JP5769465B2 - Color conversion apparatus, color conversion method and program - Google Patents

Description

  The present invention relates to a color conversion apparatus, a color conversion method, and a program for determining a color conversion condition for converting an input image signal into a device color signal corresponding to printing.

  In recent years, along with dramatic progress in inkjet technology, color large format printing that achieves both high speed and high image quality by an inkjet printing apparatus is becoming possible. This apparatus is used in a wide range of fields especially for sign / display applications, and can be applied to, for example, printing of storefront POP (Point Of Purchase), wall posters, outdoor advertisements / signboards, and the like. In the ink jet method, a printed matter can be obtained by discharging a plurality of types of ink droplets such as CMYK to form a large number of dots on a print medium.

  By the way, according to human standard visual response characteristics, it is known that the color of the gray system is most easily identified. That is, when the dots of each color have the same size, the dots formed with K ink are easier to visually recognize than the dots with other C, M, and Y inks. For this reason, in an image formed by increasing the amount of K ink used, even when the individual dots cannot be identified, a rough feeling (deterioration in graininess) is conspicuous as a whole image.

  On the other hand, by mixing C, M, and Y inks to form gray (composite black), the graininess of the image can be improved due to the smoothing effect associated with the overlapping of the dots of each color. However, since three colors of ink are used instead of one color, the total amount of ink used increases, so the running cost (hereinafter simply referred to as cost) increases.

  That is, in the inkjet method, graininess and cost are in a trade-off relationship, and image design that balances both is important. Therefore, a change amount of the total ink use amount (hereinafter simply referred to as “ink change amount”. When reducing the total ink use amount, it may be referred to as “ink reduction amount” in particular) is set in advance. Various techniques relating to color conversion processing for appropriately controlling the image quality of printed matter by finely adjusting the dot recording rate of each color have been proposed.

  Patent Document 1 discloses an apparatus and method for changing a color conversion condition for an input image signal in accordance with a set ink reduction amount.

  Patent Document 2 discloses an apparatus and method for changing lightness and saturation according to a set ink reduction amount and correcting an image signal so as to realize the lightness and saturation. For example, it is described that the ink reduction amount can be changed in accordance with the operation of a slide bar arranged on the setting screen.

  Patent Document 3 discloses an apparatus and method for calculating a distribution characteristic on an image area by estimating the total amount of ink used for each unit area and determining a color conversion condition from the distribution characteristic. Further, there is described a screen diagram that displays a preview image and a map image that visualizes the total usage corresponding to each unit area of the preview image. This also assists an operator who newly determines color conversion conditions.

JP 2006-68982 A ([0022], FIG. 6) JP 2007-196529 ([0029], FIG. 2) JP 2006-224454 A ([0011], FIG. 11)

  By the way, when changing the current color conversion conditions, the operator may want to know in advance the degree of influence (particularly harmful) on the image quality of the printed matter as the ink reduction amount increases. In particular, for printed matter that requires high image quality, there is a particularly high demand for adjusting to optimum color conversion conditions that achieve both image quality and cost.

  However, in the apparatuses and methods disclosed in Patent Documents 1 and 2, it is impossible to grasp in advance whether the image quality is good or bad with respect to the ink reduction amount, and it is necessary to confirm the image quality after actually generating the printed matter. .

  Also, when creating a color conversion table for changing the total amount of ink used, various design methods (algorithms or image design policies) can be employed. That is, the tendency of color reproduction characteristics may be different when gradation conversion processing is performed using the created color conversion table.

  However, since the apparatus and method disclosed in Patent Document 3 can grasp the distribution characteristics of the total amount of ink used, it can be a standard for ink bleeding and graininess. I couldn't figure out.

  The present invention has been made to solve the above-described problem, and provides a color conversion apparatus, a color conversion method, and a program that can easily grasp the degree of the effect on the color reproduction characteristics of a printed matter due to a change in color conversion conditions. The purpose is to provide.

  A color conversion apparatus according to the present invention is an apparatus for determining a color conversion condition for converting an input image signal into a device color signal corresponding to printing, and a reference for acquiring reference condition information related to a reference color conversion condition A condition information acquisition unit; a comparison condition information acquisition unit that acquires at least one comparison condition information related to a color conversion condition to be compared that is different from the reference color conversion condition; and the reference condition acquired by the reference condition information acquisition unit Predicting the first color reproduction characteristics under the reference color conversion condition based on the information, and under the color conversion condition of the comparison target based on the comparison condition information acquired by the comparison condition information acquisition unit A color reproduction characteristic prediction unit that predicts a second color reproduction characteristic; and the color reproduction prediction unit that is predicted by the color reproduction prediction unit based on the first color reproduction characteristic that is predicted by the color reproduction characteristic prediction unit. A comparison evaluation unit that compares and evaluates two-color reproduction characteristics based on a predetermined comparison condition, and a display image generation unit that generates a result display image for visualizing an evaluation result by the comparison evaluation unit .

  As described above, the first color reproduction characteristic under the reference color conversion condition is predicted based on the reference condition information, and the second color reproduction characteristic under the color conversion condition to be compared is calculated based on the comparison condition information. Since a color reproduction characteristic prediction unit for prediction and a comparison evaluation unit for comparing and evaluating the predicted second color reproduction characteristic based on a predetermined comparison condition based on the predicted first color reproduction characteristic are provided. The degree of influence on the color reproduction characteristics of the printed matter due to the change of the color conversion condition can be grasped in direct comparison with the color conversion condition before the change. And an operator can grasp | ascertain at a glance by producing the result display image for visualizing the evaluation result by comparative evaluation.

  The device color signal is a signal associated with a usage amount of a plurality of color materials, and the plurality of color materials includes an achromatic color material and a plurality of chromatic color materials, and the plurality of chromatic colors It is preferable that the color in the printing using the achromatic material can be reproduced by combining the materials.

  Further, the color conversion condition to be compared is different from the reference color conversion condition in that the total use amount of the plurality of color materials is different in a predetermined color range and is substantially equal on the device-independent color space. Color conversion conditions for reproducing colors are preferable.

  Furthermore, it is preferable that the color conversion condition to be compared is a color conversion condition in which a total amount of the plurality of color materials used is small in a predetermined color range as compared with the reference color conversion condition.

  Furthermore, it is preferable that the predetermined comparison condition includes at least one of color difference, tone curve continuity and smoothness, and gamut range.

  Further, the result display image is an image in which the signal value of each pixel is determined so that the evaluation result relating to the color corresponding to each pixel of the input image signal can be visualized and discriminated. Is preferred.

  Furthermore, it is preferable to further include a display unit that displays the result display image created by the display image creation unit.

  Further, a color conversion processing unit that converts the input image signal into the device color signal based on a color conversion condition selected from the reference color conversion condition and at least one color conversion condition to be compared. It is preferable to further have.

  The color conversion method according to the present invention is a method for determining a color conversion condition for converting an input image signal into a device color signal corresponding to printing, and acquiring reference condition information relating to a reference color conversion condition. A first acquisition step, a second acquisition step of acquiring at least one comparison condition information relating to a color conversion condition to be compared different from the reference color conversion condition, and the reference color conversion based on the acquired reference condition information Predicting the first color reproduction characteristics under the conditions, and predicting the second color reproduction characteristics under the color conversion conditions of the comparison target based on the acquired comparison condition information; A comparison evaluation step for comparing and evaluating the predicted second color reproduction characteristic based on a predetermined comparison condition with the first color reproduction characteristic as a reference, and an evaluation result in the comparison evaluation step are visualized Characterized in that it comprises a generation step of generating result display image Te.

  The program according to the present invention obtains reference condition information relating to a reference color conversion condition by using a computer to determine a color conversion condition for converting an input image signal into a device color signal corresponding to printing. Based on the reference condition information acquired by the acquisition unit, the comparison condition information acquisition unit that acquires at least one comparison condition information regarding a color conversion condition to be compared that is different from the reference color conversion condition, and the reference condition information acquisition unit The first color reproduction characteristic under the reference color conversion condition is predicted, and the second color reproduction under the color conversion condition to be compared based on the comparison condition information acquired by the comparison condition information acquisition unit A color reproduction characteristic prediction unit that predicts characteristics, and a color reproduction prediction unit that is predicted by the color reproduction prediction unit based on the first color reproduction characteristic predicted by the color reproduction characteristic prediction unit. A comparison evaluation unit that compares and evaluates the second color reproduction characteristics based on a predetermined comparison condition, and a display image generation unit that generates a result display image for visualizing an evaluation result by the comparison evaluation unit .

  According to the color conversion device, the color conversion method, and the program according to the present invention, the first color reproduction characteristic under the reference color conversion condition is predicted based on the reference condition information, and the comparison target information is calculated based on the comparison condition information. The second color reproduction characteristic under the color conversion condition is predicted, and the second color reproduction characteristic is compared and evaluated based on the predetermined comparison condition with the first color reproduction characteristic as a reference. The degree of influence on the color reproduction characteristics of the printed matter due to the change can be grasped in direct comparison with the color conversion conditions before the change. And an operator can grasp | ascertain at a glance by producing the result display image for visualizing the evaluation result by comparative evaluation.

1 is a schematic explanatory diagram of a printing system incorporating a color conversion apparatus according to the present embodiment. It is an electrical schematic block diagram of the color conversion apparatus shown in FIG. It is a figure showing an example of the setting screen of a change parameter. 3 is a flowchart provided for explaining the operation of the color conversion apparatus shown in FIG. 1. FIG. 5A is a schematic explanatory diagram showing a correspondence relationship between ink types and their usage before each conversion. FIG. 5B is a schematic explanatory diagram showing the correspondence between the ink type and the amount of use after the GCR conversion process. FIG. 5C is a schematic explanatory diagram illustrating a correspondence relationship between the ink type and the usage amount after the IGCR conversion processing. It is a schematic explanatory drawing showing the uniform color range on a device independent color space. FIG. 7A is a graph showing the conversion characteristics of a normal color conversion table that reproduces the gray color. FIG. 7B is a graph showing the conversion characteristics of the GCR conversion table that reproduces the gray color. FIG. 7C is a graph showing the conversion characteristics of the IGCR conversion table that reproduces the gray color. It is a screen figure showing the 1st example of the result display image produced in the result display image creation part of FIG. 9A to 9C are screen diagrams showing a second example of the result display image created by the result display image creation unit of FIG.

  Hereinafter, preferred embodiments of a color conversion method according to the present invention in relation to a color conversion apparatus and a printing system that implement the color conversion method will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a schematic explanatory diagram of a printing system 10 incorporating a color conversion apparatus according to the present embodiment.

  The printing system 10 basically includes a color conversion device 12, a printing device 14, a DTP (Desktop Publishing) device 16, and a database server 18. The color conversion device 12, the DTP device 16, and the database server 18 are electrically connected to each other by wire or wireless.

  The color conversion device 12 converts an input image signal (device color signal or page description data) from an external device into a device color signal suitable for printing by the printing device 14. Further, the color conversion device 12 outputs the converted device color signal to the printing device 14 side. Here, the device color signal means an image signal defined by device-dependent data. For example, raster format data (TIFF, bitmap, RAW) having four (CMYK) or three (RGB) color channels. Etc.). Further, as the device color signal supplied to the printing apparatus 14, unique format data with an arbitrary header added may be used.

  The printing device 14 is electrically connected to the color conversion device 12. For this connection, for example, a serial interface such as USB (Universal Serial Bus), IEEE 1394, Ethernet (registered trademark), a wireless network, or a parallel interface such as Centronics can be applied.

  The printing device 14 is a so-called inkjet printer that forms an image on the medium by ejecting ink droplets from the recording head 20 while conveying a medium (recording medium) (not shown) in a predetermined direction. As the substrate of the media, paper such as synthetic paper, cardboard, and aluminum vapor-deposited paper, resin such as vinyl chloride and PET, tarpaulin, and the like can be used.

  The recording head 20 has four types of color materials of different colors {C ink 22c (chromatic color material), M ink 22m (chromatic color material), Y ink 22y (chromatic color material), and K ink 22k (achromatic color material)}. Are composed of four line heads 24c, 24m, 24y, and 24k for discharging the droplets. Hereinafter, the C ink 22c, the M ink 22m, the Y ink 22y, and the K ink 22k may be collectively referred to as the ink 22.

  Each line head 24c, 24m, 24y, 24k is formed with a plurality of nozzles (not shown) arranged along the width direction of the medium. The C ink 22c, M ink 22m, Y ink 22y, and K ink 22k are accommodated in ink tanks 26c, 26m, 26y, and 26k as containers, respectively. The line head 24c discharges the C ink 22c supplied from the ink tank 26c through the plurality of nozzles. The line head 24m discharges the M ink 22m supplied from the ink tank 26m through the plurality of nozzles. The line head 24y discharges the Y ink 22y supplied from the ink tank 26y through the plurality of nozzles. The line head 24k discharges the K ink 22k supplied from the ink tank 26k through the plurality of nozzles.

  Note that various methods can be adopted as an ink droplet ejection mechanism by the recording head 20. For example, a method of ejecting ink droplets by deformation of an actuator composed of a piezo element (piezoelectric element) or the like may be applied. Further, a thermal jet method may be applied in which bubbles are generated by heating the ink 22 through a heating element such as a heater and ink droplets are ejected with the pressure. Further, the recording head 20 may not be a line head but may be a multi-pass method.

  The DTP device 16 can edit a material composed of characters, figures, patterns, photographs, and the like, and generates an electronic manuscript in a page description language (hereinafter referred to as PDL) by arranging the material for each page. To do. Here, PDL is a language that describes image information such as text, graphics, and other format information, position information, and color information (including density information) within a “page” that is an output unit for printing and display. . The DTP device 16 performs rasterization processing on the electronic document in the PDL format. This rasterization processing includes data format conversion processing for converting from PDL format to raster format, and color conversion processing using an ICC (International Color Consortium) profile.

  The database server 18 is a device that manages data of electronic document job tickets {for example, JDF (Job Definition Format) files}, color sample data, target profiles, or device profiles suitable for a combination of the printing device 14 and media. is there.

  FIG. 2 is an electrical schematic block diagram of the color conversion device 12 shown in FIG.

  The color conversion device 12 includes a first interface 30, a control unit 32, a memory 34, a second interface 36, a display control unit 38, a third interface 40, and a display unit 42. The memory 34 stores a program for causing it to function as the color conversion apparatus according to the present embodiment.

  The first interface 30 transmits and receives electrical signals from external devices. For example, various data (device color signal, PDL data) edited and created by the DTP device 16 can be acquired. Various information such as an ICC profile managed and stored by the database server 18 can be acquired.

  The second interface 36 transmits and receives electrical signals to and from external devices. For example, a device color signal created inside the color conversion device 12 can be supplied to the printing device 14.

  The device color signal supplied to the printing apparatus 14 is associated with the usage amount of each ink 22 in the printing apparatus 14. This association can be arbitrarily designed for each color channel. For example, the usage amount “0%” may be assigned at the lowest gradation level, the usage amount “100%” may be assigned at the highest gradation level, and the usage amount may be assigned linearly at an intermediate level.

  The control unit 32 configured by an information processing device such as a CPU includes an image processing unit 44, an ink amount change table creation unit 46, a data acquisition unit 48, a color reproduction characteristic prediction unit 50, a comparative evaluation unit 52, And a screen creation unit 54.

  The image processing unit 44 performs a gradation conversion process according to a predetermined color conversion condition with a rasterization processing unit 56 having a rasterization function similar to that of the DTP device 16 (see FIG. 1), so that the ink 22 used for printing the printed material 28. An ink amount change processing unit 58 (color conversion processing unit) for changing the total usage amount.

  The ink amount change processing unit 58 uses the ink amount change table to convert only the signal value of the device color signal without changing the type of color plate (for example, CMYK signal data). Hereinafter, the device color signal before conversion may be referred to as “pre-conversion color signal”, and the device color signal after conversion may be referred to as “post-conversion color signal”.

  The ink amount change table creation unit 46 creates an ink amount change table to be used for processing in the ink amount change processing unit 58. Here, a GCR conversion table for executing GCR (Gray-Component Replacement) conversion or an IGCR conversion table for executing IGCR (Inverse Gray-Component Replacement) conversion is created. Details of the GCR conversion process and the IGCR conversion process will be described later.

  The data acquisition unit 48 includes a reference conversion table acquisition unit 60 (reference condition information acquisition unit) that acquires a reference conversion table as reference condition information related to a reference color conversion condition, and comparison condition information as a comparison target color conversion condition. A comparison conversion table acquisition unit 62 (comparison condition information acquisition unit) that acquires at least one comparison conversion table is further provided.

  The color reproduction characteristic prediction unit 50 predicts the color reproduction characteristic based on a predetermined color conversion table. Examples of predictable color reproduction characteristics include, but are not limited to, a tone curve as a gradation characteristic and a gamut as a color reproduction range.

  The comparative evaluation unit 52 uses the color reproduction characteristics predicted by the color reproduction characteristic prediction unit 50 as a reference and the color reproduction characteristics predicted by the color reproduction characteristic prediction unit 50 as a reference. The reproduction characteristics are comparatively evaluated based on predetermined comparison conditions. For example, the color reproduction characteristics based on the reference conversion table acquired by the reference conversion table acquisition unit 60 and the color reproduction characteristics using the comparison conversion table acquired by the comparison conversion table acquisition unit 62 are compared and evaluated.

  The screen creation unit 54 creates a screen to be displayed on the display unit 42 or various images constituting a part of the screen. The screen creation unit 54 includes a result display image creation unit 64 (display image creation unit) that creates a result display image for visualizing the evaluation result by the comparative evaluation unit 52.

  The memory 34 records a target profile and a device profile suitable for the printing apparatus 14. In addition, the memory 34 may record a pre-conversion color signal, a post-conversion color signal, and a color conversion table (GCR conversion table or IGCR conversion table) created by the ink amount change table creation unit 46.

  The display control unit 38 causes the display unit 42 to display various screens (including the setting screen 100 of FIG. 3) created by the screen creation unit 54 via the third interface 40. Further, the user interface (UI unit 66) is realized by using the display function of the display unit 42 and the input function of a pointing device (not shown).

  FIG. 3 is a screen diagram illustrating an example of the setting screen 100 displayed on the display unit 42 of FIG.

  The setting screen 100 inputs a first input unit 102 for inputting the type of device profile and a parameter for changing the total usage amount of the ink 22 (hereinafter referred to as “ink amount change parameter” or simply “change parameter”). Second input units 104 and 106, a third input unit 108 for inputting the name of an image file to be printed, a fourth input unit 110 for inputting the type of target profile, and evaluation result images to be described later in windows 120 and 150 [Result Preview] button 112 for instructing display (see FIGS. 8 to 9C) and [Create] button for creating an ink amount change table in accordance with the input values of change parameters in the second input units 104 and 106 114.

  The color conversion device 12 according to the present embodiment is configured as described above. Next, the operation of the color conversion device 12 will be described with reference to the flowchart of FIG.

  First, the color conversion device 12 sets and inputs an image signal and a profile (step S1). For example, when an image file name to be printed is input via the third input unit 108 (see FIG. 3), the image signal associated with the image file name is supplied to the result display image creation unit 64. When the target profile type is input via the fourth input unit 110 (same reference), the reference conversion table acquisition unit 60 reads the target profile recorded in the memory 34, and the color conversion table included in the target profile. To get.

  Next, the reference conversion table acquisition unit 60 acquires a reference conversion table as reference condition information (step S2). For example, when the type of the device profile of the printing apparatus 14 is input via the first input unit 102 (see FIG. 3), the reference conversion table acquisition unit 60 reads the device profile recorded in the memory 34, and the device profile Obtains a predetermined color conversion table.

  Next, the color conversion device 12 sets and inputs an ink amount change parameter via the second input units 104 and 106 (step S3).

  As illustrated in FIG. 3, the second input unit 104 includes a slide bar that extends in the horizontal direction of the setting screen 100. On the other hand, the second input unit 106 includes a text box. The change parameter expressed in percentage units can be set in a range of −50 to 100%, and a value of 0% corresponds to the reference conversion table. When the value of the change parameter is positive, it represents a state where the total amount of ink 22 used is small compared to the reference conversion table. On the other hand, when the value of the change parameter is negative, it represents a state in which the total amount of ink 22 used is large compared to the reference conversion table. That is, the larger the absolute value of the change parameter, the greater the ink change amount (increase / decrease amount). For example, one of the second input units 104 and 106 is changed in accordance with the changing operation, and the instruction values of both are always matched.

  Next, the comparison conversion table acquisition unit 62 acquires a comparison conversion table as comparison conversion condition information (step S4). The ink amount change table creation unit 46 creates a comparison conversion table in which the total usage amount of the ink 22 is changed using the reference conversion table acquired in step S2 and the change parameter input in step S3. Here, various design methods (algorithms or image design policies) may be adopted as a method for creating the comparison conversion table. However, it is desirable to reproduce substantially equal colors in a device-independent color space in a predetermined color range in order to directly compare the quality of the color reproduction characteristics with respect to the reference conversion table.

  Here, the device-independent color space is a color space that does not depend on the input / output device. Specific examples include color systems such as HSV (Hue-Saturation-Value), HLS (Hue-Lightness-Saturation), CIELAB, CIEUV, and XYZ.

  As in the present embodiment (see the printing apparatus 14 in FIG. 1), by combining a plurality of chromatic color materials C ink 22c, M ink 22m, and Y ink 22y, K ink 22k that is an achromatic color material is used. When the color on the printed material 28 can be reproduced, the GCR conversion process and the IGCR conversion process are particularly effective.

  The “GCR conversion process” in this specification means that the total use amount of the ink 22 is small in a predetermined color range as compared with the process result based on the reference color conversion condition, and is substantially in the device-independent color space. Color conversion processing that reproduces the same color. In addition, the “IGCR conversion process” means that the total amount of ink 22 used in a predetermined color range is larger than that of the process result based on the reference color conversion condition, and substantially the same color in the device-independent color space. Color conversion processing that reproduces.

  Hereinafter, an outline of the GCR conversion process and the IGCR conversion process will be described with reference to FIGS. 5A to 7C.

  FIG. 5A is a schematic explanatory diagram showing a correspondence relationship between ink types and their usage before each conversion. FIG. 5B is a schematic explanatory diagram showing the correspondence between the ink type and the amount of use after the GCR conversion process. FIG. 5C is a schematic explanatory diagram illustrating a correspondence relationship between the ink type and the usage amount after the IGCR conversion processing.

  In FIG. 5B, the amounts of C ink 22c, M ink 22m, and Y ink 22y are reduced by ΔC, ΔM, and ΔY, respectively, as compared to FIG. 5A. Then, the K ink 22k is increased by ΔK in order to cancel out the decrease in density caused by the decrease in each ink 22. As a result, the total amount of ink 22 used can be reduced by (ΔC + ΔM + ΔY−ΔK) while making the color reproduction on the printed matter 28 (see FIG. 1) substantially constant.

  In FIG. 5C, the amounts of C ink 22c, M ink 22m, and Y ink 22y are increased by ΔC, ΔM, and ΔY, respectively, as compared to FIG. 5A. The K ink 22k is decreased by ΔK in order to cancel out the density increase caused by the increase in the amount of each ink 22. As a result, the total amount of ink 22 used is increased by (ΔC + ΔM + ΔY−ΔK) while color reproduction on the printed matter 28 (see FIG. 1) is substantially constant. As a result, the coverage of the dots to be formed is increased, and the graininess is generally improved.

  FIG. 6 is a schematic explanatory diagram showing the color matching range R on the device-independent color space. In the present embodiment, the ink 22 has four types of CMYK. In this figure, for convenience of explanation, it is described as three types of CMK.

Let P be the point corresponding to the device color signal value before conversion. In the device-independent color space (for example, L ^* a ^* b ^* color space), a range where the color difference Δe from the color value corresponding to the point P is equal to or less than a predetermined value (for example, 0.5) is equal color range R And That is, in this color conversion process, an arbitrary device color signal within the color matching range R is treated as being the same color as the point P.

  As shown in the figure, the color within the color matching range R of the point P and having the maximum K value (unit%) is defined as a point Q1. A GCR conversion table is created by determining a point Q1 for each point P on the device-dependent color space. Further, a color that is within the same color range R of the point P and has the smallest K value (unit%) is defined as a point Q2. An IGCR conversion table is created by determining a point Q2 for each point P on the device-independent color space.

Various known search algorithms may be adopted as a method for determining the points Q1 and Q2. For example, after calculating L ^* a ^* b ^* color values for all neighboring colors of the point P using the device profile of the printing apparatus 14, an optimal CMYK combination that satisfies the constraint conditions may be determined. In this case, the determination may be made in consideration of not only the color approximation but also the gradation characteristics (for example, the continuity / smoothness of the gradation curve).

  The characteristics of the GCR conversion table and the IGCR conversion table thus obtained will be described. 7A to 7C are graphs showing the conversion characteristics of the color conversion tables expressing the gray system colors. The horizontal axis of each graph represents the color signal value (unit%) before conversion, and the vertical axis of each graph represents the color signal value (unit%) after conversion.

  FIG. 7A is a graph showing conversion characteristics of a normal color conversion table. This graph shows a straight line with a slope slightly less than 1 rather than an equality transformation (Y = X). This is because the total amount of ink 22 used is limited to less than 400%. The usage amount of each ink 22 is the same at each gray level.

  FIG. 7B is a graph showing the conversion characteristics of the GCR conversion table. With respect to the K value, equivalence conversion (Y = X) is performed in the range of 0 ≦ K ≦ Th1. When K ≧ Th1, the slope of the curve becomes steep and saturates in a state close to 100 (%) in a range where the color signal value is high. With respect to other colors (for example, C value), equivalence conversion (Y = X) is performed in the range of 0 ≦ C ≦ Th1. When K ≧ Th1, the slope of the curve becomes gentle and increases monotonously up to the maximum range (100%). In the range exceeding Th1, the ratio of K is larger than the ratio of other colors (C, M, Y). That is, as understood from FIG. 7B, the GCR conversion table has an effect of reducing the total amount of ink 22 used in the range of Th1 to 100 (%).

  FIG. 7C is a graph showing the conversion characteristics of the IGCR conversion table. The K value is always 0 (%) in the range of 0 ≦ K ≦ Th2. When K ≧ Th2, it becomes non-zero and increases rapidly. Regarding other colors (for example, C value), in the range of 0 ≦ C ≦ Th2, it is a monotonously increasing function that is convex upward, and the maximum value (100%) is obtained when C = Th2. When K ≧ Th2, it decreases gradually. The ratio of K is smaller than the ratio of other colors (C, M, Y) over the entire range. That is, as understood from FIG. 7C, the IGCR conversion table has an effect of increasing the total amount of ink 22 used in the range of 0 to 100 (%).

  In this way, the ink amount change table creation unit 46 creates a GCR conversion table or an IGCR conversion table. Then, the comparison conversion table acquisition unit 62 acquires the comparison conversion table from the ink amount change table creation unit 46. Further, a comparative conversion table created in advance may be recorded in the memory 34 (or stored / managed by the database server 18), and read out as necessary.

  Next, referring back to FIG. 4, the color reproduction characteristic prediction unit 50 predicts the color reproduction characteristic of the printed material 28 under the standard color conversion conditions based on the reference conversion table acquired from the reference conversion table acquisition unit 60 ( Step S5). As the color reproduction characteristics predicted here, a tone curve as a gradation characteristic and a gamut as a color reproduction range may be used. Hereinafter, the color reproduction characteristics under the standard color conversion conditions are referred to as “first color reproduction characteristics”.

  Next, the color reproduction characteristic predicting unit 50 predicts the color reproduction characteristic of the printed material 28 under the color conversion condition to be compared based on the comparison conversion table acquired from the comparison conversion table acquiring unit 62 (step S6). As will be described later, in order to be able to directly compare the two, it is preferable to use the same prediction method as the method in step S5. Hereinafter, the color reproduction characteristics under the color conversion conditions to be compared are referred to as “second color reproduction characteristics”.

  Next, the comparative evaluation unit 52 compares and evaluates the second color reproduction characteristic based on a predetermined evaluation condition with the first color reproduction characteristic as a reference (step S7). The predetermined comparison condition includes at least one of color difference, tone curve continuity and smoothness, and gamut range.

When the comparison condition is a color difference, L ^* a ^* b ^* corresponding to a predetermined device color signal may be calculated and evaluated based on whether these color differences exceed a predetermined threshold. When the comparison condition is continuity of the tone curve, the evaluation may be performed based on whether or not there is a color shift (color inversion) around each color. When the comparison condition is the smoothness of the tone curve, the evaluation may be performed based on the numerical values of the first and second derivatives of the gradation curve. When the comparison condition is in the gamut range, the evaluation may be performed based on the shape, size, and boundary line.

  Moreover, as a result of the comparative evaluation, not only OK (equivalent) / NG (not equivalent) two-choice discrimination, but also three or more kinds of evaluation values, an integer or a real number may be used.

  Next, in response to the click operation of the “result preview” button 112 (see FIG. 3) by the operator, the display control unit 38 displays the result display image on the display unit 42 (step S8). Prior to display, first, the result display image creation unit 64 creates a result display image for visualizing the evaluation result by the comparative evaluation unit 52. Then, the screen creation unit 54 creates a screen including the result display image (window 120 in FIG. 8), and then supplies a control signal representing the screen to the display control unit 38 side. Then, the display control unit 38 causes the display unit 42 to display the window 120 together with the setting screen 100 via the third interface 40.

  FIG. 8 is a screen diagram illustrating a first example of the result display image created by the result display image creation unit 64 of FIG.

  On the window 120, a 3D map image 122 for visualizing a gamut difference, a 3D map image 124 for visualizing a difference in tone curve continuity, and an operation key 126 for rotating and displaying the 3D map images 122 and 124, , [Close] for displaying the window 120 and a displayed button 128 are arranged.

In the 3D map image 122, a three-dimensional coordinate system of L ^* a ^* b ^* is displayed. On this three-dimensional coordinate system, a gamut region 130 in the reference conversion table is arranged so as to overlap. In the lower part of the gamut region 130 (region close to the a ^* -b ^* plane), there is a colored region 132 (in this figure, a region with double hatching) filled with a predetermined color. Here, the coloring area 132 represents a color area that can be reproduced by the reference conversion table and cannot be reproduced by the comparison conversion table.

In the 3D map image 124, a three-dimensional coordinate system of L ^* a ^* b ^* is displayed. On this three-dimensional coordinate system, a gamut region 134 in the reference conversion table is arranged so as to overlap. In the central portion of the gamut area 134 (area close to the L ^* axis), there is a colored area 136 (in this figure, a single hatched area) filled with a predetermined color. Here, the colored region 136 represents a color region in which the continuity of the tone curve in the comparative conversion table is not sufficient.

  That is, when the colored regions 132 and 136 do not exist (or are small), it can be determined that the color reproduction characteristics under the color conversion conditions to be compared are equivalent to the color reproduction characteristics under the reference color conversion conditions. . When the colored regions 132 and 136 are large, it can be determined that the color reproduction characteristics under the color conversion conditions to be compared are inferior to the color reproduction characteristics under the reference color conversion conditions. Thus, by checking the 3D map images 122 and 124, the operator can grasp at a glance the degree of influence on the color reproduction characteristics of the printed matter 28 due to the change of the color change condition.

Note that the 3D map images 122 and 124 can be rotated counterclockwise (or clockwise) about the L ^* axis by clicking the icon 138 (or icon 140). Thereby, the presence of the colored regions 132 and 136 can be confirmed from all directions of the gamut regions 130 and 134.

  By the way, the display method in the example of FIG. 8 is suitable for grasping the quality of the color reproduction characteristics of the entire gamut, but does not represent the color reproduction characteristics of the printed material 28 actually printed. Therefore, it may be configured so that the correspondence with the image (image signal) to be printed can be easily grasped.

  9A to 9C are screen diagrams illustrating a second example of the result display image created by the result display image creation unit 64 of FIG. In practice, a color image is displayed in the window 150, but for convenience of explanation, the color is omitted and only the outline is drawn.

  In FIG. 9A, a preview image 152 when color conversion processing is performed using the reference conversion table is displayed at the center of the window 150. Below that, a check box 154 and a button 156 displayed as [Close] are provided. Here, in response to the click operation of the [Close] button 156 by the operator, the window 150 is closed and hidden.

  For example, it is assumed that the value of the change parameter is set to 100% (the ink reduction amount is maximum) via the second input units 104 and 106 (see FIG. 3). When the operator performs a click operation on the check box 154, a check mark is added to the check box 158 as shown in FIG. 9B, and the 2D map image 160 is displayed instead of the preview image 152.

  In the 2D map image 160, the value of the pixel (unit region) corresponding to the color belonging to the colored region 132 (see FIG. 8) is a color signal value corresponding to gray (for example, 8-bit gradation display, R = G = B = 30) and displayed (area shown by double hatching). Further, in the 2D map image 160, the value of the pixel corresponding to the color belonging to the colored region 136 (same reference) is a value corresponding to a value corresponding to blue (for example, 8-bit gradation display, R = G = 0) , B = 255). Thereby, the operator can grasp at a glance whether the color reproduction characteristic is good or bad while assuming the printed matter 28 to be actually printed.

  On the other hand, it is assumed that the value of the change parameter is set to 30% via the second input units 104 and 106 (see FIG. 3). When the operator performs a click operation on the check box 154, a 2D map image 162 is displayed instead of the preview image 152 as shown in FIG. 9C. Since the 2D map image 162 has few pixels that are replaced with gray or blue, the operator gives the color reproduction characteristics even when using the comparison conversion table (the change parameter is 30%) instead of the reference conversion table. It can be judged that there is little influence.

  In the result display image of the second example, the signal value of each pixel is determined (that is, colored) so that the evaluation result relating to the color corresponding to each pixel of the input image signal can be visualized and discriminated. This is convenient because the operator can easily grasp whether the color reproduction characteristics are good or not while simulating the printed matter 28.

  Next, the display control unit 38 determines whether or not a predetermined input instruction has been received from the UI unit 66 (step S9). If there is no instruction, the process returns to step S8 and continues to display the windows 120 and 150 until the instruction is accepted.

  On the other hand, when there is a new change parameter input instruction from the second input unit 104 or 106, the process returns to step S3, and the color conversion device 12 sets again a new change parameter that is the same as or different from the previous change parameter. ·input. Thereafter, steps S3 to S9 are repeated. In other words, the operator gradually changes the total amount of ink 22 used, and allows printing with this color reproduction characteristic while checking the presence of the colored regions 132 and 136 on the 3D map images 122 and 124. Determine if you can.

  Instead of the worker, the color conversion device 12 may make a determination based on a predetermined determination criterion determined in advance. Further, as a result of determining that it is not appropriate, a warning to that effect may be displayed on the display unit 42.

  Finally, the ink amount change table is determined according to the click operation of the [Create] button 114 (see FIG. 3) by the operator (step S10). Specifically, a comparison change table corresponding to the confirmed change parameter is recorded in the memory 34. Alternatively, the color conversion device 12 may transmit the comparison change table to the database server 18 side via the first interface 30.

  As described above, the first color reproduction characteristic under the reference color conversion condition is predicted based on the reference conversion table, and the second color reproduction characteristic under the color conversion condition to be compared is predicted based on the comparison conversion table. 3D map images 122 and 124 (2D map images 160 and 162) for comparing and evaluating the second color reproduction characteristic based on a predetermined comparison condition with the first color reproduction characteristic as a reference and visualizing the evaluation result Therefore, it is possible to grasp the degree of the influence on the color reproduction characteristics of the printed matter 28 due to the change of the color conversion condition in direct comparison with the color conversion condition before the change. Then, by creating the 3D map images 122 and 124 (2D map images 160 and 162) for visualizing the evaluation result by the comparative evaluation, the operator can grasp at a glance.

  In addition, this invention is not limited to embodiment mentioned above, Of course, it can change freely in the range which does not deviate from the main point of this invention.

  For example, in the present embodiment, the color conversion process is performed using the color conversion table, but the processing form is not limited, and for example, a learning model such as a neural network may be used as well as a conversion matrix and a conversion equation. . In this case, the information regarding the color conversion condition may be any of LUT (Look Up Table), matrix elements, function expressions, coefficients, and various information for constructing a learning model.

  In the present embodiment, the description has mainly focused on CMYK (four color plates), but the present invention is not limited to this, and the design can be changed to any color plate type and plate number. For example, a standard ink of CMYK may be combined with an optional ink such as light colors such as LC and LM and W (white).

  Furthermore, the printing apparatus 14 is not limited to an ink jet printer, and it goes without saying that the present invention can be applied to any system (for example, an electrophotographic system) in which a color material is deposited on a medium to form dots.

DESCRIPTION OF SYMBOLS 10 ... Printing system 12 ... Color conversion apparatus 14 ... Printing apparatus 16 ... DTP apparatus 18 ... Database server 22 ... Ink 32 ... Control part 34 ... Memory 38 ... Display control part 42 ... Display part 46 ... Ink amount change table preparation part 48 ... Data acquisition unit 50 ... color reproduction characteristic prediction unit 52 ... comparison evaluation unit 58 ... ink amount change processing unit 60 ... reference conversion table acquisition unit 62 ... comparison conversion table acquisition unit 64 ... result display image creation unit 100 ... setting screen 120, 150 ... windows 122, 124 ... 3D map images 130, 134 ... gamut areas 132, 136 ... colored areas 160, 162 ... 2D map images

Claims (9)

A color conversion device that determines a color conversion condition for converting an input image signal into a device color signal corresponding to printing,
A reference condition information acquisition unit for acquiring reference condition information on a reference color conversion condition;
A comparison condition information acquisition unit that acquires at least one comparison condition information regarding a color conversion condition to be compared that is different from the reference color conversion condition;
Based on the reference condition information acquired by the reference condition information acquisition unit, the first color reproduction characteristic under the reference color conversion condition is predicted, and the comparison condition information acquired by the comparison condition information acquisition unit A color reproduction characteristic prediction unit that predicts a second color reproduction characteristic under the color conversion condition of the comparison target based on
A comparative evaluation unit that compares and evaluates the second color reproduction characteristic predicted by the color reproduction characteristic prediction unit based on a predetermined comparison condition with the first color reproduction characteristic predicted by the color reproduction characteristic prediction unit as a reference. When,
A display image creation unit for creating a result display image for visualizing the evaluation result by the comparative evaluation unit,
The color conversion conditions of the comparison are compared to the color conversion conditions of the reference, unlike the total amount of color materials multiple Te predetermined color range odor, and, substantially equal color in a device-independent color space Is a color conversion condition that reproduces
A color conversion device characterized in that the total amount of use of the plurality of color materials is variable. The color conversion device according to claim 1,
The device color signal is a signal associated with the amount of the plurality of color material,
The plurality of color materials include an achromatic color material and a plurality of chromatic color materials, and the colors in the printing using the achromatic color material can be reproduced by combining the plurality of chromatic color materials. A color conversion device characterized by the above. The color conversion device according to claim 1,
The color conversion apparatus according to claim 1, wherein the color conversion condition to be compared is a color conversion condition in which a total use amount of the plurality of color materials is less in a predetermined color range than the reference color conversion condition. The color conversion apparatus according to any one of claims 1 to 3,
The color conversion device according to claim 1, wherein the predetermined comparison condition includes at least one of a color difference, a continuity and smoothness of a tone curve, and a gamut range. In the color conversion device according to any one of claims 1 to 4,
The result display image is an image in which a signal value of each pixel is determined so that the evaluation result regarding the color corresponding to each pixel of the input image signal can be visualized and discriminated. Color conversion device. In the color conversion device according to any one of claims 1 to 5,
The color conversion apparatus further comprising a display unit that displays the result display image created by the display image creation unit. The color conversion device according to any one of claims 1 to 6,
A color conversion processing unit that converts the input image signal into the device color signal based on a color conversion condition selected from the reference color conversion condition and at least one color conversion condition to be compared; A color conversion device comprising: A color conversion method for determining a color conversion condition for converting an input image signal into a device color signal corresponding to printing,
A first acquisition step of acquiring reference condition information relating to a reference color conversion condition;
A second acquisition step of acquiring at least one comparison condition information regarding a color conversion condition to be compared that is different from the reference color conversion condition;
Based on the acquired reference condition information, the first color reproduction characteristic under the reference color conversion condition is predicted, and based on the acquired comparison condition information, the first color reproduction characteristic under the color conversion condition of the comparison target is predicted. A prediction step for predicting two-color reproduction characteristics;
A comparative evaluation step for comparing and evaluating the predicted second color reproduction characteristic based on a predetermined comparison condition based on the predicted first color reproduction characteristic;
Creating a result display image by visualizing the evaluation result in the comparative evaluation step,
The color conversion conditions of the comparison are compared to the color conversion conditions of the reference, unlike the total amount of color materials multiple Te predetermined color range odor, and, substantially equal color in a device-independent color space Is a color conversion condition that reproduces
A color conversion method characterized in that the total amount of use of the plurality of color materials is variable. In order to determine a color conversion condition for converting the input image signal into a device color signal corresponding to printing, the computer is
A reference condition information acquisition unit for acquiring reference condition information on a reference color conversion condition;
A comparison condition information acquisition unit that acquires at least one comparison condition information related to a color conversion condition to be compared that is different from the reference color conversion condition;
Based on the reference condition information acquired by the reference condition information acquisition unit, the first color reproduction characteristic under the reference color conversion condition is predicted, and the comparison condition information acquired by the comparison condition information acquisition unit A color reproduction characteristic prediction unit that predicts a second color reproduction characteristic under the color conversion condition of the comparison target based on
A comparative evaluation unit that compares and evaluates the second color reproduction characteristic predicted by the color reproduction characteristic prediction unit based on a predetermined comparison condition with the first color reproduction characteristic predicted by the color reproduction characteristic prediction unit as a reference. ,
Function as a display image creation unit for creating a result display image for visualizing the evaluation result by the comparative evaluation unit; and
The color conversion conditions of the comparison are compared to the color conversion conditions of the reference, unlike the total amount of color materials multiple Te predetermined color range odor, and, substantially equal color in a device-independent color space Is a color conversion condition that reproduces
A program for causing a total usage amount of the plurality of color materials to be variable.

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