JP4851369B2 - Image forming apparatus, image processing method, and image processing program - Google Patents

Description

  The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus that performs color conversion processing based on a lookup table that has been subjected to smoothing processing.

2. Description of the Related Art Conventionally, a printer device converts a multidimensional color signal input from a host computer or the like into another multidimensional color signal and outputs it, and outputs a three-dimensional lookup table (LookUpTable: hereinafter abbreviated as “LUT”). A suitable color conversion process can be performed by referring to the LUT, and a desired image output process can be performed (see, for example, Patent Document 1).
For example, in color signal processing of a color printer, in order to convert an RGB three-dimensional color signal of a display display system into a printer color signal such as CMYK, the RGB space is divided into lattice points on each axis, and the lattice point that is the vertex An LUT in which the output value CMYK is set at the position is used.

However, such a LUT simply applies numerical values that the manufacturer or its designer considers optimal, and does not necessarily ensure the gradation and continuity of the output values.
For this reason, an image output by a conventional printer device is not necessarily smooth, and unnatural color reproduction processing may be performed, which has been a problem.
Therefore, conventionally, the space represented by the input image data is divided into a grid pattern, the image data after color conversion at the grid points is calculated and smoothed, and the smoothed image data is converted into grid point data as a conversion table. And an image processing apparatus that performs color conversion using the conversion table has been proposed (see, for example, Patent Document 2).

JP2003-348365 (5th page, Fig. 1-2) Japanese Unexamined Patent Publication No. 2001-144981 (page 1-2, FIG. 11)

However, in the conventionally proposed image processing apparatus and the like as described above, the output values corresponding to the respective grid points when the RGB space is divided into grids are all uniformly smoothed, and the data after the smoothing process is processed. It is only necessary to generate a conversion table using the lattice point data. That is, in such smoothing processing, gradation processing with particular attention to the hue plane is not performed.
For this reason, when image processing is performed by such an image processing apparatus, when the target input image has a certain color tendency, the gradation continuity of the output image after conversion is lost, and an unnatural image is still output. There was a problem that there is a high possibility of being.

  The present invention has been proposed in order to solve the above-described problems of the conventional technology, and by setting a predetermined hue plane and using a LUT subjected to smoothing processing based on the hue plane, An object of the present invention is to provide an image forming apparatus that prevents a decrease in gradation continuity and an unnatural color conversion process in a certain hue range.

To achieve the above object, an image forming apparatus of the present invention is an image forming apparatus including a three-dimensional look-up table output CMYK data is stored corresponding to the input RGB data, a predetermined grating in the three-dimensional look-up table Grid point extraction means for extracting points, hue plane setting means for setting a predetermined hue plane for each of the extracted one or more grid points, and a predetermined attention point on the set one or more hue planes Attention point setting means for setting CMYK data, CMYK calculation means for calculating CMYK data corresponding to the attention point set by the attention point setting means, and by applying a predetermined smoothing process to the calculated CMYK data. Smoothing means for calculating CMYK data and the other CMYK data as the three-dimensional lookup table A smoothing LUT generation means for storing in association with each lattice point of a configuration equipped with.

According to the image forming apparatus of the present invention having such a configuration, the CMYK data is smoothed for each predetermined hue plane, and the LUT is created using the smoothed CMYK data.
The color conversion process is performed by the LUT.
Thereby, in the output image by the image forming apparatus according to the present invention, the balance and continuity of gradation on the hue plane are improved, and smooth gradation expression is possible.
Further, since the smoothing process is performed on the LUT itself, it is not necessary to perform a smoothing process again after the color conversion process, and unnecessary processing and labor are not generated.
Furthermore, since the LUT can be created based on a normal LUT mounted in advance, the image forming apparatus of the present invention can be realized with a simple configuration and can be provided at low cost.

The image forming apparatus of the present invention, the lattice point extracting means is adapted to be extracted highest grid point of saturation in the LUT.

According to the image forming apparatus of the present invention having such a configuration, a point having the highest saturation (Chromatic Peak Point) is extracted from the lattice points on the LUT, and a point constituting the hue plane is extracted. Like to do.
For this reason, when creating a new LUT, it is not necessary to set a hue plane for all the lattice points, so that the amount of data to be handled can be minimized and the processing speed can be improved.
Therefore, it is possible to quickly and easily create an LUT capable of improving tone continuity in the hue plane for an output image, and to quickly and easily realize an image forming apparatus equipped with such an LUT, Can be provided.

The image forming apparatus of the present invention, the hue plane setting means, a closed area formed by the lattice points and the black point and white point extracted by the grid point extracting means so as to set as one of the hue plane It is.

According to the image forming apparatus of the present invention having such a configuration, a certain closed area is set on the LUT, and an output value corresponding to the input value on such a closed area is set as a smoothing target.
Specifically, a plurality of triangular planes formed by one grid point on the LUT and black and white points are set and used for subsequent smoothing processing.

Accordingly, in the present invention, since the hue plane can be specified with a certain regularity, it is possible to suppress the necessary data amount and improve the processing speed when setting the hue plane.
Further, by adopting a chromatic peak point as the lattice point, this effect can be further enhanced.
Furthermore, by using such a hue plane, it is possible to efficiently extract a point where a point of interest arranged on the hue plane and a lattice point on the LUT coincide with each other, and a new LUT can be easily and accurately obtained. Can be created.
As described above, according to the present invention, it is possible to easily and accurately create an LUT capable of improving gradation continuity in the hue plane for an output image, and to easily provide an image forming apparatus equipped with such an LUT. Can be realized and provided.

The image forming apparatus of the present invention, the point of interest setting means, the LUT is when formed by n ³ grid, on the closed region formed by the hue plane setting means, to form the closed area Parallel lines that equally divide each line segment into (n-1) pieces are generated, and a point where these generated parallel lines intersect is set as a point of interest.

According to the image forming apparatus of the present invention having such a configuration, the points of interest on the closed region coincide with the lattice points on the LUT by arranging the points of interest on the closed region in a grid pattern. It is possible to extract effectively.
For this reason, when creating a new LUT, the addresses of known grid points on the LUT can be used as they are, and the correspondence with the LUT can be assigned easily and accurately.
In addition, since a general LUT that can be expressed in three dimensions can be used regardless of the difference in the number of lattices, versatility and expandability can be improved.
In this way, it is possible to easily create an LUT that not only has a smoothing effect but also has a wide adaptive range, and is equipped with such an LUT, so that it has excellent versatility and expandability, and gradation. An excellent image forming apparatus can be easily realized and provided.

In the image forming apparatus according to the aspect of the invention, the smoothing unit performs other smoothing processing on the CMYK data calculated by the CMYK calculation unit using a target point adjacent to the target point. Is calculated.

In particular, the image forming apparatus of the present invention, the smoothing means, by the target point setting means, the grid pattern is disposed a target point of the i rows × j columns, arithmetic expressions A '(i + 1) ( j- 1) = {(Aij + A (i + 2) (j-2)) / 2 + A (i + 1) (j-1)} / 2 is performed to obtain an arbitrary attention point A (i + 1) (j The CMYK data A ′ (i + 1) (j−1) after the smoothing process in -1) is calculated.
The image forming apparatus of the present invention, the smoothing means, by the target point setting means, the grid pattern is disposed a target point of the i rows × j columns, arithmetic expressions A'i (j + 1) = { By performing the processing according to (Aij + Ai (j + 2)) / 2 + Ai (j + 1)} / 2, the CMYK data A′i (j−1) after smoothing processing at an arbitrary attention point Ai (j−1) is obtained. I am trying to calculate.

According to the image forming apparatus of the present invention having such a configuration, the output data related to an arbitrary point of interest is smoothed using the output data related to the point of interest arranged adjacent to the front, rear, or right and left of the output data. Yes.
Specifically, all the smoothing processes can be performed uniformly using the above two equations.
As a result, the LUT subjected to the smoothing process in consideration of the hue plane can be created quickly and accurately, and an image forming apparatus equipped with the LUT can be provided.

The image forming apparatus of the present invention utilizes a three-dimensional look-up table output CMYK data is stored corresponding to the input RGB data, image processing for creating a look-up table which smoothing is applied to each color plane A method of extracting predetermined grid points in the three-dimensional lookup table; setting a predetermined hue plane for each of the extracted one or more grid points; and one or more set one or more By setting a predetermined attention point on the hue plane, calculating CMYK data corresponding to the set RGB data of the attention point, and performing a predetermined smoothing process on the calculated CMYK data Calculating other CMYK data, and converting the other CMYK data into the three-dimensional lookup. There as a method having the steps of storing in association with each lattice point of the table, the.

Thus, the present invention can be realized not only as the device invention described above but also as a method invention.
Therefore, the invention can be implemented without being restricted by the hardware configuration, and thus can be provided as a method having excellent versatility and expandability.

The image processing program of the present invention, a computer constituting an image forming apparatus including a three-dimensional look-up table output CMYK data is stored corresponding to the input RGB data, predetermined lattice points in the three-dimensional look-up table A grid point extracting unit for extracting a hue point, a hue plane setting unit for setting a predetermined hue plane for each of the one or more extracted grid points, and setting a predetermined attention point on the set one or more hue planes Attention point setting means, CMYK calculation means for calculating CMYK data corresponding to the set RGB data of the attention point, and smoothing means for calculating other CMYK data by applying a predetermined smoothing process to the calculated CMYK data , The other CMYK data to each grid point of the three-dimensional lookup table Smoothing LUT creation means for storing in association response is as a program to function as a.

Thus, the present invention can also be realized as a program.
As a result, the present invention can be realized by installing this program on various image forming apparatuses such as a copying machine, a facsimile machine, or a multi-function machine as well as a printer, and the versatility and expandability are improved. It can be provided as an excellent image processing program.

  According to the present invention, it is possible to quickly and easily create a look-up table having a good tone balance on the hue plane and excellent in continuity, and using such a look-up table, a natural and smooth color can be obtained. Reproduction output is possible.

A preferred embodiment of the present invention will be described below with reference to FIGS.
Here, the image forming apparatus (printer apparatus) of the present embodiment described below is realized by processing, means, and functions executed by a computer in accordance with instructions of a program (software). The program sends a command to each component of the computer to perform predetermined processing and functions as shown below. That is, each processing / means in the image forming apparatus (printer apparatus) of the present embodiment is realized by specific means in which a program and a computer cooperate.
Note that all or part of the program is provided by, for example, a magnetic disk, optical disk, semiconductor memory, or any other computer-readable recording medium, and the program read from the recording medium is installed in the computer and executed. The The program can also be loaded and executed directly on a computer through a communication line without using a recording medium.

FIG. 1 is a flowchart showing an operation procedure of an image forming apparatus according to an embodiment of the present invention.
FIG. 2 is a schematic diagram of a three-dimensional lookup table (LUT) 10 provided in advance in the image forming apparatus according to the present embodiment.
In the image forming apparatus according to this embodiment shown in these drawings, by referring to the LUT 10 shown in FIG. 2, arbitrary input image data (RGB) is converted into output image data (CMYK), and image output is performed. .
Then, a smoothing process for each hue plane is performed on the LUT 10 to easily and quickly create a look-up table with good tone balance on each hue plane and excellent continuity.

Specifically, first, RGB data of all orthogonal lattices on the LUT 10 are converted into angle values and calculated (step S1).
Here, as a method of converting RGB data into angle values, for example, RGB → HSB (Hue Saturation
It can be obtained by calculating H (Hue: hue) in Brightness conversion.

Hereinafter, a specific processing procedure of the angle conversion performed in step S1 of FIG. 1 will be described with reference to the flowcharts of FIGS.
FIG. 3 is a flowchart of the former stage for calculating the angle value managed in the image forming apparatus according to the present embodiment, and FIG. 4 is a flowchart showing the procedure of the latter stage.
Here, the procedure for calculating the angle value of the Green grid point will be specifically described as a representative example. However, the same procedure can be used for Red and Blue.

Further, in this angle calculation process, RGB data relating to all grid points on the LUT 10 is targeted. The initial values of the RGB data in this process are set as r = 0, g = 0, b = 0, min = 0, max = 0 for convenience, but the RGB data is substituted in the range of 0 to 1. Is converted into a predetermined angle value.
However, the RGB data is not limited to the above range, and may be a value expressed in a range of 0 to 255, assuming that the maximum value is 255 assuming a case of 256 gradations.

First, since the RGB data indicating Green is (R, G, B) = (0, 1, 0), R <G (A01: YES) and B <G (A02: YES). Therefore, it is determined that max = G (A03).
Further, in such RGB data, R> G is not satisfied (A04: NO), and B> R is not satisfied (A05: NO), so it is determined that min = B (A06).
As a result, margin = max−min = 1 (A07) and margin> 0 (A08: YES).
Since R = max (A09: NO), G = max (A10: YES), and B = min (A11: YES), Hue = {(max−R) / margin} × 60 + 60 = {( 1-0) / 1} × 60 + 60 = 120, and the angle value indicating Green is 120 [deg] (A12).
Thereafter, similarly, processing for converting RGB data into angle values is performed for all grid points on the LUT 10.

In addition, since the calculated | required angle value shall be the range of 0 [deg] or more and less than 360 [deg], the angle value of Red (1, 0, 0) will be 0 [deg], for example.
In step A08, when margin> 0 is not satisfied (A08: NO), hue = −1 is defined, which defines that it corresponds to a gray scale portion. Therefore, when max = min (margin = 0), it does not correspond to the chromatic peak point and is excluded from the target of the smoothing process.

Next, a process of extracting only the chromatic peak point (Chromatic Peak Point) which is the highest chroma point from all the angle values calculated in step S1 in FIG. Step S2).
Specifically, as shown in FIG. 2, the chromatic peak point is represented by each line segment of Red-Yellow, Yellow-Green, Green, Green-Cyan, Cyan-Blue, Blue-Magenta, and Magenta-Red on the LUT 10 (see FIG. 2 on the thick line).
Therefore, step S2 is to extract chromatic peak points at each lattice point on the line segment.

Here, a specific chromatic peak point calculation method will be described in detail with reference to the main flowchart of FIG. 5 and the sub-flowcharts of FIGS.
FIG. 5 is a flowchart showing a procedure for extracting a grid point corresponding to a chromatic peak point from grid points on the LUT 10 mounted in the image forming apparatus according to the present embodiment and calculating the RGB data.

As shown in the figure, the pattern angle is first calculated (B01). As shown in FIG. 6, the known angle values corresponding to the lattice points of the LUT 10 are classified into cases 0 to 6 according to a certain range.
As a result, when the angle value (deg) is 0 [deg] ≦ deg <60 [deg] (B101: YES), in the case of case1, 60 [deg] ≦ deg <120 [deg] (B102: YES) ), In case 2, 120 [deg] ≦ deg <180 [deg] (B103: YES), in case 3, case 180 [deg] ≦ deg <240 [deg] (B104: YES), Case 4 and 240 [deg] ≦ deg <300 [deg] (B105: YES) are classified as case 6 in case 5 and 300 [deg] ≦ deg <360 [deg] (B106: YES), respectively. Will be.
Case 0 is a case where the angle value is not included in the range of 0 [deg] ≦ deg <360 [deg], and such an angle value is excluded from the processing target.

Next, prior to performing a binary search described later, necessary basic data (initial values) are set (B02).
Specifically, the basic data of Point A, Point B, and Point C are set based on the procedure shown in FIG.
For example, in case 1 (B201: YES), the chromatic peak point between the line segments Red to Yellow is extracted by binary search, so that the basic data of Point A and Point B is converted to RGB data (2) (1, 0, 0) and (1, 1, 0) are set (B202), and basic data having Point C as the midpoint (1, 0.5, 0) is obtained (B203).

Next, all chromatic peak points are extracted based on the basic data set in step B02 (B03).
Specifically, according to the procedure shown in FIG. 8 and FIG. 9, processing for sequentially obtaining chromatic peak points is performed based on the binary search method.
FIG. 8 is a flowchart of the former stage showing the procedure for calculating the chromatic peak point in the image forming apparatus according to the present embodiment, and FIG. 9 is a flowchart showing the latter stage.

Hereinafter, the procedure of the process taking the case 1 as an example will be described in detail with reference to the flowcharts shown in FIGS.
In Case 1, as described above, the initial values of Point A, Point B, and Point C have already been obtained, and the RGB data are (1, 0, 0), (1, 1, 0), (1, 0.5, 0), respectively. ). For this reason, the angle values initially assigned to degree A, degree B, and degree C are degree A = 0 [deg], degree B = 60 [deg], and degree C = 30 [deg], respectively (B301).
Here, a predetermined calculation process is performed by substituting an arbitrary angle value (deg) (B302, B304, B306), and an angle value where each of marginA, marginB, and marginC becomes a minimum value is extracted (B303: YES, B305: YES, B307: YES). Specifically, deg when each margin is included in the range of −0.0001 ≦ margin ≦ 0.0001 is recognized as a chromatic peak point (get = 1), and the angle value is extracted.
Therefore, in the case of Case 1, angle values 0 [deg], 30 [deg], and 60 [deg] are extracted as a result of such processing, and these are converted into RGB data, respectively (1, 0, 0), ( 1,0.5,0) and (1,1,0), and the first chromatic peak point is extracted.

Next, in order to extract other chromatic peak points, corresponding angle values are extracted in the ranges of degree A <deg <degree C and degree C <deg <degree B (B308, B309).
In this example, the procedure is to obtain the corresponding angle values for the ranges of 0 <deg <30 and 30 <deg <60.
If the angle value is in the preceding range (B308: YES), the value of Point A is left as is, and the value of PointC is set to PointB (B310). If the angle value is in the subsequent range (B309: YES), the value of PointB As is, the value of PointC is set to PointA (B311), and RGB data of PointC, which is the next chromatic peak point, can be obtained by performing calculations using PointA and PointB, respectively (B312).
Specifically, the chromatic peak point located at the midpoint between Point A and Point B is calculated by the arithmetic expression Point C = (Point A + Point B) / 2.

Thereafter, by repeating the processes of Step B301 to Step B312 a predetermined number of times, all chromatic peak points in the range of case1 (0 ≦ deg ≦ 60) can be extracted, and the RGB data can be calculated.
Further, in cases 2 to 6, by performing the same processing as described above, all chromatic peak points on the LUT 10 are extracted, and the RGB data is calculated.

Next, a hue plane is set based on the chromatic peak point extracted in step S2 of FIG. 1 (S3).
Specifically, as shown in FIG. 10A, the hue plane is set by setting an arbitrary chromatic peak point on the LUT 10 (in this example, Red), White (1, 1, 1), and It can be set as a triangular closed region composed of Black (0, 0, 0).

Then, predetermined attention points are set on these triangular closed regions (S4).
Specifically, when the LUT 10 is composed of n ³ lattices, the parallel lines are drawn so that the chromatic peak point-white, chromatic peak point-black, and white-black line segments are equally divided (n-1). These intersection points are set as arbitrary points.
For example, on the hue plane where the chromatic peak point is a red lattice point, as shown in FIG. 10B, 45 set points are arranged in a lattice shape.
This is to effectively match the lattice points on the LUT 10 with the attention point on the hue plane, and to facilitate the creation of a new LUT 10 ′ after the smoothing process.

Next, CMYK data corresponding to the RGB data of the target point set in step S4 of FIG. 1 is calculated (S5).
Specifically, CMYK data can be calculated by interpolation calculation such as cube interpolation or tetrahedron interpolation using an existing LUT 10 installed in the image forming apparatus.
Then, the smoothing process is performed on the CMYK data for each hue plane calculated in step S5 (S6).

Specifically, the smoothing process is performed according to the procedure shown in FIG.
FIG. 11 is a flowchart showing the procedure of the smoothing process performed in the image forming apparatus according to the present embodiment.
As shown in the figure, first, CMYK data Aij (Pij) corresponding to all points of interest on the hue plane are extracted (C01).
Specifically, the initial values of i and j are set to 0, and the attention points P00... P08, P10... P17, P20 ... P26, P30 ... P35, P40 ... P44, P50. By selecting P53, P60... P62, P70, P71, P80, CMYK data corresponding to all the points of interest on the hue plane obtained in step S5 are picked up (loop 1, shown in FIG. 11). Loop 2).

Next, in the loop 3 shown in FIG. 11, a first smoothing process is performed (C02).
Specifically, if CMYK data at an arbitrary point of interest extracted in step C01 is Aij, the smoothed CMYK data is calculated by the following equation (1).
(1) A '(i + 1) (j-1) = {(Aij + A (i + 2) (j-2)) / 2 + A (i + 1) (j-1)} / 2
Thus, for example, when smoothing is performed for A17 shown in FIG. 12A, the value after such smoothing is A17 ′ = ((A08 + A26) / 2 + A17) / 2, and FIG. When smoothing is performed on the indicated A26, the value after such smoothing is A26 ′ = ((A17 ′ + A35) / 2 + A26) / 2.

Subsequently, the second smoothing process is performed by the loop 4 and the loop 5 shown in FIG. 11 (C03).
Specifically, if CMYK data at the attention point that could not be smoothed at least in step C02 is Aij, the CMYK data subjected to the smoothing process is calculated by the following equation (2).
(2) Ai (j + 1) = {(Aij + Ai (j + 2)) / 2 + Ai (j + 1)} / 2
Thus, for example, when smoothing is performed for A01 shown in FIG. 13A, the value after such smoothing is A01 ′ = ((A00 + A02) / 2 + A01) / 2, and FIG. When smoothing is performed on the indicated A02, the value after such smoothing is A02 '= ((A01' + A03) / 2 + A02) / 2.
As a result of the above, as shown in FIG. 14, a hue plane is formed by performing smoothing processing on CMYK data related to all the points of interest existing on one hue plane.

Next, a process of creating a new LUT is performed based on the smoothed CMYK data obtained in step S6 of FIG. 1 (S7).
This is to create a new LUT 10 ′ reflecting the smoothing effect on the hue plane by assigning the CMYK data after the smoothing process to the existing LUT 10 mounted in advance in the image forming apparatus.
In the present embodiment, an example using interpolation calculation will be described as a method for creating the LUT 10 ′.
Specifically, the optimal three grids are extracted by arranging the RGB data on the original LUT 10 for all the hue planes after the smoothing process in step S6, and CMYK is extracted from the optimal three grids by interpolation calculation. A method for calculating the value will be described.

First, a method for extracting the optimum three grids will be described with reference to FIG.
FIG. 15A shows a state after all the points of interest existing on the hue plane consisting of three points of Red, White, and Black are smoothed in the RGB space. It is assumed that the RGB data is known in advance and the smoothed CMYK data has already been calculated in step S6.

Here, the RGB data of the lattice points on the existing LUT 10 are arranged on this hue plane, and the sum SumDis of the three RGB distances included in the small triangle centering on the arrangement position P as shown in FIG. Try to find the smallest point.
In particular,
Dis1 = sqrt ((R1-R) (R1-R) + (G1-G) (G1-G) + (B1-B) (B1-B))
Dis2 = sqrt ((R2-R) (R2-R) + (G2-G) (G2-G) + (B2-B) (B2-B))
Dis3 = sqrt ((R3-R) (R3-R) + (G3-G) (G3-G) + (B3-B) (B3-B))
Each RGB distance is obtained by the above, and a small triangle (three grids) where the total value SumDis = Dis1 + Dis2 + Dis3 is minimized is extracted.

Next, corresponding CMYK values are obtained from the three grids by a predetermined interpolation calculation.
Specifically, the inner product S of the optimal three lattices is
S = V1 ・ V2 = ((R3-R2) (R1-R2) + (G3-G2) (G1-G2) + (B3-B2) (B1-B2)) / 2
Ask for.
Then, by the same method, inner products S1, S2, and S3 of triangles P1P2P, P2P3P, and P3P1P that form the optimum three lattices are also obtained.
Thus, CMYK data corresponding to the grid point P on the LUT 10 ′ can be obtained by the following equation.
C = (S1 / S × C3) + (S2 / S × C1) + (S3 / S × C2)
M = (S1 / S × M3) + (S2 / S × M1) + (S3 / S × M2)
Y = (S1 / S × Y3) + (S2 / S × Y1) + (S3 / S × Y2)
K = (S1 / S × K3) + (S2 / S × K1) + (S3 / S × K2)

  As described above, RGB data and corresponding CMYK data are obtained and stored in the existing LUT 10 to complete a new LUT 10 ′ that has been subjected to smoothing processing for each hue plane.

As described above, according to the image forming apparatus of this embodiment, a predetermined attention point is set for each hue plane, and the CMYK data corresponding to the attention point is smoothed.
Then, a new LUT 10 ′ is created based on the CMYK data after the smoothing process, and the color conversion process is performed.
For this reason, it is possible to realize an image forming apparatus that provides an output image having a good tone balance and continuity on the hue plane and smoothly reproducing colors.

In addition, focusing on a specific hue plane centered on the chromatic peak point and performing smoothing processing through arithmetic processing according to certain rules, while reducing the amount of data and processing burden, quality It is possible to ensure high gradation continuity.
Furthermore, a new LUT 10 ′ can be easily created using the LUT 10 mounted in advance, and it is possible to correspond to various image forming apparatuses equipped with such a lookup table. Yes.
Therefore, an image forming apparatus excellent in processing efficiency and versatility can be easily realized and provided at low cost.

The image forming apparatus according to the present invention has been described with reference to the preferred embodiments. However, the image forming apparatus according to the present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the present invention. It goes without saying that implementation is possible.
For example, the image forming apparatus of the present invention is not limited to a printer apparatus, but may be other image forming apparatuses such as a facsimile machine and a copier.

  The present invention can be suitably used for an image forming apparatus provided with a lookup table.

4 is a flowchart illustrating an operation procedure of the image forming apparatus according to the embodiment of the present disclosure. It is a schematic diagram of a three-dimensional lookup table provided in advance in the image forming apparatus according to the first embodiment of the present invention. 6 is a flowchart illustrating a previous procedure for calculating an angle value managed in the image forming apparatus according to the embodiment of the present disclosure. 6 is a flowchart illustrating a subsequent procedure for calculating an angle value managed in the image forming apparatus according to the embodiment of the present disclosure. 4 is a main flowchart showing a procedure for extracting a grid point corresponding to a chromatic peak point from grid points on an LUT mounted on an image forming apparatus according to an embodiment of the present invention and calculating RGB data thereof. FIG. 6 is a sub-flowchart showing a procedure for calculating a pattern angle in the main flowchart shown in FIG. 5. FIG. 6 is a sub-flowchart showing a procedure for setting basic data in the main flowchart shown in FIG. 5. In the main flowchart shown in FIG. 5, it is the sub-flowchart of the front | former stage which showed the procedure which calculates a chromatic peak point. 6 is a subsequent sub-flowchart showing a procedure for calculating a chromatic peak point in the main flowchart shown in FIG. 5. FIG. 6 is an explanatory diagram illustrating an example of a hue plane set in an LUT mounted on an image forming apparatus according to an embodiment of the present invention. 6 is a flowchart illustrating a procedure of smoothing processing performed in the image forming apparatus according to an embodiment of the present invention. FIG. 8 is an explanatory diagram for describing a specific example of smoothing processing performed in the image forming apparatus according to an embodiment of the present invention. FIG. 8 is an explanatory diagram for describing a specific example of smoothing processing performed in the image forming apparatus according to an embodiment of the present invention. FIG. 8 is an explanatory diagram for describing a specific example of smoothing processing performed in the image forming apparatus according to an embodiment of the present invention. It is explanatory drawing for demonstrating the method of extracting the optimal grating | lattice from the grating | lattice data in a hue surface, and calculating CMYK data by interpolation calculation.

Explanation of symbols

10 Existing 3D look-up table 10 'Newly created 3D look-up table

Claims (7)

In an image forming apparatus including a three-dimensional lookup table in which output CMYK data corresponding to input RGB data is stored,
Grid point extracting means for extracting predetermined grid points in the three-dimensional lookup table;
A hue plane setting means for setting a predetermined hue plane for each of the one or more extracted grid points;
Attention point setting means for setting a predetermined attention point on one or more of the set hue planes;
CMYK calculation means for calculating CMYK data corresponding to the attention point set by the attention point setting means;
Smoothing means for calculating new CMYK data by performing a predetermined smoothing process on the calculated CMYK data;
Smoothing LUT creation means for storing the new CMYK data in association with each grid point of the three-dimensional lookup table ;
The attention point setting means is
When the three-dimensional lookup table is formed by n ³ lattices, each line segment forming the hue plane is equally divided into (n−1) pieces on the hue plane formed by the hue plane setting unit. Set the point where parallel lines intersect as the point of interest,
The smoothing means comprises:
By arranging the RGB data on the three-dimensional lookup table for all the hue planes after the smoothing process, the optimum three grids are extracted from the attention points on the hue plane after the smoothing process. A CMYK data corresponding to the RGB data on the three-dimensional lookup table is calculated from the optimum three grids by interpolation calculation . The lattice point extraction means includes:
The image forming apparatus according to claim 1, wherein a lattice point having the highest saturation in the three-dimensional lookup table is extracted. The hue plane setting means includes
3. The image forming apparatus according to claim 1, wherein a closed region formed by the lattice point extracted by the lattice point extracting unit, the black point, and the white point is set as one hue plane. 4. The smoothing means comprises:
With respect to the attention points arranged in a grid of i rows × j columns by the attention point setting means,
The CMYK data A ′ (i + 1) (j−1) after smoothing processing at an arbitrary attention point A (i + 1) (j−1) is calculated by performing the following arithmetic processing. Item 4. The image forming apparatus according to any one of Items 1 to 3 .
A ′ (i + 1) (j−1) = {(Aij + A (i + 2) (j−2)) / 2 + A (i + 1) (j−1)} / 2 The smoothing means comprises:
  With respect to the attention points arranged in a grid of i rows × j columns by the attention point setting means,
  5. The CMYK data A ′ i (j−1) after the smoothing process at an arbitrary attention point A i (j−1) is calculated by performing the following arithmetic processing. The image forming apparatus described in 1.
  A'i (j + 1) = {(Aij + Ai (j + 2)) / 2 + Ai (j + 1)} / 2 An image processing method for creating a smoothed look-up table for each hue plane using a 3D look-up table storing output CMYK data corresponding to input RGB data,
  Extracting predetermined grid points in the three-dimensional lookup table;
  Setting a predetermined hue plane for each of the one or more extracted grid points;
  Setting a predetermined attention point on one or more of the set hue planes;
  Calculating CMYK data corresponding to the set RGB data of the attention point;
  Calculating new CMYK data by applying a predetermined smoothing process to the calculated CMYK data;
  Storing the new CMYK data in association with each grid point of the three-dimensional lookup table,
In the step of setting the predetermined attention point,
  The three-dimensional lookup table is n ³ When formed by a lattice, on the closed region formed by the step of setting the predetermined hue plane, parallel lines that equally divide each line segment forming the closed region into (n-1) pieces are generated. , And set the point where these generated parallel lines intersect as the point of interest,
In the step of calculating the new CMYK data,
  By arranging the RGB data on the three-dimensional lookup table for all the hue planes after the smoothing process, the optimum three grids are extracted from the attention points on the hue plane after the smoothing process. A CMYK data corresponding to the RGB data on the three-dimensional lookup table is calculated from the optimum three grids by interpolation calculation. A computer constituting an image forming apparatus including a three-dimensional lookup table storing output CMYK data corresponding to input RGB data;
Grid point extraction means for extracting predetermined grid points in the three-dimensional lookup table;
A hue plane setting means for setting a predetermined hue plane for each of the one or more extracted grid points;
Attention point setting means for setting a predetermined attention point on one or more of the set hue planes;
CMYK calculating means for calculating CMYK data corresponding to the set RGB data of the attention point;
Smoothing means for calculating new CMYK data by performing a predetermined smoothing process on the calculated CMYK data;
In functioning as a smoothing LUT creation means for storing the new CMYK data in association with each grid point of the three-dimensional lookup table,
In the attention point setting means,
When the three-dimensional lookup table is formed by n ³ lattices, each line segment forming the closed region is equally divided into (n−1) pieces on the closed region formed by the hue plane setting unit. Generate parallel lines, and set the point of intersection of the generated parallel lines as the attention point,
For the smoothing means,
By arranging the RGB data on the three-dimensional lookup table for all the hue planes after the smoothing process, the optimum three grids are extracted from the attention points on the hue plane after the smoothing process. An image processing program for causing CMYK data corresponding to RGB data on the three-dimensional lookup table to be calculated from the optimum three grids by interpolation calculation .

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