JPH10173952A - Noise eliminating device from color image, its method and recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a device and method for eliminating noise from a color image, which surely eliminate noise even from a color image and easily prevent unnatural coloring. SOLUTION: A color image is scanned by a filter to detect a color component of each pixel included in a local pixel group to be scanned. Then a color component ratio is calculated from two detected color components and its median is obtained. Even when a pixel Pa9 corresponding to a noise is included in the local pixel group, a pixel Pa5 as a pixel corresponding to the median is selected and the color component of the pixel Pa5 is used for an output of the filter, then the noise is surely eliminated. Furthermore, as to the pixel corresponding to the median, since pixels in existence originally like pixels Pa5, Pb5 are selected and its color component is outputted from the filter, unnatural coloring is easily prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an apparatus and a method for removing noise from a color image and a computer-readable recording medium storing a color image noise removal program for providing a high-quality color image. .

[0002]

2. Description of the Related Art Generally, in an image processing apparatus, noise removal and sharpening of an image are performed in order to provide a high quality image. This noise removal is processing for removing noise mixed in from an image input device or the like by using a spatial filter.

[0003] Conventionally, as a noise removal filter,
A filter that averages pixel data of a local pixel group centering on a target pixel and outputs the result as pixel data of the target pixel, that is, a filter that removes high-frequency components by an integration operation has been used. By scanning this filter on the image and taking a local moving average, noise of the image can be removed.

However, when such a filter is used, high-frequency components of an image are smoothed and lost, so that noise is removed, but the sharpness of a contour portion in the image is also lost. Therefore, in general, a median filter is used as a method for removing noise without deteriorating information that gives visual sharpness such as an outline portion in an image. This median filter outputs the median of the pixel data of each pixel constituting the local pixel group as the pixel data of the pixel of interest. Therefore, since the output pixel data is pixel data of a pixel (including the pixel of interest) actually existing in a region near the pixel of interest, it is necessary to remove noise while preserving the sharpness of the outline in the image. Can be.

[0005]

When the above method is applied to a monochrome image, noise can be removed without any problem. However, applying this method to color images introduces new problems. That is,
As is well known, a color image is composed of planes of a plurality of color elements (for example, red (R), green (G), and blue (B)). In such a color image, when noise is removed using a conventional median filter, a median is obtained for each plane, and the median is output as an output value of the filter in each plane. Therefore, when looking at each plane, although noise is accurately removed, when viewed in a color image space, pixel data of pixels that did not originally exist are output as output values of the filter, The median filter cannot perform its original function, resulting in unnatural coloring and the like.

In view of the above-mentioned problems, the present invention provides a color image noise elimination apparatus, method, and color image noise elimination method that can accurately remove noise from a color image and easily prevent unnatural color formation. It is an object of the present invention to provide a computer-readable recording medium recording a removal program.

[0007]

According to an aspect of the present invention, there is provided a method for scanning a color image with a filter including a plurality of pixels to remove noise from the color image. a) a color component detection step of detecting a plurality of color components for each of the pixels that are being scanned by the filter at that time; and (b) each pixel from at least two color components of the plurality of color components. A scalar amount calculating step of calculating one scalar amount for each of: (c) a median value calculating step of obtaining a median value of the scalar amounts of the respective pixels; and (d) a median value calculating step. A pixel selecting step of selecting a pixel corresponding to the median value as a selected pixel, and (e) filter output control for providing a color component of the selected pixel as an output of the filter at that time. And a degree.

According to a second aspect of the present invention, in the color image noise elimination method according to the first aspect of the present invention, the scalar amount calculating step includes calculating each of the pixels from two color components of the plurality of color components. , A color component ratio calculating step of calculating one color component ratio is included, and the median value calculating step is a step of calculating a median value of the color component ratio for each of the pixels.

According to a third aspect of the present invention, in the color image noise elimination method according to the first aspect of the present invention, the scalar amount calculating step includes the step of calculating each of the pixels from three color components of the plurality of color components. , A luminance component calculating step of obtaining one luminance component is included, and the median value calculating step is a step of calculating a median value of the luminance component for each of the pixels.

According to a fourth aspect of the present invention, in the method for removing noise of a color image according to the first aspect of the present invention, the scalar amount calculating step includes calculating each of the pixels from three color components of the plurality of color components. , A saturation calculation step of calculating one saturation is included, and the median value calculation step is a step of calculating the saturation median value of each pixel.

According to a fifth aspect of the present invention, there is provided an apparatus for removing a noise of the color image by scanning the color image with a filter composed of a plurality of pixels, wherein (a) the filter is scanned by the filter at that time. (B) a scalar for calculating one scalar amount for each of the pixels from at least two color components of the plurality of color components. Amount calculation means, (c) a median value calculation means for finding a median of the scalar amounts for each of the pixels,
(d) pixel selection means for selecting a pixel corresponding to the median as a selected pixel, and (e) filter output control means for providing a color component for the selected pixel as an output of the filter at that time. ing.

According to a sixth aspect of the present invention, in the color image noise elimination apparatus according to the fifth aspect of the present invention, the scalar amount calculating means uses each of the pixels from two color components of the plurality of color components. , A color component ratio calculating means for calculating one color component ratio is included, and the median value calculating means is means for calculating a median value of the color component ratio for each of the pixels.

According to a seventh aspect of the present invention, in the color image noise elimination apparatus according to the fifth aspect of the present invention, in the scalar amount calculating step, each of the pixels is calculated from three color components of the plurality of color components. , A luminance component calculating means for calculating one luminance component is included, and the median value calculating means is means for calculating a median value of the luminance component for each of the pixels.

According to an eighth aspect of the present invention, in the color image noise elimination apparatus according to the fifth aspect of the present invention, in the scalar amount calculating step, each of the pixels is calculated from three color components of the plurality of color components. , A saturation calculating means for calculating one saturation is included, and the median value calculating means is means for calculating a median of the saturation for each pixel.

According to a ninth aspect of the present invention, there is provided a computer comprising: (a) a color component detecting a plurality of color components for each pixel of a color image being scanned by a filter comprising a plurality of pixels at that time; A detection procedure, (b) a scalar quantity calculation procedure for calculating one scalar quantity for each of the pixels from at least two color components of the plurality of color components, and (c) the scalar quantity for each of the pixels A median calculation procedure for determining the median, (d) a pixel selection procedure for selecting a pixel corresponding to the median determined in the median calculation step as a selected pixel, and (e) a color for the selected pixel. A filter output control procedure for providing a component as an output of the filter at that time; and a computer-readable recording medium storing a color image noise removal program for executing the filter output control procedure. It is.

The scalar amount calculating step may include a color component ratio calculating step of obtaining one color component ratio for each of the pixels from two color components of the plurality of color components. 10. The recording medium according to claim 9, wherein the median value calculating step is a step of obtaining a median value of the color component ratio for each of the pixels.

Further, according to the present invention, the scalar amount calculating step includes a luminance component calculating step of obtaining one luminance component for each of the pixels from three color components of the plurality of color components, 10. The recording medium according to claim 9, wherein the median value calculating step is a step of calculating a median value of the luminance component for each of the pixels.

In the twelfth aspect of the present invention, the scalar amount calculating step includes a saturation calculating step of obtaining one saturation for each of the pixels from three color components of the plurality of color components. 10. The recording medium according to claim 9, wherein the median value calculating step is a step of calculating a median value of the saturation for each of the pixels.

Here, the "median value" means a value that is the center in the order when arranged in order of magnitude. Generally, when a filter composed of n pixels (n is an integer of 2 or more) is used, when n = odd, the one having the {(n + 1) / 2} -th size becomes the median value, When n = even, the one having the (n / 2) th or {(n / 2) +1} th size is set as the median. In the latter case, (n
It is sufficient to determine in advance whether to use the (/ 2) th or {(n / 2) +1} th.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION

[0021]

First Embodiment An embodiment of the present invention will be described below in detail with reference to the drawings. In this specification, first, an outline of an image processing apparatus including a color image noise elimination apparatus according to the present invention will be described, and then a color image noise elimination method according to the present invention will be described.

A. Overview of Image Processing Apparatus: FIG. 1 is a block diagram showing an electrical configuration of an image processing apparatus 100 incorporating a color image noise removing apparatus according to the present invention.
The image processing apparatus 100 includes a control unit 50 that performs a noise removal process described later and gives a command to each unit.
An operation unit 10, a display unit 20, an image input unit 30, and an image output unit 40 are provided.

The operation unit 10 is a means for an operator to give an instruction to the image processing apparatus 100, and comprises a keyboard and a mouse. The display unit 20 is a color display on which an operator can confirm an image to be processed and a message from the control unit 50. The image input unit 30 is an input unit (such as an input scanner) for reading a color image to be processed and inputting pixel data of the color image to the image processing apparatus 100. Output means (output scanner, imagesetter, etc.) for outputting a processed color image.

In the above-described image processing apparatus 100, the operator gives an appropriate command to the control unit 50 via the operation unit 10 so that the color image data inputted from the image A removal process can be performed. Then, the operator can visually confirm the processing result on the display unit 20 and can confirm the final output result by outputting the processing result from the image output unit 40.

The control unit 50 is configured using a computer, and includes an image data storage unit 60 and an image processing unit 70. The image data storage unit 60 is a RAM that stores a noise removal processing program and image data. The image data storage unit 60 has a disk drive 90
It is also possible to read out the program and data from a disk D as a recording medium in which a processing procedure described later is stored as a program and execute the following processing.

The image processing section 70 has a color component detection means 71 and a noise removal processing section 80. The color component detection unit 71 is a unit that detects a color component of a pixel constituting a pixel group scanned by a filter F described later.

In this specification, the color component of a pixel indicates the signal value of each of the three colors R, G, and B in the pixel data indicating the pixel. Further, the image data is used as a term indicating a set of pixel data for forming an image.

The noise removal processing unit 80 includes a scalar amount calculation unit 81, a median value calculation unit 82, and a pixel selection unit 83
And a filter output control means 84. These units 81 to 84 represent processing contents executed in accordance with the program stored in the image data storage unit 60, and the processing contents will be described later.

B. Noise Removal Method: FIG. 2 is a flowchart illustrating an example of a noise removal process performed in the image processing apparatus 100. It should be noted that a program for executing the processing procedure shown in the figure is recorded in advance on a disk D or the like as a recording medium, the program is read out from the disk D by the disk drive 90, and the control unit 5
0 may automatically execute the processing procedure shown in FIG.

First, prior to the noise removal process, a color image to be processed is read by the image input unit 30 (step S1). The image data read here is a set of pixel data expressed in RGB, is stored in the image data storage unit 60, and is displayed as a color image on the display of the display unit 20.

Next, the color component detecting means 7 of the image processing unit 70
1, the color component of each pixel of the local pixel group is detected (step S2). FIG. 3 is a conceptual diagram illustrating a local pixel group to be detected. A local pixel group is selected by scanning a color image with a filter F composed of a 3 × 3 pixel matrix and indicated by a thick line in the drawing. At this time, the filter F starts from the upper left corner of the color image in the X direction (main scanning direction) in the figure.
, And reaches the upper right corner of the color image, then scans in the X direction from the leftmost pixel adjacent in the Y direction (sub scanning direction), and so on until the filter F reaches the lower right corner of the color image. The procedure will be repeated. Then, the local pixel group scanned by the filter F at a certain time becomes the selected local pixel group, and the color components of the nine pixels constituting the local pixel group are detected.

Next, proceeding to step S3, the color component ratio of each pixel constituting the local pixel group is determined. At this time, the ratio of two color components among the three color components of R, G, and B of each pixel is obtained. In the example considered here, R and G
, Ie, the value of “R / G”. This is because B is not so stimulating to human eyes that even if it remains as noise, the color does not become unnatural. At this time, if the value of G is "0", it is impossible to obtain the value of "R / G". In such a case, the control unit 50 (see FIG. 1) handles the value. The maximum possible signal value is defined as the color component ratio “R / G”.

Then, the process proceeds to step S4, in which the obtained color component ratios are arranged in the order of magnitude, and a median value is obtained. The state of the processing at this time will be described with reference to FIGS.

FIG. 4 is a conceptual diagram for explaining how the filter F scans a color image on the display unit 20, and FIG. 5 shows how the median color component ratio is obtained. It is a conceptual diagram for performing. As shown in FIG. 4, a noise N and an image E are displayed on a screen 21 of the display unit 20. When the filter F scans the positions F1 and F2, the noises are included in the local pixel groups. N and the outline of the image E will be included. In the example considered here, both the image E and the noise N have different colors from the background A.

When the filter F scans the position F1, that is, when the noise N is included in the local pixel group, only the pixel Pa9 corresponding to the noise N is present as shown in FIG. It has a color component ratio that is significantly different from the pixels Pa1 to Pa8 corresponding to the background A. Here, the magnitudes of the color component ratios are arranged in the order of the pixels Pa1, Pa2,... Pa9 from the largest, and the median value of the fifth value, that is, the pixel Pa5 (corresponding to the background A) The color component ratio will be selected.

On the other hand, when the filter F scans the position F2, that is, when the local pixel group includes the contour of the image E, as shown in FIG.
And the same number of pixels Pb1 to Pb4 corresponding to the background A are present. Here, the magnitude of the color component ratio is determined from the pixel Pb1,
Pb9 are arranged in the order of Pb2... Pb9, and the fifth value, that is, the color component ratio of the pixel Pb5 (corresponding to the image E) is selected as the median value.

Returning to FIG. 2, next, a pixel having a color component ratio having a median value is determined as a selected pixel (step S5), and the selected pixel is output on the original image as an output of the filter. (Step S6). Therefore, in FIG. 5A described above, the pixel Pa5 corresponding to the background A is determined as the selected pixel, and is output on the original color image as an output pixel at the position F1 of the filter F. In FIG. 5B, the pixel Pb5 corresponding to the image E is determined as the selected pixel, and is output on the original color image as an output pixel at the position F2 of the filter F. At this time, the values of the selected pixel are output for all the colors of R, G, and B.

In this manner, noise can be accurately removed, and a color component which is originally present is selected as a selected pixel and its color component is output from the filter F. Therefore, unnatural color formation can be easily prevented. .

Then, the process proceeds to a step S7, wherein the filter F is scanned by one pixel. The operation procedure of the filter F is as described above. Then, after the filter F has finished processing up to the pixel at the lower right corner, in step S8,
It is determined that a series of processing is completed, and the noise removal processing ends. If the filter F has not reached the lower right corner, it is determined that the process has not been completed, and the process returns to step S2.
The noise removal processing is performed again. That is, the above series of processing is repeated until the filter F reaches the lower right corner.

In the first embodiment, the ratio "R / G" of the two color components R and G is used as the color component ratio. However, the present invention is not limited to this. The ratio "G
/ B "or the ratio of B to R," B / R ".

Further, two color components to be used may be determined in consideration of the distribution of the color components in the local pixel group scanned by the filter F. Specifically, a variance value is obtained for each of the R, G, and B signal values of the pixels included in the local pixel group, and two color components other than the color component having the smallest variance value are selected, and the two color components are selected. The ratio of the components may be used. However, in this case, it is necessary to determine the color component to be used for each local pixel group.
The processing time is longer than the processing method described in the first embodiment.

Further, some pixels are randomly extracted from the color image, and a variance value is obtained for each of the R, G, B signal values of the extracted pixels, and two pixels other than the color component having the smallest variance value are obtained. One color component may be selected, and the ratio of the two color components may be used for the entire color image.

[0043]

Second Embodiment In the first embodiment, one scalar amount (color component ratio) is obtained from two color components of three color components. However, all three color components are used. 1
One scalar quantity may be obtained. In the second embodiment, a description will be given of a noise removal processing method for obtaining one scalar amount using all three color components.
Note that the configuration of the image processing apparatus is the same as that of the first embodiment, and a description thereof will not be repeated.

FIG. 6 is a flowchart showing another example of the noise removal processing performed in the image processing apparatus 100. The processing procedure in FIG. 6 is also recorded on the disk D as a program, read out by the disk drive 90, and causes the control unit 50 to automatically execute the processing procedure shown in FIG. It may be.

First, in the same manner as described above, after the color image to be processed is read by the image input unit 30 in step S11, the process proceeds to step S12, where the color component detection unit 71 sets the nine pixels constituting the local pixel group. Are detected respectively.

Next, the process proceeds to step S13, where the luminance component Y of each pixel of the local pixel group is obtained. FIG. 7 is a conceptual diagram for explaining the relationship between luminance and saturation and color components. The luminance is a term for expressing whether it is bright or dark, and the luminance component Y is calculated by the following equation.

[0047]

(Equation 1)

As is apparent from Equation 1, the luminance component Y
Is obtained by calculating one scalar quantity using all three color components of R, G, and B. In step S13 in FIG. 6, a luminance component Y is obtained for each pixel included in the local pixel group.

Next, the process proceeds to step S14, where the calculated luminance components Y are arranged in the order of magnitude, and the median thereof is obtained. In the example considered here, since the local pixel group includes nine pixels, the luminance component Y of the pixel having the fifth value is the median value.

Next, a pixel having the luminance component Y having the median value is determined as a selected pixel (step S15), and the selected pixel is controlled so as to be output on the original image as an output of the filter (step S15). S16). Then, as in the first embodiment, the filter F is scanned by one pixel (step S17). After the filter F completes processing up to the pixel at the lower right corner, it is determined that a series of processing is completed in step S18. It is determined, and the noise removal processing ends. If the filter F has not reached the lower right corner,
It is determined that the process has not been completed, and the process returns to step S12, where the noise removal process is performed again. That is, the above series of processing is repeated until the filter F reaches the lower right corner.

According to the above-described method, noise can be accurately removed, and a color component that is originally present is selected as a selected pixel and its color component is output from the filter F. Therefore, unnatural color formation can be easily prevented. it can. Also, R, G, B
One luminance component Y is obtained by using all of the three color components, and the median of the luminance component Y is selected. Therefore, noise is more accurately removed than using two color components. be able to.

In the second embodiment, R, G,
Although one luminance component Y is determined using all three color components B, another scalar amount, for example, saturation (see FIG. 7) may be determined from the three color components. .

The term “saturation” is a term for expressing the color density, and the value of the saturation s is calculated by the following equation.

[0054]

(Equation 2)

In Equation 2, Y is the luminance component Y described above. Again, as is apparent from Equation 2, the saturation s
Represents 1 using all three color components of R, G and B.
Are two scalar quantities. Therefore, the same effect as described above can be obtained by selecting a pixel having the median value of the saturation s and using that pixel as the output value of the filter F.

Although the filter in the noise elimination processing technology of the first and second embodiments is a 3 × 3 pixel matrix, it may be a filter of another shape or size.

[0057]

As described above, according to the first, second, fifth and sixth aspects of the present invention, the color component of each pixel scanned by the filter at a certain point in time is detected. Since one scalar amount is calculated for each pixel from at least two of the color components, a pixel corresponding to the median of the scalar amount is selected, and the color component of the pixel is used as the output of the filter. Since noise can be accurately removed and the color component that is originally present is selected as a selected pixel and the color component is output from the filter, unnatural color formation can be easily prevented.

According to the third, fourth, seventh, and eighth aspects of the present invention, one scalar amount is calculated for each pixel from three color components, so that two color components are calculated. Noise can be more accurately removed than calculated from components.

According to the ninth and tenth aspects of the present invention, the computer reads and executes a color image noise elimination program recorded on a computer-readable recording medium, whereby the first, second, and third aspects of the present invention are implemented.
The same effects as the inventions of claims 5 and 6 can be obtained efficiently.

According to the eleventh and twelfth aspects of the present invention, the computer reads and executes a color image noise elimination program recorded on a computer-readable recording medium. The same effects as the inventions of claims 7 and 8 can be obtained efficiently.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an electrical configuration of an image processing apparatus incorporating a color image noise removing apparatus according to the present invention.

FIG. 2 is a flowchart illustrating an example of a noise removal process performed in the image processing apparatus of FIG. 1;

FIG. 3 is a conceptual diagram illustrating a local pixel group to be subjected to color component detection.

FIG. 4 is a conceptual diagram illustrating a state where a filter scans a color image on a display unit.

FIG. 5 is a conceptual diagram for explaining how to calculate a median value of a color component ratio.

FIG. 6 is a flowchart illustrating another example of the noise removal processing performed in the image processing apparatus of FIG. 1;

FIG. 7 is a conceptual diagram for explaining a relationship between luminance and saturation and a color component.

[Description of Signs] 71 color component detection means 81 scalar amount calculation means 82 median value calculation means 83 pixel selection means 84 filter output control means 90 disk drive 100 image processing device D disk

Continued on the front page (51) Int.Cl. ⁶ Identification symbol FI H04N 1/409 G06F 15/68 410 1/46 H04N 1/40 101C 1/46 Z

Claims (12)

[Claims] 1. A method of scanning a color image with a filter composed of a plurality of pixels to remove noise from the color image, comprising the steps of: (a) selecting a pixel for each pixel scanned by the filter at that time; A color component detecting step of detecting a plurality of color components; (b) a scalar amount calculating step of calculating one scalar amount for each of the pixels from at least two color components of the plurality of color components; A) a median calculation step of calculating a median of the scalar amounts for the respective pixels, and (d) a pixel selection step of selecting a pixel corresponding to the median determined in the median calculation step as a selected pixel. (e) a filter output control step of providing a color component for the selected pixel as an output of the filter at that time, noise of a color image, Way removed by. 2. The method for removing noise from a color image according to claim 1, wherein the scalar amount calculating step determines one color component ratio for each of the pixels from two color components of the plurality of color components. A color component ratio calculating step, wherein the median value calculating step is a step of obtaining a median value of the color component ratio for each of the pixels. 3. The method for removing noise from a color image according to claim 1, wherein the scalar amount calculating step includes: obtaining a luminance component for each of the pixels from three color components of the plurality of color components. A method for removing noise from a color image, comprising: a component calculation step; wherein the median value calculation step is a step of obtaining a median value of the luminance component for each of the pixels. 4. The method for removing noise from a color image according to claim 1, wherein the scalar amount calculating step obtains one saturation for each of the pixels from three color components of the plurality of color components. A method for removing noise from a color image, comprising: calculating a median value; wherein the median value calculating step is a step of calculating a median value of the saturation for each of the pixels. 5. An apparatus for scanning a color image by a filter composed of a plurality of pixels to remove noise from the color image, comprising: (a) an apparatus for scanning each pixel scanned by the filter at that time; Color component detection means for detecting a plurality of color components; (b) scalar quantity calculation means for calculating one scalar quantity for each of the pixels from at least two color components of the plurality of color components; ) A median value calculating means for calculating a median value among the scalar amounts for each of the pixels, (d) a pixel selecting means for selecting a pixel corresponding to the median value as a selected pixel, and (e) for the selected pixel. And a filter output control unit for providing a color component as an output of the filter at that time. 6. The color image noise elimination device according to claim 5, wherein the scalar amount calculation unit obtains one color component ratio for each of the pixels from two color components of the plurality of color components. A color image noise removing apparatus, comprising: a color component ratio calculating unit, wherein the median value calculating unit is a unit that obtains a median value of the color component ratio for each of the pixels. 7. The color image noise elimination device according to claim 5, wherein the scalar amount calculating step calculates a luminance component for each of the pixels from three color components of the plurality of color components. An apparatus for removing noise from a color image, comprising: a component calculation unit; wherein the median value calculation unit is a unit that obtains a median value of the luminance component for each of the pixels. 8. The color image noise elimination device according to claim 5, wherein the scalar amount calculation step calculates one saturation for each of the pixels from three color components of the plurality of color components. A noise removing apparatus for a color image, comprising: a degree calculating means; wherein the median value calculating means is means for calculating a median of the saturation for each of the pixels. 9. A computer comprising: (a) a color component detection procedure for detecting a plurality of color components for each pixel of a color image being scanned by a filter composed of a plurality of pixels at the time; A scalar amount calculating step of calculating one scalar amount for each of the pixels from at least two color components of the plurality of color components; and (c) a center for calculating a median value of the scalar amounts for the pixels. A value calculation procedure, (d) a pixel selection procedure of selecting a pixel corresponding to the median determined in the median calculation step as a selection pixel, and (e) a color component for the selected pixel, A computer-readable recording medium recording a color image noise removal program for executing a filter output control procedure to be provided as an output of the filter. 10. The scalar amount calculating step includes a color component ratio calculating step of obtaining one color component ratio for each of the pixels from two color components of the plurality of color components, and the median value calculating step. 10. The recording medium according to claim 9, wherein the step of obtaining the median value of the color component ratio for each of the pixels. 11. The scalar amount calculating step includes a luminance component calculating step of obtaining one luminance component for each of the pixels from three color components of the plurality of color components. The median value calculating step includes: 10. The recording medium according to claim 9, wherein a procedure for obtaining a median value of the luminance component for each of the pixels is performed. 12. The scalar amount calculation step includes a saturation calculation step of calculating one saturation for each of the pixels from three color components of the plurality of color components. The median value calculation step includes: 10. The recording medium according to claim 9, wherein a procedure for obtaining a median of the saturation for each pixel is performed.