JP2010232975A - Color conversion table creation method, printer with color conversion table created by the color conversion table creation method, color conversion table created by color conversion table creation method, and printer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enhance time and efforts for creating a new LUT corresponding to other print sheets by effectively utilizing a created LUT corresponding to specific print sheets when the LUT has been created. <P>SOLUTION: In a reference print sheet A and a print sheet B of which the quantity of inks to be fixed per unit area is different from that of the print sheet A, an LUT (reference LUT) has been created for the print sheet A. A deviation between an ink saturation degree (=[the quantity of inks to be used]/[the maximum quantity of inks to be ejected]) for each of output colors of the reference LUT and an ink saturation degree for each of output colors of an LUT (new LUT) for the print sheet B is defined as a target function ΔE. The quantity of inks to be used to minimize the target function ΔE is calculated, and a correspondence relationship between input colors of the print sheet A and the quantity of inks to be used is predetermined to create the LUT for the print sheet B. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

The present invention relates to a color conversion table creation method, a printing apparatus including a color conversion table created by the color conversion table creation method, a color conversion table created by the color conversion table creation method, and a printing apparatus.

Since the recording medium such as printing paper has different ink fixing characteristics depending on the type, the desired printing result can be obtained even when printing on other printing paper with the amount of ink that can be printed on a certain printing paper to obtain a suitable printing result. It may not be obtained. In order to obtain the desired print results for each paper type, the gradation values of the element colors (R, G, B, etc.) of the image data can be set with a printing device such as a printer or a driver that controls the printer. Ink colors used by the printer (C, M, Y, K, etc.)
The color conversion process for converting to the gradation value is necessary. In this color conversion process, the color conversion LUT (Look
Generally, image data is converted into an ink amount set based on the correspondence relationship of up Table).

In order to obtain the correspondence relationship of the color conversion LUT, it is necessary to print and measure colors of patches of a plurality of ink amount sets. In general, the number of patches necessary to create an LUT is the number of grid points formed in the ink amount space by setting n representative points on each ink amount axis in the ink amount space. . That is, if the printer for printing with ink of m colors, n ^m pieces of patch printing and colorimetry is necessary, if further printing paper is x types x × n ^m pieces of patch printing and colorimetry Is required.

In view of such a situation, for example, Patent Document 1 discloses a technique for reducing the amount of work in creating a color correspondence. According to Patent Document 1, first, CMYKX (X
Prints and measures color gradation patches for each color (special color ink) to obtain ink characteristics, and obtains printer characteristics by printing and measuring mixed color patches with the execution area ratio of each color ink changed at equal intervals. Based on the ink characteristics and the printer characteristics, an output value at an arbitrary ink placement amount is calculated. Then, the pixel having the smallest color difference from the pixel of interest (RGB for which the color correspondence is being created) is searched from the already created RGB and CMYKX color correspondences, and color reproduction is performed using the ink ejection amount as an initial value. By calculating the error and comparing it with the color reproduction error of the ink placement amount in the vicinity of the ink placement amount, the ink placement amount that minimizes the color reproduction error is obtained.

JP 2005-47186 A

In the technique of Patent Document 1 described above, although the number of printing / colorimetric patches is reduced, at least printing of gradation patches for obtaining ink characteristics and mixed color patches for obtaining printer characteristics is indispensable.

The present invention has been made in view of the above-described problems. When a color conversion table corresponding to a specific print target has been created, another print target can be obtained by effectively using the created color conversion table. A color conversion table creation method capable of improving the trouble of creating a new color conversion table corresponding to the above, a printing apparatus having a color conversion table created by the color conversion table creation method, and a color conversion table creation method An object is to provide a color conversion table and a printing apparatus.

In order to solve the above-described problem, in the invention according to claim 1 of the present invention, in a situation where a color conversion table that defines the correspondence between color data and recording material usage is created for the first print target, A second printing object having a recording material fixing amount per unit area different from that of the first printing object is obtained by using a recording material fixing amount for the first printing object and the second printing object. Create a color conversion table for the print target.

In the present invention, first, the recording material saturation of the recording material usage amount in the color conversion table and the second
The deviation of the recording material saturation of the printing object is a so-called objective function, and the recording of the second printing object that minimizes the objective function while variously changing the recording material usage amount of the second printing object Calculate material usage. Then, among the recording material usage amounts of the color conversion table, the color data corresponding to the recording material usage amount used for the objective function is associated with the calculated recording material usage amount of the second print target. A color conversion table is created, and this is used as the second print target color conversion table.

In the above configuration, the printing target is a printing paper, a label surface of a disk-shaped recording medium, a fabric, a film, or the like, and is a target on which an image is printed. The recording material fixing amount is the maximum amount that can be fixed within a predetermined drying time when the recording material is adhered to a printing target. This recording material fixing amount corresponds to a so-called ink duty limit when the recording material is ink. The recording material saturation is a ratio of the recording material usage amount to the recording material fixing amount.

According to the above configuration, when a color conversion table corresponding to the first print target has been created, a new color corresponding to the second print target is effectively utilized by using the created color conversion table. The conversion table can be created without the need for patch printing or color measurement.
Therefore, the trouble of creating the color conversion table is greatly improved.

By the way, when the change rate of the recording material usage amount changes within a predetermined range where the recording material usage amount starts to be generated, the impression of the printing result may be greatly changed. As a selective aspect of the present invention suitable for such a case, the recording material usage amount of the created color conversion table is composed of a plurality of element colors, and the recording material usage is used to eliminate the deviation. It may be configured to preferentially minimize deviations of element colors whose amounts are within a predetermined range. According to this aspect,
Since the usage amount of the recording material that should express the subtle hue is preferentially optimized, a color conversion table capable of expressing the subtle hue is created.

Further, as a selective aspect of the present invention for preferentially optimizing the amount of recording material to be used to express a subtle hue, a recording material of a color conversion table that has been created in minimizing the deviation. Depending on the S-shaped tone curve with respect to the usage amount, weighting may be performed such that a small value approaches 0 and a large value approaches the recording material fixing amount. In this aspect, the value of the recording material to be used to express a subtle hue is less likely to increase, so that the amount of recording material to be used to express a subtle hue represents a subtle hue. The amount of recording material that is not used is biased so that the respective characteristics remain, as is not the case. Therefore, a color conversion table capable of expressing subtle hues is created.

Further, as a selective aspect of the present invention for preferentially optimizing the amount of recording material to be used to express subtle hues, the S-shaped tone curve is recorded in the created color conversion table. Different ones may be prepared for each of a plurality of element colors constituting the material usage amount. Therefore, a color conversion table capable of expressing a subtle hue according to the recording material is created.

The color conversion table creation method described above is implemented as part of another method or a color conversion table creation device provided with means corresponding to each process, the color conversion table created by the color conversion table creation method, the color conversion Various aspects such as a printing apparatus having a table and a printing control apparatus are included. It is also possible for the printing apparatus or the print control apparatus to include means corresponding to each step of the color conversion table creation method, and to dynamically create the color conversion table when executing printing or print control. The present invention also provides a color conversion table creation system provided with the color conversion table creation device, a program for causing a computer to realize functions corresponding to the configuration of the method described above, a computer-readable recording medium on which the program is recorded, and the like. It is feasible. The invention of these color conversion table creation system, color conversion table creation device, color conversion table creation program, and medium on which the program is recorded also has the above-described actions,
There is an effect. Of course, the configurations described in claims 2 to 4 are also applicable to the system, the apparatus, the program, and the recording medium.

It is a block diagram which shows the hardware constitutions of a LUT production apparatus. It is a block diagram which shows the software structure of a LUT production apparatus. It is an example of the recording material fixing amount. It is a figure explaining a specific area. It is an example of an S-shaped tone curve. It is an example of an S-shaped tone curve. It is a flowchart of a printing process. It is a flowchart of a LUT creation process. It is a figure explaining a mode that the representative point of a new LUT is produced | generated by an objective function. 10 is a flowchart of LUT creation processing according to Modification 1; It is a block diagram of the hardware constitutions concerning modification 2. 10 is a flowchart of LUT creation processing according to Modification 2;

Hereinafter, embodiments of the present invention will be described in the following order.
(1) Configuration of the present invention:
(1-1) Hardware configuration:
(1-2) Software configuration:
(2) Printing process:
(3) LUT creation processing:
(4) Modification 1:
(5) Modification 2:
(6) Modification 3:
(7) Summary:

(1) Configuration of the present invention:
(1-1) Hardware configuration:
FIG. 1 is a block diagram showing a hardware configuration of an LUT creation apparatus according to an embodiment of the present invention. In the present embodiment, the computer 100 constitutes an LUT creation apparatus, and the application APL executed on the computer 100 constitutes an LUT creation program. Note that the LUT creation apparatus of the present embodiment does not need to be connected to the printer 200 that actually performs printing using the LUT created by the LUT creation apparatus, and a new LUT for the reference LUT and the printer 200 is used. It is only necessary to store the recording material fixing amount of the printing paper to be created. The reference LUT is an LUT that is adjusted so that a suitable print result can be obtained when color conversion is performed with reference to the printer 200 when printing on predetermined paper.

A computer 100 shown in FIG. 1 executes, controls, and monitors a program through a predetermined system program. Specifically, a central processing unit (CPU) 10, a random access memory (RAM) 11, and a RO arranged on a system board (not shown).
M (Read Only Memory) 12 and a built-in or external hard disk (HD) 13 are provided, and the CPU 10 reads a required program from the HD 13 as appropriate and stores it in the RAM 12.
Necessary processing and control are executed using the RAM 12 as a work area. The HD 13 stores an application APL that generates a new LUT based on the reference LUT.

The computer 100 includes a display device 14 having a display screen, an operation input device 15 for receiving user operation input, a reading device 16 for reading information from a recording medium such as an optical disk drive and a flexible disk drive, and a local area network (LAN).
) And the communication control device 17 serving as a connection interface with the Internet. The display device 14 is configured to display a user interface screen such as a dialog window in response to an instruction from a system program, APL, or the like.

Note that by executing only the above APL, not only functions as an LUT creation device are formed, but a basic program such as an operating system running on the computer 100 based on an instruction of the APL is used for actual processing. A function as an LUT creation apparatus may be realized through some processing.

(1-2) Software configuration:
FIG. 2 is a block diagram showing a software configuration of the LUT creation apparatus according to the embodiment of the present invention. As shown in the figure, by executing APL with the LUT creation device, each unit M1
A function corresponding to ~ M6 is realized.

The paper receiving unit M1 receives an input of the designated type of printing paper, and instructs the recording material fixing amount acquisition unit M2 and the reference color correspondence acquisition unit M3 to create an LUT corresponding to the printing paper. It should be noted that the recording material such as ink may be attached to the printer by various things such as the label surface of the optical disc, the fabric and the film, and the recording material can also be attached to the ceramic or wood. . Therefore, as a concept including paper, optical disc label surface, fabric, film, ceramic, wood, etc., these are collectively referred to as a printing object or printing medium, and a paper receiving unit M
1 may accept the type of print object or print medium.

The recording material fixing amount acquisition unit M2 acquires the recording material fixing amount of each color ink for the designated printing paper. This recording material fixing amount is the maximum value of the ink that completes fixing on the printing paper when the paper is discharged at a predetermined speed while ink is attached to the predetermined printing paper. More conceptually, it can be said to be the maximum value of ink that can be fixed on the printing paper within a specified drying time. The recording material fixing amount is also the maximum amount that causes no significant bleeding when the recording material is attached to the printing paper.

As shown in FIG. 3, the recording material fixing amount is set in advance for each type of printing paper. In this embodiment, the recording material fixing amount of each printing paper scheduled to be printed by the printer 200 is It is stored in advance in a storage medium such as an HDD.
For example, in the present embodiment, the recording material fixing amount D _n1 (n) for each of the primary colors (for example, cyan (C), magenta (M), yellow (Y), and black (K)) of the ink set.
1 = C, M, Y, K) and secondary colors (C + M, M + Y, Y +) of color ink (C, M, Y)
C) Recording material fixing amount D _n2 (n2 = C + M, M + Y, Y + C) for each, recording material fixing amount D _n3 (n3 = C + M + Y + K) with respect to the sum of all inks (C + M + Y + K),
Are prepared for each printing paper and stored in the HD 13.

The reference color correspondence acquisition unit M3 sequentially acquires color correspondences one by one from the reference LUT. In the reference LUT, color correspondence relationships regarding a plurality of representative points are defined.
The color correspondence is, for example, a plurality of points having red (R), green (G), and blue (B) as element colors in the case of an LUT that converts RGB gradation values into CMYK gradation values. Correspondence between gradation values and gradation values having CMYK as an element color is defined. Hereinafter, the conversion source color in the color correspondence relationship is referred to as “input color”, and the conversion destination color is referred to as “output color”.
In general, the representative points are set uniformly in a predetermined color space and not overlapping each other. For example, in an LUT that converts RGB gradation values into CMYK gradation values, R, G,
In general, a plurality of points are set on the axis of each color B, and a plurality of lattice points formed in the ink amount space by the plurality of points are generally used as representative points.

The objective function generation unit M4 receives the recording material fixing amount D _{NEW of} the printing paper received by the paper receiving unit M1, the output color of the representative point Gn of the reference LUT, and the recording material fixing amount D of the printing paper corresponding to the reference LUT.
_An objective function ΔE is generated based on _ORG .
In this embodiment, the recording material fixing amount D _NEW refers to three types of recording material fixing amounts D _n1 , D _n2 , and D _n3 of the printing paper corresponding to the new LUT, and the recording material fixing amount D _ORG corresponds to the reference LUT. The recording material fixing amounts D _n1 , D _n2 , and D _n3 of the printing paper to be used are indicated. Further, n of the representative point Gn is a subscript for identifying each representative point, for example, n = 1, 2, 3,.

すなわちインク飽和度とは、代表点に設定された出力色の各インク量Ｉが記録材定着量Ｄ
に対して飽和している度合を示す量であるといえる。 The objective function ΔE is the ink saturation for each color of CMYK, which is the output color of the representative point Gn,
It is created for each representative point as a deviation from the ink saturation of the output color to be defined in the new LUT with respect to the input color of the representative point Gn. Here, the ink saturation is a ratio of the ink amount I to the recording material fixing amount D set for at least one color ink as shown in the following formula (1), and the recording material fixing amount D: The ink saturation is maximized when the ink amount I is equal to the ink amount I, and is minimized when the ink amount is zero.

In other words, the ink saturation is defined as the amount of ink I of the output color set as the representative point is the recording material fixing amount D.
It can be said that this is an amount indicating the degree of saturation with respect to.

The optimization processing unit M5 searches for a combination of ink colors that minimizes the objective function ΔE. For the optimization process for minimizing the objective function ΔE, a known optimization method such as a gradient method or a least square method can be used. The ink amount of the new LUT when the objective function ΔE is minimized is registered in the new LUT in association with the grid value acquired by the reference color correspondence acquisition unit M3. The new LUT created in this way is stored in the HD 13 in association with the type of printing paper designated in the paper designation unit M1.

The exception determination unit M6 determines whether or not the color correspondence acquired by the reference color correspondence acquisition unit M3b corresponds to data of a specific region that should express a delicate hue, and performs exception processing if applicable. . The specific area is an area where an ink amount starts to be generated with at least one color ink.
More specifically, when the ink amount Ink of any color ink falls within a “specific range” of 0 ≦ Ink ≦ [predetermined value], it can be said that the data is in a specific region.

The [predetermined value] serving as one threshold value in this specific range is, for example, a gradation value included in an output color having a color correspondence defined in the reference LUT, and the smallest value next to 0 is set for each color ink. [Predetermined value] can be considered. That is, in the color correspondence defined in the reference LUT, when the minimum value for C is gradation 0 and the second smallest C value is gradation 16, this gradation 16 is set to [predetermined value]. And so on. Accordingly, the specific range may differ for each ink color.

FIG. 4 is a diagram illustrating a specific area in the Lab space. This figure is a diagram showing the color gamut of the reference LUT projected onto the Lab color space, cut at a predetermined hue. In the figure, the part indicated by the thick arrow and its periphery correspond to the specific area. That is, a region from pure color to black, a region from white to pure color, and the like correspond to the specific region. The pure color is, for example, L ^* a ^* b ^*
When the color gamut when the ink is printed on the predetermined printing paper with the ink of the printer 200 in the color space is expressed, the color having the highest saturation among the hues of the color gamut is referred to. The pure color can also be said to be a color obtained by mixing two of the primary colors (C, M, and Y if the ink is four colors of CMYK).

In the specific area, the ink amount of the color ink corresponding to the specific range is small, and the ink saturation of the new LUT tends to deviate from the ink saturation of the reference LUT. If the ink saturation of the new LUT deviates in a direction larger than the ink saturation of the reference LUT, there is a possibility that gradation will not be smooth in a specific area when color conversion is performed based on the new LUT.

Therefore, when the exception determination unit M6 acquires a color correspondence corresponding to the specific region, the exception determination unit M6 causes the optimization processing unit M5, which will be described later, to correspond to a specific range compared to an ink color that does not correspond to the specific range. An optimization process is executed such that the ink saturation level of the ink color tends to approach the ink saturation level of the reference LUT, and the ink saturation level becomes smaller than the ink saturation level of the reference LUT.

For example, the exception determination unit M6 causes the objective function generation unit M4 to create an objective function with a higher weight for the ink amount data corresponding to the specific range, or causes the optimization processing unit M5 to generate the ink amount data corresponding to the specific range. For example, the optimization process is performed first to fix the value.

As a weighting method, it is conceivable to use an S-shaped tone curve as shown in FIG. When the ink amount data is converted using the S-shaped tone curve shown in the same figure, data with a small ink amount is converted into a smaller value, and data with a large ink amount is converted into a larger value. Therefore, since the ink saturation of data with a small amount of ink is optimized so as to converge to a value smaller than the value to be converged, there is a possibility of optimization to a value larger than the ink saturation of the reference LUT. Is very small, and the possibility that the gradation of a specific area in the new LUT becomes coarser than that of the reference LUT is reduced. Of course, the weighting method is not limited to the S-shaped tone curve, and weighting may be performed so that the objective function expands more sensitively as the ink amount data of the output color becomes smaller.

The weighting method may be different for each ink color. This is because the color difference that occurs when the ink amount changes in unit amount for each ink color is different, and the range that is desired to be set as the specific region also differs for each ink color. Specifically, for example, as shown in FIG. 6, the rising point of the S ink tone curve of the M ink is set to a lower gradation side than the S ink tone curve of the C ink, or the rising edge of the S character tone curve is made steep. To do. This is because the M ink has a larger color difference per unit amount than the C ink. In this way, by applying different S-shaped tone curves for each ink color, it is possible to control for each ink color a specific area where it is desired to maintain a subtle hue change in the reference LUT in the gradation realized by the new LUT.
Hereinafter, the printing process executed using the created new LUT will be briefly described, and then the LUT creation process executed by the APL will be described.

(2) Printing process:
FIG. 7 is a flowchart of the printing process. The printing process shown in the figure is executed by the printer driver (PRTDRV) controlling the printer 200 in the computer 100 in which the LUT created by the LUT creation device is installed. The printing process shown in the figure is started when the user instructs printing that designates image data to be printed. Note that the image data to be printed may be raster data or vector data. The print target may be not only image data but also text data such as document data, or data in which a document and an image are mixed.

In step S100 (hereinafter, description of “step” is omitted), PRTDRV.
Accepts the input of image data, and causes the language interpreter to interpret the print data as necessary, thereby generating bitmap image data in which each pixel is expressed by a gradation value of each RGB color, and performs resolution conversion processing. The language interpretation unit interprets a print job language such as PDL, and instructs PRTDRV to generate image data in which the layout, format, and the like are changed according to the interpretation result. The resolution conversion process is a process for converting the resolution of the received image data into a resolution (printing resolution) at which the printer 200 intends to print an image. When the print resolution is higher than the resolution of the image data, the resolution is increased by performing an interpolation operation to generate new image data between pixels. Conversely, when the resolution of the image data is higher than the print resolution, the resolution is lowered by thinning out the read image data at a certain ratio.

In S105, PRTDRV performs color conversion processing of image data. The color conversion process in the present embodiment is an LUT associated with a print sheet designated when printing is instructed.
The RGB color image data expressed by a combination of R, G, and B gradation values is converted into image data expressed by a combination of gradation values of each color used for printing. It is processing. The printer 200 prints an image using four color inks of C, M, Y, and K. Therefore, in the color conversion process of this embodiment, a process of converting image data expressed by RGB colors into data expressed by gradation values of C, M, Y, and K colors is performed.

In S110, PRTDRV performs halftone processing on the CMYK image data. This halftone process is a process for determining the presence or absence of dot formation for each pixel in order to generate dots at an appropriate density according to the gradation value of the gradation data. For example, a method such as a dither method or an error diffusion method Done in The PRTDRV converts the pixel data into control data indicating dot on / off, and outputs the converted data to the printer 200 as spool data.

In step S115, the control unit 21 of the printer 200 performs printing according to the control data.
The control unit 21 prints an image by forming dots on the printing paper in accordance with the control data created by the halftone processing unit. That is, the control unit 21 drives the paper feed mechanism 27c, and ejects ink droplets from each print head of the print head unit 25c based on the dot data in accordance with this movement. As a result, ink dots of appropriate colors are formed at appropriate positions on the printing paper, and image data is printed.

(3) LUT creation processing:
FIG. 8 is a flowchart of LUT creation processing executed by the APL, and FIG. 9 is a diagram for explaining how representative points of a new LUT are generated by an objective function. The process of FIG. 8 is executed when the user gives a predetermined instruction to the APL via the user interface or the like. The predetermined instruction includes an instruction for designating a reference LUT to be used as a base for LUT creation processing from among the created LUTs stored in the HD 13, and an instruction for creating a new LUT based on the reference LUT.

In S200, the sheet receiving unit M1 receives the designation of the printing sheet. For example, the paper reception unit M
1 displays a list of print sheets that can be printed by the printer 200 on the display device 14 except for print sheets associated with the reference LUT and print sheets associated with the already created LUT. When the user operates the operation input device 15 to select a desired printing paper from the list, the paper receiving unit M1 receives the selected printing paper.

In S205, the recording material fixing amount acquisition unit M2 acquires the recording material fixing amount of the printing paper received by the paper receiving unit M1 in S200 from the HD 13 as the recording material fixing amount D_NEW, and the printing paper associated with the reference LUT. Is obtained from the HD 13 and is set to D_ORG.

In S210, the reference color correspondence acquisition unit M3 acquires the data of the reference LUT from the HD 13, and selects one unselected one from the representative points of the reference LUT. When returning from S240 and executing S210, only the process of selecting one unselected one from the representative points of the reference LUT is executed.

In S215, the exception determination unit M6 determines whether or not the output color of the grid data selected in S210 corresponds to the specific area. The exception determination unit M6 proceeds to S220 if the input grid data corresponds to the specific area, and proceeds to S225 if not.

In S225, the optimization processing unit M5 records the recording material fixing amount D_ORG and the recording material fixing amount D_N.
Based on the EW and the output color I_ORG of the representative point selected in S210, the output color I_NEW of the new LUT is determined. At this time, for each ink color constituting the representative point of the new LUT, I_NEW is calculated such that the reference LUT approximates the ink saturation. For this purpose, the optimization processing unit M5 causes the objective function generation unit M4 to create an objective function ΔE. For example, the following equation (2) can be adopted as the objective function ΔE.

As shown in the above equation (2), the objective function ΔE is the recording material fixing amounts D _n (n = C, M, Y, K, C +
Ink saturation (= I_ORG /) of the reference LUT every M, M + Y, Y + C, C + M + Y + K)
D_ORG) and the new LUT ink saturation (= I_NEW / D_NEW) are calculated, and these deviations are sums of squares.

In S230, the optimization processing unit M5 generates a gradation value of each color of CMYK using a predetermined algorithm and inputs it to the objective function ΔE, and searches for a combination of gradation values of each color of CMYK that minimizes the objective function ΔE. . Any known optimization method such as a gradient method or a least square method can be adopted as an algorithm for generating gradation values for each color of CMYK in this optimization process. The gradation value combination searched for minimizing the objective function ΔE is the combination whose relationship with the ink saturation of the representative point acquired in S210 is the closest overall.

In S235, the optimization processing unit M5 determines the output color optimized in S230 and S21.
The input color of the representative point selected at 0 is associated with and registered in the new LUT.

On the other hand, when the process proceeds from S215 to S220, the exception determination unit M6 preferentially optimizes the color data constituting the output color of the representative point that falls within a specific range.
In other words, the exception determination unit M6 causes the objective function generation unit M4 to create the objective function ΔE1 configured only by the ink saturation determined only by the color data corresponding to the specific range, and minimizes the objective function ΔE1. The optimization processing unit M5 is caused to perform optimization processing for searching for gradation value combinations.

For example, the output color of the representative point acquired in S210 is (C, M, Y, K) = (255, 1, 1).
, 1), M, Y, and K fall within a specific range. Therefore, as shown in the following equation (3), the ink saturation is determined only by M, Y, and K. Generated objective function ΔE ₁ is generated.

なお、目的関数ΔＥ２を最小化させる際は、目的関数ΔＥ１の最適化処理によって探索済
みの階調値組合せについては固定した状態で実行する。 Exception determination unit M6 minimizes the objective function Delta] E ₁ of the optimization processing unit M5 (3) formula M
, Y, K after searching for the gradation value combination, the objective function generator M4 uses the objective function ΔE2 of the following equation (4) configured with ink saturation that is not determined only by the color data corresponding to the specific range.
The optimization processing unit M5 performs an optimization process of searching for a gradation value combination that minimizes the objective function ΔE2.

When the objective function ΔE2 is minimized, the gradation value combinations that have been searched for by the optimization process of the objective function ΔE1 are executed in a fixed state.

By performing the optimization process in the above order, the ink saturation of the color data corresponding to the specific range is closer to the ink saturation of the reference LUT than the ink saturation of the color data not corresponding to the specific range. The output color gradation value combination is calculated as follows. Therefore, the ink amount data that has been color-converted based on the new LUT inherits the subtle gradation expressed by the reference LUT in the gradation of the specific area.
As described above, when the search for the tone value combination optimized by using the equations (3) and (4) is completed, the optimization processing unit M5 proceeds to S235 and searches for the tone value combination that has been searched for as a new LUT. Register with.

If all the color data constituting the output color of the representative point acquired in S210 falls within a specific range, the process proceeds from the decision branch of S215 to S225 and is optimized using the objective function of the equation (2). Alternatively, an objective function is generated for each color from the high priority colors as shown in the above formulas (3) and (4) based on the predetermined priority for each color, and optimized in order of priority. Also good.

In S240, the reference color correspondence acquisition unit M3 determines whether all representative points of the reference LUT have been selected in S210. The reference color correspondence acquisition unit M3 ends the LUT creation process when all the representative points have been selected, and when there is an unselected representative point, returns to S210 to select an unselected representative point and performs S210 to S210. The process of S240 is repeated. When the processing of S210 to S240 is executed for all grid data, a new LUT in which the same number of color correspondences as the color correspondences registered in the reference LUT is created. The created new LUT is stored in the HD 13 in association with the printing paper selected in S200.

(4) Modification 1:
In the above-described embodiment, the LUT creation process that selectively uses the optimization process and the exception process depending on whether or not it is the representative point of the specific area has been described. However, in the first modification, the optimization process is not properly used. Instead, the same optimization process is performed by weighting the color data before creating the objective function.
FIG. 10 is a flowchart of the LUT creation process according to the first modification. In the figure, steps common to the LUT creation processing of FIG. 8 are denoted by the same step numbers.
Also, description of steps common to those in FIG. 8 will be omitted below.

In S315, the exception determination unit M6 weights each color data constituting the output color of the representative point selected in S210 with, for example, an S-shaped tone curve shown in FIG. Each color data after this weighting is changed so as to be closer to 0 than the original value for the data corresponding to the specific range, and maximum for the data not corresponding to the specific range than the original value. It is changed to approach the gradation. That is, when weighting is performed with the S-shaped tone curve, whether or not each color data falls within a specific range becomes conspicuous.

In S320, the optimization processing unit M5 creates an objective function ΔE ′ shown in the following equation (5). In the following equation (5), W _S is the weighting factor of the S-shaped tone curve.

In the equation (5), since the ink amount saturation of the output color of the representative point selected in S210 is calculated using each color data W _S × I_ORG _n weighted in S315, this objective function ΔE ′ is minimized. i - new _n which is searched to reduction is also optimized to approach the _{W S} × I_ORG _n. That is, when color conversion is performed based on the new LUT created in the first modification,
The possibility that the precision of gradation in a specific area will be lower than when color conversion is performed based on the reference LUT can be made extremely low. In the first modification, weighting is performed with the same S-shaped tone curve for all colors, but different S-shaped tone curves may be used for each color as shown in FIG.

(5) Modification 2:
In the embodiment and the modification described above, the example in which the LUT creation process is executed by the computer 100 not connected to the printer 200 has been described.
The T creation process may be executed by the printer driver of the computer 100 that controls the printing process of the printer 200. In this case, the connection between the computer 100 and the printer 200 is essential, and the computer 100 constitutes an LUT creation apparatus and a print control apparatus.

FIG. 11 is a block diagram of a hardware configuration according to the second modification, and FIG. 12 is a flowchart of an LUT creation process according to the second modification. The LUT creation process according to the second modification is executed as part of the printing process. Since each component of the software is the same as that in the above-described embodiment, description of common components is omitted, and steps common to the above-described embodiment are assigned the same step numbers in the LUT creation processing and printing processing, Description is omitted.

As shown in FIG. 11, the printer 200 of this embodiment is an ink jet printer that prints by forming CMYK (cyan, magenta, yellow, black) ink from a print head to form ink dots on a print medium. is there. Of course, an ink jet printer that uses other types of ink may be employed as the printer 200, and an ink sublimation printer, a laser printer that uses toner ink, or the like may be employed as the printer 200.
The printer 200 includes a control unit 21, an operation unit 22, a control circuit 25a, an ink cartridge 25b, a print head unit 25c, an ASIC 26a, and a head drive unit 26b.
And an I / F 27a, a carriage mechanism 27b, and a paper feed mechanism 27c.

The control unit 21 includes a CPU 21a, a ROM 21b, and a RAM 21c.
In accordance with a control program CP (not shown) recorded in b, the CPU 21a controls the entire printer 200 using the RAM 21c as a work area. The units 21, 22, 23, 24, 25a, 26a, and 27a constituting the printer 200 are connected via a system bus so that they can communicate with each other. The control unit 21 includes the units 21, 22, 23, 24, 25a, 26a, 2
7a is controlled to perform printing based on the image data.

A carriage that reciprocates in the main scanning direction by the carriage mechanism 27b is provided with a cartridge holder in which each ink cartridge 25b is mounted, and a print head unit 25c having a print head is mounted.
The head drive unit 26b receives the applied voltage data corresponding to the print data from the ASIC 26a, generates an applied voltage pattern to the piezo element, and causes the print head incorporating the piezo element to eject ink droplets of four colors in dot units. . The carriage mechanism 27b and the paper feed mechanism 27c connected to the interface (I / F) 27a perform the sub-scan by sequentially feeding the sheet-like print medium while performing the main scanning of the print head unit 25c or performing the page break operation as appropriate. To go.

The LUT creation process in the second modification is called and executed by the PRTDRV at any stage after the image data is input and the printing process is started until the color conversion process performs color conversion with reference to the LUT. Is done.
When the LUT creation process shown in FIG. 12 is started, in S500, the sheet receiving unit M1 determines whether or not an LUT corresponding to the print sheet designated in the printing process has already been created and stored in the HD 13. If the LUT corresponding to the printing paper has been created, the paper reception unit M1 ends the process. If the LUT corresponding to the printing paper has not been created, the paper reception unit M1 proceeds to S205, and creates a new LUT based on the reference LUT. . When the creation of the new LUT is completed, P
Notify RTDRV that the creation of a new LUT has been completed. The PRTDRV that received the notification
Color conversion is performed with reference to the new LUT, and subsequent halftone processing or the like is executed.

As described above, in the second modification, the LUT corresponding to the frequently used paper is used as the reference LUT.
For other printing papers, only the recording material fixing amount data is held, and an LUT can be dynamically created as necessary. Therefore, it is not necessary to hold the LUT for printing paper that is not frequently used, and the storage area of the LUT can be saved. In addition,
The created new LUTs may be retained, and those exceeding a predetermined number may be deleted sequentially except for the reference LUT according to the usage frequency. In addition, the recording material fixing amount of each printing paper is displayed on the display such as a user interface for inputting the recording material fixing amount when it is necessary to create a new LUT even if it is not stored in the HD 13 or the like in advance. Then, the user may input it.

(6) Modification 3:
In the embodiment and the modification described above, the example in which the computer 100 executes the LUT creation process has been described. However, the LUT creation process may be executed by the printer 200. In this case, a program (for example, firmware or the like) that controls the printer 200 executes the LUT creation process, and the printer 200 constitutes a printing apparatus, and the computer 100 constitutes an LUT creation apparatus and a print control apparatus.

In the third modification, a control program capable of executing a process corresponding to the PRTDRV that executes the above-described printing process is stored in the ROM 21b, and the LU of the second modification described above.
A program capable of executing a process corresponding to the T creation process is also stored in the ROM 21b. When image data is input to the printing apparatus by specifying a print sheet together with a print command, the control program executes the LUT creation process while performing the same print process as in the above-described modification example 2,
A new LUT is dynamically created as necessary, and the created LUT is stored in a rewritable nonvolatile memory such as the EEPROM 28.

In the second modification, the same operational effects as those of the above-described embodiment and the second modification are achieved. In particular, the storage area saving effect described in the second modification is a printer having a very small storage area compared to the computer 100. At 200, it is remarkable.

(7) Summary:
In the embodiment described above, an LUT (reference LUT) has been created for the print sheet A, the print sheet A serving as a reference, and the print sheet B having a different ink fixing amount per unit area. In the situation, the ink saturation (= [ink usage amount] / [ink fixing amount]) for each output color of the reference LUT and the LUT (new LU) for the printing paper B
The deviation from the ink saturation for each output color of T) is set as the objective function ΔE, the ink usage amount that minimizes the objective function ΔE is calculated, and the correspondence relationship between the input color of the printing paper A and the calculated ink usage amount Is a new LUT. Therefore, when the reference LUT has been created, a new LUT can be easily created by effectively utilizing the reference LUT.

Note that the present invention is not limited to the above-described embodiments and modifications, and the configurations disclosed in the above-described embodiments and modifications are mutually replaced, the combinations are changed, the known technology, and the above-described implementations. Configurations in which the configurations disclosed in the embodiments and modifications are replaced with each other or combinations are also included.

10 ... CPU, 11 ... RAM, 12 ... ROM, 13 ... hard disk, 14 ... display device,
15 ... Operation input device, 16 ... Reading device, 17 ... Communication control device, 100 ... Computer,
DESCRIPTION OF SYMBOLS 200 ... Printer, M1 ... Paper reception part, M2 ... Recording material fixing amount acquisition part, M3 ... Standard color correspondence acquisition part, M4 ... Objective function generation part, M5 ... Optimization processing part, M6 ... Exception determination part

Claims (7)

When a color conversion table that defines the correspondence between color data and recording material usage has been created for the first print target,
For a second print object having a recording material fixing amount per unit area different from that of the first print object, the recording material saturation of the recording material usage amount in the color conversion table and the recording material saturation of the second print object Color conversion table creation for calculating the recording material usage amount of the second printing target so as to eliminate the deviation from the degree, and creating a color conversion table that defines the correspondence between the calculated recording material usage amount and the color data Method. The recording material usage of the created color conversion table is composed of a plurality of element colors.
The color conversion table creation method according to claim 1, wherein, when the deviation is eliminated, the deviation of the element colors whose recording material usage is within a predetermined range is preferentially minimized. In minimizing the deviation, the recording material usage amount of the created color conversion table is S
3. The color conversion table creation method according to claim 1, wherein weighting is performed so that a small value approaches 0 and a large value approaches a recording material fixing amount according to a character tone curve. 4. The color conversion table creation method according to claim 3, wherein different S-shaped tone curves are prepared for a plurality of element colors constituting the recording material usage of the created color conversion table. A printing apparatus in which a color conversion table created by the color conversion table creation method according to any one of claims 1 to 4 is recorded,
When printing for the second print target is instructed, the input color data is converted into a recording material usage amount with reference to the created color conversion table, and the recording material usage amount is converted into the recording material usage amount. A printing apparatus that is attached to a printing object of No. 2. When a color conversion table that defines the correspondence between color data and recording material usage has been created for the first print target,
For a second print object having a recording material fixing amount per unit area different from that of the first print object, the recording material saturation of the recording material usage amount in the color conversion table and the recording material saturation of the second print object A color conversion table created by associating the calculated recording material usage amount with the color data by calculating the recording material usage amount of the second printing target so as to eliminate the deviation from the degree. A printing apparatus in which a color conversion table defining a correspondence relationship between color data and recording material usage for a first print target is recorded,
For a second print object having a recording material fixing amount per unit area different from that of the first print object, the recording material saturation of the recording material usage amount in the color conversion table and the recording material saturation of the second print object Calculating the recording material usage amount of the second printing target so as to eliminate the deviation from the degree, and creating a color conversion table that defines the correspondence between the calculated recording material usage amount and the color data;
When printing on the second print target, the input color data is converted into a recording material usage amount with reference to the created color conversion table, and the recording material of this recording material usage amount is converted into the second recording material.
A printing apparatus characterized by adhering to an object to be printed.

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