JP2009010499A - Color correction apparatus and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To maintain high color reproducibility without degrading image quality even when performing calibration processing using not a test chart but a normal original image. <P>SOLUTION: When performing the calibration processing, a grating point data updating part 402 uses respective grating point data before updating stored in a three-dimensional DLUT 201 as base data, and resets the value of the grating point data in the three-dimensional DLUT 201 using the base data and sampling data obtained from the colorimetric result of the original image. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a color correction technique for eliminating a color difference between an input image and an output image.

  For example, in Patent Document 1, in an image forming apparatus, color information of an input original image is compared with color information of an output image obtained by printing the original image, and an output ICC profile (look-up table). And a calibration process is performed using a normal document image printed by the image forming apparatus instead of a test chart such as a patch image prepared in advance. Further, this Patent Document 1 specifically describes that calibration processing is performed as follows.

That is, for the original image (input image), as shown in FIG. 5A of the same document 1, an average color is obtained for each of the sampling regions A1, A2, and A3, while for the output image, As shown in b), each color tone is detected by the color sensor 76 in the sampling areas B1 to B3 corresponding to the sampling areas A1 to A3. For example, if the average color value in the sampling area A1 is CMYK_a1 and the average color value in the sampling area B1 is Lab_b1, the relationship Lab_b1 = F (CMYK_a1) is established between the two. Similar relationships sampling region A2 and the sampling region B2, since also holds for the sampling area A3 and the sampling region B3, updates the look-up table for the inverse conversion table F ^-1 of F from here.
JP 2005-217747 A

  By the way, when the calibration process is performed using the test chart, a large number of color targets whose colors are gradually changed from the reference color are printed as a test chart, so that a plurality of grid points stored in the lookup table are used. It is possible to correct the data values uniformly for all colors. On the other hand, when the calibration process is performed using a normal document image as described in Patent Document 1, a document image in which various colors are used uniformly, similar to the test chart, is used. If there is a large number of sampling areas in the original image and the average color is not measured, the grid point data corrected by the calibration process is limited to a small number. Bias occurs.

In particular, according to the calibration process described in Patent Document 1, only the grid point data corresponding to the color is corrected using only the measurement result of the average color for the original image. As shown in FIG. 6, when the lookup table is updated using the measurement value indicated by “x” in the figure, only the lattice point data (indicated by “●” in the figure) corresponding to this measurement value is obtained. May be corrected to a value corresponding to the measured value (indicated by “■” in the figure), and the color correction characteristics using the updated look-up table may be changed as indicated by the dotted line. In this case, the Coverage hardly changes even if L ^* (brightness) changes in the region X, and therefore, when color correction is performed using the updated look-up table, a pseudo contour is generated in the region X. However, the image quality is deteriorated. In addition, when only a part of the grid point data is adjusted by the calibration process and the degree of the adjustment is large, there is a drop in the color transition at the boundary between the area where the color is adjusted and the area where the color is not adjusted. As a result, in addition to the pseudo contour, image quality deterioration such as tone jump and color skip is caused.

  In addition, image quality defects such as streaks, bands, white spots, and color points may occur in the print image (output image). If such image quality defects are included in the sampling areas B1 to B3, the image is updated. Due to the color correction using the look-up table, image quality deterioration such as pseudo contour, tone jump, and color skip is likely to occur.

  The present invention has been made in view of the circumstances described above, and its purpose is to reduce image quality degradation such as tone jump even when calibration processing is performed using a normal document image instead of a test chart. In other words, the high color reproducibility can be maintained.

  In order to solve the above-mentioned problems, an invention according to claim 1 is directed to an input unit for inputting an image, an input image by the input unit, and an output of the input image from an image forming apparatus provided at a subsequent stage of the color correction apparatus. For each grid point defined in the color space, color information before correction indicated by the grid point, and after correction for this color information A color correction table for storing grid point data composed of the color information, color correction means for correcting the color of the input image using the color correction table, and an input image corrected by the color correction means. An output unit that outputs to the image forming apparatus; a first acquisition unit that acquires color information of an arbitrary region from an input image before correction by the color correction unit; and Measuring the color of the area from which the information was acquired, acquiring the color information of the area, the color information acquired by the first acquisition means, and the second acquisition means A color correction apparatus comprising: update means for updating the value of the grid point data using color information and base data that is a combination of a plurality of color information before correction and color information after correction I will provide a.

  The invention described in claim 2 is characterized in that, in the invention described in claim 1, each grid point data stored in the color correction table is used as the base data.

  According to a third aspect of the present invention, in the first aspect of the present invention, the update unit includes the color information acquired by the first acquisition unit and the color information acquired by the second acquisition unit. The grid point data is re-determined based on data added to the base data.

  According to a fourth aspect of the present invention, in the first aspect of the present invention, the update unit includes the color information acquired by the first acquisition unit and the color information acquired by the second acquisition unit. When the configured measurement data is within a predetermined allowable range for the color correction characteristic determined by each grid point data stored in the color correction table, the measurement data and each grid point data And the color information value after correction is updated for one or more of the grid point data.

  According to a fifth aspect of the present invention, in the first aspect of the present invention, an input unit for inputting an image, an input image by the input unit, and an image formation in which the input image is provided at a subsequent stage of the color correction device. For each grid point defined in the color space, used for color correction processing to eliminate a color difference from the output image obtained by outputting from the apparatus, color information before correction indicated by the grid point, and this color information A color correction table that stores grid point data composed of color information after correction for the color information, and color information to be corrected when the color of the input image is corrected using the color correction table. In the color space, the coordinate points indicated by the color information to be corrected are included in the color space, and each vertex is the lattice information. Color correction means for calculating color information after correction for the color information to be corrected using the grid point data corresponding to each vertex of the polyhedron, and after correction by the color correction means Output means for outputting the input image to the image forming apparatus, first acquisition means for acquiring color information of an arbitrary region from the input image before correction by the color correction means, and Measuring the color of the area from which the color information is acquired by the acquisition means, acquiring the color information of the area, the color information acquired by the first acquisition means, and the second acquisition Generating means for generating new grid point data other than the grid point data stored in the color correction table using the color information acquired by the means, and the grid point data generated by the generation means color Adding means for adding to the main table, and when the grid correction data is added to the color correction table, the color correction means determines the grid point indicated by the added grid point data when defining the polyhedron. It is used as one or more vertices of the polyhedron.

  According to a sixth aspect of the present invention, there is provided a color for eliminating a color difference between an input unit for inputting an image, an input image by the input unit, and an output image obtained by outputting the input image from the image forming apparatus. For each grid point defined in the color space, used in the correction process, grid point data composed of color information before correction indicated by the grid point and color information after correction for this color information is stored. A color correction table, a color correction unit that corrects the color of the input image using the color correction table, an image forming unit that forms an output image using the input image corrected by the color correction unit, and the color Color information is acquired by the first acquisition unit in the first acquisition unit that acquires color information of an arbitrary region from the input image before correction by the correction unit and the output image formed by the image forming unit. A second acquisition means for measuring the color of the area and acquiring the color information of the area; the color information acquired by the first acquisition means; the color information acquired by the second acquisition means; An image forming apparatus is provided, comprising: update means for updating the value of the grid point data using a plurality of color information before correction and base data that is a combination of color information after correction.

  According to a seventh aspect of the invention, there is provided a color for eliminating a color difference between an input unit for inputting an image, an input image by the input unit, and an output image obtained by outputting the input image from the image forming apparatus. For each grid point defined in the color space, used in the correction process, grid point data composed of color information before correction indicated by the grid point and color information after correction for this color information is stored. Color correction table and color information before correction of any grid point data in which color information to be corrected is stored in the color correction table when correcting the color of the input image using the color correction table In the color space, a polyhedron that includes coordinate points indicated by the color information to be corrected and each vertex is the lattice point is defined, and a lattice point corresponding to each vertex of the polyhedron A color correction unit that calculates color information after correction of the color information to be corrected using an imager, and an image forming unit that forms an output image using an input image corrected by the color correction unit. A first acquisition unit that acquires color information of an arbitrary region from an input image before correction by the color correction unit; and an output image formed by the image formation unit, and the color information is acquired by the first acquisition unit. Second acquisition means for measuring the color of the acquired area and acquiring color information of the area; color information acquired by the first acquisition means; and color information acquired by the second acquisition means And generating means for generating new grid point data other than the grid point data stored in the color correction table, and adding the grid point data generated by the generating means to the color correction table And when the grid point data is added to the color correction table, the color correction unit determines one or more grid points indicated by the added grid point data when defining the polyhedron. An image forming apparatus characterized by being used as the apex of the image forming apparatus is provided.

  According to the present invention, even when calibration processing is performed using a normal document image instead of a test chart, image quality degradation such as tone jump does not occur and high color reproducibility can be maintained. .

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[First Embodiment]
FIG. 1 is a block diagram illustrating a configuration of an image forming system 1 according to the first embodiment.
In the figure, the controller 10 rasterizes the original data so that it can be printed by the printer 30. The color correction apparatus 20 is a printer server, for example, and has a three-dimensional DLUT (Direct Look Up Table) 201. In the color correction device 20, color conversion processing and color correction processing are performed using the three-dimensional DLUT 201. The color conversion process is a process for converting image data in L ^* a ^* b ^* format or RGB format input from the controller 10 into image data in CMYK format. The color correction process is a process for eliminating (reducing) a color difference between an input image to the printer 30 and an output image obtained by printing the input image with the printer 30 and maintaining the color reproducibility of the printer 30. is there.

The three-dimensional DLUT201 (color correction / color conversion table), for each was lattice points arranged in a color space, the color information of the pre-correction (before conversion) [L ^* a ^* b ^* or RGB, where L ^* a ^* b ^* ] and grid point data composed of corrected (converted) color information [CMYK] is stored. For example, in the case of a three-dimensional DLUT for a 9 × 9 × 9 grid, a total of 729 grid point data are stored. In the case of a three-dimensional DLUT for a 17 × 17 × 17 grid, a total of 4913 grid point data are stored. These lattice point data are set according to a combination of a plurality of predetermined color information [CMYK] and color information [L ^* a ^* b ^* ].

  The printer 30 prints an image on a recording sheet such as printing paper or an OHP sheet based on the CMYK format image data output from the color correction device 20. The DLUT update device 40 is a device that updates the three-dimensional DLUT 201 stored in the color correction device 20, and includes a colorimetric sensor 401 and a lattice point data update unit 402. The color measurement sensor 401 measures the color of the output image printed on the recording sheet by the printer 30. The colorimetric sensor 401 may be incorporated in the printer 30. A color image scanner can be used as the colorimetric sensor 401.

The grid point data update unit 402 receives the CMYK format image data output from the color correction device 20 and the L ^* a ^* b ^* format image data read by the colorimetric sensor 401. In other words, the lattice point data updating unit 402, the input image to the printer 30 (CMYK format) and the output image (L ^* a ^* b ^* format) is input. Although details will be described later, the lattice point data update unit 402 resets the values of the lattice point data stored in the three-dimensional DLUT 201 based on the colorimetric results of the input image and output image to the printer 30. The reset grid point data is transmitted from the DLUT update device 40 to the color correction device 20, thereby updating the three-dimensional DLUT 201 stored in the color correction device 20.

  Next, calibration processing executed in the image forming system 1 will be described with reference to FIG. The calibration process can be executed at an arbitrary timing designated by the administrator or user of the printer 30. Whether the calibration process is performed at a predetermined cycle, such as once a day, or whether the calibration process is performed according to a predetermined probability value each time printing of document data is commanded. The structure which determines this may be sufficient.

  Similarly to the invention described in Patent Document 1, in this embodiment, calibration processing is performed using a normal document image printed by the printer 30 instead of the test chart. The document image used when the calibration process is performed can be arbitrarily designated by the administrator or user of the printer 30. If the calibration process is performed at a predetermined cycle as described above, the calibration process is performed using the original image that is first instructed to print after the timing for performing the calibration process arrives. Done.

When the execution of the calibration process is instructed, first, the controller 10 rasterizes document data to be used instead of the test chart and outputs it to the color correction apparatus 20. The color correction device 20 performs color conversion processing and color correction processing on the L ^* a ^* b ^* format or RGB format image data input from the controller 10 using the three-dimensional DLUT 201. As a result, the L ^* a ^* b ^* format or RGB format image data input from the controller 10 is converted into CMYK format image data, and at the same time, the color for eliminating the color difference between the input image and the output image in the printer 30. Correction processing is performed. As described above, in the color correction apparatus 20 according to the present embodiment, the color conversion process and the color correction process are simultaneously performed using the three-dimensional DLUT 201. In the color conversion process and the color correction process using the three-dimensional DLUT 201, the color correction apparatus 20 obtains a color other than the grid points by, for example, an interpolation calculation from a plurality of adjacent grid points.

The CMYK format image data obtained in this way is output from the color correction device 20 to the printer 30 and the DLUT update device 40, and the printer 30 generates an image on a recording sheet based on the CMYK format image data. Print. The output image printed on the recording sheet is read by the colorimetric sensor 401 of the DLUT update device 40. As a result, the CMYK format image data output from the color correction device 20 and the L ^* a ^* b ^* format image data read by the colorimetric sensor 401 are input to the lattice point data update unit 402. That is, an input image (CMYK format) and an output image (L ^* a ^* b ^* format) for the printer 30 are input to the lattice point data update unit 402.

First, the grid point data update unit 402 extracts color information of pixels at the same position, for example, from a set of input images and output images. Next, the lattice point data update unit 402 resets the value of the lattice point data for a pair of the color information [CMYK] extracted from the input image and the color information [L ^* a ^* b ^* ] extracted from the output image. As sampling data (measurement data), the data is stored in a memory (not shown) provided in the DLUT update device 40.

  In addition, the position of the pixel from which color information is extracted in the input image or the output image, and the number of sampling data acquired from one set of the input image and the output image can be arbitrarily determined. Further, it is also possible to use color information of a region constituted by a plurality of adjacent pixels instead of color information of one pixel. In addition, the position of the pixel or area from which the color information is extracted is determined in advance, and only the color information of the pixel or area at the position determined in advance from the color correction device 20 or the colorimetric sensor 401 is a lattice point. The configuration may be such that the data is input to the data updating unit 402.

Next, the grid point data update unit 402 uses, as base data, a combination of a plurality of color information [CMYK] and color information [L ^* a ^* b ^* ] used when the grid point data of the three-dimensional DLUT 201 is first set. The value of one or more grid point data in the three-dimensional DLUT 201 is reset using this base data and sampling data stored in a memory (not shown). When resetting the value of grid point data, for example, using a linear regression model or a neural network, the printer model (L ^* a ^* b ^* ) = F (CMYK ) And determining the inverse transformation (CMYK) = F ⁻¹ (L ^* a ^* b ^* ) of the printer model, the value of the grid point data can be obtained. As the base data, a combination of a plurality of color information [CMYK] and color information [L ^* a ^* b ^* ] used when the grid point data of the three-dimensional DLUT 201 is first set as described above may be used. It is also possible to use the grid point data immediately before updating the three-dimensional DLUT 201.

  In this way, not only the sampling data but also the value of the grid point data is reset using the base data before update or the value of each grid point data. For example, as shown in FIG. Even when the three-dimensional DLUT 201 is updated using one point of sampling data (indicated by “x” in the figure) acquired from the image, in addition to this sampling data, each grid point data before update (base Data) values (indicated by “◯” and “●” in the figure) are added, and the value of the grid point data is reset. Accordingly, not only one grid point data corresponding to the sampling data but also a plurality of grid points located in the vicinity (neighborhood) thereof is corrected as necessary.

  As described above, when sampling data is added to the base data before update, in the case of the example shown in FIG. 2, the color correction by the updated three-dimensional DLUT 201 with respect to the color correction characteristics by the three-dimensional DLUT 201 before update indicated by a solid line The characteristics are shown by dotted lines. In FIG. 2, the values of the grid point data and sampling data before the update are the same as those shown in FIG. 6 so that the comparison with the prior art is easy. As apparent from the comparison between the color correction characteristic (dotted line) by the updated three-dimensional DLUT 201 shown in FIG. 2 and the color correction characteristic (dotted line) by the updated lookup table shown in FIG. According to the calibration process in the present embodiment, the value of only some of the grid point data is not greatly changed.

When one or more grid point data values are reset by the grid point data update unit 402 in this way, the reset grid point data values are transferred from the DLUT update device 40 to the color correction device 20. Sent. Incidentally, it is reset by the grid point data updating unit 402, among the color information after correction [CMYK] and color information before correction constituting the grid point data [L ^* a ^* b ^* or RGB], corrected Only the subsequent color information [CMYK]. Therefore, only the corrected color information [CMYK] of the reset grid point data may be transmitted to the color correction apparatus 20. The color correction device 20 rewrites the value of the grid point data stored in the three-dimensional DLUT 201 in accordance with the data received from the DLUT update device 40 (grid point data update unit 402). As a result, the color correction device 20 subsequently performs color conversion processing and color correction processing on the image data input from the controller 10 using the updated three-dimensional DLUT 201.

  As described above, according to the present embodiment, when resetting the value of the grid point data, the sampling data is added to the base data before update stored in the three-dimensional DLUT 201, so that it can be used as compared with the test chart. Even when calibration processing is performed using a normal document image with a biased color, the value of only some grid point data in the three-dimensional DLUT 201 is not greatly changed. Therefore, image quality degradation such as pseudo contour, tone gap, and color skip does not occur, and the color reproducibility of the printer 30 can be maintained with high accuracy. In addition, image quality defects such as streaks, bands, white spots, and color points are included in the output image, so that even if the sampling data takes a value far from the base data, The degree to which the value of the grid point data is changed in a direction that reduces the color reproducibility of the printer 30 can be reduced. Of course, since a test chart becomes unnecessary, the downtime required for the calibration process can be eliminated, and waste of toner and recording paper can be eliminated.

  Note that the lattice point data update unit 402 uses not only sampling data acquired from one original image but also sampling data acquired from other original images and stored in the memory in the past, as the value of the lattice point data. It is also possible to reset. With such a configuration, the number of sampling data used when resetting the value of the grid point data increases, so it is assumed that some sampling data may become base data due to image quality defects that occur in the output image. Even in the case where the values take values that are far from each other, the degree to which the value of the grid point data is changed in such a direction as to decrease the color reproducibility of the printer 30 by such sampling data can be reduced.

  However, the color reproducibility of the printer 30 is mainly due to deterioration with time and environmental fluctuations, for example, when the toner or ink used is changed to another type or when a failure occurs in the printer 30. Therefore, when resetting the value of grid point data, for example, it is not a good idea to use sampling data acquired six months ago or one year ago. Therefore, it is desirable to limit the sampling data used when resetting the grid point data to those acquired within a predetermined period, such as data acquired up to one week ago. In this case, the DLUT update device 40 includes a timer for measuring the current time. For example, the DLUT update device 40 acquires time information (year / month / day / hour / minute / second) when the sampling data is acquired or when the sampling data is stored in the memory. This time information is added to the sampling data. Further, a storage period in which the sampling data is stored in the memory may be determined, and the sampling data that has passed the storage period may be sequentially deleted from the memory.

  Further, the grid point data update unit 402 performs different weighting on the base data and the sampling data when resetting the value of the grid point data. For example, the grid point data update unit 402 sets the weight value for the base data to each sampling data. It may be made larger than the weighting value. Also, the weighting values for individual sampling data may be increased as the value is acquired more recently according to the sampling data acquisition time.

  Further, when resetting the value of the grid point data, the grid point data update unit 402 compares the value of the sampling data with the value of the base data, and takes a value that is too far from the value of the base data. The data can be determined as sampling data affected by image quality defects or the like generated in the output image, and the data of the grid point data can be reset by excluding this sampling data. In this case, for example, the grid point data update unit 402 has a color correction characteristic indicated by the sampling data within a predetermined allowable range with respect to a color correction characteristic determined by each grid point data stored in the three-dimensional DLUT 201 (for example, , Within ± 5.0% range, etc.), and sampling data not within the allowable range is excluded.

  Further, when the grid point data update unit 402 extracts color information of pixels (or regions) at the same position from a set of input images and an output image, the color difference between the two is determined based on a predetermined threshold value. If it is too large, it may be determined that the output image is affected by image quality defects and the like, and such sampling data may be deleted without being stored in the memory.

[Second Embodiment]
Next, a second embodiment will be described. In addition, in this embodiment, the same code | symbol shall be used about the part which is common in 1st Embodiment. Further, description of portions common to the first embodiment is omitted.

FIG. 3 is a block diagram illustrating a configuration of the image forming system 2 according to the second embodiment.
In the first embodiment described above, the case where the color conversion process and the color correction process are simultaneously performed using the three-dimensional DLUT 201 has been described. However, in the present embodiment, the three-dimensional DLUT 501 specialized for the color conversion process, the color correction, and the like. The main difference from the first embodiment is that a three-dimensional DLUT 601 specialized for processing is provided.

In the image forming system 2 shown in the figure, the color conversion apparatus 50 performs color conversion processing using a three-dimensional DLUT 501. In this three-dimensional DLUT 501, color information before conversion [L ^* a ^* b ^* or RGB] and lattice point data constituted by the converted color information [C′M′Y ′] are stored. The color correction device 60 performs color correction processing using the three-dimensional DLUT 601. The three-dimensional DLUT 601 includes color information [C′M′Y ′] before correction and post-correction for each lattice point. The grid point data constituted by the color information [CMY] is stored. Further, the DLUT update device 41 obtains an input image (CMY format) for the printer 30 from the color correction device 60 and updates the three-dimensional DLUT 601 stored in the color correction device 60. Different from the DLUT update device 40 in the embodiment.

Next, the operation of calibration processing in this embodiment will be described.
First, the controller 10 rasterizes the document data and outputs it to the color conversion device 50. The color conversion device 50 performs color conversion processing using the three-dimensional DLUT 501 and converts image data in the L ^* a ^* b ^* format or RGB format input from the controller 10 into image data in the C′M′Y ′ format. Convert. In addition, the color correction device 60 performs color correction processing using the three-dimensional DLUT 601, and the input image and the output image of the printer 30 for the C′M′Y ′ format image data input from the color conversion device 50. Perform color correction to eliminate color differences. In the color conversion process using the three-dimensional DLUT 501 and the color correction process using the three-dimensional DLUT 601, colors other than the grid points are obtained by, for example, interpolation calculation from a plurality of adjacent grid points.

The CMY format image data obtained in this way is output from the color correction device 60 to the printer 30 and the DLUT update device 41, and the printer 30 generates an image on a recording sheet based on the CMY format image data. Print. The output image printed on the recording sheet is read by the colorimetric sensor 401 of the DLUT update device 41. As a result, the grid point data update unit 402 receives the CMY format image data output from the color correction device 60 and the L ^* a ^* b ^* format image data read by the colorimetric sensor 401. That is, an input image (CMY format) and an output image (L ^* a ^* b ^* format) for the printer 30 are input to the lattice point data update unit 402.

  Thereafter, the lattice point data update unit 402 performs processing for updating the three-dimensional DLUT 601 stored in the color correction device 60 in the same manner as in the first embodiment described above. That is, the grid point data update unit 402 uses each grid point data before update stored in the three-dimensional DLUT 601 as base data, and acquires the base data and the original image and stores them in the memory. The value of one or more grid point data in the three-dimensional DLUT 601 is reset using the sampling data. When resetting the value of the grid point data, for example, the sampling data acquired from other document images in the past and stored in the memory is used, or the base data and the sampling data are weighted differently. For sampling data that takes values that are too far apart from the values of the base data. Various processing methods described in the first embodiment, such as resetting the value of, can be employed.

  When one or more grid point data values are reset by the grid point data update unit 402 in this way, the reset grid point data values are transferred from the DLUT update device 41 to the color correction device 60. Sent. As a result, the three-dimensional DLUT 601 stored in the color correction device 60 is rewritten. Thereafter, the color correction device 60 uses the updated three-dimensional DLUT 601 to perform color correction on the image data input from the color conversion device 50. Process.

  As described above, the image forming system 2 according to the present embodiment updates grid point data values in the color correction three-dimensional DLUT 601 provided separately from the color conversion three-dimensional DLUT 501. Even if it is such a structure, the effect similar to the case of 1st Embodiment can be acquired. Further, as in the present embodiment, when the color conversion function and the color correction function are separated and the color correction function is made independent and provided in the color correction device 60, for example, the color conversion function (or even the color correction function) Even if the color conversion function (which also has a color conversion function) is incorporated in a controller or the like made by another company, it can be handled.

[Modification]
(1) For example, in the second embodiment, instead of changing the value of the grid point data stored in the three-dimensional DLUT 601, the sampling data acquired from the document image is stored in the three-dimensional DLUT 601 as new grid point data. It may be configured to additionally register. The sampling data calculation method is as described in the first embodiment. However, the sampling data calculated in the second embodiment is the color information [C′M′Y ′] before correction. Since the data is composed of the corrected color information [CMY], this corresponds to the grid point data of different positions in the color space.

  Therefore, the lattice point data update unit 402 transmits the sampling data acquired from the document image to the color correction device 60, and the color correction device 60 uses the received sampling data as new lattice point data, for example, as shown in FIG. In this way, additional registration is performed in the three-dimensional DLUT 602. Note that the 3D DLUT 602 shown in FIG. 4 is originally a 3D DLUT for a 2 × 2 × 2 grid. A total of 8 grid point data from “1” to “8” are stored in advance. This is grid point data (sampling data) in which data after “9” is newly added.

In addition, when new grid point data is additionally registered in the three-dimensional DLUT 602, the color correction device 60 performs color correction processing using the three-dimensional DLUT 602 as follows.
That is, when the color information [C′M′Y ′] of a certain pixel is corrected for the C′M′Y ′ format image data input from the color conversion device 50, the color correction device 60, for example, 4 The color information [CMY] after correction is calculated by performing face body interpolation. At this time, for example, as shown in FIG. 5, the color information [C′M′Y ′] to be corrected indicates in the color space. In determining a tetrahedron containing coordinate values (indicated by “□” in the figure), No. 1 additionally registered in the three-dimensional DLUT 602 (see FIG. 4) is registered for at least one vertex constituting the tetrahedron. Grid data after “9” is used. If the lattice point data additionally registered for at least one vertex is used, the remaining vertexes are stored in the No. stored in the three-dimensional DLUT 602 in advance. Lattice point data from “1” to “8” can be used.

  Then, the color correction device 60 performs an interpolation operation using the values of the grid point data corresponding to the vertices of the tetrahedron determined in this way, and calculates corrected color information [CMY]. In the color correction processing described above, a polyhedron other than a tetrahedron can be used. In short, a lattice additionally registered in the three-dimensional DLUT 602 as any one or more vertices when defining a polyhedron. By using the point data, the color adjustment result by the calibration process may be reflected in the color correction process.

  In FIG. 5, preset grid points are indicated by “◯”, and additionally registered grid points are indicated by “●”. Further, the grid point data additionally registered in the three-dimensional DLUT 602 may not be the sampling data itself. For example, in FIG. 5, grid point data corresponding to the midpoint of any two grid points set in advance in FIG. A value may be obtained from a plurality of sampling data, and the lattice point data thus obtained may be additionally registered in the three-dimensional DLUT 602.

(2) For example, in the image forming system 1 shown in FIG. 1, the color correction device 20 and the DLUT update device 40 may be configured as an integrated color correction device. Similarly, in the image forming system 2 illustrated in FIG. 3, the color correction device 60 and the DLUT update device 41 may be configured as an integrated color correction device. In the image forming system 1 shown in FIG. 1, the color correction device 20, the DLUT update device 40, and the printer 30 may be configured as an integrated image forming device (for example, a printer, a copier, or the like) In the image forming system 2 shown in FIG. 3, the color correction device 60 and the DLUT update device 41 and the printer 30, or the color conversion device 50, the color correction device 60, the DLUT update device 41 and the printer 30 are integrated as an image forming device. It may be configured. In the case of the image forming apparatus, the input of the document image used when performing the calibration process is not limited to communication, and for example, the configuration may be such that the document image is read and input using an image scanner, The document image data may be read and input from a recording medium such as a memory card.

(3) A program for realizing the calibration process described in the first and second embodiments and a program for realizing the calibration process and the color correction process described in the modification (1) are stored on a magnetic disk, It can be provided by being recorded on a recording medium such as a flexible disk or an optical recording medium. It is also possible to provide the program by communication.

1 is a block diagram illustrating a configuration of an image forming system 1 according to a first embodiment. It is a graph for demonstrating the color correction characteristic of three-dimensional DLUT201 updated by a calibration process. It is a block diagram which shows the structure of the image forming system 2 which concerns on 2nd Embodiment. It is a figure which shows the data structure of 3D DLUT602 which concerns on a modification (1). It is a figure for demonstrating the color correction process which concerns on a modification (1). It is a graph for demonstrating the subject of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,2 ... Image forming system 10 ... Controller 20,60 ... Color correction device 30 ... Printer 40,41 ... DLUT update device 50 ... Color conversion device 201,501,601,602 ... 3D DLUT, 401: Colorimetric sensor, 402: Lattice point data update unit.

Claims (7)

An input means for inputting an image;
Used in a color correction process for eliminating a color difference between an input image by the input means and an output image obtained by outputting the input image from an image forming apparatus provided at a subsequent stage of the color correction apparatus, A color correction table that stores grid point data composed of color information before correction indicated by the grid point and color information after correction for the color information,
Color correction means for correcting the color of the input image using the color correction table;
An output unit that outputs an input image corrected by the color correction unit to the image forming apparatus;
First acquisition means for acquiring color information of an arbitrary region from an input image before correction by the color correction means;
In the output image, a second acquisition unit that measures the color of the area from which the color information is acquired by the first acquisition unit and acquires the color information of the area;
Using color information acquired by the first acquisition means, color information acquired by the second acquisition means, and base data that is a combination of a plurality of color information before correction and color information after correction And a updating unit that updates the value of the grid point data.   2. The color correction apparatus according to claim 1, wherein each grid point data stored in the color correction table is used as the base data. The update means re-determines the grid point data based on data obtained by adding the color information acquired by the first acquisition means and the color information acquired by the second acquisition means to the base data. The color correction apparatus according to claim 1. The updating unit includes each grid in which measurement data including color information acquired by the first acquisition unit and color information acquired by the second acquisition unit is stored in the color correction table. When the color correction characteristic determined by the point data is within a predetermined allowable range, using the measurement data and each grid point data, the corrected color for one or more grid point data The value of information is updated. The color correction apparatus of Claim 1 characterized by the above-mentioned. An input means for inputting an image;
Used in a color correction process for eliminating a color difference between an input image by the input means and an output image obtained by outputting the input image from an image forming apparatus provided at a subsequent stage of the color correction apparatus, A color correction table that stores grid point data composed of color information before correction indicated by the grid point and color information after correction for the color information,
When correcting the color of the input image using the color correction table, if the color information to be corrected does not match the color information before correction of any grid point data stored in the color correction table In the color space, a polyhedron including coordinate points indicated by the color information to be corrected and each vertex being the lattice point is defined, and lattice point data corresponding to each vertex of the polyhedron is used. Color correction means for calculating corrected color information for the color information to be corrected;
An output unit that outputs an input image corrected by the color correction unit to the image forming apparatus;
First acquisition means for acquiring color information of an arbitrary region from an input image before correction by the color correction means;
In the output image, a second acquisition unit that measures the color of the area from which the color information is acquired by the first acquisition unit and acquires the color information of the area;
New grid point data other than the grid point data stored in the color correction table using the color information acquired by the first acquisition unit and the color information acquired by the second acquisition unit Generating means for generating
Adding means for adding grid point data generated by the generating means to the color correction table;
When the grid point data is added to the color correction table, the color correction unit uses the grid point indicated by the added grid point data as one or more vertices of the polyhedron when determining the polyhedron. A color correction device characterized by the above. An input means for inputting an image;
Used in color correction processing for eliminating a color difference between an input image by the input means and an output image obtained by outputting the input image from the image forming apparatus, and for each grid point defined in the color space, A color correction table storing grid point data composed of color information before correction indicated by the grid point and color information after correction for the color information;
Color correction means for correcting the color of the input image using the color correction table;
Image forming means for forming an output image using the input image corrected by the color correcting means;
First acquisition means for acquiring color information of an arbitrary region from an input image before correction by the color correction means;
In the output image formed by the image forming means, a second acquisition means for measuring the color of the area from which the color information has been acquired by the first acquisition means and acquiring the color information of the area;
Using color information acquired by the first acquisition means, color information acquired by the second acquisition means, and base data that is a combination of a plurality of color information before correction and color information after correction And an update means for updating the value of the grid point data. An input means for inputting an image;
Used in color correction processing for eliminating a color difference between an input image by the input means and an output image obtained by outputting the input image from the image forming apparatus, and for each grid point defined in the color space, A color correction table storing grid point data composed of color information before correction indicated by the grid point and color information after correction for the color information;
When correcting the color of the input image using the color correction table, if the color information to be corrected does not match the color information before correction of any grid point data stored in the color correction table In the color space, a polyhedron including coordinate points indicated by the color information to be corrected and each vertex being the lattice point is defined, and lattice point data corresponding to each vertex of the polyhedron is used. Color correction means for calculating corrected color information for the color information to be corrected;
Image forming means for forming an output image using the input image corrected by the color correcting means;
First acquisition means for acquiring color information of an arbitrary region from an input image before correction by the color correction means;
In the output image formed by the image forming means, a second acquisition means for measuring the color of the area from which the color information has been acquired by the first acquisition means and acquiring the color information of the area;
New grid point data other than the grid point data stored in the color correction table using the color information acquired by the first acquisition unit and the color information acquired by the second acquisition unit Generating means for generating
Adding means for adding grid point data generated by the generating means to the color correction table;
When the grid point data is added to the color correction table, the color correction unit uses the grid point indicated by the added grid point data as one or more vertices of the polyhedron when determining the polyhedron. An image forming apparatus.

Images