Image processing device, image processing method, and program

Abstract

To provide an image processing device, an image processing method, and a program are provided that, in multi-color printing using light inks, reduce the total amount of ink used while simplifying user operations and internal processing.SOLUTION: An image processing device (image processing unit 10) includes a color conversion unit 12 that performs color conversion to a plurality of ink colors CMYK, and a color separation unit 13 that separates the ink amount of one of the plurality of ink colors (e.g., black K) into the ink amount of this separation ink color K and the ink amount of a light ink color (e.g., gray G). The color conversion unit 13 performs color conversion using a color profile that is set to reduce the color conversion amount of the separation ink color K to a first density region A1 of intermediate density, and to increase the color conversion amount of the separation ink color K to other ink colors CMY of the plurality of ink colors CMYK in the first density region A1.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an image processing device, an image processing method, and a program. [Background technology]

[0002] Conventionally, in areas of color space where the amount of light cyan ink applied is large, which is prone to causing uneven gloss, and the amount of other inks applied is small, a method has been proposed in which the amount of light cyan ink applied is reduced and that amount is replaced with the amount of cyan ink applied (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-088660 Summary of the Invention [Problem to be solved by the invention]

[0004] Incidentally, a multi-color printing method using light inks such as gray (G), light cyan (LC), and light magenta (LM) is commonly known. These light inks are used in multi-color printing with five or more colors, along with black (K), cyan (C), magenta (M), and yellow (Y).

[0005] The method for creating a four-color CMYK color profile is well established, and there are many tools available that even general users without the necessary know-how can use, but the difficulty of creating a color profile increases dramatically when there are five or more colors, making it difficult for general users without the necessary know-how to create a color profile with five or more colors.

[0006] Therefore, in the case of a multi-color printer equipped with light inks, as shown in Figure 9, it is possible to first perform color conversion based on RGB image data into four colors (CMYK) using a color profile, and then perform color separation from K ink to G ink (light ink) by internal processing by referencing a KG separation table, which is a simple one-dimensional conversion table. This KG separation table outputs the G ink amount corresponding to the input ink amount of K ink, so color separation can be performed with simpler processing than with a five-color profile. As a result, as long as the density does not change before and after the separation from K to K and G, from the user's perspective, using a CMYK four-color profile has the advantage of allowing for easy five-color separation.

[0007] On the other hand, this five-color separation does not allow for as flexible ejection control as a five-color profile, because it only references the amount of K ink in each pixel to perform color separation from K to K and G. As a result, in the medium density range of K, where the effects of using G ink to improve graininess and color stability are less than in the low density range of K, a small amount of K is converted into K (K1) and a large amount of G (G1) (for example, around a gradation value of 50), as shown in Figure 10.

[0008] For example, as shown in Figure 11, when the amount of CMYK ink from the solid red area to the solid black area is decomposed into K1 and G1 using the KG decomposition table, the amount of G1 ink becomes large in the area where the amount of K ink is small as shown in Figure 11, as shown in Figure 12.

[0009] As a result, the total amount of ink used for each color increases significantly, which in turn leads to poor print quality in inkjet systems, such as print show-through for oil-based inks and increased curl for water-based inks.

[0010] The object of the present invention is to provide an image processing device, an image processing method, and a program that can reduce the total amount of ink used in multi-color printing using light inks while simplifying user operations and internal processing. [Means for solving the problem]

[0011] In one aspect, an image processing device includes a color conversion unit that performs color conversion to a plurality of ink colors, and a color separation unit that separates the ink amount of a separation ink color, which is one of the plurality of ink colors, into the ink amount of the separation ink color and the ink amount of a light ink color, and the color conversion unit performs the color conversion using a color profile that is set to reduce the color conversion amount of the separation ink color to a first density region of intermediate density and to increase the color conversion amount of the separation ink color to other ink colors of the plurality of ink colors in the first density region. [Effects of the Invention]

[0012] According to this aspect, in multi-color printing using light inks, it is possible to reduce the total amount of ink used while simplifying user operations and internal processing. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 2 is a block diagram showing a control configuration of the inkjet printing apparatus according to the embodiment. [Figure 2] 1 is a flowchart illustrating an image processing method according to an embodiment. [Figure 3] FIG. 2 is an explanatory diagram illustrating data optimization of a four-color profile according to an embodiment. [Figure 4] 10 is a graph for explaining the ink amounts of each color when color conversion using a four-color profile without data optimization and KG color separation are performed in Comparative Example 1. [Figure 5] 10 is a graph for explaining ink amounts after color conversion using a five-color profile in Comparative Example 2. [Figure 6] 10 is a graph showing ink amounts of each color when color conversion is performed using a four-color profile with data optimization (before KG color separation) according to one embodiment. [Figure 7] 10 is a graph illustrating ink amounts of each color when color conversion using a four-color profile with data optimization and KG color separation are performed according to an embodiment. [Figure 8] 10 is a table comparing effects of an embodiment and comparative examples 1 and 2. [Figure 9] FIG. 10 is an explanatory diagram for explaining five-color separation in the reference technique. [Figure 10] 10 is a graph for explaining a KG decomposition table. [Figure 11] 10 is a graph for explaining CMYK ink amounts before KG color separation in a reference technique. [Figure 12] 10 is a graph for explaining the ink amounts of CMYKG after KG color separation in a reference technique. DETAILED DESCRIPTION OF THE INVENTION

[0014] An image processing device, an image processing method, and a program according to an embodiment of the present invention will be described below with reference to the drawings.

[0015] FIG. 1 is a block diagram showing the control configuration of an inkjet printing apparatus 100 according to this embodiment.

[0016] The inkjet printing apparatus 100 includes a control unit 1, a printing unit 110, a transport unit 120, and an interface unit .

[0017] The control unit 1 includes an image processing unit 10, a head control unit 20, and a transport control unit 30.

[0018] The control unit 1 includes, for example, one or more processors (e.g., CPU: Central Processing Unit) that function as an arithmetic processing device that controls the operation of each unit of the inkjet printing apparatus 100, and one or more memories. This memory may be, for example, a read-only semiconductor memory (ROM) in which a predetermined control program is pre-recorded, or a random access memory (RAM) that is a semiconductor memory that can be written and read at any time and is used as a working memory area as needed when the processor executes various control programs. The processor reads and executes a predetermined program from, for example, the memory or a storage medium (a non-transitory computer-readable recording medium) that is detachable from the inkjet printing apparatus 100, thereby functioning as the image processing unit 10 (RIP processing unit 11, color conversion unit 12, color separation unit 13, and halftone processing unit 14), the head control unit 20, and the transport control unit 30. In this way, the control unit 1 functions as an example of a computer that executes a program.

[0019] The image processing unit 10 includes a RIP (Raster Image Processor) processing unit 11, a color conversion unit 12, a color separation unit 13, and a halftone processing unit 14. The image processing unit 10 is an example of an image processing device. This image processing device may be arranged independently of a printing device such as the inkjet printing device 100.

[0020] The RIP processor 11 performs RIP processing on print job data in PDL (Page Description Language) format transmitted from a user terminal or the like, and generates image data in RGB format.

[0021] The color conversion unit 12 and color separation unit 13 will be described later. The color conversion unit 12 converts image data in RGB format into image data in CMYK format using a four-color profile. The color separation unit 13 separates the ink amount of black (K), which is an example of a separated ink color, into the ink amount of K and the ink amount of gray (G). Gray (G) is an example of a light ink color.

[0022] The halftone processing unit 14 performs halftone processing on the generated CMYKG image data to generate ink ejection data.

[0023] The head control unit 20 causes the ink jet heads 111 to 113 to eject ink from the nozzles based on the ink ejection data generated by the image processing unit 10.

[0024] The transport control unit 30 controls the transport unit 120 to transport a printing medium such as paper.

[0025] The printing unit 110 has multiple inkjet heads 111-113. Each of these inkjet heads 111-113 has multiple head modules arranged in a staggered pattern along a main scanning direction perpendicular to the transport direction (sub-scanning direction) of the printing substrate. That is, these multiple head modules are arranged along the main scanning direction with their positions in the sub-scanning direction shifted alternately. The multiple head modules of each of the inkjet heads 111-113 have two rows of nozzles that eject different inks. Therefore, when three inkjet heads 111-113 are arranged, a maximum of six colors of ink (five colors if there are two rows of black) can be ejected. Note that the configuration of the printing unit 110 is merely an example, and the printing unit 110 is not particularly limited as long as it ejects ink of multiple colors.

[0026] The transport unit 120 has transport members such as rollers and belts that transport the printing medium, flippers for switching the transport path, and actuators such as motors that drive these transport members and flippers. The drive control of these actuators is performed by the transport control unit 30 described above.

[0027] The interface unit 130 exchanges various information with external devices such as a user terminal, and receives print job data sent from the user terminal.

[0028] Next, the image processing method according to this embodiment will be described with reference to the flowchart of FIG.

[0029] The process shown in FIG. 2 is performed by the image processing unit 10, for example, when the interface unit 130 of the inkjet printing apparatus 100 receives print job data from a user terminal or the like.

[0030] First, the RIP processing unit 11 of the image processing unit 10 performs RIP processing on print job data in PDL format to generate image data in RGB format (step S1).

[0031] Next, the color conversion unit 12 performs data optimization of the four-color profile (step S2). This data optimization of the four-color profile will be described later with reference to Figures 3 to 7. Note that if the data optimization of the four-color profile has been performed in advance, the data optimization process of step S2 can be omitted.

[0032] The color conversion unit 12 performs color conversion based on the ink amount information of Ca, Ma, Ya, and Ka (see FIG. 6) after data optimization assigned to the grid points of the Lab color space of the LUT (Look Up Table) using the four-color profile, and generates image data in CMYK format from image data in RGB format (step S3).

[0033] Then, the color separation unit 13 separates Ka into Ka1 and Ga1 (see FIG. 7) by referring to the KG separation table (step S4). The KG separation table may be, for example, one that outputs a G gradation value corresponding to an input of a K gradation value.

[0034] Next, the halftone processing unit 14 performs halftone processing such as known error diffusion processing or dither mask processing on the generated image data of Ca, Ma, Ya, Ka1, and Ga1 to generate ink ejection data (step S5). Then, the processing shown in Fig. 2 ends. After this, the head control unit 20 preferably performs printing by ejecting ink from the nozzles of the inkjet heads 111 to 113 based on the generated ink ejection data.

[0035] 3, the color conversion unit 12 acquires CMYK ink amount information assigned to grid points in the Lab color space of the LUT using the four-color profile before data optimization. In the four-color profile with data optimization in this embodiment, K ink amount subtraction and CMY addition and subtraction are performed in a predetermined density region of K (first density region A1 and second density region A2 described below), and ink amount information of Ca, Ma, Ya, and Ka is assigned to each grid point.

[0036] Here, the ink amounts for each color in Comparative Example 1 shown in Figure 4 are an example of a case where CYMK color conversion is performed using a four-color profile without data optimization, and color separation into K1 and G1 is performed using a KG separation table, and the example shows a color change from skin color to solid black.

[0037] The ink amount of K (shown by the dashed line in FIG. 6) increases from flesh tones to solid black, and the ink amount of K1 after KG color separation shown in FIG. 4 also gradually increases toward solid black.

[0038] In the low-density region of K, which is close to skin tones, using G ink can improve graininess and color stability more effectively than using K ink alone. On the other hand, in the medium-density region of K (e.g., a somewhat vivid, dark color), the printing rate is originally high, so the color is not prone to noticeable graininess, and even if G ink is printed, the density saturates, resulting in an increased ink volume required to reproduce the target color. Thus, near the medium density of K, the above-mentioned effects of using G ink are not very noticeable. Therefore, in this region, it is desirable to increase the K ink, C ink, etc., and reduce the G ink. However, as the K ink volume begins to increase, the G1 ink volume after KG color separation also increases. This increase is significantly greater than, for example, the G ink volume in the five-color profile of Comparative Example 2 shown in Figure 5.

[0039] Therefore, as shown in Figure 6, with regard to the ink amounts of CMYK at each grid point of the four-color profile, it is desirable to reduce the ink amount of K indicated by the dashed-dotted line to Ka indicated by the solid line in the first density region A1 of the intermediate density of K, and increase the ink amounts of CMY indicated by Ca, Ma, and Ya indicated by the dashed-dotted lines. In other words, K is converted to the other colors CMY in the first density region A1. This makes it possible to significantly reduce the ink amount of Ga1 after KG color separation shown in Figure 7 in the region corresponding to the first density region A1 of K compared to the ink amount of G1 in the case without data optimization of the four-color profile (the same amount as Comparative Example 1 in Figure 4, indicated by the dashed-dotted line).

[0040] Here, in order to prevent gradation jumps caused by sudden changes in ink amount in the first density region A1, it is advisable to set the ink amount so that it changes smoothly from the Lch information of the input grid point, and to do so, it is advisable to use the input and output information of the KG separation table as parameters.

[0041] The first density region A1 is a region of higher density than the low density region of K (from 0 ink amount to a specified amount). Also, the range in which the ink amounts of the other colors, CMY, are increased does not have to completely match the first density region A1 of K, as shown in Fig. 6. Also, a mode in which all other colors are not increased may be employed, such as a mode in which the total ink amount of CMY is increased by increasing only the other color, CM, in the first density region A1.

[0042] As shown in Figure 6, it is preferable to reduce the amount of ink of other colors in a second K density region A2, which has a higher density than a first density region A1 in which the amount of K ink is reduced. In this second K density region A2, conversion may be performed to increase the amount of K ink and reduce the amount of CMY ink. In this case, too, it is desirable to perform conversion so that the density and color tone after printing do not change. Note that the second density region A2 may be at least a portion of the region up to the solid black region, but from the perspective of reducing the total ink amount, it is desirable for it to be a high-density region closer to the first K density region A1 than to the region close to the solid black.

[0043] In determining the ink amounts for Ca, Ma, and Ya, as shown in Figure 3, variables include the input lightness of the LUT, the ink amount for Ka, and the total ink amount when KG color separation is performed after color conversion using a four-color profile without data optimization, and the ink amounts can be determined so that after KG color separation, the total ink amount does not increase with a four-color profile with data optimization compared to a four-color profile without data optimization.

[0044] Furthermore, while the above description has been given using gray (G) as an example of a light ink, light cyan (LC) obtained by color separation from cyan (C) or light magenta (LM) obtained by color separation from magenta (M) may also be used as the light ink. For example, when light cyan (LC) is used as the light ink, it is preferable to optimize the color profile data by swapping K and C in the above description, reducing the color conversion amount of C in the first density region of the intermediate density of C, and increasing the color conversion amount of the other colors, MYK. This can prevent an increase in the ink amount of LC after color separation in the first density region of the intermediate density of C. Similarly, when light magenta (LM) is used as the light ink, it is preferable to swap K and M in the above description, reducing the color conversion amount of M in the first density region of the intermediate density of M, and increasing the color conversion amount of the other colors, CYK. This can prevent an increase in the ink amount of LM after color separation in the first density region of the intermediate density of M.

[0045] In the embodiment described above, an image processing unit 10, which is an example of an image processing apparatus, includes a color conversion unit 12 that performs color conversion to a plurality of ink colors (CMYK) and a color separation unit 13 that separates the ink amount of a separation ink color (K), which is one of the plurality of ink colors (CMYK), into the ink amount of this separation ink color (K1) and the ink amount of a light ink color (G1). The color conversion unit 12 performs color conversion using a color profile (a four-color profile after data optimization) that is set to reduce (Ka) the color conversion amount of the separation ink color (K) to a first density region A1 of intermediate density and increase (Ca, Ma, Ya) the color conversion amount of the separation ink color (K) to the other ink colors (CMY) of the plurality of ink colors (CMYK) in the first density region A1.

[0046] The image processing method according to the present embodiment is an image processing method performed by a computer (e.g., the control unit 1 or the image processing unit 10), and includes performing color conversion to a plurality of ink colors (CMYK) (step S3 in FIG. 2 ) and separating the ink amount of a separation ink color (K), which is one of the plurality of ink colors (CMYK), into the ink amount of this separation ink color (K1) and the ink amount of a light ink color (G1) (step S4). The color conversion (step S3) is performed using a color profile (a four-color profile after data optimization) that is set to reduce (Ka) the color conversion amount of the separation ink color (K) to the first density region A1 of intermediate density and increase (Ca, Ma, Ya) the color conversion amount of the separation ink color (K) to the other ink colors (CMY) of the plurality of ink colors (CMYK) in the first density region A1 (steps S2 and S3).

[0047] The program according to the present embodiment also causes a computer (e.g., the control unit 1 or the image processing unit 10) to implement a function for performing color conversion to a plurality of ink colors (CMYK) (step S3 in FIG. 2 ) and a function for separating the ink amount of a separation ink color (K), which is one of the plurality of ink colors (CMYK), into the ink amount of this separation ink color (K1) and the ink amount of a light ink color (G1) (step S4). The color conversion function (step S3) performs color conversion using a color profile (a four-color profile after data optimization) that is set to reduce (Ka) the color conversion amount of the separation ink color (K) to the first density region A1 of intermediate density, and to increase (Ca, Ma, Ya) the color conversion amount of the separation ink color (K) to the other ink colors (CMY) of the plurality of ink colors (CMYK) in the first density region A1 (steps S2, S3).

[0048] As a result, by using G ink, an example of a light ink color, in the low-density region of K, an example of a separation ink color, effects such as improved graininess and improved color stability can be achieved, while an increase in the amount of G ink, an example of a light ink color, can be suppressed in the first density region A1 of the medium density of K, where this effect is less likely to be achieved, thereby suppressing an increase in the total ink amount. Therefore, by suppressing the occurrence of bleed-through in oil-based inks and curl in water-based inks, deterioration in print quality can be prevented. As shown in FIG. 8, this print quality can be evaluated as "△" (almost good) when compared to the KG color separation of the four-color profile without data optimization in Comparative Example 1 (see FIG. 4) which is rated "×" (poor) due to the increase in G1, and the five-color profile of Comparative Example 2 (see FIG. 5) which is rated "◯" (good).

[0049] Furthermore, because users can use color profiles such as four-color profiles for which creation methods have been established, the user operability can be rated as "good." From this user operability perspective, the KG color separation of the four-color profile without data optimization in Comparative Example 1 (see FIG. 4) is similarly rated as "good," while the use of the five-color profile in Comparative Example 2 (see FIG. 5) is rated as "poor" because it is difficult for users to create it.

[0050] Furthermore, from the viewpoint of processing speed, since all that is required is data optimization of the four-color profile, if a four-color profile that has already been data optimized is used, the result can be said to be "good" (o), and even if data optimization is performed, the result can be said to be "almost good" (△). In contrast, the KG color separation of the four-color profile without data optimization in Comparative Example 1 is "good" (o), and when the five-color profile in Comparative Example 2 (see Figure 5) is used, the result can be said to be "almost good" (△).

[0051] As described above, by using the four-color profile for which data optimization has been performed according to this embodiment, there are no "poor" (x) evaluations in terms of print quality (bleed-through or curl due to an increase in the total ink amount), user operability, or processing speed. Thus, according to this embodiment, in multi-color printing using light inks such as gray (G), it is possible to reduce the total ink amount while simplifying user operation and internal processing.

[0052] In addition, in this embodiment, the color profile is set so as to reduce the amount of color conversion to other ink colors (CMY) in the second density region A2, which is higher in density than the first density region A1 of the separated ink color (K).

[0053] This makes it possible to reduce the ink amount not only in the first density region A1 where the ink amount of the light ink color (G) after color separation is reduced by reducing the ink amount of the separated ink color (K), but also in the second density region A2.

[0054] The present invention is not limited to the above-described embodiments, and the components can be modified and embodied without departing from the spirit of the invention. Furthermore, various inventions can be formed by appropriately combining the multiple components disclosed in the above-described embodiments. For example, all of the components shown in the embodiments can be appropriately combined. Naturally, various modifications and applications are possible without departing from the spirit of the invention. The invention as originally claimed in the present application is described below.

[0055] [Appendix 1] a color conversion unit that performs color conversion into a plurality of ink colors; a color separation unit that separates an ink amount of a separation ink color, which is any one of the plurality of ink colors, into an ink amount of the separation ink color and an ink amount of a light ink color, the color conversion unit performs the color conversion using a color profile that is set to reduce the amount of color conversion to a first density region of intermediate density of the separation ink colors and to increase the amount of color conversion to other ink colors of the plurality of ink colors in the first density region of the separation ink colors. 1. An image processing device comprising:

[0056] [Appendix 2] The color profile is set to reduce the amount of color conversion to the other ink color in a second density region that is higher in density than the first density region of the separation ink color. 2. The image processing device according to claim 1,

[0057] [Appendix 3] 1. A computer-implemented image processing method, comprising: Performing color conversion to a plurality of ink colors; separating an ink amount of a separation ink color, which is any one of the plurality of ink colors, into an ink amount of the separation ink color and an ink amount of a light ink color, The color conversion is performed using a color profile that is set to reduce the amount of color conversion to a first density region of intermediate density of the separation ink colors and to increase the amount of color conversion to other ink colors of the plurality of ink colors in the first density region of the separation ink colors. An image processing method comprising:

[0058] [Appendix 4] The function to convert colors to multiple ink colors, a program that causes a computer to realize a function of separating an ink amount of a separation ink color that is one of the plurality of ink colors into an ink amount of the separation ink color and an ink amount of a light ink color, The function of performing the color conversion performs the color conversion using a color profile that is set to reduce the amount of color conversion to a first density region of intermediate density of the separation ink colors and to increase the amount of color conversion to other ink colors of the plurality of ink colors in the first density region of the separation ink colors. A program characterized by: [Explanation of symbols]

[0059] 1. Control section 10 Image processing unit (image processing device) 11 RIP processing section 12 Color conversion unit 13 Color separation section 14 Halftone processing section 20 Head control unit 30 Conveyance control section 100 Inkjet printing device 110 Printing Department 111~113 Inkjet head 120 Conveyor 130 Interface section A1 1st concentration region A2 2nd concentration area

Claims

1. a color conversion unit that performs color conversion into a plurality of ink colors; a color separation unit that separates an ink amount of a separation ink color, which is any one of the plurality of ink colors, into an ink amount of the separation ink color and an ink amount of a light ink color, the color conversion unit performs the color conversion using a color profile that is set to reduce the amount of color conversion to a first density region of intermediate density of the separation ink colors and to increase the amount of color conversion to other ink colors of the plurality of ink colors in the first density region of the separation ink colors.

1. An image processing device comprising:

2. The color profile is set so as to reduce the amount of color conversion to the other ink color in a second density region that is higher in density than the first density region of the separated ink color.

2. The image processing device according to claim 1, wherein:

3. 1. A computer-implemented image processing method, comprising: Performing color conversion to a plurality of ink colors; decomposing an ink amount of a separation ink color, which is any one of the plurality of ink colors, into an ink amount of the separation ink color and an ink amount of a light ink color; The color conversion is performed using a color profile that is set to reduce the amount of color conversion to a first density region of intermediate density of the separation ink colors and to increase the amount of color conversion to other ink colors of the plurality of ink colors in the first density region of the separation ink colors. An image processing method comprising:

4. The function to convert colors to multiple ink colors, a program that causes a computer to realize a function of separating an ink amount of a separation ink color that is one of the plurality of ink colors into an ink amount of the separation ink color and an ink amount of a light ink color, The function of performing the color conversion performs the color conversion using a color profile that is set to reduce the amount of color conversion to a first density region of intermediate density of the separation ink colors and to increase the amount of color conversion to other ink colors of the plurality of ink colors in the first density region of the separation ink colors. A program characterized by:

Images