JP2011201062A - Color management method and apparatus therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image processing method and an image processing device useful when obtaining the printed result in color near to an original color image by changing printing order of inks.SOLUTION: If a color image can not be formed in color whose color difference from target color of color image data is within tolerance in a color reproduction range obtained by ejecting the respective color inks to recording paper in printing order in accordance with the array of head units, by collating a plurality of correction pattern tables for regulating the color reproduction range classified by the printing order of the color inks and printing time intervals, the correction pattern table having respective values of Labthat a value ΔE(=√{ΔL+Δa+Δb}) expressing a color difference from each value of Labof the color image data is minimum is extracted (step S111). If the value ΔE expressing the color difference of the correction pattern table is within the tolerance (YES in step S117), the color image data is converted into CMYK color system based on the correction pattern table (step S121).

Description

  The present invention relates to an image processing method and apparatus for performing a color matching process between an input device and a printing device that prints a color image using color image data input from the input device.

  Conventionally, when a color image based on color image data input from an input device is output from an output device, color matching is performed between the input device and the output device. In this color matching, the input color image data is converted into a color space that does not depend on the input device, and in this color space, after the color image data is re-mapped within a range corresponding to the color reproduction range of the output device, Conversion into color image data in a color space depending on the output device is performed.

  At this time, if the output device is a printing device, the color space of the printing device is a very narrow color reproduction range compared to the color space of the input device, and the color image on the recording paper printed by the printing device is imaged by the user. Sometimes it does not match the color.

  Therefore, in Patent Document 1, in a color inkjet printer, the color reproduction range is changed from the default content by changing the ink ejection order, so that colors that cannot be expressed in the default color reproduction range can be printed with a small color difference. It has been proposed.

JP 2004-155181 A

  In the above-mentioned Patent Document 1, it is pointed out that the color ejected first is more dominant than the color superimposed later, and in accordance with this assumption, the color of the ink when printing color image data that cannot be reproduced is determined. It determines how to change the discharge sequence. However, how the color reproduction range changes by changing the order in which ink is printed on recording paper in the printing device has room for factors other than the ink printing order.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to perform color matching processing on color image data between a printing device and an input device having a color reproduction range different from that of the printing device. An image processing method useful for obtaining a print result of a color closer to the original color image than when the ink print order is not changed by changing the color reproduction range of the printing device by changing the ink print order; and An object of the present invention is to provide an image processing apparatus suitable for use in carrying out the method.

In order to achieve the above object, the present invention provides:
Between an input device (for example, the RGB dot image input unit in FIG. 1) and a printing device (for example, the printing apparatus 20 in FIG. 1) that prints a color image based on color image data input from the input device, In performing color matching processing,
The color image data is prepared according to the printing order and printing time intervals of a plurality of color inks for the same pixel in the printing device, and the color reproduction range of the printing device having a plurality of patterns (for example, FIGS. 8B and 8C). The color reproduction range pattern including the approximate color that minimizes the color difference from the target color in the color image data is extracted (for example, steps S103 to 105, 111 to 115 in FIG. 9). ) And
The color image data is converted into a data format corresponding to the printing device according to the color reproduction range of the extracted pattern (for example, steps S107 and 121 in FIG. 9),
The color image data obtained by converting the data format is associated with print order and print time interval data of the plurality of color inks corresponding to the color reproduction range of the extracted pattern, and output to the printing device (for example, FIG. 9). Steps S109 and 123)
It is characterized by that.

  According to the above invention, the pattern of the color reproduction range including the approximate color that minimizes the color difference from the target color in the color image data based on the color reproduction range independent of the printing device is extracted. Then, the input color image data is associated with printing order and printing time interval data of a plurality of color inks corresponding to the color reproduction range of the extracted pattern, and is output to the printing device.

  For this reason, the best color reproduction range including approximate colors in the color reproduction range of color image data depending on the printing device that minimizes the color difference from the target color in the color image data of the color reproduction range that does not depend on the printing device. Is selected from multiple combinations of multiple color ink printing order and printing time interval on the printing device, and the color image is printed with an approximate color that is closer to the target color by minimizing the amount of color compression of the color image data. become able to.

  Therefore, when color matching processing for color image data is performed between the input device and the printing device, the change in the color reproduction range of the printing device due to the change in the printing order of the ink is greater than when the printing order of the ink is not changed. In obtaining a print result with a color close to that of the original color image, an appropriate print time interval for each color ink can be selected so that the print result can be obtained with a color closer to that of the original color image.

In the above invention,
In extracting a pattern of the color reproduction range including the approximate color from the color reproduction range of a plurality of patterns,
The color image data is collated with a default color reproduction range of the printing device, and a color difference between the target color and a color having a minimum color difference between the target color in the default color reproduction range is determined as a default color difference. (For example, step S103 in FIG. 9)
When the default color difference is out of an allowable range, the color image data is stored in the color reproduction range of a plurality of patterns, and the printing order and printing time interval of a plurality of color inks for the same pixel in the printing device are the default color. The target color in the other color reproduction range is checked by collating with another color reproduction range (for example, the correction pattern table in FIG. 8C) different from the printing order and printing time interval of the plurality of color inks in the reproduction range. And extracting a pattern of another color reproduction range including a color having a minimum color difference (for example, steps S111 to S115 in FIG. 9),
Furthermore, in extracting the pattern of the other color reproduction range in which the color difference between the approximate color and the target color in the other color reproduction range is minimized,
When there are a plurality of other color reproduction range patterns including a color having a minimum color difference from the target color in the other color reproduction range, the other color reproduction with the shortest printing time interval of the plurality of color inks Select and extract a range pattern (eg, step S115 in FIG. 9).
It is characterized by that.

  According to the above invention, the target color of the color image data in the color reproduction range that does not depend on the printing device and the target color in the default color reproduction range (default printing order and printing time interval) of the color image data that depends on the printing device. Only when the color difference from the color with the minimum color difference is outside the allowable range, the print order and print time interval of the multi-color ink is targeted for other color reproduction ranges different from the default color reproduction range, Collation with the target color of the color image data is performed.

  Then, a pattern of another color reproduction range including a color that minimizes the color difference from the target color is extracted from the other color reproduction ranges of the target to be collated, and the pattern according to the other color reproduction range of the extracted pattern is extracted. Thus, the color image data is converted into a data format corresponding to the printing device. The converted color image data is output to a printing device after associating printing order and printing time interval data of a plurality of color inks corresponding to the corrected color reproduction range of the extracted pattern.

  For this reason, with the colors in the default color reproduction range of color image data that depends on the printing device, only when the target color of the color image data in the color reproduction range that does not depend on the printing device cannot be printed with a color difference within the allowable range. This is the basis for converting the data format of color image data from the color reproduction range when the printing order and printing time interval of multiple color inks in the printing device are different from the default printing order and printing time interval. Extraction of the optimum color reproduction range is executed.

  Therefore, when it is possible to print a color image in the default color reproduction range without changing the printing order and printing time interval of the multiple color inks, the target color is set for other color reproduction ranges other than the default color reproduction range. It is possible to eliminate the need for collation with.

  In addition, as the pattern of the other color reproduction range including the color that minimizes the color difference from the target color in the other color reproduction range, the pattern of the other color reproduction range that minimizes the printing time interval of the multiple color inks is selected. The

  For this reason, when high-speed printing is required in a printing device, the color image is printed with an approximate color that is closer to the target color by suppressing the color compression amount of the color image data as much as possible, and the printing time of the color image is longer. It will be able to be completed in a short time. Therefore, when performing color matching processing on color image data, the extension of the required printing time due to the change in the color reproduction range of the printing device due to the change in the printing order of ink is suppressed as much as possible, and the color tone closer to the original color image is obtained. The printing result can be obtained by a printing device.

  Further, in the above invention, the other color reproduction range of each pattern uses a reversal recording paper conveyance path (for example, a path from the switching mechanism 381 to the switching mechanism 383 in FIG. 2) of the printing device. The recording paper repeatedly supplied to the print head (for example, the head unit 310 in FIG. 2) is prepared corresponding to the combination pattern of the printing order and the printing time interval of the plurality of color inks for the same pixel on the same surface. The printing device outputs data to the printing device in the printing order and printing time interval data. Based on the data, the printing device repeatedly feeds the recording paper to the print head and feeds each time. It is characterized in that it can determine whether or not each color ink is printed by the print head at the time.

  According to the above invention, the printing device uses a reversing recording paper conveyance path that is provided for double-sided printing on recording paper, and makes it possible to change the number of times the recording paper is fed to the print head, thereby allowing a plurality of colors. When changing the printing order and printing time interval for ink recording paper to a printing order and printing time interval different from the default, the recording paper is fed to the print head several times, and the number of times of feeding the print head Thus, whether to print each color ink on the recording paper is determined based on the printing order and printing time interval data of the plurality of color inks corresponding to the other color reproduction range of the extracted pattern.

  For this reason, the printing device can effectively utilize the reverse recording paper conveyance path for double-sided printing, and the printing device can print a plurality of color inks on the recording paper at a printing order and a printing time interval different from the default. Therefore, when performing color matching processing on color image data, it is possible to efficiently obtain a printing result closer to the original color image by using the reversal recording paper conveyance path already installed in the printing device. Can do.

  According to the present invention, when color matching processing relating to color image data is performed between an input device and a printing device, the ink printing order is changed by changing the color reproduction range of the printing device by changing the ink printing order. In order to obtain a print result closer to the original color image than when not, select an appropriate print time interval for each color ink so that the print result can be obtained with a color closer to the original color image. be able to.

1 is a block diagram illustrating a functional configuration of a color conversion apparatus according to an embodiment of an image processing apparatus according to the present invention to which an image processing method according to the present invention is applied, and a printing apparatus connected thereto. It is a figure which shows the outline | summary including the circulation conveyance path of the printing apparatus 20 of FIG. FIG. 3 is a schematic view of a sheet conveyance path from a registration roller to a head unit in FIG. 2 as viewed from above. FIG. 2 is a block diagram illustrating an electrical detailed configuration of the printing apparatus of FIG. 1. It is a block diagram which shows the specific example of a system configuration. It is a figure explaining the outline | summary of the color space handled by this embodiment. It is a figure which shows the procedure which converts into a CMYK format using a lookup table from RGB format. It is explanatory drawing which shows the content of the look-up table provided in the color conversion process part of FIG. 9 is a flowchart showing color matching processing (image processing) of color image data performed by the color conversion processing unit of the color conversion apparatus of FIG. 1 using the lookup table of FIG.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a functional configuration of a color conversion apparatus according to an embodiment of an image processing apparatus according to the present invention to which an image processing method according to the present invention is applied and a printing apparatus connected thereto. The color conversion apparatus of this embodiment indicated by reference numeral 10 in FIG. 1 includes an RGB dot image input unit 110 (corresponding to an input device in the claims) for inputting RGB dot image data, and RGB format image data. A color conversion processing unit 120 that converts image data in CMYK format, a printing condition acquisition unit 130 that acquires printing conditions in the printing apparatus 20 (corresponding to the printing device in the claims), and dot image data in CMYK format are output. And a CMYK dot image output unit 140.

  The RGB dot image input unit 110 inputs, for example, RGB dot image data represented by 8 bits for each color, that is, color image data, from an external device or another function unit in the device. The color conversion processing unit 120 includes a plurality of types of lookup tables (LUTs) 122, and converts RGB dot image data into CMYK dot image data with reference to any one of the lookup tables 122. The look-up table 122 is a table in which the correspondence between RGB representative values and CMYK values is recorded. Therefore, the color conversion processing unit 120 includes a memory (corresponding to storage means in claims) for storing the lookup table 122. Which lookup table 122 is used to perform color conversion is set based on the printing condition acquired by the printing condition acquisition unit 130. Specifically, it can be set based on color / monochrome, recording paper type, and the like.

  The printing condition acquisition unit 130 acquires printing conditions set by the user. As described above, the printing conditions include color / monochrome, recording paper type, and the like. However, some of them may be used. The print condition may be received by the print condition acquisition unit 130 from the user, or the print condition acquisition unit 130 may acquire the print condition received by the other functional unit from the user.

  The CMYK dot image output unit 140 (corresponding to the output means in the claims) performs halftone processing on the dot image data converted into the CMYK format and outputs the result to the printing apparatus 20. Here, the halftone process is a process for expressing, for example, a CMYK dot image represented by 8 bits for each color in a gradation that can be printed by the printing apparatus 20.

  As illustrated in FIG. 1, the printing apparatus 20 includes a CMYK dot image input unit 210 that inputs dot image data in CMYK format, a printing mechanism 220, and a paper supply / discharge mechanism 230 that performs a recording paper supply / discharge operation. I have.

  In the present embodiment, the printing mechanism 220 includes a plurality of inkjet heads that extend in a direction orthogonal to the paper conveyance direction and in which a large number of nozzles are formed, and performs printing by ejecting black or color ink from each inkjet head. Inkjet method is adopted. However, other methods may be adopted.

  FIG. 2 is a diagram showing an outline including the circulation conveyance path of the printing apparatus 20 of FIG. FIG. 2 particularly shows the recording paper conveyance path in detail. As shown in FIG. 2, the paper supply / discharge mechanism 230 of the printing apparatus 20 includes a side paper feed base 320 exposed to the outside of the side surface of the housing and a plurality of paper feed trays (330a, 330b, 330c, 330d). The paper feed / discharge mechanism 230 includes a face-down paper discharge port 340 and a face-up paper discharge port 360 as a paper discharge mechanism for discharging printed recording paper. The paper discharged from the face-down paper outlet 340 is stacked on the face-down paper outlet 350, and the paper discharged from the face-up paper outlet 360 is stacked on the face-up paper outlet 362.

  In the printing apparatus 20, the recording sheets fed one by one from one of the side feed tray 320 and the feed tray 330 are fed by a feed mechanism transport path (see FIG. 2), and is guided to the resist portion Rg. Here, the registration unit Rg is provided to perform alignment and skew correction of the leading edge of the recording paper, and includes a pair of registration rollers 370. The fed recording paper is temporarily stopped at the registration unit Rg and conveyed toward the printing mechanism 220 at a predetermined timing.

  The printing apparatus 20 of the present embodiment is an inkjet line color printer that performs printing in units of lines by discharging black or color ink from each inkjet head. Therefore, the printing apparatus 20 includes a plurality of head units 310 that include an inkjet head that extends in a direction orthogonal to the paper conveyance direction and has a large number of nozzles as the printing mechanism 220. The plurality of head units 310 are provided further on the conveyance direction side of the resist portion Rg. The recording paper is conveyed in units of lines by ink ejected from the ink jet heads provided in each head unit 310 while being conveyed at a speed determined by printing conditions by an annular conveying belt 352 provided on the opposite surface of the head unit 310. An image is formed.

  When the recording paper printed on the upper surface is discharged from the face-up discharge port 360, the recording paper is conveyed in the direction of the face-up discharge port 360 by the switching mechanism 382, and is discharged as it is with the print side up. The sheets are stacked on the face-up discharge tray 362. When the paper is discharged from the face-down paper discharge port 340, the paper is further conveyed through the housing by a switching mechanism 382 and a driving mechanism such as a roller. The switching mechanism 381 guides the sheet to the face-down sheet discharge port 340 and discharges the sheet. The sheet is stacked on the face-down sheet discharge table 350 provided as a receiving base for the face-down sheet discharge port 340. .

  The face-down discharge tray 350 and the face-up discharge tray 362 have a tray shape protruding from the casing, and have a certain thickness. The face-down discharge tray 350 and the face-up discharge tray 362 are inclined, and are discharged from the face-down discharge outlet 340 and the face-up discharge outlet 360 by the wall formed at the lower position of the inclination. The recording paper that slides down is arranged naturally and overlaps.

  In the case of double-sided printing in which printing is performed on both sides of a recording sheet, the front side (the first printed side is “front side” and the next printed side is “back side”). Without being guided to the face-up discharge tray 362, the switching mechanism 381 further conveys the inside of the housing. Then, it is drawn into the switchback path SR, performs switchback, and the front and back are reversed with respect to the transport path. After reversing the front and back, it is guided again to the registration portion Rg by a driving mechanism such as a roller and temporarily stops. Thereafter, the sheet is conveyed in the direction of the printing mechanism 220 at a predetermined timing, and the back side is printed by the same procedure as that for the front side. The recording paper on which the back side is printed and images are formed on both sides is guided to the face-down paper discharge port 340 or the face-up paper discharge port 360 according to the specification of the paper discharge port included in the printing conditions, and is discharged. Then, the sheets are stacked on the face-down discharge tray 350 or the face-up discharge tray 362.

  In the printing apparatus 20, switchback at the time of double-sided printing is performed using a space provided in the face-down paper discharge tray 350. The space provided in the face-down paper discharge tray 350 is covered so that the recording paper cannot be taken out from the outside at the time of switchback. This can prevent the user from accidentally pulling out the recording paper during the switchback operation. In addition, the face-down paper discharge tray 350 is originally provided in the printing apparatus 20, and by performing switchback using the space in the face-down paper discharge tray 350, the face-down paper discharge tray 350 is separately provided in the printing apparatus 20. It is not necessary to provide a switchback space. Therefore, an increase in the size of the housing can be prevented. Furthermore, since the face-down discharge port 340 and the switchback path are not shared, the switchback process and the discharge of other sheets can be performed in parallel.

  In the present embodiment, a switching mechanism 383 that bypasses the switchback path SR is provided in order to circulate the recording paper without being reversed. That is, after printing, the printing paper further transported through the housing by the switching mechanism 381 can be guided again to the registration unit Rg by the switching mechanism 383 without being guided to the switchback path SR. In this case, since the recording paper is not reversed, printing can be performed on the same surface as the first printing surface. In this embodiment, the path between the switching mechanism 381 and the switching mechanism 383 and the switchback path SR correspond to the reversal recording paper conveyance path in the claims. Then, by using the path from the switching mechanism 381 to the switching mechanism 383, a path for refeeding the recording paper to the head unit 310 is configured together with the path from the switching mechanism 383 to the registration unit Rg. ing.

  A sheet position sensor 380 for measuring the position of the recording sheet in the sub-scanning direction is provided between the registration unit Rg and the head unit 310. The paper position sensor 380 measures the position of the recording paper in the sub-scanning direction by detecting the edge of the leading edge in the recording paper conveyance direction, for example.

  FIG. 3 is a schematic view of the sheet conveyance path from the registration roller to the head unit in FIG. 2 as viewed from above. In FIG. 3, the recording paper 400 is drawn in the direction of the head unit 310 by the registration rollers 370, is attracted to the transport belt 352, and is transported below the head unit 310. The head unit 310 is configured for each color of CMYK, and each unit is provided with an ink jet head 312 in which a large number of nozzles are arranged on the lower surface side in units of blocks. In FIG. 3, one inkjet head 312 is composed of six blocks. The nozzles are arranged obliquely in a predetermined number unit in order to increase the resolution, and one or a plurality of rows are formed in each block. In this embodiment, the head units 310 for the respective color inks are arranged in the order of C (cyan), K (black), M (magenta), and Y (yellow) from the upstream side in the conveyance direction of the recording paper 400.

  A wall-shaped guide 390 is provided in the paper transport path to regulate the position of the recording paper 400 in the main scanning direction, and the recording paper 400 is transported along the guide 390.

  FIG. 4 is a block diagram showing a detailed electrical configuration of the printing apparatus of FIG. As shown in FIG. 4, the paper supply / discharge mechanism 230 of the printing apparatus 20 shown in FIG. 1 includes a conveyance drive unit 231 including a drive roller and the like in the conveyance path in addition to the paper position sensor 380 described above. 1 includes a transport drive control unit 221 that controls the transport drive unit 231, a multi-pass control unit 222 that controls multi-pass processing to be described later, an image processing unit 223 that performs image processing, and a print execution unit. 224. The image processing unit 223 performs image processing for supplying image data to the printing mechanism 220 according to the ink discharge amount at each printing time. The print execution unit 224 includes a head driver 225 that controls ink ejection from the nozzles included in the inkjet head 312 in addition to the inkjet head 312 described above.

  In the present embodiment, the multi-pass control unit 222 performs the transport operation of the recording paper 400 by the transport driving unit 231 based on the position in the transport direction of the recording paper 400 detected by the paper position sensor 380 at the time of refeeding. The process which makes the conveyance drive control part 221 perform this control is performed.

  When the CMYK dot image input unit 210 receives the dot image data from the color conversion apparatus 10 in FIG. 1, the image processing unit 223 converts the image data into image data, and the head driver 225 generates an ink ejection signal based on the image data. Ink is ejected by the inkjet head 312.

  The color conversion apparatus 10 and the printing apparatus 20 as shown in FIG. 1 can be specifically realized as a system configuration as shown in FIG. 5, for example. FIG. 5A shows an example in which the system is configured by the PC 40 having the printer driver 410 and the ink jet printer 50 having the ink jet printing mechanism 510. In this system, the printer driver 410 includes a color conversion unit 412, and image data in RGB format created by an application of the PC 40, image data read from a digital camera or the like is developed into dot images on the PC 40 side, and further CMYK. A color conversion process is performed on the format and output to the inkjet printer 50. In this case, the PC 40 functions as the color conversion device 10 and the ink jet printer 50 functions as the printing device 20.

  FIG. 5B shows an example in which the system is configured by the image reading device 60, the PC 70 provided with the printer driver 710, the dot image development unit 810, the color conversion unit 820, and the ink jet printing mechanism 830. Is shown. In this system, the RGB color image data read by the image reading device 60 is color-converted by the color conversion unit 820 of the inkjet printer 80 and printed by the inkjet printing mechanism 830. Alternatively, the page description language output from the printer driver 710 of the PC 70 is developed into a dot image by the dot image development unit 810 of the inkjet printer 80, and the color conversion unit 820 performs color conversion into the CMYK format and prints by the inkjet printing mechanism 830. I do. In this case, the inkjet printer 80 functions as the color conversion device 10 and the printing device 20.

  Although not shown, the present invention can also be applied to a configuration in which the printing apparatus 20 includes an image reading unit and performs printing based on color image data read by the image reading unit. In this case, the color conversion apparatus 10 is built in the printing apparatus 20, and color image data read by the image reading unit is subjected to image processing by the color conversion apparatus 10 in the printing apparatus 20.

Here, an outline of the color space handled in the present embodiment will be described with reference to FIG. In this embodiment, the L ^* a ^* b ^* color system standardized by the International Commission on Illumination (ICE) is handled. In the L ^* a ^* b ^* color system, lightness is represented by L ^* , and chromaticity indicating hue and saturation is represented by a ^* and b ^* . As shown in FIG. 6 (a), a ^* and b ^* indicate the color direction, + a ^* is the red direction, -a ^* is the green direction, + b ^* is the yellow direction, and -b ^* is the blue direction. Indicates direction. That is, the angle in the a ^* b ^* plane represents the hue. Also, the color becomes brighter as the distance from the center increases, and the color becomes duller as the distance from the center increases. That is, the distance from the center indicates the saturation, and the central portion is achromatic. FIG. 6B is a three-dimensional representation of the color space of the L ^* a ^* b ^* color system, also displaying the L ^* axis direction. This space represents a space in which a color image can be expressed. In general, the color reproduction range that can be actually expressed by the printing apparatus is narrower than the color reproduction range of color image data. For this reason, when printing is performed using color image data, color conversion is performed to compress the color space so as to adapt to the color reproduction range of the printing apparatus.

Next, an outline of color conversion processing in the color conversion apparatus 10 of FIG. 1 configured by the color conversion unit 412 of the PC 40 and the color conversion unit 820 of the ink jet printer 80 shown in FIGS. 5A and 5B will be described. . As described above, the color conversion apparatus 10 uses the lookup table 122 provided in the color conversion processing unit 120 to convert dot image data in RGB format into dot image data in CMYK format. Here, the look-up table 122 is a correspondence table between the RGB color space and the CMYK color space. In creating the correspondence table, as shown in FIG. 7, the L ^* a ^* b ^* color specification is obtained from the RGB format. Set the correspondence to the system. In general, since the color reproduction range of a printing apparatus is narrower than the color reproduction range of a digital camera or a display apparatus, color conversion is set to compress the color gamut in the L ^* a ^* b ^* color system. Then, by setting the correspondence from the L ^* a ^* b ^* color system after color conversion to the CMYK format, a lookup table from the RGB format to the CMYK format is created.

In the printing apparatus 20 of the present embodiment, the printing order of the CMYK color inks may be changed from the default printing order as necessary, and the printing time interval of the color inks may be changed as necessary. Therefore, in the color conversion apparatus 10 of the present embodiment, a correspondence relationship from the L ^* a ^* b ^* color system to the CMYK format is set for each printing order and printing time interval pattern of each CMYK ink in the printing apparatus 20. Each lookup table 122 is created.

FIG. 8 is an explanatory diagram showing the contents of a lookup table provided in the color conversion processing unit of FIG. The look-up table 122 of this embodiment shows a correspondence relationship when color image data input to the RGB dot image input unit 110 in FIG. 1 is converted from the RGB color system to the L ^* a ^* b ^* color system. A table (see FIG. 8 (a)), one default pattern table (see FIG. 8 (b)) for setting the correspondence from the L ^* a ^* b ^* color system to the CMYK format, and a plurality of correction patterns Table (see FIG. 8C).

The default pattern table is stored in the print execution unit 224 in FIG. 4 on the recording paper 400 in the order of arrangement of the head units 310 in FIG. 2, C (cyan), K (black), M (magenta), Y (yellow). The correspondence relationship from the L ^* a ^* b ^* color system to the CMYK format is set corresponding to the color reproduction range of the printing apparatus 20 obtained by ejecting (printing) each color ink in this order.

  In the default pattern table, the recording paper 400 is fed once to the print execution unit 224, and the CKMY color inks are printed at equal time intervals according to the conveyance speed of the recording paper 400 and the intervals of the head units 310. The content is assumed to be discharged to 400. Therefore, in the present embodiment, the printing time interval of each color ink in the default pattern table is “0”.

Each correction pattern table is obtained by causing the printing execution unit 224 to discharge CMYK color inks onto the recording paper 400 on the recording paper 400 in an order different from the arrangement order of the head units 310 of FIG. Correspondence from the L ^* a ^* b ^* color system to the CMYK format is set corresponding to the color reproduction range.

  The head unit 310 in FIG. 2 corresponding to the ink discharged onto the recording paper 400 after the second color conveys the recording paper 400 more than the head unit 310 in FIG. 2 corresponding to the ink discharged onto the recording paper 400 first. In the case where the ink is disposed on the upstream side in the direction, the ink of the target color cannot be ejected at the same time when paper is fed the same time as the ink ejected on the recording paper 400 first. In such a case, the target color ink is ejected onto the recording paper 400 at the next and subsequent feedings. Therefore, after the ink of the immediately preceding color is ejected onto the recording paper 400, the immediately preceding color and the target color are determined depending on how many times the paper is ejected onto the recording paper 400. The printing time interval of both inks can be arbitrarily set.

  The printing apparatus 20 connected to the color conversion apparatus 10 according to the present embodiment performs multicolor printing by subtractive color mixture using the three primary colors of C (cyan), M (magenta), and Y (yellow) as primary colors. When the primary colors are discharged on the same pixel, a secondary color is obtained by subtractive color mixture, and when a primary color is further overlapped on the secondary color, a tertiary color is obtained by subtractive color mixture. In the following description, the primary color, secondary color, and tertiary color represent the primary color, secondary color, and tertiary color in printing as described above.

  Incidentally, although the tendency may be reversed depending on the characteristics of the ink, secondary colors (colors other than the primary color) obtained by discharging a plurality of colors of ink on the same pixel position of the recording paper 400 are as follows: The shorter the printing time interval between the front and rear inks, the stronger the tendency to be governed by the color of the ink previously ejected onto the recording paper 400, and the longer the printing time interval between the front and rear inks, the later ejection onto the recording paper 400. The tendency to be dominated by the color of the ink becomes stronger. For example, when red is obtained by discharging M (magenta) and Y (yellow) on the same pixel, if time is discharged after discharging M (magenta) and Y (yellow) is discharged to the same pixel, time Compared to the case where both colors are continuously discharged to the same pixel without placing a red, a slightly reddish red is obtained.

  The reason is considered as follows. First, if the printing time interval (ejection interval) of the front and rear inks is short, the next color ink is ejected at the stage where the previously ejected color ink has penetrated the recording paper 400. It is considered that ink tends to flow on the recording paper 400. On the other hand, if the printing time interval (ejection interval) of the front and rear inks is long, the next color ink is ejected when the previously ejected color ink is fixed (dried) on the recording paper 400, so the next color This ink is considered to be fixed on the recording paper 400 by overlapping with the previously ejected color ink.

  By actively using such a tendency, when inks of different colors are ejected in the same pixel position on the same recording surface of the recording paper 400, the printing time interval of the front and rear inks is changed to change CMYK. The color reproduction range that can be reproduced by each color ink can be changed. Therefore, in this embodiment, the printing order of CMYK inks is the same in each correction pattern table (however, it is different from the order of arrangement of the head units 310 in FIG. 2), but the printing time interval of each color ink Have different patterns. In addition, the printing time interval of each color ink can be expressed by three times: a time interval between the first color and the second color, a time interval between the second color and the third color, and a time interval between the third color and the fourth color.

That is, as shown in FIG. 8C, in each correction pattern table, when each color ink is ejected onto the recording paper 400 according to the printing order and printing time interval of each color ink of CMYK, and the printing order and printing time interval. Corresponding relations from the L ^* a ^* b ^* color system to the CMYK format corresponding to the obtained color reproduction range are defined in association with each other. In FIG. 8C, some correction pattern tables are extracted and described, and other correction pattern tables are omitted. Further, the correction pattern table partially shown in FIG. 8C is a printing condition set by the user acquired by the printing condition acquisition unit 130 of FIG. 1, for example, the type of recording paper 400 to be used, the printing quality, and the like. Different contents may be prepared for each factor that affects the color conversion range when a color image is printed.

  Next, color matching processing (image processing) of color image data performed by the color conversion processing unit 120 of the color conversion apparatus 10 according to the present embodiment using the lookup table 122 will be described with reference to the flowchart of FIG.

First, the color conversion processing unit 120 converts the RGB dot image data (color image data) input from the RGB dot image input unit 110 into L ^* a from the RGB color system using the table shown in FIG. ^* B ^* Convert to color system (step S101). Then, the color of each pixel in the converted color image data is set as a target color, and an approximate color that is closest to the target color (a color difference is minimum) is a color defined in the table in the lookup table 122. In order to select from the above, the color conversion processing unit 120 executes the following processing. First, the color image data after the ^conversion, the L ^* a * ^{b *} each value, matching the default values of ^L * ^a * ^{b *} of the pattern table shown in Figure 8 (b). This matching, the smallest color color difference between a color represented by each value of L ^* a ^* b ^* in the color image data (corresponding to the target color in claims), L ^* a in the default pattern table ^* b. Extract from each color defined by each value of ^* . Note that the magnitude of the color difference between the two colors is determined by a value ΔE (= √ {ΔL ^{* 2} + Δa ^{* 2} + Δb ^{* 2} }) expressed using each value of L ^* a ^* b ^* indicating both colors. . Then, a value ΔE representing the color difference between the extracted color and the color of the color image data (target color) is detected as a value representing the default color difference (step S103).

  Next, it is determined whether or not the detected value ΔE representing the default color difference is within an allowable range (step S105). “Within the permissible range” represents a color difference that can be regarded as the same color in operation as the original RGB dot image data (color image data) when reproduced in the CMYK color system. This is shown in the range of the value ΔE.

If the value ΔE representing the default color difference detected in step S103 is within the allowable range (YES in step S105), the color extracted from the colors defined in the default pattern table in the middle of step S103 This corresponds to the approximate color that minimizes the color difference from the color (target color) of the color image data. Therefore, each value of L ^* a ^* b ^* of the color having the minimum color difference value ΔE defined in the default pattern table as a value indicating the approximate color is determined based on the association in the default pattern table. Then, each value in the CMYK color system is converted (step S107), and color image data in the converted CMYK color system is output from the CMYK dot image output unit 140 to the printing apparatus 20 (step S109). finish.

On the other hand, if the minimum color difference ΔE between the values of ^L * ^a * ^{b *} in ^{the L} * ^a * ^{b *} values and default pattern table of the color image data is not within the allowable range (NO in step S105), Each value of L ^* a ^* b ^* of the color image data is collated with each value of L ^* a ^* b ^* of the correction pattern table partially shown in FIG. This matching, the smallest color color difference between the color (target color) represented by each value of L ^* a ^* b ^* in the color image data, at each value of L ^* a ^* b ^* in the correction pattern table Extract from each specified color. Then, the correction pattern table in which each value of L ^* a ^* b ^* indicating the extracted color is defined is extracted as a correction pattern table in which the color having the smallest color difference from the color (target color) of the color image data is defined. (Step S111).

  Next, the value ΔE representing the color difference between the color specified in the extracted correction pattern table, that is, the color extracted in the middle of step S111 and the color of the color image data (target color) is obtained in step S105. It is determined whether or not the value is within the allowable range used for determination (step S117).

  If there are a plurality of correction pattern tables extracted in step S111 (YES in step S113), the printing time intervals of each color ink defined in each correction pattern table (the time interval between the first color and the second color, the second color) One correction pattern table having the shortest time interval between the third color and the time interval between the third color and the fourth color is selected (step S115), and the color of the color image data (target) in the selected correction pattern table is selected. In step S117, the value ΔE representing the color difference between the color having the smallest color difference from the color) and the color of the color image data (target color) is determined.

If the value ΔE representing the color difference is not within the allowable range (NO in step S117), color compression processing for setting the value ΔE representing the color difference within the allowable range is performed for each value of L ^* a ^* b ^* of the color image data. (Step S119), and the process proceeds to Step S121 described later. On the other hand, if the value ΔE representing the color difference is within the allowable range (YES in step S117), the process proceeds to step S121.

In step S117, it is determined that the value ΔE representing the color difference is within the allowable range, and the color extracted from the colors defined in the correction pattern table has the smallest color difference from the color of the color image data (target color). Corresponds to the approximate color. If color compression processing is performed on each value of L ^* a ^* b ^* of the color image data in step S119, it is determined in step S117 that the value ΔE representing the color difference does not fall within the allowable range. The color extracted from the colors defined in the correction pattern table also corresponds to the approximate color that minimizes the color difference from the color of the color image data (target color). Therefore, L ^* a ^* b ^* of the color image data in which the value ΔE representing the color difference from the color (target color) of the color image data defined in the correction pattern table as a value indicating the approximate color is within the allowable range. each value, or the correction pattern table of L ^* a ^* b ^* of the L ^* a ^* b ^* values of the color image data subjected to color compression process to within the allowable range values ΔE representing the color difference between the respective values Is converted into each value in the CMYK color system based on the association in the single correction pattern table extracted in step S111 or the association in the single correction pattern table selected in step S115.

Then, the color image data in the converted CMYK color system is converted into each color specified in the correction pattern table used for converting the color image data from the L ^* a ^* b ^* color system to the CMYK color system in step S121. After the ink printing order and the printing time interval data are associated and output from the CMYK dot image output unit 140 to the printing apparatus 20 (step S123), a series of processing ends.

  By performing the processing shown in the flowchart of FIG. 9 described above for each pixel constituting the color image data, the color conversion apparatus 10 can reproduce the copy color closest in color from the color image of the input color image data. A pattern table having an optimum color reproduction range for obtaining an image by the printing apparatus 20 is selected, and color image data converted based on the pattern table is output from the CMYK dot image output unit 140 to the printing apparatus 20. It will be.

  On the other hand, the printing apparatus 20 that has received the color image data in the CMYK color system output from the color conversion apparatus 10 records the recording paper according to the printing order and the printing time interval of each color ink indicated by the data associated with the color image data. The number of repeated feedings to the 400 head units 310 and the number of times of feeding the CMYK inks are determined. Then, while the recording paper 400 is fed to the head unit 310 by the paper feeding / discharging mechanism 230 for the determined number of paper feeding times, the printing mechanism 220 applies the recording paper 400 to the recording paper 400 at the determined number of feeding times. Discharge each.

  As a result, the recording paper 400 has a CYMK with a printing order and a printing time interval different from the default printing order and the printing time interval corresponding to the arrangement order of the head units 310 indicated by the data received from the color conversion device 10. Each color ink is discharged. Then, the color reproduction range changes according to the change in the printing order and printing time interval of each color ink.

  As described above, according to the color conversion apparatus 10 of the present embodiment, the ejection order (printing order) of the CMYK color inks to the recording paper 400 in the printing apparatus 20 is made different from the order in which the head units 310 are arranged. When changing the color reproduction range so that it approximates the color of the color image based on the color image data, each color is set so that the approximate color with the smallest color difference from the target color of the color image data can be reproduced. An appropriate time is selected for the ink printing time interval. For this reason, it is possible to obtain a print result with a color closer to that of the original color image.

Note that the above description with reference to the flowchart of FIG. 9 is based on the assumption that the color image data includes a color other than the primary color in printing (secondary color in printing or a color of tertiary or higher). It is. Therefore, in step S103, step S105, step S111 to step S119, it is necessary to select a color having the smallest color difference from the color of the color image data from the default pattern table and the correction pattern table. However, when the color image data is composed of only primary colors in printing, there is no need (room) for changing the ejection order (printing order) of the CMYK inks. Therefore, after the color image data is converted from the RGB color system to the L ^* a ^* b ^* color system in step S101, it is confirmed whether or not the color image data is composed only of primary colors in printing. Also good. If it is confirmed that the image is composed of primary colors, the process of step S103 and step S105 is not performed, and immediately in step S107, the color image data is converted to L ^* a based on the association in the default pattern table. ^* B ^{* The} color system may be converted to the CMYK color system.

In the present embodiment, when an approximate color whose color difference from the target color of the color image data is within the allowable range can be reproduced within the color reproduction range of the default pattern table (YES in step S105 in FIG. 9), the color image The configuration is such that the L ^* a ^* b ^* values of the data are not compared with the L ^* a ^* b ^* values of the correction pattern tables. However, each of L ^* a ^* b ^* of the color image data regardless of whether or not an approximate color whose color difference from the target color of the color image data is within the allowable range can be reproduced within the color reproduction range of the default pattern table. values, against the respective values of L ^* a ^* b ^* of the default pattern table of the L ^* a ^* b ^* values and the correction pattern table, approximation color difference is minimized between the target color of the color image data A configuration may be adopted in which a pattern table of a color reproduction range capable of reproducing colors is extracted.

  In such a configuration, when the extracted pattern table is the default pattern table, the same printing order of CKMY (default printing order) as the arrangement order of the head units 310 in FIG. 2 and the printing time of each color ink Data indicating that each interval is “0” (all ink is ejected onto the recording paper 400 by one paper feed) is output in association with color image data in the CMYK color system. May be.

Incidentally, when configured as in the present embodiment, when an approximate color whose color difference from the target color of the color image data is within the allowable range can be reproduced within the color reproduction range of the default pattern table, the color image data L ^* it is possible to dispense without unnecessary collation with a ^* b ^* values of the L ^* a ^* b ^* values and the correction pattern table, it is advantageous.

  Further, when there is no possibility that a plurality of correction pattern tables are extracted in step S111 in FIG. 9, the processes in steps S113 and S115 may be omitted.

  Furthermore, in this embodiment, the printing apparatus 20 uses the path for reversing the recording paper 400 from the switching mechanism 381 to the switching mechanism 383, and the recording paper 400 is returned to the registration unit Rg by switching the switching mechanism 383. The case where a paper feeding path is configured has been described. Therefore, the recording paper 400 is fed to the head unit 310 in the printing apparatus 20 according to the printing order and printing time interval of each color ink indicated by the data output from the color conversion apparatus 10 in association with the color image data in the CMYK color system. It is assumed that the printing apparatus 20 determines the number of times and how many times the ink is ejected to the recording paper 400 at the time of feeding.

  However, the configuration for ejecting each color ink onto the recording paper 400 in the printing device 20 in the printing order and printing time interval of each color ink indicated by the data output from the color conversion device 10 is the printing device 20 of the present embodiment. You may implement | achieve with structures other than the structure demonstrated. Specifically, by repeatedly reciprocating the head unit 310 on the recording paper 400, a printing order different from the order in which the head units 310 are arranged and printing different from the case where each color ink is ejected onto the recording paper with one paper feed. A configuration may be adopted in which each color ink is ejected onto the recording paper 400 at time intervals.

In the present embodiment, the case where the color space is converted from the RGB color system to the L ^* a ^* b ^* color system has been described. However, instead of the L ^* a ^* b ^* color system, the printing apparatus 20 includes The color space may be converted from another independent color space to the CMYK color system.

10 color conversion device 20 printing device 40 PC
50 Inkjet printer 60 Image reading device 70 PC
DESCRIPTION OF SYMBOLS 80 Inkjet printer 110 RGB dot image input part 120 Color conversion process part 122 Lookup table 130 Print condition acquisition part 140 CMYK dot image output part 210 CMYK dot image input part 220 Printing mechanism 221 Transport drive control part 222 Multipass control part 223 Image Processing unit 224 Print execution unit 225 Head driver 230 Feed / discharge mechanism 231 Transport drive unit 310 Head unit 312 Inkjet head 320 Side paper feed tray 330 Paper feed tray 340 Face down paper discharge port 350 Face down paper discharge tray 352 Conveying belt 360 Face Up discharge port 362 Face up discharge tray 370 Registration roller 380 Paper position sensor 381 Switching mechanism 382 Switching mechanism 383 Switching mechanism 390 Guide 4 0 recording paper 410 printer driver 412 color conversion section 510 inkjet printing mechanism 710 printer driver 810 dot image expansion section 820 color conversion section 830 inkjet printing mechanism Rg registration unit SR switchback path

Claims (6)

An image processing method for performing a color matching process between an input device and a printing device that prints a color image based on color image data input from the input device,
The color image data is collated with a color reproduction range of the printing device of a plurality of patterns prepared for each printing order and printing time interval of the plurality of color inks for the same pixel in the printing device, and the color image data in the color image data Extracting a pattern of a color reproduction range including an approximate color that minimizes a color difference from the target color;
Converting the color image data into a data format corresponding to the printing device according to a color reproduction range of the extracted pattern;
Associating the color image data obtained by converting the data format with printing order and printing time interval data of the plurality of color inks corresponding to the color reproduction range of the extracted pattern, and outputting to the printing device;
An image processing method comprising: The step of extracting a pattern of a color reproduction range including the approximate color from the color reproduction range of a plurality of patterns,
The color image data is collated with a default color reproduction range of the printing device, and a color difference between the target color and a color having a minimum color difference between the target color in the default color reproduction range is determined as a default color difference. Detecting as a
When the default color difference is out of an allowable range, the color image data is stored in the color reproduction range of a plurality of patterns, and the printing order and printing time interval of a plurality of color inks for the same pixel in the printing device are the default color. Other colors including colors that minimize the color difference from the target color in the other color reproduction range by collating with other color reproduction ranges different from the printing order and printing time interval of the multiple color inks in the reproduction range. Extracting a reproduction range pattern; and
Contains
The step of extracting a pattern of another color reproduction range including a color having a minimum color difference from the target color in the other color reproduction range,
When there are a plurality of other color reproduction range patterns including a color having a minimum color difference from the target color in the other color reproduction range, the other color reproduction with the shortest printing time interval of the plurality of color inks Including selecting and extracting a range pattern;
The image processing method according to claim 1.   The other color reproduction range of each pattern includes the printing order and printing of a plurality of color inks on the same pixel on the same side of the recording paper repeatedly fed to the print head using the reversing recording paper conveyance path of the printing device. Prepared in correspondence with a combination pattern of time intervals, and the printing order and printing time interval data of the plurality of color inks to be output to the printing device are determined based on the data by the printing device. 3. The image processing method according to claim 2, wherein the number of times the recording paper is repeatedly fed to the printer and whether or not each color ink is printed by the print head at each feeding is determined. An image processing apparatus that performs color matching processing between an input device and a printing device that prints a color image using color image data input from the input device,
Storage means for storing the color reproduction range of the printing device of a plurality of patterns prepared for each printing order and printing time interval of the plurality of color inks for the same pixel in the printing device;
Extracting the color image data with the color reproduction range stored in the storage means to extract a color reproduction range pattern including an approximate color that minimizes the color difference from the target color in the color image data Means,
Conversion means for converting the color image data into a data format corresponding to the printing device according to the color reproduction range of the pattern extracted by the extraction means;
The color image data whose data format has been converted by the converting means is associated with the printing order and printing time interval data of the plurality of color inks corresponding to the color reproduction range of the pattern extracted by the extracting means, and is associated with the printing device. An output means for outputting;
An image processing apparatus comprising: The extraction means includes
A color difference between the target color and a color that minimizes the color difference between the target color in the default color reproduction range by comparing color data of the color image data with a default color reproduction range of the printing device. A default color difference determining means for determining whether or not the default color difference is outside the allowable range;
When the default color difference determining unit determines that the default color difference is outside the allowable range, the color image data is printed in the printing order of the plurality of color inks for the same pixel in the printing device in the color reproduction range of the plurality of patterns. The color difference from the target color in the other color reproduction range is determined by collating with the other color reproduction ranges different from the printing order and the printing time interval of the plurality of color inks in the default color reproduction range. Extract other color gamut patterns including the smallest color,
When there are a plurality of other color reproduction range patterns including a color having a minimum color difference from the target color in the other color reproduction range, the other color reproduction with the shortest printing time interval of the plurality of color inks Select and extract a range pattern,
The image processing apparatus according to claim 4.   The other color reproduction range of each pattern includes the printing order and printing of a plurality of color inks on the same pixel on the same side of the recording paper repeatedly fed to the print head using the reversing recording paper conveyance path of the printing device. Prepared in correspondence with a combination pattern of time intervals, and the printing order and printing time interval data of the plurality of color inks to be output to the printing device are determined based on the data by the printing device. 6. The image processing apparatus according to claim 5, wherein the image processing apparatus is capable of determining the number of times the recording paper is repeatedly fed and whether or not each color ink is printed by the print head at each feeding.

Images