JP3785282B2 - Color image processing apparatus, color image processing method, and computer-readable recording medium storing a program for causing a computer to execute the method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a color image processing apparatus, a color image processing method, and a program for causing a computer to execute a method for intentionally and arbitrarily converting a certain color in a color image or converting a specified color to another specified color. The present invention relates to a computer-readable recording medium on which is recorded.
[0002]
[Prior art]
Conventionally, as a device for extracting a hue region, for example, in Japanese Patent Application Laid-Open No. 1-114267, multiplication processing is performed according to the magnitude of the largest signal among a plurality of digital color images (R, G, B). There has been proposed a hue detection apparatus that detects a hue using a multiplied image signal.
[0003]
In Japanese Patent Laid-Open No. 1-269365, a hue region to which a color indicated by an image signal belongs is determined, a set of predetermined parameters is selected according to the determined region, and an image signal is output based on the selected parameter. A color image processing apparatus in which color conversion is made variable by processing has been proposed.
[0004]
In a conventional apparatus for extracting a hue area, such as the hue detection apparatus according to Japanese Patent Laid-Open No. 1-114267 and the color image processing apparatus according to Japanese Patent Laid-Open No. 1-269365, the boundary for detecting the hue is detected. Are separated by a straight line.
[0005]
[Problems to be solved by the invention]
However, the hue variation in the actual color is curved as shown in the hue variation characteristic of FIG. Therefore, in the conventional correction technique, when an operator converts a certain color to an arbitrary color, for example, when changing red to cyan, the color may not be converted as expected by the operator. There was a problem that there was.
[0006]
This is because, as can be seen from the hue variation characteristics shown in FIG. 10, the hue variation of red due to the CMY image is not linear between the low saturation and the high saturation.
[0007]
In order to eliminate the above-described problems caused by the conventional example, the present invention provides a color image processing apparatus, a color image processing apparatus capable of performing color conversion as expected by an operator when a specified color is color-converted to another specified color. An object of the present invention is to provide a computer-readable recording medium on which an image processing method and a program for causing a computer to execute the method are recorded.
[0008]
[Means for Solving the Problems]
In order to solve the above-described problems and achieve the object, a color image processing apparatus according to the present invention converts a color space represented by an input color image signal into a plane and generates a plane signal. A saturation identification unit that identifies the saturation of the color image signal based on the plane signal generated by the plane signal conversion unit and generates a saturation identification signal; and the plane generated by the plane signal conversion unit A hue area identifying means for identifying a hue area in the color image signal based on the signal and generating a hue area identifying signal; a saturation identifying signal generated by the saturation identifying means; and a hue area identifying means And color conversion means for performing color conversion of the color image signal based on the hue area identification signal.
[0009]
According to the present invention, it is possible to intentionally arbitrarily perform color conversion on a certain color in a color image even in an image with different saturation.
[0010]
The color image processing apparatus according to the present invention further comprises color conversion instruction means for instructing conversion from a designated color designated by an operator to another designated color in the above invention, wherein the color conversion means However, color conversion of the color image signal is performed based on the other specified color.
[0011]
According to the present invention, even in an image with different saturation, it is possible to intentionally arbitrarily convert a certain color in the color image based on the operator's color designation.
[0012]
Further, the color image processing apparatus according to the present invention, in the above invention, further includes a masking coefficient calculating means for calculating a masking coefficient of a plurality of hue regions, and a masking coefficient calculated by the masking coefficient calculating means. Masking coefficient selection means for selecting a masking coefficient based on the saturation identification signal generated by the saturation identification means and the hue area identification signal generated by the hue area identification means, and the color conversion means, The color conversion of the color image signal is performed using the masking coefficient selected by the masking coefficient selection means.
[0013]
According to the present invention, it is possible to select an optimal masking coefficient when performing color conversion.
[0014]
[0015]
[0016]
Further, the color image processing method according to the present invention is generated by the plane signal conversion step of converting the color space represented by the input color image signal into a plane and generating a plane signal, and the plane signal conversion step. Saturation identification step for identifying the saturation of the color image signal based on a plane signal and generating a saturation identification signal, and the hue of the color image signal based on the plane signal generated by the plane signal conversion step A hue region identifying step for identifying a region and generating a hue region identifying signal; a color based on the saturation identifying signal generated by the saturation identifying step and the hue region identifying signal generated by the hue region identifying step; And a color conversion step of performing color conversion of the image signal.
[0017]
According to the present invention, it is possible to intentionally arbitrarily perform color conversion on a certain color in a color image even in an image with different saturation.
[0018]
The color image processing method according to the present invention further includes a color conversion instruction step for instructing conversion from a specified color specified by an operator to another specified color in the above-described invention, wherein the color conversion step includes: Color conversion of the color image signal is performed based on the other specified color.
[0019]
According to the present invention, even in an image with different saturation, it is possible to intentionally arbitrarily convert a certain color in the color image based on the operator's color designation.
[0020]
Further, in the color image processing method according to the present invention, in the above invention, a masking coefficient calculation step for calculating a masking coefficient of a plurality of hue regions, and a masking coefficient calculated by the masking coefficient calculation step, A masking coefficient selection step for selecting a masking coefficient based on the saturation identification signal generated by the saturation identification step and the hue region identification signal generated by the hue region identification step, and the color conversion step includes The color conversion of the color image signal is performed using the masking coefficient selected in the masking coefficient selection step.
[0021]
According to the present invention, it is possible to select an optimal masking coefficient when performing color conversion.
[0022]
[0023]
[0024]
Further, the recording medium according to the present invention records a program that causes a computer to execute the method described above, so that the program can be read by a machine, and thus the above operation can be realized by a computer. It is.
[0025]
DETAILED DESCRIPTION OF THE INVENTION
Exemplary embodiments of a color image processing apparatus, a color image processing method, and a computer-readable recording medium storing a program for causing the computer to execute the method will be described below in detail with reference to the accompanying drawings. To do.
[0026]
The color image processing apparatus according to the present embodiment is a color image processing apparatus that allows a person to arbitrarily convert a specified color to another specified color in accordance with the characteristics even when an input device having different characteristics is used in a scanner or the like. It is.
[0027]
First, an outline of a color image processing apparatus according to this embodiment will be described. FIG. 1 is a block diagram showing a functional configuration of a color image processing apparatus according to this embodiment of the present invention. In FIG. 1, the color image processing apparatus includes a scanner unit 101, a plane signal conversion unit 102, a saturation identification unit 103, a hue area identification unit 104, a color conversion unit 105, and a printer unit 106. .
[0028]
The scanner unit 101 reads an image on the document 100. The plane signal conversion unit 102 converts the color space represented by the color image signal input from the scanner unit 101 or the like into a plane and generates a plane signal.
[0029]
The saturation identification unit 103 identifies the saturation of the color image signal based on the plane signal generated by the plane signal conversion unit 102, and generates a saturation identification signal. Further, the hue area identification unit 104 identifies a hue area in the color image signal based on the plane signal generated by the plane signal conversion unit 102, and generates a hue area identification signal.
[0030]
The color conversion unit 105 performs color conversion of the color image signal based on the saturation identification signal generated by the saturation identification unit 103 and the hue region identification signal generated by the hue region identification unit 104. The printer unit 106 prints the color image signal converted by the color conversion unit 105.
[0031]
The color conversion instruction unit 110 instructs conversion from a specified color specified by the operator to another specified color. The color conversion unit 105 performs color conversion of the color image signal based on another designated color instructed to be converted by the color conversion instruction unit 110.
[0032]
Next, the operation of the color image processing apparatus will be described. First, the document 100 is converted into an image signal by the scanner unit 101. An image signal which is an output signal of the scanner unit 101 is converted into a plane signal by the plane signal conversion unit 102.
[0033]
Here, the contents of the plane signal will be described. FIG. 2 is an explanatory diagram showing a color space graph of a color image signal represented by three axes of read densities R, G, and B. In FIG. 2A, the plane signal can be identified by the direction 201 from the straight line R = G = B. In order not to break the relationship of the direction 201, the plane 202 is converted into a plane 202 having an achromatic color as the origin. This plane 202 is shown in FIG.
[0034]
Based on the output signal of the planar signal conversion unit 102, the saturation identification unit 103 identifies the saturation. Further, the hue area identification unit 104 also identifies an arbitrary hue area based on the output signal of the planar signal conversion unit 102.
[0035]
Color conversion is performed in the color conversion unit 105 based on the output signal from the saturation identification unit 103, the output signal from the hue region identification unit 104, and the image signal from the scanner unit 101. An image output device such as the printer unit 106 forms a color image based on the output image signal and outputs the color image.
[0036]
Next, the color conversion will be described in more detail. FIG. 3 is a block diagram showing a more detailed configuration of the color image processing apparatus according to this embodiment. The same components as those of the color image processing apparatus shown in FIG. 1 are denoted by the same reference numerals, and description thereof is omitted.
[0037]
In FIG. 3, the color image processing apparatus includes a plane signal conversion unit 102, a saturation identification unit 103, a hue region conversion unit 104, a color conversion unit 105, a color conversion instruction unit 110, and an image signal input unit 301. A hue area selection unit 302, a masking coefficient calculation unit 303, and a masking coefficient selection unit 304.
[0038]
The image signal input unit 301 inputs an image signal. The image signal input unit 301 includes the scanner unit 101 and can also input an image signal by communication or the like.
[0039]
The hue area selection unit 302 selects a hue area in the color image signal. The masking coefficient calculation unit 303 calculates masking coefficients for a plurality of hue regions. The plurality of hue areas may be prepared in advance, or may be selected by the hue area selection unit 302.
[0040]
The masking coefficient selection unit 304 performs masking based on the masking coefficient calculated by the masking coefficient calculation unit 303, the saturation identification signal generated by the saturation identification unit 103, and the hue region identification signal generated by the hue region identification unit 104. Select a coefficient.
[0041]
The color conversion unit 105 performs color conversion of the color image signal using the masking coefficient selected by the masking coefficient selection unit.
[0042]
Further, the hue area selection unit 302 selects a hue area in the color image signal based on another designated color instructed to be converted by the color conversion instruction unit 110.
[0043]
Note that the scanner unit 101, the plane signal conversion unit 102, the saturation identification unit 103, the hue region conversion unit 104, the color conversion unit 105, the printer unit 106, the color conversion instruction unit 110, the image signal input unit 301, and the hue region selection unit 302. As shown in the block diagram of FIG. 4, the masking coefficient calculation unit 303 and the masking coefficient selection unit 304 are provided on a recording medium such as a ROM 403, a RAM 402 or a hard disk (HD) 404, and a floppy disk (FD) 405 as a removable memory. The CPU (central processing unit) 401 or the like executes the instruction processing according to the instructions described in the recorded program, thereby realizing the functions of the respective units.
[0044]
In FIG. 4, each component (CPU 401, RAM 402, ROM 403, HD 404, FD 405) is connected by a bus 400. In addition, an input unit 411 that inputs data, an output unit 412 that outputs data, and a display unit 413 that displays data are connected to the bus 400.
[0045]
Next, an operation related to color conversion of the color image processing apparatus will be described. First, the color conversion instruction unit 110 receives an instruction to convert an arbitrary specified color into another arbitrary specified color, and sends data related to the color conversion instruction to the hue area selection 302.
[0046]
FIG. 5 is an explanatory diagram showing an example of an operation panel 500 for a color conversion instruction of the color image processing apparatus according to the present embodiment. In FIG. 5, an operation panel 500 includes a first display field 501 for displaying color information to be converted, a first selection button group 502 for selecting a color to be converted, and color information after conversion. Is displayed, and a second selection button group 504 for selecting a color to be converted is included.
[0047]
The first selection button group and the second selection button group are set so as to correspond to the target color, and information on the color (for example, the name of the color) is displayed on the button, or the button itself Is displayed in the color.
[0048]
The operator designates a color for color conversion. The designation method is performed by pressing a selection button of a desired color from the first selection button group 502 of the operation panel 500.
[0049]
In FIG. 5, the second button from the upper left side is selected from the first selection button group 502, the color “red” corresponding to the button is designated, and the character “ “Red” is displayed in the first display field 501 and the selection is completed.
[0050]
The same applies to the case of designating the color after conversion, and a desired color is designated by the second selection button group 503. By pressing the second button from the lower right in the second selection button group 504, the characters “cyan” are displayed in the second display field 503, and the selection is completed.
[0051]
The hue area selection unit 302 prepares several hue areas based on the color conversion instruction from the color conversion instruction unit 110, that is, the data specified by the operation panel 500.
[0052]
6 and 7 are explanatory diagrams showing other color space graphs of color image signals represented by three axes of read densities R, G, and B. FIG. Here, it is assumed that the prepared hue area is as shown in FIG. That is, the area delimited by the boundaries 601, 602, and 603 is a hue area.
[0053]
However, if such a boundary is maintained, there is a color conversion instruction. According to the instruction, when the saturation of R is high, the color that the operator intends does not change. Therefore, a boundary 701 is also provided in addition to the boundary 601 shown in FIG.
[0054]
Here, in the hue region set by the hue region selection unit 302, the hue region of the image signal input by the image signal input unit 301 is identified by the hue region identification unit 104. Further, the saturation identifying unit 103 identifies the saturation of the input image signal.
[0055]
Further, based on the data designated by the color conversion instruction unit 110, a masking coefficient calculation unit 303 calculates a masking coefficient for each hue region. Here, the masking coefficient calculation unit 303 calculates the coefficient in each region so as to convert the designated color in the color conversion instruction unit 110 or the like into another designated color. Each area is, for example, a hue area prepared first, that is, an area delimited by a boundary as shown in FIG.
[0056]
In the masking coefficient selection unit 304, the masking coefficients in the plurality of hue regions calculated by the masking coefficient calculation unit 303, the saturation identification signal generated by the saturation identification unit 103, and the hue region generated by the hue region identification unit 104 Based on the identification signal, an optimal masking coefficient is selected.
[0057]
In the masking coefficient selection unit 304, for example, when the hue region identification unit 104 identifies that the hue region is between the boundary 601 and the boundary 701 in FIG. Refer to the degree identification signal. At this time, if it is identified that the saturation is low, the hue area selects the masking coefficients in the areas of the boundary 601 and the boundary 602 in FIG.
[0058]
On the other hand, referring to the saturation identification signal generated by the saturation identification unit 103, the saturation is high Is identified, the masking coefficient refers to the value in the area delimited by the boundary 601 and the boundary 603.
[0059]
In this way, the coefficient of the region that originally performs the intended color conversion is used without using the coefficient of the identified hue region depending on the saturation.
[0060]
Based on the result selected by the masking coefficient selection unit 304, the color conversion is performed on the image signal input by the image signal input unit 301 by the color conversion unit 105.
[0061]
Next, the contents of a series of processes of the color image processing apparatus according to this embodiment will be described. FIG. 8 is a flowchart showing a series of processing procedures of the color image processing apparatus according to this embodiment. In the flowchart of FIG. 8, first, a color image signal is input (step S801), the color space of the input color image signal is converted into a plane, and a plane signal is generated (step S802).
[0062]
Next, the saturation of the color image signal is identified based on the plane signal generated in step S802, and a saturation identification signal is generated (step S803). Similarly, the hue area of the color image signal is identified based on the plane signal generated in step S802, and a hue area identification signal is generated (step S804).
[0063]
Thereafter, color conversion of the color image signal is performed based on the saturation identification signal generated in step S803 and the hue region identification signal generated in step S804 (step S805).
[0064]
Printing is performed based on the color image signal converted in step S805 (step S806), and a series of processing ends.
[0065]
FIG. 9 is a flowchart showing a sequence of processing up to masking coefficient selection in the color image processing apparatus according to this embodiment. In the flowchart of FIG. 9, first, it is determined whether or not there is an instruction for color conversion (step S901), and after waiting for an instruction for color conversion (Yes in step S901), among the plurality of hue regions The first hue region is extracted (step S902), and the masking coefficient of the extracted hue region is calculated (step S903).
[0066]
In step S904, it is determined whether or not the extraction of all the hue regions is completed. If the extraction of all the hue regions is not completed (No in step S904), the next hue region is extracted (step S905). Thereafter, the process proceeds to step S903, and thereafter, the processes of steps S903 to S905 are repeated.
[0067]
On the other hand, in step S904, when extraction of all the hue regions is completed (Yes in step S904), the saturation identification signal and the hue region identification signal are then selected from the masking coefficients calculated in step S903. A masking coefficient is selected based on (step S906).
[0068]
Thereafter, the process proceeds to step S805 in FIG. 8, and color conversion is performed using the masking coefficient selected in step S906 (step S805).
[0069]
As described above, according to the color image processing apparatus according to the present embodiment, a color in a color image is intentionally arbitrarily selected based on an operator's color designation even in an image with different saturation. Color conversion can be performed.
[0070]
Further, when performing color conversion based on the operator's color designation, an optimal masking coefficient can be selected.
[0071]
【The invention's effect】
As described above, according to the present invention, the plane signal conversion unit converts the color space represented by the input color image signal into a plane, generates a plane signal, and the saturation identification unit converts the plane into the plane. Based on the plane signal generated by the signal conversion means, the saturation of the color image signal is identified, a saturation identification signal is generated, and the hue area identification means is based on the plane signal generated by the plane signal conversion means. A hue region in the color image signal is identified, a hue region identification signal is generated, and the color conversion unit generates the saturation identification signal generated by the saturation identification unit and the hue generated by the hue region identification unit. Since the color conversion of the color image signal is performed based on the area identification signal, it is possible to intentionally arbitrarily convert a color in the color image even if the image has different saturation. Accordingly, when the color conversion specified color to another designated color, an effect that the operator of the expected color image processing apparatus capable of performing color conversion is obtained.
[0072]
According to this invention, in the above invention, the color conversion instruction means instructs conversion from a specified color specified by an operator to another specified color, and the color conversion means specifies the other specified color. Since the color conversion of the color image signal is performed on the basis of the color image, a color in the color image is intentionally arbitrarily converted based on the operator's color designation even in an image with different saturation. As a result, a color image processing apparatus capable of performing color conversion as expected by the operator when the specified color is converted to another specified color is obtained.
[0073]
According to the invention, in the above invention, the masking coefficient computing means computes a masking coefficient for a plurality of hue regions, and the masking coefficient selecting means is selected from the masking coefficients computed by the masking coefficient computing means. A masking coefficient is selected based on the saturation identification signal generated by the saturation identification means and the hue area identification signal generated by the hue area identification means, and the color conversion means is selected by the masking coefficient selection means Since the color conversion of the color image signal is performed using the masking coefficient, the optimal masking coefficient can be selected when performing the color conversion, so that the specified color can be converted to another specified color. In addition, the color image processing apparatus capable of performing color conversion as expected by the operator is obtained. That.
[0074]
According to the invention, in the above invention, the hue area selection unit selects a hue area in the color image signal based on another designated color instructed to be converted by the color conversion instruction unit. When performing color conversion based on the operator's color specification, the optimal masking coefficient can be selected, so that when the specified color is converted to another specified color, the color as expected by the operator There is an effect that a color image processing apparatus capable of performing conversion can be obtained.
[0075]
Further, according to the present invention, the plane signal conversion step converts the color space represented by the input color image signal into a plane to generate a plane signal, and the saturation identification step is performed by the plane signal conversion step. Saturation of the color image signal is identified based on the generated plane signal, a saturation identification signal is generated, and a hue region identification step is performed based on the plane signal generated by the plane signal conversion step. A hue region in the signal is identified, a hue region identification signal is generated, and a color conversion step is performed on the saturation identification signal generated by the saturation identification step and the hue region identification signal generated by the hue region identification step. Based on the color conversion of the color image signal, it is possible to intentionally arbitrarily convert a color in the color image even if the image has different saturation. The when color conversion to other designated color, an effect that the color image processing method capable of performing color conversion of the expected operator is obtained.
[0076]
According to the invention, in the above invention, the color conversion instruction step instructs conversion from a designated color designated by the operator to another designated color, and the color conversion step comprises the other designated color. Since the color conversion of the color image signal is performed on the basis of the color image, a color in the color image is intentionally arbitrarily converted based on the operator's color designation even in an image with different saturation. As a result, a color image processing method capable of performing color conversion as expected by the operator when the specified color is converted to another specified color is obtained.
[0077]
Further, according to the present invention, in the above invention, the masking coefficient calculation step calculates a masking coefficient of a plurality of hue regions, and the masking coefficient selection step includes the masking coefficients calculated by the masking coefficient calculation step. A masking coefficient is selected based on the saturation identification signal generated by the saturation identification process and the hue area identification signal generated by the hue area identification process, and the color conversion process is selected by the masking coefficient selection process. Since the color conversion of the color image signal is performed using the masking coefficient, the optimal masking coefficient can be selected when performing the color conversion, so that the specified color can be converted to another specified color. In addition, it is possible to obtain a color image processing method capable of performing color conversion as expected by the operator. That.
[0078]
According to the invention, in the above invention, the hue area selection step selects a hue area in the color image signal based on another designated color instructed to be converted by the color conversion instruction step. When performing color conversion based on the operator's color specification, the optimal masking coefficient can be selected, so that when the specified color is converted to another specified color, the color as expected by the operator There is an effect that a color image processing method capable of performing conversion can be obtained.
[0079]
Further, according to the present invention, recording a program that causes a computer to execute the method described above makes the program machine-readable, thereby enabling the above operation to be realized by a computer. There is an effect that a medium can be obtained.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a functional configuration of a color image processing apparatus according to an embodiment of the present invention.
FIG. 2 is an explanatory diagram illustrating a color space graph of a color image signal represented by three axes of read densities R, G, and B.
FIG. 3 is a block diagram showing a more detailed functional configuration of the color image processing apparatus according to the present embodiment.
FIG. 4 is a block diagram showing a hardware configuration of a color image processing apparatus according to the present embodiment.
FIG. 5 is an explanatory diagram showing an example of an operation panel for a color conversion instruction of the color image processing apparatus according to the present embodiment;
FIG. 6 is an explanatory diagram showing another color space graph of a color image signal represented by three axes of read densities R, G, and B.
FIG. 7 is an explanatory diagram showing another color space graph of a color image signal represented by three axes of read densities R, G, and B.
FIG. 8 is a flowchart showing a series of processing procedures of the color image processing apparatus according to the present embodiment.
FIG. 9 is a flowchart showing a sequence of processing up to masking coefficient selection in the color image processing apparatus according to the present embodiment;
FIG. 10 is an explanatory diagram showing color variation characteristics.
[Explanation of symbols]
101 Scanner section
102 Planar signal converter
103 Saturation identification unit
104 Hue area identification section
105 color converter
106 Printer section
110 Color conversion instruction section
301 Image signal input unit
302 Hue area selection unit
303 Masking coefficient calculator
304 Masking coefficient selection unit
400 bus
401 CPU
402 RAM
403 ROM
404 HD
405 FD
411 input section
412 Output section
413 Display unit
500 Operation panel
501 First display field
502 First selection button group
503 Second display field
504 Second selection button group
601 602 603 701 boundary

Claims (3)

Plane signal conversion means for converting a color space represented by the input color image signal into a plane and generating a plane signal;
Saturation identification means for identifying the saturation of the color image signal based on the plane signal generated by the plane signal conversion means, and generating a saturation identification signal;
Hue area identification means for identifying a hue area in the color image signal based on the plane signal generated by the plane signal conversion means, and generating a hue area identification signal;
Color conversion means for performing color conversion of the color image signal based on the saturation identification signal generated by the saturation identification means and the hue area identification signal generated by the hue area identification means;
A masking coefficient calculation means for calculating a masking coefficient of a plurality of hue regions;
A masking coefficient is selected from the masking coefficients calculated by the masking coefficient calculation means based on the saturation identification signal generated by the saturation identification means and the hue area identification signal generated by the hue area identification means. Masking coefficient selection means;
With
The color image processing apparatus, wherein the color conversion means performs color conversion of the color image signal using the masking coefficient selected by the masking coefficient selection means. A plane signal conversion step of converting the color space represented by the input color image signal into a plane and generating a plane signal;
A saturation identification step of identifying the saturation of the color image signal based on the plane signal generated by the plane signal conversion step, and generating a saturation identification signal;
A hue region identification step for identifying a hue region in the color image signal based on the planar signal generated by the planar signal conversion step, and generating a hue region identification signal;
A color conversion step for performing color conversion of the color image signal based on the saturation identification signal generated by the saturation identification step and the hue region identification signal generated by the hue region identification step;
A masking coefficient calculation step for calculating a masking coefficient of a plurality of hue regions;
A masking coefficient is selected from the masking coefficients calculated by the masking coefficient calculation process based on the saturation identification signal generated by the saturation identification process and the hue area identification signal generated by the hue area identification process. A masking coefficient selection step;
Including
In the color conversion process, the color image signal is color-converted using the masking coefficient selected in the masking coefficient selection process. A computer-readable recording medium having recorded thereon a program for causing a computer to execute the method according to claim 2 .

Images