JP2007137013A - Printer and its calibration method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce variation in color reproducibility among engines in a device performing distributed processing of a print job among a plurality of print engines. <P>SOLUTION: An inspection chart generator 600 generates an inspection chart including the primary colors of CMYK and patches of high order colors mixing them and the inspection chart is printed on print units 200 and 300. Print results are read out by means of a reader 451 and a colorimetric value calculating section 702 measures the color of each patch from an image read out. Based on the measurements, color reproduction regions of the print units 200 and 300 are calculated and their common part, i.e. a common color reproduction region, is calculated at a common color reproduction region calculating section 706. A parameter regulating section 708 alters the data of DLUTs 506A and 506B for converting the color of print data into the value in color space of the print units 200 and 300 so that the print units 200 and 300 perform color reproduction in the common color reproduction region. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a printing apparatus that sorts and prints print jobs to a plurality of print engines.

  A number of printing systems aiming at efficient system operation by managing a plurality of printers with a single print server have been proposed. In such a system, when printing a page of one print job by distributing it to a plurality of printers, it is a problem that the print image quality is different for each printer. In particular, in the case of a system for creating a printed product as a product, it is required to match the print image quality at a high level.

  Color reproduction is an important print quality, and a mechanism for correcting a difference in color reproduction between printers has been proposed.

  For example, in the system of Patent Document 1, the server receives print result data of a plurality of color printers, and for each color of C (cyan), M (magenta), Y (yellow), and K (black) from the received print result data. Then, the maximum density value is obtained, the minimum data among them is specified, and calibration for other printers is executed in accordance with the density value that can be output by the color printer having the specified print result data. That is, individual differences in color reproducibility are suppressed by controlling each printer so that the minimum value is set as the target of the maximum density for each color. Patent Document 2 also shows a similar system.

JP 2002-254710 A JP 2003-246126 A

  The color reproduction correction methods of the systems disclosed in Patent Documents 1 and 2 can make the color reproducibility consistent among a plurality of printers for the primary colors, that is, the colors of CMYK. However, since these conventional systems only calibrate each primary color, secondary colors (R (red), G (green), B (blue), etc.) that can be formed by combining two primary colors, There is a problem that it is not guaranteed that the color reproducibility of the tertiary color, the quaternary color, etc., formed by mixing three to four kinds of primary colors is the same.

  A printing apparatus according to the present invention is a printing apparatus that distributes print jobs to a plurality of print engines, and prints each primary color and each higher-order color patch that is a combination of the primary colors to each print engine. An inspection chart printing means for supplying inspection chart data to be printed on a predetermined medium, a color measurement means for measuring each patch in the inspection chart printed on the predetermined medium by the print engine, and a color measurement result of each patch For each print engine, a color gamut calculation means that calculates a color gamut that takes into account higher-order colors and a common color gamut that calculates a common color gamut between the calculated color gamuts of each print engine Calculation parameters and conversion parameters used when converting print data according to the color reproduction characteristics of each print engine are set for each print within the common color gamut. Engine provided in a parameter adjusting means for adjusting respectively to reproduce colors, the.

  Here, the “printing apparatus for distributing print jobs to a plurality of print engines” includes not only an integrated printing apparatus having a plurality of print engines but also separate printers each having a print engine at the print server. A system for controlling and performing sorting printing is also included. Further, the concept of “colorimetric means” is not limited to a colorimeter, and the test chart printing result is optically read, and the colorimetric value is calculated from the color data of each patch in the read image data. A device is also included.

  In a preferred aspect of the present invention, the conversion parameter may be set to M (M is 3) unique to the print engine for each color value in an N-dimensional color space of input print data (N is an integer of 3 or more). The integer value) is registered in the multi-dimensional lookup table in which the color value in the dimensional color space is registered, and the parameter adjusting means adjusts the value registered in the multi-dimensional lookup table.

  In a preferred aspect of the present invention, the printing apparatus further includes means for generating and outputting an ICC (International Color Consortium) profile based on the common color gamut calculated by the common color gamut calculating means.

  In a preferred aspect of the present invention, the common color gamut calculation means calculates a common color gamut only between print engines that distribute and print the same print job.

  The best mode for carrying out the present invention (hereinafter referred to as “embodiment”) will be described below with reference to the drawings.

  FIG. 1 is a diagram illustrating a schematic configuration of an example of a printing apparatus to which the present invention is applied.

  The printing apparatus includes one paper feeding unit 100, two printing units 200 and 300, and one paper discharge unit 400.

  The paper feed unit 100 includes a plurality of paper feed trays (three are illustrated in the figure) 101, 102, and 103. The paper fed from each of the paper feed trays 101 to 103 is supplied to the printing unit 200 connected to the subsequent stage of the paper feed unit 100 through the paper feed conveyance path 105.

  The two printing units 200 and 300 include electrophotographic print engines 201 and 301 for full-color printing, respectively.

  In this example, the print engines 201 and 301 have a configuration in which four color developing units 203 and 303 of Y (yellow), M (magenta), C (cyan), and K (black) are arranged in tandem (columns). Yes. Each of these four-color developing sections 203 and 303 forms a toner image of each color by electrophotography, and these four-color toner images are transferred onto the intermediate transfer belts 205 and 305, respectively. A full-color toner image is formed. The full-color toner images on the intermediate transfer belts 205 and 305 are transferred to the paper by the transfer units 207 and 307. The sheet on which the toner image is transferred is sent to the fixing units 209 and 309, where the toner image is fixed on the sheet. In the case of performing double-sided printing, after fixing the front surface, the fixed paper is once sent to the switchback paths 214 and 314, and then conveyed in the reverse direction to carry the reverse conveying paths 216 and 316. The paper is reversed by introducing the paper to the transfer unit 207, 307 and the back side is printed.

  Since the present invention does not depend on the configuration of the print engine, the configuration of the print engines 201 and 301 illustrated here is merely an example.

  The two printing units 200 and 300 are connected in tandem. That is, the printing unit 200 receives paper from the paper supply unit 100, and the printing unit 300 receives paper discharged from the printing unit 200. Then, the paper discharged from the printing unit 300 is introduced into the paper discharge unit 400 and discharged to the paper discharge stacker 401 through the paper discharge transport path 405. Hereinafter, for identification, the upstream printing unit 200 in the tandem arrangement as viewed from the paper feeding unit side is referred to as A unit, and the downstream printing unit 300 is referred to as B unit.

  The configuration of both the A and B units (200 and 300) will be described in detail as follows.

  That is, the A unit accepts a sheet supplied from the sheet feeding conveyance path 105 of the sheet feeding unit 100, and when printing on the sheet by the A unit, the sheet 210 conveys the sheet conveyance path by the print engine 201. To the transport path 212 toward As a result, the sheet is introduced into the print engine 201, the toner image is transferred by the transfer unit 207, and the toner image is fixed by the fixing unit 209. When performing double-sided printing on the paper, the paper for double-sided printing is transported as described above, and the back side is printed. In this way, the paper on which printing has been completed is sent to the B unit through the paper discharge transport path 217. The above is the case where the A unit performs printing on the paper supplied from the paper feeding unit 100. However, when printing is not performed on the paper using the A unit, the paper passes by switching the gate 210. Is sent to the transport path 215, and further to the B unit through the transport path 217 for paper discharge.

  Although the operation of the A unit has been described above, the operation of the B unit is the same. That is, when printing is performed on the paper supplied from the A unit by the B unit, the paper is sent to the transport path 312 toward the print engine 301 by switching the gate 310, and after the image is printed, the paper discharge unit. It is discharged to 400. Further, when printing is not performed in the B unit, the sheet is similarly discharged by the switching of the gate 310 to the paper discharge unit 400 through the passing conveyance path 315.

  Depending on the configuration of the printing apparatus, a post-processing unit that performs post-processing such as stapling and punching may be provided. In such a case, the post-processing unit can be provided at the rear stage of the paper discharge unit 400. .

  The A unit control unit 220 and the B unit control unit 320 are responsible for the control of paper conveyance and printing in both the A and B units as described above. The control units 220 and 320 and the control units (not shown) of the paper feeding unit 100 and the paper discharge unit 400 are respectively provided in the units in accordance with instructions from a printer controller (not shown) that controls the entire printing apparatus. By controlling the above, integrated operation control is realized as the entire printing apparatus.

  The printing apparatus of FIG. 1 has two printing units 200 (A unit) and 300 (B unit), so that a high-speed printing operation is possible.

  That is, in this printing apparatus, printing is performed by alternately supplying sheets supplied from the sheet feeding unit 100 to the A unit and the B unit for each sheet. That is, the individual sheets are printed only in one of the units A and B, and the other unit passes through the passing conveyance path 215 or 315 (that is, passes through that unit without printing). In the sheet conveyance paths 105 and 405 common to both units (all sheets pass through this path), the sheet conveyance paths 212, 214, 216, 312, 314, and 316 in the individual print engines 201 and 301 are doubled. Convey paper at a speed of. As a result, the entire printing apparatus can perform printing at twice the printing speed of the individual print engines 201 and 301. Similarly, the paper may be transported at the double speed (or higher speed) in the passing transport paths 215 and 315.

  Further, in this printing apparatus, reading for reading the printing result on the upstream side of the paper discharge tray 401 (and the branch point to the subsequent unit) on the paper discharge conveyance path 405 passing through the paper discharge unit 400. A device 451 is provided. The reading device 451 may be a colorimeter or a color image reading device such as a line sensor or a two-dimensional area sensor. When a color image reading device is used as the reading device 451, an image read by the reading device 451 can be used for print quality inspection and normal color reproduction characteristics can be obtained during normal printing for printing print data from a client. At the time of calibration, the color of each patch of the inspection chart can be measured from this read image.

  The mechanical aspects of the printing apparatus have been described above. Next, the control mechanism of the printing apparatus of the present embodiment will be described with reference to FIG. In FIG. 2, the same reference numerals are given to the components corresponding to the components shown in FIG. In FIG. 2, the paper supply unit 100 and the paper discharge unit 400 are not shown.

In FIG. 2, a printer controller 500 is a control unit that controls a printing unit 200 (A unit) or 300 (B unit) to perform a printing operation. In the printer controller 500, a PDL interpreter 502 is a unit that interprets PDL (page description language) data 1000 to be printed sent from a computer that is a client. The PDL interpreter 502 interprets the PDL data 1000 and performs color space conversion to generate intermediate code data in which the rendering content indicated by the PDL data 1000 is expressed by a predetermined intermediate code. The color space conversion here is a unique reference color space (for example, sRGB color space or ITU L ^* a ^* b ^* color) that does not depend on the device directly from the color space of the PDL data 1000 (often in the RGB color system). Space).

The renderer 504 processes the intermediate code data generated by the PDL interpreter 502 to generate raster image data. The color space of the raster image data is the above-described reference color space, such as the sRGB color space or the L ^* a ^* b ^* color space. Both the sRGB color space and the L ^* a ^* b ^* color space are three-dimensional color spaces, but here, the dimension of the reference color space generated inside the printer controller 500 is assumed to be N.

  The PDL interpreter 502 and the renderer 504 are conventionally known.

DLUTs (Direct Look-Up Tables) 506A and 506B are lookups for converting colors expressed in the reference color space into color representations in color spaces specific to the printing units 200 and 300 (ie, device-dependent), respectively. It is a table. Generally, the color space in the printing apparatus is a four-dimensional color space composed of a combination of four colors of CMYK, but here it is generalized as an M-dimensional color space. Each of the DLUTs 506A and 506B is a table that stores, for each point in the N-dimensional reference color space, a color value in the M-dimensional color space depending on the printing unit corresponding to the point. For example, when the reference color space is L ^* a ^* b ^* space, the printing unit-dependent color space is CMYK space, and each of L ^* , a ^* , b ^* and C, M, Y, K is expressed by 8-bit data The DLUTs 506A and 506B are ideally tables each having 256 × 256 × 256 data entries, and 8 bits × 4 = 32 bits of data are registered in each data entry. Actually, since the number of data entries becomes too large, each DLUT usually uses 16 + 1 grid point data for each of the 16 axes of R, G, B, and a total of 17 × 17 × 17 = 4913 data entries. In general, a complementary operation is performed between lattice points.

  Since there is an individual difference in color reproduction characteristics between the A unit and the B unit, in this embodiment, two DLUTs, an A DLUT 506A and a B DLUT 506B, are provided.

Each color component (for example, L ^* , a ^* , b ^* ) in the raster image data generated by the renderer 504 is a value (for example, C, M, Y, K) in the A unit color space of the A DLUT 506A. In the B DLUT 506B, the values are converted into values in the color space for the B unit. As a result, raster image data corrected in accordance with the color reproduction characteristics of the A unit is supplied from the print controller 500 to the A unit 200 and the B unit 300, respectively.

  The A unit 200 and the B unit 300 include M one-dimensional LUTs 222 and 322, halftone processing units 224 and 324, and print engines 201 and 301, respectively.

  The one-dimensional LUTs 222 and 322 are look-up tables used to compensate for the change in print color reproducibility of each unit 200 and 300 over time, and one for each of the M primary colors in the print unit dependent color space. It is provided one by one. That is, the one-dimensional LUTs 222 and 322 correct tone reproduction for each primary color (primary color) in the color space depending on the printing unit. On the other hand, the DLUTs 506A and 506B provided in the printer controller 500 perform more comprehensive color space conversion in consideration of the mutual influence between primary colors. That is, after the comprehensive conversion is performed by the DLUTs 506A and 506B, the change with time is corrected by the one-dimensional LUTs 222 and 322. Note that the one-dimensional LUTs 222 and 322 and the halftoning processing units 224 and 324 described above are conventionally known.

  The print engines 201 and 301 are the same as described with reference to FIG.

  For the calibration that reduces the difference in color reproduction characteristics between the A unit 200 and the B unit 300 described above, the printing apparatus according to the present embodiment includes an inspection chart generator 600, a reading device 451, and a calibration calculation unit 700. Is provided. FIG. 3 shows the flow of calibration processing using such a calibration mechanism. Hereinafter, the calibration mechanism of this embodiment will be described with reference to FIGS. 2 and 3 as appropriate.

  The inspection chart generator 600 generates raster image data of an inspection chart for inspecting color reproduction characteristics. The inspection chart used in this inspection is a patch (small area filled with a single color) having different levels of density of M colors (primary colors or primary colors) used in the printing units 200 and 300, and the respective colors. Patches of a secondary color obtained by mixing two colors, a tertiary color obtained by mixing three colors, and a quaternary color mixed by four colors are arranged on a page area of a predetermined paper size. For the second, third, and fourth-order higher-order colors, several types of patches in which the combinations of the densities of the primary colors are variously arranged are arranged for the same combination of primary colors. For example, in the case of the CMYK space, assuming that there are four levels of density for each of C, M, Y, and K (density 0 is also one level), an inspection chart in which 256 patches are arranged is generated. It will be. If all patches do not fit on one page, divide them into multiple pages.

  The raster image data of the inspection chart reproduced in this way is supplied to the A unit 200 and the B unit 300, respectively. The A unit 200 and the B unit 300 each print this inspection chart on a predetermined sheet fed in accordance with an instruction from the printer controller 500 (S10). The printed matter 1100 (printing results of the A and B units) as the printing result is read in color by the reading device 451 on the paper discharge transport path 405 (S12). As a result, color read image data obtained by reading the inspection chart is output from the reading device 451.

In the calibration calculation unit 700, the colorimetric value calculation unit 702 performs image processing on the color read image data from the reading device 451, extracts each patch, and calculates the colorimetric value of each patch (S12). . The colorimetric value is a value in a reference color space (for example, L ^* a ^* b ^* ) that does not depend directly on the device. Here, the colorimetric value of each patch is calculated for the reading result of each inspection chart printed by the A unit and the B unit. Note that when a colorimeter is used as the reading device 451, reading, that is, color measurement, is performed, and the colorimetric value of each patch is output from the reading device 451.

The color gamut calculation unit 704 calculates the respective color gamuts of the A unit and the B unit based on the colorimetric values of the patches of the inspection charts of the A unit and the B unit calculated by the colorimetric value calculation unit 702. (S14). The color gamut of one printing unit is an area in which colorimetric values of patches of each color of the inspection chart printed by the unit are distributed in a colorimetric color space (for example, L ^* a ^* b ^* ). By using an inspection chart in which a large number of patches including higher-order colors are arranged, it is possible to obtain a color gamut including information on intermediate color portions that cannot be understood from an inspection chart having only patches of primary colors.

An example of the color gamut is shown in FIG. FIG. 4 shows an orthogonal projection of the color gamut in the L ^* a ^* b ^* space on the a ^* b ^* plane. In the L ^* a ^* b ^* space, the color gamut has a three-dimensional shape, but here, in order to make the explanation easy to understand, explanation will be made with a two-dimensional region of orthographic projection.

  In the figure, vertex C is a point indicating the colorimetric value of a patch having a primary color cyan density of 100% (maximum density) and other primary color magenta and yellow densities of 0 percent. Similarly, the vertices M and Y are points indicating the colorimetric values of patches in which the density of one primary color is 100% and the density of the other primary color is 0%. R is the point indicating the highest density of red (that is, the density of both yellow and magenta is 100% and cyan is 0%). Similarly, G is green (yellow and cyan) and B is blue (cyan and magenta). It is a point which shows the highest density | concentration of. As shown in the figure, the projection of the color gamut is a hexagon (and its interior) with the six points C, M, Y, R, G, and B as vertices. Of course, this shows a general tendency, and strictly speaking, the projection of the color gamut may have a shape in which each side of the hexagon is slightly uneven.

  Now, the color reproduction of the print engine deteriorates or changes due to various factors. For example, in the case of an electrophotographic print engine in which the photosensitive drums of each primary color are arranged in parallel, for example, the defect of each primary color exposure unit, development unit, and transfer unit is determined by the measured density of the primary color patch on the inspection chart. Bring about a decline. In addition, there is a problem that toner of a certain color transferred from a certain photosensitive drum is peeled off by a subsequent photosensitive drum. In this case, either a primary color patch or a secondary or higher color patch is selected. The color also changes. In the case of an engine using an intermediate transfer belt, if there is a toner transfer failure from the intermediate transfer belt to the paper, the color of the secondary or higher order color patch changes. The color gamut indicated by the broken line in FIG. 4 is an example when the maximum density of R changes to R ′ due to performance deterioration such as secondary transfer. Curves 10C, 10M, and 10Y are curves in which the colorimetric values at the densities of the primary colors C, M, and Y are connected. The curves 10R, 10G, and 10B are the secondary colors R, G, and B, respectively. It is a curve that connects colorimetric values in density. In general, the deterioration of primary color reproduction is such that the vertices C, M, and Y of the color gamut move in the direction of decreasing saturation on the curves 10C, 10M, and 10Y, respectively, whereas the secondary color Deterioration of reproduction is a combination of various factors, and the vertices R, G, B often move away from the curves 10R, 10G, 10B.

  In S <b> 14, the color gamut calculation unit 704 calculates the respective color gamuts based on the color measurement results of the inspection charts of the A unit and the B unit.

  When the color gamuts of all the printing units are calculated in this way, the common color gamut calculating unit 706 then selects a common part of the color gamuts of all the printing units (referred to as “common color gamut”). Calculate (S16). For example, as shown in FIG. 5, when the color reproduction range of the A unit (dashed line) and the color reproduction range of the B unit (broken line) are obtained, the common color reproduction range is the color reproduction range of both as shown by the solid line. It becomes the overlapping part. In FIG. 5, the sides to be overlapped are actually slightly shifted so that the color reproduction range and the common color reproduction range of each unit can be identified. For example, the side connecting the vertices of Y and G overlaps in the color reproduction range of the B unit and the common color reproduction range, but in the figure, these are displayed so as not to be shifted and shifted.

The example of FIG. 5 is an example on the orthogonal projection of the color gamut onto the a ^* b ^* plane, but the same applies to the three-dimensional color gamut in the L ^* a ^* b ^* space. The color gamut can be calculated. For example, a common color gamut can be calculated by performing an AND operation on solids indicated by the three-dimensional color gamut of each unit in the L ^* a ^* b ^* space.

  When the common color gamut is obtained in this way, the parameter adjustment unit 706 next performs color gamut compression (also called gamut compression) so that the color gamut of each of the A unit and B unit becomes the common color gamut. Is called) (S18).

  For the color gamut compression here, a gamut compression method that has been used for color matching between devices such as a display and a printer, which have greatly different color reproduction characteristics, can be used.

  For example, assume that the color reproduction of red (M100%, Y100%) is Ra for the A unit and Rb for the B unit, and the outermost point of red in the common color gamut of both units is Rx. At this time, colors outside the common color gamut such as Ra may be converted to Rx by color gamut compression.

  Further, for example, in Japanese Patent Laid-Open No. 4-40072 by the present applicant, as one method of color gamut compression, brightness and hue (also referred to as chromaticity) are set when the input color is out of the color reproduction range of the device. Keeping the color value within the device's color gamut by reducing the saturation while maintaining it (ie, setting the saturation of the input color to the maximum saturation corresponding to the combination of lightness and hue within the color gamut) A correction process of making a value is shown. In this case, correction is performed only for colors that are out of the color gamut, and conversely, if the input color is within the color gamut of the device, no correction is performed.

In order to apply this method to the color gamut compression of S18, for example, when the color gamut of the A unit is compressed, each color (L ^* , a ^* , b ^* ) belonging to the color reproduction gamut of the A unit (calculated in S14) ^. ) (L ^* , a ^* , b ^*, each of 8 bits data width, the maximum 24th data points will be considered, but usually the grid points except near the device color gamut boundary 4913 parts are taken into consideration, which is considerably less than this.) Is determined to be included in the common color reproduction range (this is included in the color reproduction range of the A unit). If the current color falls within the common gamut, no color conversion is performed.If the color is outside the common gamut, the color saturation is adjusted between the brightness and hue while maintaining the brightness and hue. Convert to maximum saturation corresponding to the combination. At this time, as shown in the publication, the common color gamut of the L ^* a ^* b ^* space is converted into an HSV (hue / saturation / lightness) space in advance, and the maximum saturation for each combination of lightness and hue is determined. If the common color gamut is expressed in the form of a registered table and each color in the color gamut of the A unit is converted to HSV, it can be easily determined whether or not the color is included in the common color gamut. Furthermore, when the color gamut deviates from the common color reproduction range, the corresponding maximum saturation can be easily obtained. Thus, by converting the saturation of the color outside the common color gamut, the color gamut of the A unit can be compressed to the common color gamut. For the B unit, the color gamut can be compressed by the same process.

  In the method disclosed in Japanese Patent Laid-Open No. 4-40072, the saturation of all colors that are out of the common color gamut is converted to the maximum saturation at the same brightness and the same chromaticity (maximum saturation within the common color gamut). For this reason, colors outside the common color gamut are all the same color if they have the same brightness and chromaticity. In order to avoid this, as shown in Japanese Patent Application Laid-Open No. 8-214175 by the present applicant, the saturation of the color outside the common color gamut is set to the ratio of the maximum saturation of the input and output. Accordingly, a linear compression method can be used (lightness and chromaticity are maintained). In the system disclosed in Japanese Patent Laid-Open No. 8-214175, input and output are different devices such as a display and a printer, respectively, but in this embodiment, the input is a color gamut of a printing unit of interest (for example, A unit). The output is a common color reproduction range. That is, for example, the maximum saturation corresponding to a combination of a certain chromaticity Ha and lightness Va in the color gamut of the A unit is CmaxA, and the maximum saturation corresponding to a combination of the same chromaticity Ha and lightness Va in the common color gamut is CmaxC. In this case, an arbitrary color (Ha, Va, C) (C is saturation) corresponding to the same combination of chromaticity Ha and lightness Va in the color gamut of the A unit is converted into (Ha, Va) by color gamut compression. , C ′) (where C ′ = C × (CmaxC / CmaxA)). According to such compression, it is possible to linearly compress the color gamut of each printing unit into a common color gamut.

Note that color values in the HSV space can be easily converted into color values in the L ^* a ^* b ^* space.

  Although several color gamut compression methods have been exemplified above, these are merely examples. There are various other color gamut compression methods, and any of these various methods may be used in S18.

  In S18, the result of such color gamut compression is reflected in the color space conversion DLUTs 506A and 506B provided in the printer controller 500.

That is, in the colorimetric process of S12, the color (C, M, Y, K) depending on the printing unit (assuming to be A unit) of each patch in the inspection chart and the colorimetric value (L ^* , a ^* , b ^* ) pairs are determined by the number of patches, and if this is stored, each color in the color gamut of the A unit (this is a value in the L ^* a ^* b ^* space) ) In the CMYK space (depending on the A unit). The A unit-dependent CMYK value corresponding to the color (L ^* , a ^* , b ^* ) without the measurement data by the patch may be obtained by interpolating information of a certain pair of data. As described above, the CMYK value of the A unit corresponding to the L ^* a ^* b ^* value in the color gamut of the A unit is obtained by the color measurement in S12 (and interpolation of the color measurement result as necessary). The correspondence relationship is stored in a storage device in the calibration calculation unit 700. Then, when a color value (L ^* , a ^* , b ^* ) is changed to another value (L ^* ′, a ^* ′, b ^* ′) by the color gamut compression in the parameter adjustment unit 708, A unit-dependent color value (C ′, M ′, Y ′, K ′) corresponding to the value (L ^* ′, a ^* ′, b ^* ′) can be obtained from the correspondence. That is, in order to print the changed color (L ^* ′, a ^* ′, b ^* ′), the color value of (C ′, M ′, Y ′, K ′) is indicated to the A unit. What should be done is required. Therefore, the DLUT 506A is converted so that the original color value (L ^* , a ^* , b ^* ) before the change is converted into the color value (C ′, M ′, Y ′, K ′) dependent on the A unit after the change. What is necessary is just to change the registration data. That is, the entry value of (L ^* , a ^* , b ^* ) in the DLUT 506A may be rewritten to (C ′, M ′, Y ′, K ′). In this way, if color space conversion is performed using the DLUT 506A, the color space conversion is automatically performed so that the color gamut is within the common color gamut.

  When the method disclosed in Japanese Patent Laid-Open No. 4-40072 is used as the color gamut compression method, the value of the DLUT 506A is updated only for entries outside the common color gamut, but in Japanese Patent Laid-Open No. 8- In the case of the method of Japanese Patent No. 214175, since linear compression is performed, values corresponding to almost all points in the color gamut of the A unit are updated.

  The A unit has been described as a representative, but the gamut compression can also be performed for the B unit by updating the DLUT 506B by the same processing.

  Through the calibration process as described above, a plurality of print engines included in the printing apparatus can be reproduced in a common color gamut. Such calibration processing is performed at a predetermined timing, for example, at the start of the printing apparatus at the beginning of the day or after a large number of sheets of a predetermined number or more have been printed. Can be prevented or reduced.

  In FIG. 2, the calibration calculation unit 700 and the inspection chart generator 600 are illustrated as separate from the printer controller 500, but the calibration calculation unit 700 and the inspection chart generator 600 are connected to the printer controller 500. Of course, it does not matter if it is implemented in the same hardware.

  As described above, in this embodiment, by using an inspection chart that includes secondary and higher order colors, a color reproduction range that also considers higher order colors is obtained for each printing unit, and color reproduction of each of these printing units is performed. A common portion of the gamut, that is, a common color gamut is obtained, and color gamut compression is performed so that each printing unit performs color reproduction in the common color gamut. According to such a configuration, each printing unit can perform color reproduction in the same color gamut (common color gamut), and the common color gamut considers higher order colors. The color reproducibility of each printing unit can be made uniform (that is, matched or close) not only for colors but also for higher-order colors.

  Further, in the present embodiment, the calibration calculation unit 700 creates an ICC (International Color Consortium) profile based on the common color gamut obtained in this way, and uses this for printing that includes a plurality of printing units. It is also preferable to enable output as a profile of the entire apparatus. If such an ICC profile is provided to a client device such as a computer that creates print data, the client device creates print data that matches the color characteristics of the printing device (for example, corrects a color that cannot be reproduced by the printing device). Etc.).

  In the above, a printing apparatus including two print engines (printing units) has been illustrated. However, it is obvious that the same calibration process can be performed for a printing apparatus including three or more print engines. It will be easily understood that the same calibration process can be applied to a network printing system in which separate printers are connected via a network and the printers are managed by the print server.

  In addition, a printing apparatus that includes two monochrome printer engines in addition to two full-color printer engines is also conceivable. In such an apparatus, the above-described calibration need only be performed for two full-color print engines.

  In the network printing system, there are cases where the same full-color printers with different performance are connected to the network. In this case, when one print job is distributed, it is distributed among printers having the same or similar performance. Therefore, in such a case, the above-described calibration may be performed between printer groups to which one print job is distributed (that is, printer groups having the same or similar performance).

1 is a diagram illustrating an example of a mechanical configuration of a printing apparatus to which the present invention is applied. It is a figure which shows the structure of the control mechanism of the printing apparatus which concerns on this invention. It is a flowchart which shows the procedure of a calibration process. It is a figure for demonstrating a color reproduction range. It is a figure for demonstrating a common color reproduction range.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 100 Paper feed unit, 200,300 Printing unit, 201,301 Print engine, 400 Paper discharge unit, 500 Printer controller, 506A A DLUT, 506B B DLUT, 600 Inspection chart generator, 700 Calibration calculation unit, 702 Measurement Color value calculation unit, 704 color reproduction range calculation unit, 706 common color reproduction range calculation unit, 708 parameter adjustment unit.

Claims (6)

A printing apparatus that distributes print jobs to a plurality of print engines for printing,
Inspection chart printing means for supplying each print engine with data of an inspection chart including patches of each primary color and each higher-order color which is a combination of the primary colors and printing the data on a predetermined medium;
A color measuring means for measuring colors of each patch in an inspection chart printed on a predetermined medium by a print engine;
Color gamut calculation means for calculating the color gamut taking into account higher-order colors for each print engine from the color measurement results of each patch,
A common color gamut calculating means for calculating a common color gamut common among the calculated color gamuts of each print engine;
Parameter adjustment means for adjusting the conversion parameters used when converting the print data according to the color reproduction characteristics of each print engine so that each print engine reproduces the color within the common color reproduction range;
A printing apparatus comprising: The conversion parameter is an M (M is an integer greater than or equal to 3) dimensional color space unique to the print engine, for each color value in an input print data in an N (N is an integer greater than or equal to 3) dimension. Is registered in the multi-dimensional lookup table in which the color value is registered,
The parameter adjusting means adjusts a value registered in the multi-dimensional lookup table;
The printing apparatus according to claim 1. A common discharge conveyance path for conveying printed sheets printed by the plurality of print engines to a common discharge section;
The printing apparatus according to claim 1, wherein the color measuring unit is provided in front of the paper discharge unit in the common paper discharge conveyance path. Means for generating and outputting an ICC (International Color Consortium) profile based on the common color gamut calculated by the common color gamut calculating means;
The printing apparatus according to claim 1, further comprising:   The printing apparatus according to claim 1, wherein the common color gamut calculation unit calculates a common color gamut between only print engines that distribute and print the same print job. A printing apparatus calibration method for distributing print jobs to a plurality of print engines for printing,
a) Supplying each print engine with inspection chart data including each primary color and each higher-order color patch which is a combination of the primary colors, and printing the data on a predetermined medium;
b) The print engine measures each patch in the inspection chart printed on a predetermined medium,
c) From each color measurement result of each patch, calculate the color gamut considering each higher order color for each print engine,
d) calculating a common color gamut that is common among the calculated color gamuts of each print engine;
e) adjusting conversion parameters used when converting print data according to the color reproduction characteristics of each print engine so that each print engine reproduces colors within the common color reproduction range;
Calibration method for printing apparatus.

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