamut, that is, when the magnitude relationship between the primary color and the secondary color is different from that of the standard gamut (S20-NG), Appropriate tone correction cannot be performed by simply applying the same tone correction method as in the example. In addition to creating a tone correction curve by the tone correction curve creating unit 254 and setting it in the tone correction processing unit 280, (S26) The primary color (Y, M, C, K) and secondary color (R = M + Y, G = Y + C, B = C + M) as shown in FIG. ) Is generated, is input to the gradation correction processing unit 280, and is output onto the paper by the image output unit 30 (S30). Then, the output image of the test chart 2 formed on the sheet is read by the test chart reading unit 244 (S32).

  Here, in the test chart 2, a test patch for each coverage (every 30% in the figure) is formed for each of the primary colors Y, M, C, K and the secondary colors R, G, B, and the black amount is appropriately set. (In the figure, 20% increments) An added test patch is also formed. For the test chart 2 generated by the test chart generation unit 242, the gradation correction processing unit 280 uses the gradation correction curve created by the test chart 1 set from the gradation correction curve creation unit 254 by the gradation correction curve. Tonal correction is added.

  In step S10, the test chart reading unit 244 is described as outputting the test chart 1 to the image output unit 30, but the test chart 1 is also output to the gradation correction processing unit 280, and the gradation correction processing unit 280 is output. It is also possible to adopt a configuration through which the gradation correction process is performed. In this case, the gradation correction processing unit 280 applies a through gradation correction parameter (input = output one-dimensional LUT (Look Up Table)) when outputting the test chart 1, and uses the test chart 1 when outputting the test chart 2. The created one-dimensional LUT may be applied.

  The read data determination unit 255 cooperates with the data storage unit 246 to determine a standard gamut and a target value of the selected gamut based on gamut selection according to a method described later, and this determined information is used as standard gamut data. The correction unit 256 is set (S34).

  The standard gamut data correction unit 256 receives the standard gamut target value input from the data storage unit 246, the target value of the output gamut size determined by the read data determination unit 255, and the test input from the read data determination unit 255. Based on the read value of the chart 2, the standard gamut target value is corrected (S35). Then, the standard gamut data correction unit 256 sets the corrected target value of the standard gamut data in the output value correction processing unit 257 (S36).

  In response, the output value correction processing unit 257 adds correction processing to the input color data L1, a1, and b1 corresponding to the target value data (S37). The second color conversion processing unit 270 converts the corrected data L2, a2, b2 into color data (Y1, M1, C1, K1 in this example) in the output color space (S38). Thereafter, the gradation correction processing unit 280 performs gradation correction of the output characteristics using the set gradation correction curve (S40).

<Details of gamut selection processing>
FIG. 8 is a diagram for explaining the details of the gamut selection process. The data storage unit 246 stores target data corresponding to the standard gamut (design time) test chart 2 in advance, and maximum density values (100 and 200) of primary colors and secondary colors of a plurality of gamuts different in size from the standard gamut. In addition to cusp (CUSP), data having a lower brightness (target value of non-standard gamut corresponding to target value of standard gamut) is stored.

  The read data determination unit 255 includes 100 and 200% data of the primary color and the secondary color of the test chart 1 obtained by reading by the test chart reading unit 244, and the primary color stored in the data storage unit 246. Compare the 100% and 200 data (cusp data) of the secondary color, and the closest one of the data of a plurality of gamuts of different sizes (2 gamut and 2 gamut in the figure) Select.

<Details of Correction Processing; First Example>
FIG. 9 is a diagram illustrating a detailed example (first example) of the color tone correction process. The output value correction processing of the first example is an application example in the case where the output data is larger than the data in the standard gamut (standard gamut <output gamut) and in the lower part of the cusp.

  Here, the “cusp lower part” means a part where the brightness data L is lower than the cusp (CUSP) point shown in the figure. In this example, the data point on the outer right side of the lower right side of the gamut is considered. .

  Data points a (a1 and a2 in the figure) are specific color data (included in the test chart 2) C1, M1, Y1, K1 (when a1), C2, M2, and so on in the standard gamut. Y2 and K2 (in the case of a2) are the target points (design values) on the lower right outline G1_1, and the data point b (b1 and b2 in the figure) is the second gamut (output gamut) for the data point a. ) Is a target point on the lower right outline G2_1. The data point b ′ (b1 ′, b2 ′ in the figure) is an actual output point on the lower right outline G2_1 in the second gamut when the color data CMYK having the value of the data point a is printed in the standard gamut. Indicates.

  Here, when there is no change in the output characteristic, when the color data C1, M1, Y1, K1 is output, it is output to the data point a1, but the output characteristic (particularly the color tone characteristic) changes as in the second gamut. As a result, the image is output to the data point b1 ′, resulting in a dark output image with a crushed feeling.

  In order to correct this output characteristic change, the standard gamut data correction unit 256 of the color tone correction processing unit 240 for the data point a outputs the data point b1 ′ to the position of the data point b1. Correct the target point.

  This correction is performed by calculating the data point a1 'on the second gamut from the following equation (1) showing the relationship between "a1, b1'" and "a2, b2 '". Similarly, it is only necessary to obtain a2 ', ... for other points.

  Here, a1a1 ', b1'b1,... indicate the distance between the point a1 and the point a1'. Expression (1) is obtained by modifying the expression from the ratio of a1a1 ': b1'b1 = a1a2: b1b2. Here, since points other than the point a1 'are target points set from the beginning or actual measurement points, the point a1' can be derived.

  The output value correction processing unit 257 performs output correction based on the newly obtained data points a1 ', a2', ... and the data points a1, a2, ....

  That is, when the value converted into the color data of the Lab color space by the first color conversion processing unit 220 is a1, if the output characteristic is not corrected, it is output with the value b1 ′. The output value correction processing unit 256 corrects a1 to a1 ′ and performs output processing, thereby preventing the output image from being a crushed dark image that is output with the value of b1.

  In this first example, data is stored only for specific points on the gamut outline, and other input values are handled by performing interpolation processing. Therefore, in this first example, it is only necessary to hold a specific point on the outline, and the correction can be made without significantly increasing the memory capacity compared to the case where the internal point is also held.

  In the interpolation processing, for example, interpolation may be performed with the L value (C = 0) of each primary color and secondary color cusp point as a target point. If the memory capacity is sufficient, only the standard gamut is held as a three-dimensional LUT including the points inside the gamut at appropriate intervals. For non-standard gamuts, only the points of the gamut outline are held. The interpolation result may be reflected in the standard gamut three-dimensional LUT, and the reflected three-dimensional LUT may be set in the output value correction processing unit 257.

<Details of Correction Processing; Second Example>
FIG. 10 is a diagram for explaining a detailed example (second example) of the color tone correction processing. The gradation correction processing of the second example is an application example in the case where the output data is larger than the data in the standard gamut (standard gamut <output gamut) and in the upper part of the cusp.

  Here, the “upper cusp” means a portion where the brightness data L is higher than the cusp (CUSP) point shown in the figure. In this example, the data point on the outer right side of the gamut is considered.

  Data points a (a1 and a2 in the figure) are specific color data (included in the test chart 2) C1, M1, Y1, K1 (when a1), C2, M2, and so on in the standard gamut. Y2 and K2 (when a2) are printed, the target point (design value) on the upper right outline G1_2, and the data point b ′ (b1 ′, b2 ′ in the figure) is the value of the data point a in standard gamut. The actual output point on the upper right outline G2_2 in the second gamut when the color data CMYK having the following is printed is shown.

  Here, when there is no change in the output characteristic, when the color data C1, M1, Y1, K1 is output, it is output to the data point a1, but the output characteristic (particularly the color tone characteristic) changes as in the second gamut. Then, the data is output to the data point b1 ′, resulting in a darker output image than at the time of design.

  In order to correct this output characteristic change, the standard gamut data correction unit 256 of the color tone correction processing unit 240 applies the standard gamut data to the data point a so that the data point b1 ′ is output at the position of the data point a1. Correct the target point.

  This correction is performed by simple proportional distribution based on the relationship between the data points a1, a2,... And the data points b1 ', b2',. Unlike the third example which will be described later, the standard gamut is smaller than the output gamut, so that the phenomenon of being crushed near the cusp does not occur.

  That is, in this second example, when the output characteristic is corrected based on the target value corresponding to the standard gamut, the output value on the gamut outline is corrected so as to be the same value as the target value of the standard gamut, The points inside the gamut are corrected with a simple proportional distribution. Note that the upper part of the cusp may be corrected so as to maintain the gradation ratio by focusing attention on the gradation surface in the same manner as the third example described later without performing such a correction process. .

<Details of Correction Processing; Third Example>
FIG. 11 is a diagram for explaining a detailed example (third example) of the color tone correction processing. The gradation correction process of the third example is an application example when the output data is smaller than the data in the standard gamut (standard gamut> output gamut).

  Data points a (a1 and a2 in the figure) are specific color data (included in the test chart 2) C1, M1, Y1, K1 (when a1), C2, M2, and so on in the standard gamut. Y2 and K2 (in the case of a2) are the target points (design values) on the lower right outline G1_1, and the data point b (b1 and b2 in the figure) is the third gamut (output gamut) for the data point a. ) In the lower right outline G3_1. The data point b ′ (b1 ′, b2 ′ in the figure) is an actual output point on the lower right outline G3_1 in the third gamut when the color data CMYK having the value of the data point a is printed in the standard gamut. Indicates.

  In addition, data points a (a3 and a4 in the figure) in the figure are specific color data (included in the test chart 2) C3, M3, Y3, K3 (when a3) and C4 in the standard gamut. The target point (design value) on the upper right outline G1_2 when M4, Y4, K4 (when a4) is printed, and the data point b ′ (b3 ′, b4 ′ in the figure) is the data point a in the standard gamut. The actual output point on the upper right outline G3_2 in the third gamut when color data CMYK having the value of is printed is shown.

  Here, when there is no change in the output characteristics, when the color data C1, M1, Y1, and K1 are output, they are output to the data point a1, but the output characteristics (particularly the color tone characteristics) change as in the third gamut. Then, it comes to be output to data point b1 ', and will become an output image with a low density.

  In order to correct this output characteristic change, the standard gamut target is corrected by the standard gamut data correction unit 256 of the color tone correction processing unit 240 for the data point a so that the data point b1 ′ is output at the position of the data point b1. Perform point correction.

  This correction is performed by calculating the data point a1 'on the third gamut from the following equation (2) showing the relationship between "a1, b1'" and "a2, b2 '". Similarly, it is only necessary to obtain a2 ', ... for other points.

  The output value correction processing unit 257 performs output correction based on the newly obtained data points a1 ', a2', ... and the data points a1, a2, ....

  That is, even in the third example applied when the output gamut is smaller than the standard gamut, the output target value of the standard gamut and the plurality of gamut sizes are similar to the first example applied when the output gamut is larger than the standard gamut. The output characteristics are corrected based on the target value corresponding to the above.

  On the other hand, regarding the upper part of the cusp (the part of the hue surface above the maximum density), when the output characteristics (particularly the color tone characteristics) change as in the third gamut, the data points b3 ′, b4 ′,. Since the output image is thinner than at the time of design, it is necessary to perform color tone correction in the direction of increasing the density. Here, in the third example, the output gamut is smaller than the standard gamut, so if you try to forcefully bring it to the target point position, it will collapse near the cusp. Similarly, paying attention to the gradation surface, correction is performed so as to maintain the gradation ratio, or correction is not performed.

  As described above, according to the color tone correction process of the present embodiment, the characteristic change in which the gamut sizes of the primary color and the secondary color region are different from the standard gamut (for example, the primary color is the standard size). Even if the secondary color is larger than the standard size), an appropriate gamut size is selected based on the data having the maximum density value for each of the primary color and the secondary color, and the data corresponding to the selected gamut size. The target point of the standard gamut data is corrected based on (especially the data on the outline), the tone correction processing is applied to the input color data based on the corrected target point, and then the gradation correction is added. As a result, even when the gamut changes in the output characteristics due to the change in the fixing characteristics, the appropriate color tone correction and gradation correction are performed in response to the change in the output characteristics. Can do.

  Since the color tone correction process can be automatically performed using the test chart, the user is not burdened. Further, since it is not necessary to hold all the points inside the gamut for each gamut size, there is no significant increase in memory.

  As mentioned above, although this invention was demonstrated using embodiment, the technical scope of this invention is not limited to the range as described in the said embodiment. Various changes or improvements can be added to the above-described embodiment without departing from the gist of the invention, and embodiments to which such changes or improvements are added are also included in the technical scope of the present invention.

  Further, the above embodiments do not limit the invention according to the claims (claims), and all combinations of features described in the embodiments are not necessarily essential to the solution means of the invention. Absent. The embodiments described above include inventions at various stages, and various inventions can be extracted by appropriately combining a plurality of disclosed constituent elements. Even if some constituent requirements are deleted from all the constituent requirements shown in the embodiment, as long as an effect is obtained, a configuration from which these some constituent requirements are deleted can be extracted as an invention.

<Regarding the configuration using an electronic computer>
Further, in the present embodiment, the mechanism for correcting the color tone in consideration of the gamut size change is not limited to being configured by a hardware processing circuit, and software using an electronic computer (computer) based on a program code that realizes the function. It can also be realized.

  Therefore, a program suitable for realizing the color tone correction method and the image forming apparatus according to the present invention by software using an electronic computer (computer) or a computer-readable storage medium storing the program is extracted as an invention. You can also. By adopting a mechanism that is executed by software, it is possible to enjoy the advantage that the processing procedure and the like can be easily changed without changing hardware.

  When the computer executes the color tone correction processing function considering the gamut size change by software, a computer (such as an embedded microcomputer) or a CPU in which a program constituting the software is incorporated in dedicated hardware (SOC) that implements the desired system by mounting functions such as (Central Processing Unit), logic circuits, and storage devices on a single chip, or installing various programs And installed on a general-purpose personal computer capable of executing various functions from the recording medium.

  The recording medium causes a state change of energy such as magnetism, light, electricity, etc. according to the description contents of the program to the reading device provided in the hardware resource of the computer, and in the form of a signal corresponding to the change. The program description can be transmitted to the reader.

  For example, a magnetic disk (including a flexible disk FD), an optical disk (CD-ROM (Compact Disc-Read Only Memory)), a DVD on which a program is recorded, which is distributed to provide a program to a user separately from a computer. (Including Digital Versatile Disc), magneto-optical disc (including MD (Mini Disc)), or package media (portable storage media) made of semiconductor memory, etc. It may be configured by a ROM, a hard disk, or the like in which a program is recorded, which is provided to the user in a state of being recorded.

  The program constituting the software is not limited to being provided via the recording medium without using the recording medium, and may be provided via a wired or wireless communication network.

  For example, a storage medium in which a program code of software that realizes a color tone correction processing function considering gamut size change is supplied to the system or apparatus, and the computer (or CPU or MPU) of the system or apparatus stores it in the storage medium By reading and executing the program code, the same effect as that achieved by the hardware processing circuit can be achieved. In this case, the program code itself read from the storage medium realizes a function of color tone correction processing in consideration of a gamut size change.

  In addition, by executing the program code read by the computer, not only a function of performing color tone correction processing in consideration of a change in gamut size is realized, but also an OS ( Operating Systems (basic software) or the like may perform a part or all of the actual processing, and a function of performing color tone correction processing considering gamut size change may be realized by the processing.

  Further, after the program code read from the storage medium is written in a memory provided in a function expansion card inserted into the computer or a function expansion unit connected to the computer, the function expansion is performed based on the instruction of the program code. The CPU or the like provided in the card or the function expansion unit may perform a part or all of the actual processing, and a function of performing color tone correction processing considering gamut size change may be realized by the processing.

  Note that the program is provided as a file describing a program code that realizes a function of performing color tone correction processing in consideration of a change in gamut size. In this case, the program is not limited to being provided as a batch program file, and is configured by a computer. Depending on the hardware configuration of the system to be implemented, it may be provided as an individual program module.

  For example, FIG. 12 shows an image processing apparatus (color tone correction processing apparatus) having a function of performing color tone correction processing in consideration of a gamut size change using software such as a CPU and a memory, that is, a computer such as a personal computer (electronic FIG. 3 is a block diagram illustrating an example of a hardware configuration when a tone correction process in consideration of a gamut size change is realized in software using a function of a computer.

  Of course, the present invention is not limited to such a configuration using a computer, and an image processing apparatus that performs color tone correction processing in consideration of gamut size changes by a combination of dedicated hardware that performs processing of each functional unit shown in FIG. It can also be configured.

  Note that in the case where the color tone correction processing function taking into account the gamut size change is incorporated in a multifunction peripheral which is an example of an image forming apparatus, the electronic computer shown in FIG. 12 includes, for example, a copying application, a printer application, and a facsimile (FAX) application. Alternatively, software similar to that in a conventional image forming apparatus (multifunction machine) such as a processing program for another application is incorporated. A control program for transmitting and receiving data to and from the outside via a network is also incorporated.

  At this time, the program is provided as a file describing a program code for realizing a color tone correction processing function taking into account a change in gamut size. In this case, the program is not limited to being provided as a batch program file, and is configured by a computer. Depending on the hardware configuration of the system, it may be provided as an individual program module. For example, it may be provided as add-in software incorporated in existing copying apparatus control software or printer control software (printer driver).

  For example, the computer system 900 reads and records data from a controller unit 901 and a predetermined storage medium such as a hard disk device, a flexible disk (FD) drive, a CD-ROM (Compact Disk ROM) drive, a semiconductor memory controller, or the like. And a recording / reading control unit 902.

  The controller unit 901 includes a CPU (Central Processing Unit) 912, a ROM (Read Only Memory) 913 which is a read-only storage unit, and a RAM (Random Access) which can be written and read at any time and is an example of a volatile storage unit. Memory) 915 and RAM (described as NVRAM) 916 which is an example of a nonvolatile storage unit.

  The NVRAM 916 includes, for example, target data corresponding to the test chart 2 of standard gamut (during design), and data having lower brightness than the cusps (CUSP) of a plurality of gamuts different in size from the standard gamut (corresponding to the target value of the standard gamut) This NVRAM 916 can function as the data storage unit 246 by storing the nonstandard gamut target value).

  In the above description, the “volatile storage unit” means a storage unit in which the stored contents are lost when the power of the apparatus is turned off. On the other hand, the “nonvolatile storage unit” means a storage unit in a form that keeps stored contents even when the main power supply of the apparatus is turned off. Any memory device can be used as long as it can retain the stored contents. The semiconductor memory device itself is not limited to a nonvolatile memory device, and a backup power supply is provided to make a volatile memory device “nonvolatile”. You may comprise as follows. Further, the present invention is not limited to a semiconductor memory element, and may be configured using a medium such as a magnetic disk or an optical disk. For example, a hard disk device can be used as a nonvolatile storage unit. In addition, it is possible to use as a nonvolatile storage unit by adopting a configuration for reading information from a recording medium such as a CD-ROM.

  In addition, the computer system 900 includes an instruction input unit 903 as a functional unit that forms a customer interface, a display output unit 904 that presents a customer with predetermined information such as a guidance screen and a processing result at the time of operation, and each functional unit And an interface unit (IF unit) 909 that performs an interface function between them.

  Note that, in order to configure the MFP, an image reading unit (scanner unit) 905 corresponding to the image acquisition unit 10 that reads an image to be processed, and a processed image are output to a predetermined output medium (for example, printing paper). An image forming unit 906 corresponding to the image output unit 30 is also provided.

  As the instruction input unit 903, for example, the operation key unit 985b of the user interface unit 985 can be used. Alternatively, a keyboard or mouse can be used.

  The display output unit 904 includes a display control unit 942 and a display device. As the display device, for example, the operation panel unit 985a of the user interface unit 985 can be used. Alternatively, other display units such as CRT (Cathode Ray Tube) or LCD (Liquid Crystal Display) can be used.

  For example, the display control unit 942 displays guidance information, the entire image captured by the image reading unit 905, and the like on the operation panel unit 985a and the display unit. It is also used as a display device for notifying the user of various information. Note that an instruction input unit 903 for inputting predetermined information with a fingertip, a pen, or the like can be configured by using a display unit having a touch panel on the display surface.

  Examples of the interface unit 909 include a system bus 991 that is a transfer path of processing data (including image data) and control data, a scanner IF unit 995 that functions as an interface with the image reading unit 905, an image forming unit 906, and the like. It has a printer IF unit 996 that functions as an interface with other printers, and a communication IF unit 999 that mediates transfer of communication data with a network such as the Internet.

  In such a configuration, the CPU 912 controls the entire system via the system bus 991. The ROM 913 stores a control program for the CPU 912 and the like. The RAM 915 is configured by SRAM (Static Random Access Memory) or the like, and stores program control variables, data for various processes, and the like. Further, the RAM 915 stores an electronic document (not only character data but also image data) acquired by a predetermined application program, image data acquired by the image reading unit 905 provided in the apparatus, and externally. An area for temporarily storing acquired electronic data and the like is included.

  For example, a program that causes a computer to execute a color tone correction processing function that takes into account changes in gamut size is distributed through a recording medium such as a CD-ROM. Alternatively, this program may be stored in the FD instead of the CD-ROM. In addition, an MO drive may be provided to store the program in the MO, or the program may be stored in another recording medium such as a nonvolatile semiconductor memory card such as a flash memory. Furthermore, the program may be downloaded from another server or the like via a network such as the Internet, or may be updated or updated.

  As a recording medium for providing the program, in addition to FD and CD-ROM, optical recording medium such as DVD, magnetic recording medium such as MD, magneto-optical recording medium such as PD, tape medium, and magnetic recording A semiconductor memory such as a medium, an IC card, or a miniature card can be used. An FD or CD-ROM as an example of a recording medium can store a part or all of the functions for realizing a color tone correction processing function considering a gamut size change.

  The hard disk device also includes an area for storing data for various processes by the control program and temporarily storing a large amount of image data acquired by the image reading unit 905, print data acquired from the outside, and the like. It is out. The hard disk device, FD drive, or CD-ROM drive is used, for example, for registering program data for causing the CPU 912 to execute processing such as content acquisition, address acquisition, or address setting by software. .

  It should be noted that a processing circuit 908 may be provided in which not all processing of each functional part for color tone correction processing considering gamut size change is performed by software, but a part of these functional parts is performed by dedicated hardware. Good. Although the mechanism performed by software can flexibly cope with parallel processing and continuous processing, the processing time becomes longer as the processing becomes complicated, so that a reduction in processing speed becomes a problem. On the other hand, it is possible to construct an accelerator system with a higher speed by using a hardware processing circuit. Even if the processing is complicated, the accelerator system can prevent a reduction in processing speed and can obtain a high throughput.

  For example, in the case of the illustrated embodiment in which a color tone correction processing function considering gamut size change is applied to a multifunction peripheral, the processing circuit 908 includes a color tone correction processing unit corresponding to the color tone correction processing unit 240 shown in FIG. 908a, a first color conversion processing unit 908b corresponding to the first color conversion processing unit 220 on the input side, a second color conversion processing unit 908c corresponding to the second color conversion processing unit 270 on the output side, and gradation correction The gradation correction processing unit 908d corresponding to the processing unit 280 may be configured by hardware.

1 is a mechanism diagram of an image forming apparatus equipped with an embodiment of a color correction processing apparatus that performs a color correction method according to the present invention. 1 is a diagram illustrating an example of a circuit configuration of an image forming apparatus focusing on color tone correction processing. It is a figure which shows an example of the reference | standard pattern used by a color tone correction process. It is a figure explaining Lab color space and a gamut change. It is a figure explaining the characteristic change of color tone. It is a flowchart which shows an example of the process sequence of a color correction process. It is a figure which shows an example of gamut size determination in the read data determination part. It is a figure explaining the detail of a gamut selection process. It is a figure explaining the 1st example of a standard gamut target value correction process. It is a figure explaining the 2nd example of standard gamut target value correction processing. It is a figure explaining the 3rd example of standard gamut target value correction processing. It is the figure which showed an example of the hardware constitutions in the case of comprising the structure which performs a color tone correction process using an electronic computer.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Color copying apparatus (built-in color tone correction processing apparatus), 10 ... Image acquisition part, 15 ... User interface apparatus, 20 ... Internal controller part, 30 ... Image output part, 31 ... Image formation part, 32 ... Photosensitive drum, DESCRIPTION OF SYMBOLS 43 ... Transfer belt, 45 ... Fixing part, 210 ... Input image data acquisition part, 220 ... 1st color conversion process part, 240 ... Color tone correction process part, 242 ... Test chart production | generation part, 244 ... Test chart reading part, 246 ... Data storage unit, 254 ... gradation correction curve creation unit, 255 ... read data determination unit, 256 ... standard gamut data correction unit, 257 ... output value correction processing unit, 270 ... second color conversion processing unit, 280 ... gradation correction Processing unit 900 ... Computer system 903 ... Instruction input unit 904 ... Display output unit 908 ... Processing circuit

Claims (8)

A color tone correction method for correcting the color tone of a color image output from an image forming apparatus,
A color patch having the maximum density of primary colors and secondary colors of a plurality of color materials used by the image forming apparatus is output from the image forming apparatus, and output characteristics are measured by reading the output color patches. A color correction method characterized by determining a color gamut size and adjusting a color tone of an output characteristic based on the determined color gamut size. A color correction device that corrects the color tone of a color image output from an image forming apparatus,
The color gamut size is determined by measuring the output characteristics by reading the color patches of the maximum density of the primary color and secondary color of the plurality of color materials used by the image forming apparatus, which are output from the image forming apparatus. And a tone correction device that adjusts the tone of the output characteristics based on the determined color gamut size. The color tone correction processing unit includes a data storage unit that stores maximum density values of primary colors and secondary colors for each of a plurality of color reproduction gamut sizes and information of lightness lower than the maximum density values;
By comparing the read maximum density values of the primary and secondary color patches with the information on the maximum density values of the primary color and secondary color of each color reproduction area size stored in the data storage unit. A read data determination unit for determining an appropriate color gamut size;
An output value correction processing unit that applies color tone correction to input color data with reference to information having a lightness lower than the maximum density value in the color gamut size determined by the read data determination unit. The color tone correction apparatus according to claim 2. The color tone correction device according to claim 2, wherein the color tone correction processing unit corrects output characteristics based on an output target value of a standard color gamut and target values corresponding to a plurality of color gamut sizes. . The color tone correction processing unit includes an output target value of the standard color gamut and target values corresponding to a plurality of color gamut sizes on a color gamut contour for a primary color and a secondary color hue plane. The color correction device according to claim 4. In the color tone correction processing unit, the target value corresponding to the plurality of color gamut sizes corresponds to the maximum saturation of each hue on the color gamut outline with respect to the hue planes of the primary color and the secondary color. The color correction device according to claim 5, wherein data less than brightness is held. An image forming apparatus for forming a color image on a predetermined output medium,
The color reproduction gamut size is determined by measuring the output characteristics by reading the color patches of the maximum density of the primary color and secondary color of the plurality of color materials used by the image forming apparatus that are output from the image forming apparatus. An image forming apparatus comprising: a color tone correction processing unit that adjusts the color tone of the output characteristics based on the determined color gamut size. A program for performing color tone correction processing for correcting the color tone of a color image output from an image forming apparatus using a computer,
In the computer,
A processing procedure for outputting, from the image forming apparatus, a color patch having a maximum density of primary colors and secondary colors of a plurality of color materials used by the image forming apparatus;
Processing procedure to read this output color patch,
A procedure for measuring the output characteristics of the read color patch and determining the color gamut size;
And a processing procedure for adjusting a color tone of an output characteristic based on the determined color gamut size.