Image processing method and apparatus configured for printing a plurality of monochrome images having different parameters

An image processing apparatus acquires monochrome image data and, for a pattern of each parameter, converts the acquired monochrome image data into intermediate image data. The intermediate image data is expressed in a set of signal values of a plurality of color elements.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image processing apparatus and an image processing method for performing pattern printing, and a storage medium storing a program.

2. Description of the Related Art

In order for a user to output a desired color, color printers have color tone adjustment functions (color balance, brightness, contrast, color tone, etc.). However, there are cases where it is difficult even for an experienced person to determine what parameters to adjust and how much to adjust them. For this reason, a pattern printing function is an example of a function for a user to determine this by looking at colors output by actually printing on a printing medium. “Pattern printing” is a function for changing the color tone of a color image multiple ways, compositing them into one color image, and printing it when a determination is to be made regarding the coloration of the color image. In the flow of image data in pattern printing, image data pieces are generated by performing predetermined color adjustment on an RGB signal for input image data, and a pattern image is generated by editing the layout of those into one piece of image data. Subsequently, the image data is printed on a printing medium after undergoing color material color development processing, halftoning processing, and printer control processing.

On the other hand, a monochrome image requires pattern printing in which different color tones such as a pure black tone, a warm black tone, and a cool black tone are reproduced. However, in the case of a monochrome image, a more refined tonal expression compared to that of a color image has been requested by users, and thus a greater degree of tonal reproduction control than in the case of color images is needed. Therefore, if color image pattern printing is used as-is in a processing flow for a monochrome image, the tonality will be insufficient. Accordingly, if color processing and monochrome processing are both used, particularly in color processing using a 3DLUT, more processing control points (number of grid points in the 3DLUT) than are used in color processing are needed to satisfy requirements for a monochrome image. Also, there is another method in which color processing and monochrome processing are separated and performed in separate processing flows. Japanese Patent Laid-Open No. 2004-142423 discloses that color processing and monochrome processing are performed separately, a pattern printing image is composited based on image data that has undergone color material color development in monochrome processing, and pattern printing of a monochrome image is performed.

However, in Japanese Patent Laid-Open No. 2004-142423, color processing and monochrome processing are performed separately and a pattern printing function is added to the monochrome processing, and therefore if configured by hardware, the image processing circuit size increases, which influences the product cost. Also, since compositing of a pattern printing image is performed after color material color development, the number of image data pieces (channels) handled in compositing processing is larger in a printing apparatus using color materials such as light cyan, light magenta, and light gray in addition to CMYK. This causes an increase in the amount of memory used for compositing processing, an increase in product cost, a decrease in printing processing speed, and the like. For example, if the compositing of a pattern printing image that has undergone color material color development is performed by software, the amount of image data after color material color development rises in proportion to the number of color materials in the printing apparatus, thereby causing a decrease in printing speed.

SUMMARY OF THE INVENTION

An aspect of the present invention is to eliminate the above-mentioned problems with the conventional technology. The present invention in its first aspect provides an image processing apparatus and an image processing method for improving the efficiency of pattern printing processing, and a storage medium for storing a program.

The present invention in its first aspect provides an image processing apparatus for processing monochrome image data so as to print a pattern of a plurality of monochrome images having different parameters, the image processing apparatus comprising: an acquisition unit configured to acquire the monochrome image data indicating a gradation of monochrome image in a predetermined number of gradations; a first conversion unit configured to, for a pattern of each of the parameters, convert the monochrome image data acquired by the acquisition unit into intermediate image data expressed in a set of signal values of a plurality of color elements; and a transfer unit configured to transfer to a determination unit configured to determine a color material amount to be used when printing the pattern of each parameter, based on image data which is converted by the first conversion unit.

According to the present invention, the efficiency of pattern printing processing can be improved.

DESCRIPTION OF THE EMBODIMENTS

Preferred embodiments of the present invention will now be described hereinafter in detail, with reference to the accompanying drawings. It is to be understood that the following embodiments are not intended to limit the claims of the present invention, and that not all of the combinations of the aspects that are described according to the following embodiments are necessarily required with respect to the means to solve the problems according to the present invention. Note that identical constituent elements will be denoted by the same reference signs, and redundant descriptions thereof will be omitted.

Configuration of Image Processing System

An image processing system in the present embodiment performs pattern printing in which multiple images obtained by performing multiple types of color adjustment (color tone, brightness, contrast, etc.) with respect to one monochrome image are printed in one group. In the image processing system, a user can select an image of a desired color tone from the printed material obtained by pattern printing, and can again output the monochrome image using the selected color tone setting.

FIG. 1is a diagram showing a configuration of an image processing system for executing pattern printing for a monochrome image according to embodiments of the present invention. A CPU101performs overall control of a host computer100. A ROM102stores programs for controlling controllers of the host computer100, and also stores data used by those programs. An HDD controller104performs data control such as data writing/readout with respect to a hard disk105. The hard disk105stores an OS and an application that run on the host computer100, as well as data used by that application. A RAM103stores the OS and the application loaded from the hard disk105via the HDD controller104. The OS and the application loaded to the RAM103are executed by the CPU101. Also, the RAM103is used as a work area as well when applications are running.

A printer107is a color printer that uses light cyan (Lc), light magenta (Lm), dark gray (Gy), and light gray (Lg) as color materials in addition to CMYK (cyan, magenta, yellow, black). An ink jet type of ink jet printing apparatus for example may be used as the color printer. An interface controller106performs reception and transmission of data between the printer107and the host computer100. When a user executes a print command in an application, print data is generated using a printer driver stored in the hard disk105, and the print data is transmitted to the printer107via the interface controller106. The print data is RGB data or color material color data for example. A display controller108controls a display apparatus109. Under control of the CPU101, an input device controller110accepts input of an instruction from the user of the host computer100given using an input device111. The input device111is a keyboard or a pointing device for example. The user of the host computer100can perform interactive operations in the application running on the host computer100by using the display apparatus109and the input device111.

Pattern Printing Flow

FIG. 2is a flowchart showing a procedure of processing in the case where color adjustment is performed in pattern printing in the present embodiment. The processing shown inFIG. 2is executed by the CPU101controlling the units inFIG. 1for example. The user starts an application for performing pattern printing, using the display apparatus109and the input device111. The application is stored in the hard disk105for example.

In step5201, the CPU101acquires monochrome image data, which is to be the pattern printing target. The CPU101may acquire the monochrome image data directly from an external device, or it may acquire the monochrome image data by receiving input of RGB image data and converting that image data to grayscale using a predetermined RGB ratio. In step S202, the CPU101acquires parameters set for pattern printing images in pattern printing.

FIGS. 3 and 4are diagrams showing examples of GUIs displayed by an application for performing pattern printing. With the setting screen inFIG. 3, the user can set central parameters for color tone, brightness, contrast, and the like for when changing multiple parameter values in pattern printing. A list box301is used when the user selects a color tone preset. Presets such as “pure black tone”, “warm black tone”, and “cool black tone” are displayed in a user-selectable manner in the list box301. Furthermore, to allow the user to perform color tone adjustment, the setting screen displays a parameter X302for adjusting the color tone in a yellow-blue direction, and a parameter Y303for adjusting the color tone in a cyan-red direction. The color tone parameter X302and the color tone parameter Y303are coordinated with the color tone presets in the list box301, and when the user changes the color tone preset, the values of the color tone parameter X302and the color tone parameter Y303also change in coordination.

When the user presses a pattern printing button304, a pattern printing setting screen inFIG. 4opens. A radio button401displays the types of parameters to be changed in pattern printing in a user-selectable manner. In the case inFIG. 4, the user can select either “color tone” or “brightness/contrast” using the radio button401. If the user selects “color tone”, pattern printing images that have undergone changes in color tone will be generated. Also, if the user selects “brightness/contrast”, pattern printing images that have undergone changes in brightness and contrast will be generated. The pattern printing setting screen inFIG. 4displays sheet size402, pattern size403, and parameter range404as list boxes. The user can select various types of sheet sizes using the sheet size402. Also, the user can select large, medium, or small using the pattern size403. Also, using the parameter range404, the user can select large, medium, or small as the degree of change when changing “color tone” or “brightness/contrast”. In FIG.4, the sheet size402is configured such that large, medium, or small is selected, but it may be configured such that the user can directly input a sheet size. Also, the parameter range404is also configured such that large, medium, or small is selected, but it may be configured such that the user can directly input number values corresponding to the parameter X302and the parameter Y303inFIG. 3. The user can set parameters needed in pattern printing using the setting screens inFIGS. 3 and 4. The parameters set in the setting screens inFIGS. 3 and 4are stored in a data region in the hard disk105.

In step S203, the CPU101generates a pattern printing image and performs printing processing. The processing in step S203is started when an instruction is given due to the user pushing a printing button405inFIG. 4using the input device111. The CPU101reads out the parameters for pattern printing set in step S202from the data region in the hard disk105, and generates pattern printing image data and image processing parameters based on the parameter values. The generated pattern printing image data and image processing parameters are transmitted to the printer107via the I/F controller106.

FIG. 5is a diagram showing an example of a pattern printing image. Color adjustment parameters are printed below the patterns in the pattern printing image. The printed color adjustment parameters are the values of the parameter X302and the parameter Y303inFIG. 3. The user can easily find out the settings of each pattern in the pattern printing image using the printed color adjustment parameters. A procedure of image processing for generating a pattern printing image will be described later. In step S204, the CPU101receives a selection of color tones set in the pattern printing image from the user. In step S205, the CPU101once again sets the color adjustment parameters corresponding to the received color tones as parameters that can be set in the setting screen inFIG. 3. If the user pushes a printing button305to give an instruction using the input device111, the CPU101starts printing processing using the color tones selected by the user with respect to the monochrome image data.

Processing in the Case of a Color Image

Here, image processing for generating a pattern printing image in step S203will be described.FIG. 6is a diagram showing a configuration of an image processing unit for generating a pattern printing image in an image processing system. Below, in the case of a color image, image data is described as being 24-bit data, each color having 8 bits, and in the case of a monochrome image, image data is described as being 8-bit data. A host computer600has, among the constituent elements of an image processing unit, a color signal input unit601, a monochrome signal input unit602, a color matching unit604, an image editing unit606, a one-to-three conversion unit605, a pattern printing information setting unit603, and a color material color coefficient generation unit607. The host computer600also has a color material color conversion table database (DB)608and a printing information DB611. Also, a printer615has, among the constituent elements of an image processing unit, a color material color development processing unit610, a color material color coefficient setting unit609, a halftoning unit613, a printing control unit614, and a printing information coefficient setting unit612. Although illustrated as described above inFIG. 6, the host computer600may further include the color material color development processing unit610and the color material coefficient setting unit609.

First, a case of a color image will be described below. The color signal input unit601receives an input of RGB data for a color image (24-bit data, each color being 8 bits), and outputs it to the color matching unit604. The color matching unit604performs color conversion from a standard sRGB space into a device RGB space, for example, by means of a three-dimensional lookup table (3DLUT). In a 3DLUT, color conversion parameters (RGB values) are set as output values on 16 grid points placed at intervals of 17 values for example (in other words, 16×16×16=4096 grid points), and RGB values between grid points are calculated using an interpolation calculation. Color conversion parameters in the 3DLUT change depending on the printing medium, such as a sheet, and the printing mode, and for example, they are created in advance, stored in the hard disk105, read out according to need, and set on the grid points. If pattern printing is to be performed, the image editing unit606performs layout processing for one piece of image data using multiple pieces of pattern printing image data. If pattern printing is not to be performed, the image editing unit606executes enlargement/reduction processing to adjust the image to a desired size.

RGB data in the device RGB space processed by the image editing unit606, image processing parameters for image processing to be performed by the printer615, and printer control parameters are transmitted to the printer615. The color material color development processing unit610performs, using the 3DLUT, color conversion of RGB data in the device RGB space into color material color data that corresponds to a color material color space. Here, “color material colors” are eight colors including Lc, Lm, Gy, and Lg, in addition to CMYK. In a 3DLUT in the color material color development processing unit610, color conversion parameters are also set as output values on 16 grid points placed in intervals of 17 values (4096 grid points), and RGB data between grid points is calculated using an interpolation calculation. The color conversion parameters in the 3DLUT in the color material color development processing unit610change depending on the printing medium and printing mode. The color conversion parameters in the 3DLUT are created in advance, stored in the color material color conversion table DB608on the hard disk105, read out by the color material color coefficient setting unit609according to need, and set on the grid points for example.

Using an ED method or the like, the halftoning unit613binarizes color material color data that has undergone color conversion by the color material color development processing unit610. Then, the printing control unit614executes processing necessary for printing, such as print path resolution, and performs printing on a printing medium. Image processing parameters used by the halftoning unit613and the printing control unit614also change depending on the printing medium and printing mode used. For example, they are created in advance, stored in the printing information DB611on the hard disk105, read out by the printing information coefficient setting unit612according to need, and set in the halftoning unit613and the printing control unit614.

Image processing in the case of a color image was described above. It is also possible to perform image processing on monochrome image data as color image data where R=G=B. However, in general, compared with color images, tone expression is particularly important in monochrome images. Accordingly, if monochrome image data is converted into color image data and undergoes image processing according to the aforementioned configuration, it is necessary for the number of grid points in the 3DLUT to be increased from 16 to 32 or 64, and for fine control to be enabled for the tone characteristics in printing. However, as a result of this, the circuit size increases, causing an increase in product cost.

Processing in the Case of a Monochrome Image

In view of this, with regards to pattern printing of a monochrome image, image processing is performed as follows in the present embodiment. First, the monochrome signal input unit602receives an input of monochrome image data that is 8-bit data, and outputs it to the one-to-three conversion unit605. Also, the pattern printing information setting unit603reads out parameters for pattern printing set in the setting screens inFIGS. 3 and 4from the hard disk105, and sets pattern printing information, which is information that is needed for pattern printing. Here, pattern printing information is number of pattern images, pattern image arrangement, pattern image size, color adjustment parameters regarding the pattern images, and information on the storage position of the color material color conversion table in the 3DLUT regarding the pattern images. The information on the storage position of the color material color conversion table in the 3DLUT regarding the pattern images will be described later. The pattern printing information setting unit603transmits pattern printing information to the one-to-three conversion unit605, the image editing unit606, and the color material color coefficient generation unit607.

The one-to-three conversion unit605receives an input of monochrome image data and converts the gray tone values on the gray lines into RGB signal values in a color space with use of a one-to-three conversion table. The converted RGB signal values correspond to the RGB signal values of input values in the 3DLUT in the downstream color material color development processing unit610. Also, the one-to-three conversion table will be described later. The conversion performed by the one-to-three conversion unit605is performed once for each pattern image. The image editing unit606receives an input of one piece of RGB data (intermediate image data) converted by the one-to-three conversion unit605for each pattern image and composites the pattern images into one piece of image data in accordance with the sizes of the pattern images and the arrangement of the pattern images, which were set by the pattern printing information setting unit603.

The color material color development processing unit610converts the RGB data transmitted from the image editing unit606into color material color signals. The 3DLUT used at that time has 4096 grid points expressed as 16 grid points for each axis of RGB, as shown inFIG. 7A. The 3DLUT used in the color material color development processing unit610is the same as that in conventional technology in terms of the number of grid points. However, the color material color data values set by the color material color coefficient setting unit609are mapped (stored) as output values on the coordinate points of the RGB signal values transmitted from the image editing unit606. The aforementioned “information on the storage position of the color material color conversion table in the 3DLUT” refers to the mapping in the 3DLUT of color material color data to coordinate points expressed by RGB signal values transmitted from the image editing unit606. In the present embodiment, RGB signal values transmitted from the image editing unit606are values following the direction of the arrow shown in the 0-th line inFIG. 9.FIG. 9shows an example of a lookup table in the present embodiment. In other words, it means that the gray tone value is converted by the one-to-three conversion unit605so as to be such an RGB signal value. Also, color material color data values are mapped to the coordinate points in the direction of the arrow shown in the 0-th line inFIG. 9. In other words, whereas gray tone values and color material data are mapped to each other in a 1DLUT as shown inFIG. 8, a gray tone value is first converted into RGB data with the one-to-three conversion table. Then, furthermore, it is converted into color material color data corresponding to RGB signal values using the 3DLUT. According to this configuration, in the present embodiment, the configuration of color material color conversion processing can be the same for a monochrome image and a color image. Then, when pattern images are composited into one piece of data, RGB data is handled rather than color material color data, and therefore the amount of data can also be reduced. Also, although described later, if interpolation processing in a normal 3DLUT is performed during color material color development processing by the color material color development processing unit610, it is possible to obtain results that are the same as with interpolation processing in a conventional 1DLUT. Accordingly, tone control similar to that in conventional technology can be performed for a monochrome image. Color material color data resulting from color conversion by the color material color development processing unit610undergoes printing processing via the half toning unit613and the printing control unit614, similarly to the case of the color image.

The color material color coefficient generation unit607generates a 3DLUT to be used by the color material color development processing unit610in accordance with color adjustment parameters for pattern images set by the pattern printing information setting unit603, and in accordance with the information on the storage position of the color material color conversion table in the 3DLUT. The color material color coefficient generation unit607acquires, from the color material color conversion table DB608, the color material color conversion table for monochrome images that corresponds to the color tone (X, Y) designated on the setting screens inFIGS. 3 and 4. The color material color conversion table DB608is a color material color conversion table (1DLUT) that corresponds toFIG. 8for example, and it stores all color tones that can be designated on the setting screens inFIGS. 3 and 4for each printing medium. The color material color coefficient generation unit607maps output values (color material color signal values) corresponding to gray tone values in the color material color conversion table acquired from the color material color conversion table DB608, in an RGB space according to the storage position information set by the pattern printing information setting unit603. It was described that the color material color conversion table608stores all color tones that can be designated on the setting screens inFIGS. 3 and 4. However, a color material color conversion table that corresponds to color tones designated on the setting screens inFIGS. 3 and 4may be obtained by performing an interpolation calculation based on color material color conversion tables stored in advance in the color material color conversion table DB608. The 3DLUT generated by the color material color coefficient generation unit607in the host computer600is transmitted to the color material color coefficient setting unit609in the printer615. Then, the color material color coefficient setting unit609sets the transmitted 3DLUT in the color material color development processing unit610.

Operation by the Color Material Color Coefficient Generation Unit

Conventionally, in the case where color material color development processing is performed with respect to monochrome image data in which the input values are gray tone values (gradation values) (i.e., the input value is 1-channel), color material color development processing is performed using a 1DLUT for conversion into color material color data, and subsequently, halftone processing is performed. Thus, the configuration was separate from that of color material color development processing performed by a 3DLUT with respect to color image data, and therefore the circuit size was bigger, which influenced product cost.

In the present embodiment, the one-to-three conversion unit605, the color material color coefficient generation unit607, and the color material color development processing unit610, which is used for color image data, are combined, and color material color development processing is performed for monochrome image data. In other words, in the present embodiment, color material color development processing for monochrome data (8 bits, 256 gradations) is not performed using a 1DLUT, and is instead performed using the color material color conversion table (a 3DLUT) in the color material color development processing unit610. As a result, it is an aim of the present invention to prevent an increase in circuit size caused by having a separate configuration for monochrome image data as in conventional technology. In the present embodiment, the term “channel” refers to an image data signal, “one channel” meaning a monochrome image signal, “3 channels” meaning an RGB signal, and “4 channels” meaning a CMYK signal for example. Besides RGB and CMYK, it is possible to use YCbCr, Lab, XYZ, or the like to express other image data signals.

Effects of the Present Embodiment

Here, effects of the present embodiment in comparison to conventional technology will be described.FIG. 12is a diagram for describing a flow of color material color development processing for monochrome image data in conventional technology. First, input monochrome image data is developed into color material color data using a 1DLUT for printing monochrome images corresponding to color tones, the developed color material color data for color tones is composited by an image editing unit, and a pattern printing image is generated on one printing medium. In the configuration inFIG. 12, the amount of data used (number of channels) in compositing increases as the number of color material colors in the printing apparatus increases, and therefore compositing processing is time-consuming, thus slowing down the printing speed. Also, since the amount of memory used for compositing processing increases as well, product cost is affected. Generally, compositing processing is performed by software on a host computer in order to prevent the increase in circuit scale that occurs in the case where compositing processing is implemented by hardware. However, since a pattern printing image after undergoing compositing processing is color material color data, it has a data amount of eight channels. Accordingly, a longer time is required for transfer when transferring data to the printer, which invites a decrease in printing speed.

FIG. 13is a diagram for describing a flow of color material color development processing for monochrome image data in the present embodiment. First, with respect to input monochrome image data, the monochrome image data is subjected to one-to-three conversion using a one-to-three conversion table that corresponds to color tones. Here, “one-to-three conversion” refers to outputting an RGB signal value for each gray tone value (gradation value). In other words, RGB data is generated with respect to the input monochrome image data, using one-to-three conversion. Then, RGB data corresponding to the color tones is composited by the image editing unit, and one piece of pattern image data is generated. In the present embodiment, pattern image data is generated as RGB data, unlike inFIG. 12. Accordingly, the amount of data to be transferred to the printer can be suppressed to three channels-worth of data, and thus it is possible to prevent a decrease in printing speed. Color material color data corresponding to RGB signal values is output by the printer using the 3DLUT of the present embodiment.

Generation of 3DLUT in the Color Material Color Development Processing Unit610

Next, the generation of a 3DLUT used by the color material color development processing unit610will be described. A 1DLUT conventionally used for monochrome image data, such as that shown inFIG. 8, maps color material color data to gray tone values. In the present embodiment, the color material color coefficient generation unit607maps gray tone values to an RGB space. At that time, the color material color coefficient generation unit607maps the gray tone values inFIG. 8to consecutive adjacent grid points in the RGB space in order. Here, “consecutive adjacent grid points” means grid points that are in a positional relationship such that, in the case of calculating an output value corresponding to an input value that is on a line segment that connects two adjacent grid points in the RGB space, interpolation calculation is performed based on only those two grid points.

For example, in this description, interpolation calculation for a 3DLUT is performed using tetrahedral interpolation. With tetrahedral interpolation, first, it is specified which cube an input value d (r, g, b) will be included in by performing a comparison with the grid points in the 3DLUT.FIG. 7Ashows a positional relationship between the grid points of the specified cube and the input value d. An output value (r′, g′, b′) of the input value d is calculated using Equation 1.
(r′,g′,b′)=(r0′,g0′,b0′)+c1×Δr/(r1-r0)+c2×Δg/(g1-g0)+c3×Δb/(b1-b0)  (1)

Here, (r0′, b0′, b0′) is the output value of the grid point (r0, g0, b0). Also, coefficients c1to c3are calculated as described below, depending on which of the six tetrahedrons (T0to T5) shown inFIG. 7Bthe output value d is included in. Here, (R′, G′, B′) rxbxgx expresses an output value on the grid point (rx, gx, bx).

If input value d is included in tetrahedron TO, i.e., if Δr/(r1-r0)≧Δg/(g1-g0)≧Δb/(b1-b0):

If input value d is included in tetrahedron T1, i.e., if Δr/(r1-r0)≧Δb/(b1-b0)≧Δg/(g1-g0):

If input value d is included in tetrahedron T2, i.e., if Δg/(g1-g0)≧Δr/(r1-r0)≧Δb/(b1-bg0):

If input value d is included in tetrahedron T3, i.e., if Δg/(g1-g0)≧Δb/(b1-b0)≧Δr/(r1-r0):

If input value d is included in tetrahedron T4, i.e., if Δb/(b1-b0)≧Δr/(r1-r0)≧Δg/(g1-g0):

If input value d is included in tetrahedron T5, i.e., if Δb/(b1-b0)≧Δg/(g1-g0)≧Δr/(r1-r0):

As described above, consecutive adjacent grid points are sets of two grid points such that interpolation calculation can be performed using only two grid points in Equation 1. The following sets of grid points apply to the cases shown inFIG. 7B.

If the input value d is included in the tetrahedron T0: a set of (r0, g0, b0) and (r1, g0, b0), a set of (r0, g0, b0) and (r1, g1, b1), and a set of (r0, g0, b0) and (r1, g1, b0).

If the input value d is included in the tetrahedron T1: a set of (r0, g0, b0) and (r1, g0, b0), a set of (r0, g0, b0) and (r1, g1, b1), and a set of (r0, g0, b0) and (r1, g0, b1).

If the input value is included in the tetrahedron T2: a set of (r0, g0, b0) and (r0, g0, b1), a set of (r0, g0, b0) and (r1, g1, b1), and a set of (r0, g0, b0) and (r1, g0, b1).

If the input value is included in the tetrahedron T3: a set of (r0, g0, b0) and (r0, g1, b0), a set of (r0, g0, b0) and (r1, g1, b1), and a set of (r0, g0, b0) and (r1, g1, b0).

If the input value is included in the tetrahedron T4: a set of (r0, g0, b0) and (r0, g1, b0), a set of (r0, g0, b0) and (r1, g1, b1), and a set of (r0, g0, b0) and (r0, g1, b1).

If the input value is included in the tetrahedron T5: a set of (r0, g0, b0) and (r0, g0, b1), a set of (r0, g0, b0) and (r1, g1, b1), and a set of (r0, g0, b0) and (r0, g1, b1).

In other words, in the case of performing an interpolation calculation with regard to an input value on a line segment of the aforementioned sets of grid points, in the calculation of Equation 1, the coefficient (at least one out of Δr, Δg, and Δb) of a grid point other than the two aforementioned grid points will be zero. Accordingly, in actuality, it will be a calculation of a linear interpolation between two grid points. In the present embodiment, color material color data in the 1DLUT inFIG. 8is mapped to consecutive grid points in such a positional relationship, in the order of the gray tone values. Due to having such a configuration, it is possible to obtain an output result that is similar to that of conventional 1DLUT processing, even if interpolation calculation is performed in a 3DLUT. Tetrahedral interpolation was described above as an example, but eight-point interpolation processing for example achieves similar results, and it is sufficient to use two grid points in a positional relationship such that linear interpolation is performed based on only two grid points.

Here, an example in which a 1DLUT is mapped to a 3DLUT will be described.FIG. 9is a diagram for describing an example in which a 1DLUT is mapped to a 3DLUT. For example, here, color material color data corresponding to a gray tone value of 0 inFIG. 8is mapped to the origin of the “0-th” arrow inFIG. 9. Then, color material color data corresponding to a gray tone value of 8 inFIG. 8is mapped to an adjacent grid point along the “0-th” arrow. Furthermore, color material color data corresponding to a gray tone value of 17 inFIG. 8is mapped to an adjacent grid point along the “0-th” arrow. This mapping continues, and then color material color data corresponding to a gray tone value of 123 inFIG. 8is mapped to the grid point 255 on the R axis, along the “0-th” arrow. Subsequently, color material color data corresponding to a gray tone value of 132 inFIG. 8is mapped to an adjacent grid point along the G axis. Subsequently, color material color data corresponding to a gray tone value of 140 inFIG. 8is mapped to an adjacent grid point along the “0-th” arrow. Hereafter, the aforementioned mapping continues up to a gray tone value of 255 inFIG. 8.

In the present embodiment, the 3DLUT is assumed to have 16×16×16=4096 grid points. Accordingly, 128 1DLUTs, each having 32 grid points as shown in FIG. 8 can be mapped. Regarding the method of mapping a 1DLUT to a 3DLUT, although mapping is performed on an RG plane that is defined by RG reference axes inFIG. 9, it may be performed on a BR plane. In other words, it need only be possible to consecutively map the aforementioned two adjacent grid points in a positional relationship such that linear interpolation is performed based on only two grid points.

In the aforementioned “information on the storage position of the color material color conversion table in the 3DLUT”, storage positions are designated at addresses from the 0-th address up to and including the 127th address, as shown inFIG. 9for example. InFIG. 9, color material color data from a 1DLUT corresponding to color tones is mapped to addresses on the G axis beginning at the position where R=G=0 (the origin), in an RG plane in the case where the B-axis value is fixed. As shown inFIG. 9, a total of 128 (i.e., 128 types of color tones) 1DLUTs from the 0-th line up to and including the 127th line are mapped to an RGB space.

FIG. 10is a diagram showing an illustration of a 3DLUT to which color material color conversion tables (1DLUTs) for four types of monochrome images have been mapped by the color material color coefficient generation unit607for example. As shown inFIG. 10, the 1DLUT for a monochrome image is mapped to grid points at the addresses in the 0-th to 3rd lines. Thus, in color material color development processing performed by the printer, color material color conversion tables (1DLUT) for a monochrome image for multiple types of color tones are mapped to one 3DLUT, and therefore color material color development processing for multiple types of color tones is performed with processing that is carried out one time. As a result, the speed of printing can be improved compared to the case where color material color development processing is carried out once for each tone.

Generation of One-to-Three Conversion Table in One-to-Three Conversion Unit

Next, the generation of a one-to-three conversion table to be used in the one-to-three conversion unit605will be described. As shown inFIG. 13, the one-to-three conversion unit605performs color conversion of input monochrome data into RGB data as the intermediate image data with use of a one-to-three conversion table. Then, color material color data corresponding to RGB data resulting from color conversion is obtained from a 3DLUT such as that described inFIG. 9andFIG. 10.

In the present embodiment, a table in which corresponding gray tone values and the RGB coordinate values thereof are mapped along the “0-th” arrow inFIG. 9is generated as the one-to-three conversion table. In other words, the gray tone value of 0 that corresponds to the origin 0 is mapped to the RGB=(0, 0, 0) of that point. Then, the gray tone value of 16 that corresponds to an adjacent grid point on the R axis is mapped to the RGB=(34, 0, 0) of that point. The one-to-three conversion table indicated by “0-th” inFIG. 11is obtained by continuing this type of mapping. In other words, change of RGB coordinate values along the “0-th” arrow inFIG. 9is indicated in the “0-th” one-to-three conversion table inFIG. 11. In this way, in each grid other than the origin, a gray gradation value is associated with a RGB coordinate value in which at least two of R, G, and B differ from each other.

For example, when performing pattern printing processing with respect to monochrome image data, first, the one-to-three conversion unit605converts monochrome image data into RGB data. For example, the gray tone value of 17 is converted into RGB data where RGB=(34, 0, 0). Then, in the downstream color material color development processing unit610in the printer107, color material color data mapped to the RGB=(25.5, 0, 0) in the 3DLUT is obtained. The color material color data that is obtained is of course color material color data that corresponds to the gray tone value of 17 inFIG. 8.

In the present embodiment, conversion in the one-to-three conversion unit605may be performed multiple times (equal to the number of the patterns) using one one-to-three conversion table, and a configuration is possible in which one-to-three conversion is performed using multiple one-to-three conversion tables. Also, in the present embodiment, a description was given regarding RGB data, in which the LUT used in color material color development processing is three-dimensional, but similar processing is possible with a four-dimensional LUT for CMYK data as well.

In Embodiment 1, a method was described in which input values not at grid points in the 3DLUT are calculated by interpolation calculation using adjacent grid points. In the present embodiment, a method of holding grid point data corresponding to all tone values of monochrome image data will be described. For example, if monochrome image data is assumed to have 256 tones in 8-bit data, data on 256 grid points are used as a table for monochrome images. In other words, grid point data for all 256 tone values of monochrome image data are held in a 3DLUT. In this case, grid point data in the 3DLUT need only be referenced, and interpolation calculation does not occur. Accordingly, when grid point data for monochrome image data is to be stored in the 3DLUT, it is not necessary to map that grid point data to adjacent grid point positions, as in the case described in Embodiment 1. In other words, grid point data of a 1DLUT can be mapped to random grid point positions in a 3DLUT. For example, if the number of grid points in the 3DLUT is 16×16×16=4096, 16 1DLUTs having 256 grid points each can be mapped to the 3DLUT, and in such a case, pattern printing of at most 16 types can be executed.

Other Embodiments

This application claims the benefit of Japanese Patent Application No. 2012-182639, filed Aug. 21, 2012, which is hereby incorporated by reference herein in its entirety.