JP6065363B2 - Image display device and printing device - Google Patents

Description

  The present invention relates to an image display device and a printing device.

A color conversion table in which color information in the output color system is associated with a plurality of grid points in the input color system is known. The color conversion table is used to convert image data expressed in an input color system into image data in an output color system (for example, a color material color system used by a printer). The image quality of the image reproduced by the image data converted by the color conversion table (represented as the image quality realized by the color conversion table) is different for each color conversion table. That is, even if an image of the same color is reproduced by the image data after color conversion, the image quality (for example, graininess) may be different if the color conversion table used for color conversion is different.
Here, a technique for displaying a color reproduction range of a device, a color distribution of an image, and the like on a monitor using an L ^* a ^* b ^* color system is known (see Patent Document 1).

JP 2006-180063 A

  As described above, the image quality realized by the color conversion table is different for each table. Therefore, in order to properly evaluate a color conversion table that has been generated or is being generated, it is necessary to grasp the degree of image quality that is realized. However, in order to grasp the level of image quality realized by the color conversion table, it is complicated to print and evaluate image data after color conversion by the color conversion table by a printer. Further, according to the above document, the color reproduction range of the device can be visually grasped through the monitor, but the various image quality levels realized by the color conversion table as described above cannot be visually grasped. .

  The present invention has been made to solve the above problems, and provides an image display device and a printing device capable of visually grasping the image quality realized by the color conversion table.

One aspect of the image display device according to the present invention is to acquire a color conversion table in which color information in the output color system is associated with a plurality of grid points in the input color system, and the acquired color conversion table the image representing at least graininess and black generation whether the constant of device-independent color system own the a indicator of image quality based on the color information, it is constituted to be displayed on a predetermined display unit.
According to this configuration, the user can visually recognize, via the display unit, an image in which the granularity that is an index of image quality realized by the color conversion table and the occurrence of black are expressed in the device-independent color system. Therefore, the color conversion table can be evaluated easily and properly.

  As one aspect of the present invention, the image display device may express the graininess by the density of points indicated in the device-independent color system. According to this configuration, by visually recognizing the density of the points distributed in the device-independent color system, it is easy to determine in which range the color reproduction range based on the color conversion table has poor graininess (graininess is noticeable). Can know.

  As one aspect of the present invention, the image display device may express the difference in the black dot size determined based on the color information when expressing the occurrence of black. According to this configuration, what kind of dot size (black) occurs in the color reproduction range according to the color conversion table by visually recognizing information indicating the occurrence or non-occurrence of black distributed in the device-independent color system. You can also know.

  As one aspect of the present invention, the image display device may express the index only in a range having an index that does not satisfy a predetermined criterion regarding image quality in the device-independent color system. According to this configuration, it is possible to grasp a range in which the image quality is low (for example, the graininess is poor) in the color reproduction range based on the color conversion table in the device-independent color system.

  As one aspect of the present invention, the image display device is an index of the image quality, wherein one or more indicators of gradation, ink amount used, non-color constancy, and glossiness are displayed in a predetermined table. An image expressed by gradation in the color system may be further displayed. According to this configuration, in addition to the presence or absence of the above-described graininess and blackness, various indicators such as gradation, amount of ink used, non-color constancy, and glossiness can be visually grasped through the display unit. Can easily and legitimately evaluate the color conversion table.

  As one aspect of the present invention, when the image display device receives a change instruction for the presence or absence of the occurrence of black by an operation on the image displayed on the display unit, the color that has changed the occurrence of black according to the change instruction. The conversion table may be generated. According to this configuration, the user can easily obtain a color conversion table in which the black generation conditions are optimized by performing a desired operation on the display unit on which the image is displayed.

As one aspect of the present invention, the image display device, when receiving an instruction to improve the graininess by an operation on the image displayed on the display unit, displays the image data expressed in the input color system. On the other hand, color conversion processing using the color conversion table and predetermined image processing for improving graininess may be performed. Further, the image display device uses the color conversion table for the image data expressed in the input color system when the color conversion table has auxiliary information corresponding to an instruction to improve the graininess. Predetermined image processing for improving color conversion processing and graininess may be performed. According to this configuration, even when the image quality realized by the color conversion table is not satisfactory in terms of graininess, the user can substantially combine the color conversion process using the color conversion table and the above image process. In particular, an image with good graininess can be obtained.

  The technical idea according to the present invention is not realized only in the form of an image display device. For example, the invention of an image display method having processing steps executed by the above-described image display device and the above-described image display device are realized. It is also possible to grasp the invention of an image display program that causes predetermined hardware (computer) to execute the function to be performed. Further, the image display device may exist alone, or may be realized as a system including a plurality of devices, or may be incorporated as a part of another device (for example, a printing device). .

It is a figure which shows the hardware constitutions and software constitution of an apparatus. It is a figure which illustrates a forward model converter and an inverse model initial stage LUT. It is a flowchart which shows the outline of a color conversion LUT creation process. It is a flowchart which shows the setting process of initial LUT. FIG. 6 is a diagram illustrating an initial LUT. It is a flowchart which shows the outline of an image quality parameter | index display process. It is a figure which shows an example of an image quality parameter | index display setting screen. It is a figure which shows an example of an image quality parameter | index display screen. It is a figure which shows the other example of an image quality parameter | index display screen. It is a figure which shows the other example of an image quality parameter | index display screen. It is a figure which shows the other example of an image quality parameter | index display screen. It is a figure which shows the other example of an image quality parameter | index display screen. It is a figure which illustrates a part of content displayed on an image quality index display screen. It is a figure which shows the other example of an image quality parameter | index display screen. It is a figure which illustrates a mode that the input tool which a user can operate on the image quality parameter | index display screen was displayed. FIG. 2 is a diagram illustrating a configuration of a printer as an image display device.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
1. FIG. 1 shows a hardware configuration and a software configuration of an image display apparatus 1 according to the present embodiment. The image display device 1 includes a computer 10 and a display 30 (display unit). The computer 10 and the display 30 may be configured integrally, such as a laptop PC or a tablet computer, or may be separate devices. In the computer 10, the CPU 12 reads a program stored in a storage unit such as a hard disk drive (HDD) 11, executes an operation according to the program while expanding the program in an internal memory such as the RAM 13, and the like. Each function of the setting unit 14, the ink amount determination unit 15, the color conversion LUT creation unit 16, the image quality index display unit 17, the image processing unit 18, the forward model converter FM, the glossiness converter SM, and the like is realized. Each of these functions will be described later.

  The HDD 11 stores a created color conversion lookup table (LUT) 400, an inverse model initial LUT 410, and the like. The color conversion LUT 400 is color information in an output color system (for example, the color system of ink used by the printer 20) for a plurality of grid points (coordinate values) in a predetermined input color system (for example, sRGB color system). 10 is a color conversion table in which (ink amount set) is associated. In this embodiment, as an example, a plurality of inks such as C (cyan) ink, M (magenta) ink, Y (yellow) ink, K (black) ink, Lc (light cyan) ink, and Lm (light magenta) ink are used. A printer 20 is assumed. The ink amount set is a combination of ink amounts (tone values) for each of the plurality of inks. The inverse model initial LUT 410 will be described later.

  The computer 10 also functions as a print control device by executing calculations according to a program and controlling the printer 20 as a printing device via a USB interface (I / F) 21 or the like. That is, in the computer 10, the image processing unit 18 acquires image data in which the color of each pixel is represented by the coordinate value of the input color system, and the image data is converted into a pixel using the created color conversion LUT 400. Color conversion is performed in units, and image data after color conversion (image data in which each pixel is represented by an ink amount set) is subjected to various image processing such as halftone processing and microweave processing to generate print data. It is also possible to output data to the printer 20 via the USB I / F 21 or the like. The printer 20 performs printing based on the print data. Of course, the computer 10 and the printer 20 may be connected by other interfaces such as infrared rays and wireless LAN. The computer 10 is connected to the display 30 via a video interface (I / F) 31, and is connected to an operation unit 40 such as a keyboard, a mouse, a touch pad, and a touch panel via an input interface (I / F) 41. ing.

As shown in FIG. 2A, the forward model converter FM includes a spectral printing model converter RC and a color converter CC. The forward model converter FM is a conversion model that converts an ink amount set into a color value (colorimetric value) of a device-independent color system. As shown in FIG. 2B, the inverse model initial LUT 410 is a conversion model that converts the color value of the device-independent color system into an ink amount set. In the present embodiment, the CIELAB color system is used as an example of a device-independent color system. Hereinafter, the color value of the CIELAB color system will be expressed as “L ^* a ^* b ^* ”.

The spectral printing model converter RC that forms the preceding stage of the forward model converter FM converts the ink amounts of a plurality of types of ink into spectral reflectances R (λ) of color patches that are printed according to the ink amounts. In the present specification, the term “color patch” is used in a broad sense including not only a chromatic color patch but also an achromatic color patch. The color converter CC constituting the subsequent stage of the forward model converter FM calculates the color value L ^* a ^* b ^* from the spectral reflectance R (λ) obtained by the spectral printing model converter RC. Conversion from the ink amount set to the color value using the forward model converter FM is performed by using a preset light source (for example, standard light D65 irradiated at an angle of 45 degrees with respect to the surface of the print paper to be observed) or printing. It is executed on the premise of observation conditions for paper (for example, glossy paper) and color patches (for example, an observation position facing the surface of the print paper to be observed). For the configuration and functions of the spectral printing model converter and the color converter, refer to JP-T-2007-511175 and JP-A-2008-263579 as appropriate.

The inverse model initial LUT 410 is obtained by, for example, dividing the L ^* a ^* b ^* space into a plurality of small cells and selecting and registering an optimum ink amount set for each small cell. This selection is performed in consideration of, for example, the image quality of the color patch printed with the ink amount set. In general, there are many ink amount sets that can reproduce one L ^* a ^* b ^* value. Therefore, in the inverse model initial LUT 410, the one that selects an optimal ink amount set from a desired viewpoint such as image quality is registered from among a large number of ink amount sets that reproduce substantially the same L ^* a ^* b ^* values. . The L ^* a ^* b ^* value that is the input value of the inverse model initial LUT 410 is a representative value of each small cell. On the other hand, the ink amount set as an output value reproduces any L ^* a ^* b ^* value in the cell. Therefore, in the inverse model initial LUT 410, the L ^* a ^* b ^* value that is the input value and the ink amount set that is the output value do not correspond exactly, and the ink amount set of the output value is converted to the forward model converter. When converted to an L ^* a ^* b ^* value by FM, a value slightly different from the input value of the inverse model initial LUT 410 is obtained. However, as the inverse model initial LUT 410, an input value and an output value that completely correspond to each other may be used. As a method of creating an inverse model initial LUT 410 by selecting an optimal ink amount set for each small cell, for example, a method described in Japanese Patent Publication No. 2007-511175 can be employed.

2. Color Conversion LUT Creation Processing In this embodiment, the image display apparatus 1 executes image display for evaluating the image quality realized by the color conversion LUT 400 on the display 30. First, the color to be evaluated is described below. A process for creating the conversion LUT 400 will be described.
FIG. 3 is a flowchart showing an outline of the color conversion LUT creation process executed by the computer 10 according to the program.
In step S100, an initial LUT 510 having a plurality of grid points to be determined for the ink amount set is set mainly by the function of the initial LUT setting unit 14.
FIG. 4 is a flowchart showing details of the process in step S100.
In step S110, the initial LUT setting unit 14 sets an initial value for creating the initial LUT 510 according to the operation of the operation unit 40 by the user.

  FIG. 5 shows an example of the configuration of the initial LUT 510 and its initial value setting. As an input value of the initial LUT 510, an input value in a predetermined input color system, for example, a value at substantially equal intervals predetermined as each value of RGB (red, green, blue) is set. Since one set of RGB values represents a point in the RGB color space, one set of RGB values corresponds to an input grid point in the initial LUT 510. In step S110, the initial value of the ink amount set for some small number of input grid points selected in advance from among the plurality of input grid points is input by the user. It is preferable to select at least an input grid point corresponding to a vertex of a three-dimensional color solid in the RGB color space as the input grid point to which the initial value is set. At the apex of this three-dimensional color solid, each RGB value takes the minimum value or the maximum value of the definition range. Specifically, when each RGB value is expressed by 8 bits, (R, G, B) = (0, 0, 0), (0, 0, 255), (0, 255, 0) , (255, 0, 0), (0, 255, 255), (255, 0, 255), (255, 255, 0), (255, 255, 255). The initial value of the set is set. The ink amounts for the input grid points of (R, G, B) = (255, 255, 255) are all set to zero. The initial value of the ink amount set for the other selected input grid points is arbitrary, and is set to 0, for example.

In step S120, the initial LUT setting unit 14 determines an ink amount set for other input grid points based on the initial value (FIG. 5) of the ink amount set. For example, the ink amount I _{j (R, G, B)} corresponding to a certain input grid point RGB is determined according to the following equations (1) and (2).




The subscript _{j of the} ink amount I _{j (R, G, B)} corresponds to each ink type constituting the ink amount set, and the ink types are C, M, Y, K, Lc as in this embodiment. , Lm, j = 1-6. The ink amounts I _{j (0,0,0)} , I _{j (0,0,255)} ... For the input grid points whose RGB values take 0 or 255 are values input in advance by the user in step S110. According to (1) and (2), it is possible to obtain the ink amount I _{j (R, G, B)} in any of the RGB values, the ink amount I _{j (R} in such an ink type _{basis, G , B)} is determined as an ink amount set for the arbitrary RGB value. Hereinafter, an ink amount set composed of the ink amounts I _j of the respective ink types C, M, Y, K, Lc, and Lm is expressed as (C, M, Y, K, Lc, Lm).

In step S130, the initial LUT setting unit 14 converts the ink amount set for each input grid point obtained by the processing up to step S120 into the color value L ^* a ^* b ^* using the forward model converter FM. As a result, each color value L ^* a ^* b ^* associated with each input grid point of the initial LUT 510 is obtained.

In step S140, the initial LUT setting unit 14 converts each color value L ^* a ^* b ^* obtained in step S130 into an ink amount set again using the inverse model initial LUT 410. The reason why the ink amount set is converted again using the inverse model initial LUT 410 is that the initial value of the ink amount set or the value of the ink amount set determined in step S120 reproduces the color value L ^* a ^* b ^*. It is because it is not necessarily a preferable value as a set. On the other hand, in the inverse model initial LUT 410, a preferable ink amount set in consideration of the image quality and the like is registered. If the color value L ^* a ^* b ^* is converted again into the ink amount set using this, the color value L A preferred ink amount set for realizing ^* a ^* b ^* can be obtained for each input grid point. However, step S140 may be omitted.

As a result of the processing in step S100 described above, an initial LUT 510 in which the following values are set is obtained.
Value of input grid point of initial LUT 510: (R, G, B)
Color value corresponding to each input grid point: (L ^* , a ^* , b ^* )
Ink amount set corresponding to each input grid point: (C, M, Y, K, Lc, Lm)
Since the ink amount set in the initial LUT 510 is optimized by processing to be described later, strict correctness is not required for these values. Therefore, the process of step S100 is not limited to the above-described process, and it is only necessary to obtain information defining a certain ink amount set as the initial LUT 510 for a plurality of input grid points in a predetermined input color system.

In step S200 (FIG. 3), the input grid points (target grid points) that are targets of the ink amount set determination process are sequentially selected from the input grid points of the initial LUT 510 mainly by the function of the ink volume determination unit 15. Then, an ink amount set determination process is performed for the selected target grid point by optimizing the ink amount set. A process for optimizing the ink amount set (C, M, Y, K, Lc, Lm) associated with one target grid point will be described. The ink amount determination unit 15, as an example, to optimize the ink amount set by obtaining the evaluation function E _p by the following equation (3).

The evaluation function E _p calculated for a certain ink amount set indicates that the smaller the value, the higher the overall printing performance (image quality) by the ink amount set. ψ represents an ink amount set (C, M, Y, K, Lc, Lm). The first term of the formula (3) is a term having a graininess index GI representing the graininess of the printed matter, and the second term is a noncoloring constant representing the non-color constancy (color inconstancy) with respect to the light source fluctuation of the printing color. The third term is a term having a gradation index SI representing the gradation property (smoothness of color change) of the printed matter, and the fourth term is an ink constituting the ink amount set. This is a term having a total ink amount index TI representing the sum of the amounts. Any term constituting the evaluation function E _p is a scalar normalized with the same scale (for example, 0 to 1.0), and the smaller the value, the higher the performance (image quality). Also, the first to fourth terms corresponding to each performance element are linearly combined while adjusting the weights with predetermined weighting factors w ₁ , w ₂ , w ₃ , w ₄ , so that the overall printing performance (image quality) is achieved. ) Defines an evaluation function E _p that can be evaluated.

Ink amount determining unit 15, evaluation ink amount sets the function E _p is minimized (C, M, Y, K , Lc, Lm) sequentially calculated for the target lattice point. For example, locally moving the ink amount sets the position of the ink amount space initial ink amount set in (ink amount set associated with the input grid points in the initial LUT 510), minimizing the evaluation function E _p when the The ink amount set to be calculated is calculated. By this, the position of the ink amount set in the ink amount space is modified in a direction that minimizes the evaluation function E _p. Furthermore, likewise locally moving the ink amount sets the position of the corrected, continue to calculate the ink amount sets which minimize the evaluation function E _p at that time. By repeatedly executing the above processing (for example, 200 times), the ink amount set for the target grid point is finally optimally set to a value where the evaluation function _Ep is extremely small (overall printing performance is high). The optimized ink amount set is determined as the ink amount set for the target grid point. The above movement of the ink amount set (updated) may be completed to optimize the ink amount set with to perform a specified number of times, and the optimization with the value of the evaluation function E _p is below a predetermined threshold value It may be completed.

In this optimization processing, it is necessary to calculate the evaluation function E _p for the ink amount sets (C, M, Y, K, Lc, Lm) that are sequentially updated. A graininess index GI, a color constancy index CII, a gradation index SI, and a total ink quantity index TI corresponding to the ink amount set are calculated, and an evaluation function _Ep is obtained. The spectral printing model converter RC and the color converter CC also predict the color value L ^* a ^* b ^* when performing optimization. In the present embodiment, the grid point optimization technique disclosed in Japanese Patent Application Laid-Open No. 2006-197080 can also be applied. In this case, a virtual force in the direction in which the evaluation function E _p is 0 is applied to each lattice point in the ink amount space, and the position of the lattice point in the ink amount space is converged to a steady state by the force. .

Note that the graininess index GI corresponding to the ink amount set can be calculated using various graininess prediction models, and can be calculated by, for example, the following equation (4).


In Equation (4), a _L is a brightness correction term, WS (u) is a winner spectrum of an image, VTF is a visual spatial frequency characteristic, and u is a spatial frequency. The granularity index GI obtains a power spectrum of a spatial wave existing in the image by Fourier-transforming image data obtained by imaging a color patch with a scanner or the like with respect to the image plane, and a visual spatial frequency characteristic VTF with respect to the power spectrum. Is calculated by convolving. In general, lightness image data is used as the image data. Thus, it can be said that the graininess index GI is a value obtained by accumulating the magnitude of the spatial wave of brightness existing in the color patch with respect to all the spatial frequencies in consideration of the weighting by the spatial frequency characteristic VTF. Therefore, it is possible to quantify the noticeable graininess. The contribution of the overall brightness to the graininess index GI is reduced by the brightness correction term a _L. For the calculation of the graininess index GI, the description of Makoto Fujino, Image Quality Evaluation of Inkjet Prints, Japan Hardcopy '99, p.291-294, JP-T-2007-511161 and JP-A-2008-263579 is described. Use.

The non-color constancy index CII corresponding to the ink amount set can be calculated by, for example, the following equation (5) using a color converter CC or the like.


In Expression (5), ΔL ^* indicates a lightness difference of the color patch under two different observation conditions (under different light sources), ΔC ^* _ab indicates a chroma difference, and ΔH ^* _ab indicates a hue difference. When calculating the non-color constancy index CII, the L ^* a ^* b ^* values under two different viewing conditions are converted to standard viewing conditions (eg, under the observation of standard light D65) using chromatic adaptation transformation (CAT). Converted. The calculation of the color constancy index CII is described in Billmeyer and Saltzman's Principles of Color Technology, 3rd edition, John Wiley & Sons, Inc, 2000, p.129, pp. 213-215, and Japanese Patent Application Laid-Open No. 2008-263579. Is used.

The gradation index SI corresponding to the ink amount set is, for example, a difference in color value (L ^* a ^* b) between a target grid point and a plurality of input grid points (a plurality of adjacent grid points) adjacent to the target grid point. ^* The average or minimum value of the distance in the color space. The color value L ^* a ^* b ^* of the adjacent grid point is obtained by inputting the ink amount set for the adjacent grid point to the forward model converter FM. Color value L ^* a ^* b ^* is also for the target lattice point are obtained by inputting the attachment of the (process of updating) the ink amount set is used to calculate the time evaluation function E _p in the forward model converter FM . Alternatively, the gradation index SI corresponding to the ink amount set is the difference in ink amount (difference between C inks) between the target grid point and a plurality of input grid points (a plurality of adjacent grid points) adjacent to the target grid point. M ink difference, Y ink difference, K ink difference, Lc ink difference, Lm ink difference).

The ink amount determination unit 15 performs an ink amount set determination process on all input lattice points of the initial LUT 510 as target lattice points.
In step S300 (FIG. 3), the color conversion LUT creation unit 16 creates the color conversion LUT 400 based on the initial LUT 510 after the ink amount set for each input grid point is determined by optimization as described above. In this case, the color conversion LUT creation unit 16 forwards the color value L ^* a ^* b ^* corresponding to the optimized ink amount set (C, M, Y, K, Lc, Lm) for each input grid point. Calculated by model converter FM. Then, an ink profile is created that describes the correspondence between the color values L ^* a ^* b ^* and the ink amount sets (C, M, Y, K, Lc, Lm) that correspond to each other. Then, the color conversion LUT creation unit 16 creates a color conversion LUT 400 based on the ink profile.

As described above, the color conversion LUT 400 is a color conversion table for converting, for example, coordinate values of the sRGB color system into combinations of ink amounts (ink amount sets) of a plurality of types of ink used by the printer 20. As for the sRGB color system, a correspondence relationship (sRGB profile) with the CIELAB color system is defined based on the CIE standard. Therefore, a predetermined number (for example, the cube of 16) of RGB values and the ink amount set (C, M) defined in the ink profile by the color value L ^* a ^* b ^* defined in the ink profile. , Y, K, Lc, Lm) by specifying and profiling the correspondence relationship, the color conversion LUT 400 can be created.

However, the color conversion LUT 400 created in this embodiment is not limited to the one that describes the correspondence between the sRGB color system and the ink color system (ink amount set), but the color value L ^* a ^* b ^* and the ink table. Ink color systems and other color systems, such as those describing the relationship between color systems (the above ink profiles), and describing the correspondence between CMY color systems and CMYK color systems and ink color systems It may be a description of the relationship with the system. The procedure for creating the color conversion LUT 400 described above is only an example, and any procedure can be used as long as it can create the color conversion LUT 400 in which an ink amount set is associated with a grid point of an input color system. May be adopted. Further, the image display device 1 does not necessarily have a function of creating the color conversion LUT 400. Even if the image display apparatus 1 does not create the color conversion LUT 400 itself, the image display apparatus 1 may hold the color conversion LUT 400 in a storage unit such as the HDD 11 or input and hold it from an external device.

3. Image Quality Index Display Processing Next, image quality index display processing for evaluating image quality by the color conversion LUT 400, which is executed by the image display device 1, will be described.
FIG. 6 is a flowchart showing an outline of image quality index display processing executed by the computer 10 according to the program. This process is mainly executed by the function of the image quality index display unit 17.
When the user operates the operation unit 40 at an arbitrary timing and instructs the computer 10 to start the image quality index display process, an image quality index display setting screen 31 as shown in FIG. 7 is displayed on the display 30 as an example. Is done.

  The user can arbitrarily select a color conversion LUT to be evaluated in the LUT selection field 31 a in the image quality index display setting screen 31 by operating the operation unit 40. In the selection field 31a, a list of color conversion LUTs that can currently be evaluated is displayed. The color conversion LUT is stored in the HDD 11 or the like, for example, for each model of the printer 20 or for each medium (printing paper) type used for printing.

Further, by operating the operation unit 40, the user can arbitrarily select a color system for displaying an index, which will be described later, in the display color system selection field 31b in the image quality index display setting screen 31. . Here, the L ^* a ^* b ^* color system or the sRGB color system can be selected. Further, the user operates the operation unit 40 to check one of a plurality of check boxes 31c provided in the image quality index display setting screen 31, thereby displaying a plurality of types displayed corresponding to each check box 31c. The index desired to be displayed graphically can be arbitrarily selected from these indices (granularity, K generation point, gradation, ink amount, color inconstancy, glossiness, etc.). Only one indicator or a plurality of indicators for graphic display may be selected. After finishing such selection, the user operates the operation unit 40 to click the OK button 31d in the image quality index display setting screen 31. As a result, the processing after step S400 is executed.

In step S400, the image quality index display unit 17 selects one color conversion LUT 400 selected as an evaluation target on the image quality index display setting screen 31 (for example, a color in which an ink amount set is associated with each grid point of the sRGB color system). The conversion LUT 400) is acquired (read) from the HDD 11 or the like.
In step S420, the image quality index display unit 17 acquires (calculates, etc.) the index selected on the image quality index display setting screen 31 based on the ink amount set specified for each grid point by the acquired color conversion LUT 400. . Here, it is assumed that “granularity” and “K generation point” are selected as an example. Since “granularity” means the first term (term having the granularity index GI) in the evaluation function, the image quality index display unit 17 sets the “granularity” for each ink amount set specified by the color conversion LUT 400. calculate. The “K generation point” means a grid point where the K ink amount is generated. The image quality index display unit 17 assigns a flag “1” indicating that there is a K ink amount to a lattice point where the K ink amount is not 0 in the ink amount set of the color conversion LUT 400, and the K ink amount is 0. A flag “0” indicating that there is no K ink amount is assigned to the lattice point.

Further, when the index “gradation” is selected on the image quality index display setting screen 31, the image quality index display unit 17 sets the third term (floor) in the evaluation function for each ink amount set of the color conversion LUT 400. The term having the tonality index SI) is calculated. At this time, the difference in ink amount between the target grid point and the adjacent grid point is used as the gradation index SI so that it is easy to grasp a portion where the color change with the surrounding grid points is not smooth (poor gradation). It is preferable to adopt the maximum value of.
Further, when the index “ink amount” is selected on the image quality index display setting screen 31, the image quality index display unit 17 sets the fourth term (total ink) for each ink amount set of the color conversion LUT 400. A term having a quantity index TI) is calculated. Alternatively, a specific ink amount (maximum ink amount) among the ink amounts of CMYKLcLm constituting the ink amount set may be used as an index “ink amount” for each lattice point of the color conversion LUT 400.
In addition, when the index “color inconstancy” is selected on the image quality index display setting screen 31, the image quality index display unit 17 sets the second term in the evaluation function (for each ink amount set of the color conversion LUT 400). A term having a non-color constancy index CII) is calculated.

Further, when the index “glossiness” is selected on the image quality index display setting screen 31, the image quality index display unit 17 sets the ink amount for each grid point of the color conversion LUT 400 and the glossiness converter SM (FIG. 1). Based on the above, the “glossiness” is calculated for each ink amount set. Here, “glossiness” is represented by a color value L ^* obtained when the color patch reproduced by the ink amount set is measured under the specular reflection observation condition. Similar to the forward model converter FM described above, the glossiness converter SM is a conversion model that inputs an ink amount set and outputs a color value L ^* a ^* b ^* . However, the forward model converter FM is constructed (learned) on the assumption that the forward model converter FM is irradiated with a light source at an incident angle of 45 degrees with respect to the observation target surface and observed at a position facing the observation target surface. The converter SM is different in that it is constructed (learned) on the assumption that the light source is irradiated at an incident angle of 45 degrees with respect to the observation target surface and the reflected light of 45 degrees from the observation target surface is observed. The image quality index display unit 17 inputs the ink amount set for each grid point of the color conversion LUT 400 to the glossiness converter SM, thereby the “glossiness” corresponding to the ink amount set (the color value L output by the glossiness converter SM). ^* ) To get.

Thus, the index acquired based on the ink amount set is associated with the grid point of the color system selected on the image quality index display setting screen 31. If the selected color system is the sRGB color system, each index is associated with a grid point of the sRGB color system corresponding to the ink amount set from which the index is acquired. If the selected color system is the L ^* a ^* b ^* color system, each index is an L ^* a ^* b ^* value (ink quantity set) corresponding to the ink quantity set from which the index is acquired. To L ^* a ^* b ^* value obtained by inputting to the forward model converter FM.

In step S440, the image quality index display unit 17 interpolates the correspondence between the index acquired in step S420 and the color system grid point selected on the image quality index display setting screen 31. This is because these correspondences are obtained only for the number of grid points defined by the color conversion LUT 400. For example, if the color system selected on the image quality index display setting screen 31 is the sRGB color system, the grid point to be interpolated in the sRGB color system (the grid point to which the acquired index is not associated). Are calculated by a method such as tetrahedral interpolation based on the relationship with neighboring grid points (lattice points with which the acquired index is associated), and are associated with the interpolation target grid points. Similarly, if the color system selected on the image quality index display setting screen 31 is the L ^* a ^* b ^* color system, the grid points (obtained in the L ^* a ^* b ^* color system) An index for a grid point that is not associated with an index is calculated by a method such as tetrahedral interpolation based on the relationship with a neighboring grid point (a grid point with which the acquired index is associated) Corresponds to the grid point to be interpolated.

The index indicating “K generation point” is a value of “0” or “1”. However, when interpolation is performed as described above, the index generated by interpolation becomes a value between 0 and 1. . Therefore, the interpolated “K generation point” index is forcibly distributed to a value of “0” or “1” according to a predetermined threshold, for example.
In step S460, the image quality index display unit 17 indicates the correspondence relationship between the index acquired in the processing up to step S440 and the color system grid points selected on the image quality index display setting screen 31 on the display 30. Graphic display as a display screen.

FIG. 8 shows an image quality index display screen 32 as an example of an image displayed on the display 30 in step S460. In the example of FIG. 8, the index “granularity” is shown in a state where the L ^* a ^* b ^* color system is selected as the color system for graphic display. On the image quality index display screen 32, a cross section of the color reproduction range (color solid) CS by the color conversion LUT 400 to be evaluated, which passes through the L ^* axis and the b ^* axis (L ^* b ^* plane, a ^* = 0) , The same shall apply hereinafter). The + direction of the b ^* axis corresponds to the yellow direction, and in the LUT color reproduction range, there is often a tendency that the graininess is particularly inferior (graininess is conspicuous) in the region corresponding to yellow. Therefore, on the image quality index display screen 32 for evaluating the graininess, the L ^* b ^* plane is displayed to make it easy to grasp the graininess particularly in the vicinity of yellow.

  On the image quality index display screen 32, the degree of graininess within the color reproduction range CS is represented by the density of dots (or circles, etc.). Specifically, the density of the dots is increased in a region with good graininess, and the density of the dots is sparser in a region with poor graininess. Since the granularity as the index is obtained for each grid point in the color reproduction range CS, the granularity for each predetermined unit area obtained by dividing the color reproduction range CS is displayed on the image quality index display screen 32, for example. The density of the points displayed in the unit area is changed according to the average value for each unit area. According to such display, the user can accurately and easily grasp which region of the color reproduction range CS by the color conversion LUT 400 is inferior in granularity by looking at the density of points.

  In the example shown in FIG. 8, the points indicating the degree of graininess are drawn in a distributed manner only in a partial range surrounded by a chain line in the cross section of the color reproduction range CS. The partial range is a range in which the granularity is predicted to be particularly inferior in the color reproduction range CS, that is, a range having an index that does not satisfy a predetermined standard regarding image quality. As described above, the degree of the index (granularity) is not expressed in the distribution over the entire color reproduction range CS, but only in the range (the partial range described above) where the degree of the index (granularity) should be particularly confirmed. By drawing, the user can be informed of the location where the degree of index (granularity) is a problem. However, the index level may be drawn over the entire color reproduction range CS.

  As described above, when the degree of the index is drawn only in the range having the index that does not satisfy the predetermined standard regarding the image quality, there are various ways of determining the standard. As an example, the user may set this criterion. For example, in the case of “granularity” as an index value, a user sets a predetermined threshold value as the reference in advance, and limits it to an area having a graininess larger than the threshold value in the color reproduction range CS. The degree of granularity due to the density of points as shown in FIG. Alternatively, the importance of the graininess in the printing result varies depending on the type of printing paper. For example, when printing an image on plain paper, even if the graininess is somewhat conspicuous, the user often does not regard it as a problem. Therefore, the threshold value (for example, the threshold value of plain paper> the threshold value of glossy paper) according to the type of printing paper (the printing paper selected when using the color conversion LUT 400 that is the object of evaluation). 8), the degree of graininess due to the dot density as shown in FIG. 8 is limited to a region having a graininess larger than the threshold corresponding to the printing paper in the color reproduction range CS. It may be expressed.

FIG. 9 shows an image quality index display screen 33 as an example of an image displayed on the display 30 in step S460. As described above, since the indexes selected on the image quality index display setting screen 31 (FIG. 7) are “granularity” and “K generation point”, the image quality index display screen 33 corresponding to the index “K generation point”. Is also displayed. The image quality index display screen 33 is displayed on the display 30 when, for example, the button 32a of the image quality index display screen 32 (FIG. 8) is clicked by the user. Alternatively, the contents of the image quality index display screen 32 and the image quality index display screen 33 may be displayed simultaneously on the same screen. Similarly to the image quality index display screen 32, the image quality index display screen 33 also graphically displays the L ^* b ^* plane of the color reproduction range CS by the color conversion LUT 400. This is because the generation of K ink has a great influence on the graininess of the printed material, and the yellow area is an area where the graininess tends to be poor.

  On the image quality index display screen 33, the position of the grid point to which the flag “1” indicating “K generation point” is given among the grid points in the color reproduction range CS is represented by a point (or a circle). . However, in FIG. 9, the points according to the flag “1” are shown only for each lattice point near the boundary where K ink is generated on the high lightness side in the color reproduction range CS, and the lightness side is lower than the boundary. For the sake of convenience, the notation of the points is omitted for each lattice point (basically a lattice point where K ink is generated). According to this display, the user looks at the position of the point to determine how light the K ink is generated in the color reproduction range CS by the color conversion LUT 400, the K ink generation start point in the vicinity of the yellow region, and the like. Can be accurately and easily grasped.

FIG. 10 shows an image quality index display screen 34 as an example of an image displayed on the display 30 in step S460. Similar to the image quality index display screen 32 (FIG. 8), the image quality index display screen 34 is drawn by distributing points indicating the degree of graininess in a part of the L ^* b ^* plane of the color reproduction range CS. At the same time, the generation of each K ink dot size is shown. The printer 20 used for printing is capable of ejecting dots having different ink ejection amounts per dot (different dot sizes). For example, three types of dots having different dot sizes (large dot, medium dot, small dot in descending order) ) Can be discharged. The occurrence of such large, medium, and small dots is basically determined according to the ink amount in the ink amount set that represents the pixels of the image data. Therefore, the ink amount of the K ink associated with each grid point of the color conversion LUT 400 is not only the presence / absence of the ink amount, but any of large, medium, and small dots is generated when the ink amount is present. It can be said that it also roughly defines what to do. Therefore, in the image quality index display screen 34, the shape of each point (graphic) constituting the distribution indicating the degree of granularity is the first shape (square) that means the occurrence of large dots, and the second that means the occurrence of medium dots. It is represented by a shape (triangle) and a third shape (circle) meaning the occurrence of small dots. Note that whether the shape of each point (figure) constituting the distribution indicating the degree of graininess is expressed by any of the first, second, and third shapes is, for example, the unit that is the target for calculating the average graininess. It is determined according to the average amount of K ink in each region. Of course, such large, medium, and small dot representations may be distinguished not by differences in figures but by differences in colors (or shades). The image quality index display screen 34 may be displayed instead of the image quality index display screens 32 and 33, or may be displayed in addition to the image quality index display screens 32 and 33. According to the image quality index display screen 34, the user can simultaneously grasp the distribution of the degree of granularity and the distribution of occurrence of large, medium, and small dots.

FIG. 11 shows an image quality index display screen 35 as an example of an image displayed on the display 30 in step S460. In the example of FIG. 11, unlike FIGS. 8 to 10, a cross section of the color reproduction range CS by the color conversion LUT 400 and a cross section passing through the a ^* axis and the b ^* axis (a ^* b ^* plane, L ^* = 50. ) Is displayed graphically. The displayed index is, for example, “granularity”. In the example of the image quality index display screen 35, the a ^* b ^* plane is divided into a plurality of (three in FIG. 11) areas according to the difference in graininess, and different colors (or the same colors with different densities) are assigned to the respective areas. It is attached and drawn. In FIG. 11, by giving dense hatching to the region with the worst granularity, sparse hatching to the region with the next worst granularity, and not hatching the region with the best granularity, For the sake of convenience, the difference in color or the like between regions is shown.

Alternatively, the image quality index display unit 17 may graphically display an image quality index display screen 35 as illustrated in FIG. FIG. 12 differs from FIG. 11 in that the color reproduction range CS (a ^* b ^* plane) is not divided into a plurality of regions according to the difference in index (granularity), but on the screen according to the difference in index. The gradation of the color is continuously changed. For example, a position with poor graininess is displayed dark, and a position with good graininess is displayed light. The user can accurately and easily evaluate the unevenness of graininess in the color reproduction range CS by looking at such an image quality index display screen 35. The image quality index display screen 35 may be displayed instead of the image quality index display screens 32, 33, 34, or may be displayed in addition to the image quality index display screens 32, 33, 34.

  Of course, in step S460, even if the index selected on the image quality index display setting screen 31 (FIG. 7) is “gradation”, “ink amount”, “color inconstancy”, “glossiness”, or the like. These indicators are displayed on the image quality indicator display screen. For example, FIGS. 11 and 12 show the granularity, but similarly, gradations or the like in which the shades of the respective positions are changed according to the difference in “gradation” of each position in the color reproduction range CS are displayed. It is also possible. Similarly, gradation or the like with different shades at each position is displayed according to the difference in “ink amount” at each position in the color reproduction range CS, or “color inconstancy” at each position in the color reproduction range CS. Display gradations etc. with different shades at each position according to the difference, or display gradations etc. with different shades at each position according to the “glossiness” at each position in the color reproduction range CS Is also possible. By viewing such a display result, the user can check whether the gradation is uneven in the color reproduction range by the color conversion LUT 400, whether the ink amount is increased or decreased according to the position, non-color constancy unevenness, gloss Unevenness of degree can be accurately and easily evaluated.

8 to 12 exemplify a specific cross section of the color reproduction range CS in the L ^* a ^* b ^* color system, the cross section of the color reproduction range CS displayed on the image quality index display screen is as described above. Not limited. Further, on the image quality index display screen, the color reproduction range CS may be drawn as a three-dimensional color solid as illustrated in FIG. 13 instead of being represented by any cross section, and the distribution of the index may be expressed with respect to the solid. Good. In FIG. 13, on the surface of the color solid representing the color reproduction range CS, gradation of the indices (“gradation”, “ink amount”, “color inconstancy”, “glossiness”, etc.) for each grid point is gradation. The example expressed by is shown. Of course, such gradation is applied not only to one curved surface as shown in FIG. 13 but also to the entire color solid.

  Further, FIG. 14 shows an image quality index display screen 36 as an example of an image displayed on the display 30 in step S460. In the example of FIG. 14, the distribution of the above-described index (for example, “ink amount”) is displayed in gradation with the sRGB color system selected as the color system for graphic display.

  As described above, according to the present embodiment, for the color conversion LUT 400 to be evaluated, various indexes related to image quality are acquired based on the ink amount set for each grid point, and a predetermined color system (device-independent color system) is obtained. And the like, the distribution of these indices is displayed graphically on the display 30. Therefore, a user who visually recognizes these via the display 30 can legitimately and easily evaluate the image quality realized by the color conversion LUT 400 as an evaluation target based on various determination factors. Note that the color conversion LUT to be evaluated in the present embodiment is not limited to the color conversion LUT once completed according to the flowchart shown in FIG. 3, but is being created (for example, optimization of the ink amount set for some grid points). The LUT may be in a state in which the process is completed. That is, by evaluating the LUT that is being created as a target of image quality index display processing, the subsequent LUT creation guideline can be appropriately corrected.

4). Other Embodiments The present invention is not limited to the above-described embodiments, and can be implemented in various modes without departing from the gist thereof. For example, the following embodiments are also possible. The contents obtained by appropriately combining the embodiments are also within the scope of disclosure of the present invention. In addition, below, description is abbreviate | omitted suitably about the matter similar to the item demonstrated so far.

  So far, the scene where the image quality index display screen for evaluating the image quality realized by the color conversion LUT 400 is output to the display 30 has been described. However, the user can modify the color conversion LUT 400 based on the display contents on the display 30. Creation) may be instructed. For example, the user may instruct to change the K generation point in the color conversion LUT 400.

For example, as shown in FIG. 15, an input tool that can be operated by the user via the operation unit 40 is displayed on the image quality index display screen 33 (FIG. 9). Here, an operation bar BA is shown as an example of the input tool. The user can designate the L ^* value corresponding to the K generation point by operating the operation unit 40 to move the position of the operation bar BA up and down in the L ^* axis direction. When the L ^* value of the K generation point is specified by the user as described above, the ink amount determination unit 15 performs step S200 based on the specification and the color conversion LUT 400 that is the evaluation target on the image quality index display screen 33. The process of (FIG. 3) is performed. That is, the ink amount set associated with the lattice points of the initial LUT is sequentially optimized while regarding the color conversion LUT 400 that is the evaluation target as the initial LUT.

At this time, the ink amount determination unit 15 determines an optimal ink amount set using the above-described evaluation function, but the color value (L ^* value higher than L ^{* of the} designated K generation point) ( When determining an ink amount set corresponding to L ^* a ^* b ^* coordinate values in the color system), an optimal ink amount set is determined from among the ink amount sets in which the K ink amount is zero. After step S200, step S300 is executed by the color conversion LUT creation unit 16. As a result, the color conversion LUT 400 that complies with the restriction on the K generation point specified by the user via the image quality index display screen 33 is generated.

  Further, as a result of confirming the image quality index display screen described above, if the user is not satisfied with the graininess realized by the color conversion LUT 400 to be evaluated, an instruction to improve the graininess is given via the operation unit 40. Can be done. When such an instruction is received, for example, the color conversion LUT creation unit 16 adds predetermined incidental information indicating that there is an instruction to improve graininess to the color conversion LUT 400 that is the evaluation target. To the HDD 11.

  Then, the image processing unit 18 determines whether or not the supplementary information is included in the color conversion LUT 400 used for the color conversion process when executing the print process (print data generation) based on the image data arbitrarily designated by the user. However, if there is incidental information, predetermined image processing for improving graininess is performed on the image data. That is, image processing is performed to eliminate the low granularity (conspicuous graininess) of the image represented by the image data after color conversion by the color conversion LUT 400. The image processing referred to here is, for example, blurring processing of an image using a predetermined filter, and suppresses graininess by blurring (bluring) the image. The timing for executing the image processing is, for example, after the color conversion processing. Further, the blurring process as described above is performed by limiting to the range on the image data in which the color gamut (for example, yellow) designated by the user judging that the granularity is particularly low by looking at the image quality index display screen. You may do it. According to such a configuration, the image quality (granularity) that cannot be realized by the ability of the color conversion LUT 400 is supplemented by image processing, so that an image quality substantially satisfied by the user can be obtained in the print result.

  FIG. 16 shows the configuration of the printer 20 corresponding to an example of the image display apparatus according to the present invention. That is, the image display device may be embodied by the printer 20. In the printer 20, the CPU 50 executes an operation according to a predetermined program in an internal memory such as a RAM 51 or a ROM, thereby having the same functions as those of the computer 10 described above. The image quality index display unit 17 and the image processing unit. 18. Implement each function such as gloss converter SM. The printer 20 inputs various instructions from the user via the operation unit 56 such as various buttons or a touch panel. In the printer 20, the image processing unit 18 acquires image data in which the color of each pixel is represented by the coordinate values of the input color system, and acquires the image data from the computer 10 or the like via the I / F 54. The color conversion is performed using the color conversion LUT 400, and the image data after the color conversion is subjected to various image processing such as halftone processing and microweave processing to generate print data, and printing based on the print data is performed by the printer engine. 53. In addition, the printer 20 includes the image quality index display unit 17, the glossiness converter SM, and the like, so that the image quality index display process (FIG. 6) for evaluating the color conversion LUT 400 is performed on the display 55 as in the computer 10 described above. Can be done.

  In the present specification, “ink” is used in a broad sense including not only liquid ink used in an ink jet printer and offset printing, but also toner used in a laser printer. As other terms having such a broad meaning of “ink”, “coloring material”, “coloring material”, and “coloring agent” can also be used.

DESCRIPTION OF SYMBOLS 1 ... Image display apparatus, 10 ... Computer, 11 ... HDD, 12 ... CPU, 13 ... RAM, 14 ... Initial LUT setting part, 15 ... Ink amount determination part, 16 ... Color conversion LUT creation part, 17 ... Image quality index display part , 18 ... Image processing unit, 20 ... Printer, 30 ... Display, 31 ... Image quality index display setting screen, 32, 33, 34, 35, 36 ... Image quality index display screen, 40 ... Operation unit, 50 ... CPU, 51 ... RAM 53 ... Printer engine, 55 ... Display, 56 ... Operating unit, 400 ... Color conversion LUT, 410 ... Inverse model initial LUT, 510 ... Initial LUT, FM ... Forward model converter, RC ... Spectral printing model converter, CC ... Color converter , SM ... Glossiness converter, CS ... Color reproduction range

Claims (8)

A color conversion table in which color information in the output color system is associated with a plurality of grid points in the input color system is acquired, and is an image quality index based on the color information in the acquired color conversion table and at least granularity the image display apparatus characterized by a an image representing the black generated whether a constant of the device-independent color system own the to be displayed on a predetermined display unit.   The image display apparatus according to claim 1, wherein the graininess is expressed by a density of points indicated in a device-independent color system.   3. The image display device according to claim 1, wherein when the occurrence of black is expressed, a difference in black dot size determined based on the color information is also expressed.   The image display apparatus according to claim 1, wherein the index is expressed only in a range having an index that does not satisfy a predetermined criterion relating to image quality in the device-independent color system.   Further displaying an image of the image quality, wherein one or more of the gradation, ink amount used, non-color constancy, and glossiness are expressed in gradation in a predetermined color system. The image display device according to claim 1, wherein:   The color conversion table in which the generation of black is changed according to the change instruction when the change instruction for the occurrence of black is received by an operation on the image displayed on the display unit. The image display device according to claim 5.   When the color conversion table has incidental information corresponding to an instruction to improve the graininess, color conversion processing and graininess using the color conversion table are performed on the image data expressed in the input color system. 7. The image display device according to claim 1, wherein predetermined image processing is performed for improvement.   A printing apparatus comprising the image display device according to claim 1.