JP2014110499A - Image processor and image processing program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent occurrence of a pseudo contour without deteriorating image quality.SOLUTION: An image processor includes: a color conversion processing section 110 for color-converting an input color value (RGB value) of a target image into a corresponding output color value (CMYK value) and obtaining it as a temporary output color value (temporary CMYK value); a modulation difference generating section 111 for generating each combination constituted by setting a value equivalent to minimum resolution of the temporary output color value for each C, M, Y and K, which make the temporary output color value, or by not setting it as a modulation difference; a color value modulating section 112 for performing modulation in which the modulation difference selected at random is added to the temporary output color value or the difference is subtracted; and an output section 12 for outputting the target image in response to a modulated color value.

Description

  The present invention relates to an image processing apparatus and an image processing program for performing image processing such as color conversion, and more specifically, a pseudo contour generated at the time of image processing using a technique in which gradation is expressed in a pseudo manner by a set of dots. The present invention relates to an image processing apparatus and an image processing program capable of solving the above problem.

In an image forming apparatus such as a printer or MFP, an image using an area gradation method or a pseudo gradation method (such as a systematic dither method or an error diffusion method) that artificially expresses a multi-value gradation by a set of dots. Processing is performed.
However, according to such image processing, even when gradation expression is possible in principle, the number of gradations is limited for reasons such as improving stability and obtaining a desired gradation curve. May cause visual discontinuity in the image, resulting in a so-called pseudo contour (pseudo contour), which may significantly reduce the image quality.
Therefore, various techniques have been proposed in order to solve such a problem of pseudo contour (see, for example, Patent Documents 1 to 5).
According to such a technique, for example, noise is added to a portion lacking in continuity in input / output characteristics (see Patent Document 1), or a standard value of an error diffusion method is changed (see Patent Document 5). Generation of a pseudo contour is prevented by performing correction or the like for improving gradation.

JP 2010-259111 A JP-A-9-98290 JP 2001-53969 A JP-A-6-101788 Japanese Patent Application Laid-Open No. 11-261819

However, the pseudo contour may be generated when the same color value continues in a certain area, such as appearing around the outline of the color area at the time of so-called gamut mapping performed to correct the difference in the color area. This technique cannot effectively prevent such pseudo contours.
That is, in the past, there has been a technique for solving the problem by focusing on the problem relating to the gradation that is the cause of the pseudo contour, but the problem of the pseudo contour that occurs when the same color value continues is directly solved. There was no technology to solve.
Further, if correction or processing for preventing the false contour is performed more than necessary, the image quality may be deteriorated. However, conventionally, there is no technology that can solve such a trade-off problem. It was.

  The present invention has been made in view of the above-described circumstances, and prevents the occurrence of a pseudo contour without impairing the image quality by irregularly applying fine modulation to the temporary output color value obtained by color conversion. An object is to provide an image processing apparatus and an image processing program.

  In order to achieve the above object, an image processing apparatus according to the present invention includes a color conversion processing unit that performs color conversion of an input color value of a target image into a corresponding output color value to obtain a temporary output color value, and a minimum temporary output color value. A value corresponding to the resolution is set for each color component forming the temporary output color value, or modulation difference generating means for generating each combination constituted by not setting as a modulation difference, and the temporary output color value Further, color value modulation means for performing modulation for adding or subtracting a randomly selected modulation difference and output means for outputting the target image based on the color value after modulation are provided.

  Further, the image processing program of the present invention is a color conversion processing means for converting the input color value of the target image into a corresponding output color value and obtaining it as a temporary output color value, and the minimum resolution of the temporary output color value. Corresponding values are set for each color component forming the provisional output color value, or modulation difference generation means for generating each combination constituted by not setting as a modulation difference, randomly for the provisional output color value It is made to function as color value modulation means for performing modulation for adding or subtracting the selected modulation difference, and output means for outputting the target image based on the color value after modulation.

  According to the present invention, it is possible to prevent the occurrence of a pseudo contour while maintaining the image quality.

1 is a schematic configuration diagram of an image processing apparatus according to an embodiment of the present invention. 1 is a functional block diagram of an image processing apparatus according to a first embodiment of the present invention. It is a functional block diagram of the image processing apparatus which concerns on 2nd embodiment of this invention. It is a figure for demonstrating a modulation channel selection means. It is a functional block diagram of the image processing apparatus which concerns on 3rd embodiment of this invention. It is a figure for demonstrating the other aspect of a color conversion process.

FIG. 1 is a schematic configuration diagram of an image processing apparatus according to an embodiment of the present invention.
As shown in FIG. 1, the image processing apparatus 1 according to the present embodiment includes an input unit 10 that inputs a target image, a control unit 11 that performs necessary image processing on the input target image, and an image by the control unit 11. An output unit 12 that performs printing or the like based on the processed image is provided. For example, a color printer or an MFP (Multifunction Peripheral) image forming apparatus is applicable.
Examples of image processing in the control unit 11 include processing for converting an input color value of a target image into an output color value, and processing for generating a dot image using the above-described area gradation method or the like.
More specifically, print data input from a personal computer or the like is interpreted, and RGB values (input color values) attached to the target object are color-converted into corresponding CMYK values (output color values), rasterization processing, screen A dot image is generated through processing and the like.
Then, a printing process is performed on the generated dot image by applying toners of cyan (C), magenta (M), yellow (Y), and black (K).

Here, the image processing apparatus 1 according to the present embodiment generates a modulation difference corresponding to the minimum resolution for each output color value of C, M, Y, and K for the CMYK value after the color conversion process, It is characterized in that modulation is performed by adding or subtracting a modulation difference randomly selected from these.
In this case, since the output color value is finely and irregularly modulated, among the pseudo contours generated as a detrimental effect of the image processing using the area gradation method or the like, the same color is particularly continuous. Generation of a pseudo contour can be effectively prevented.
Hereinafter, the image processing apparatus 1 that exhibits such characteristic operational effects will be described with reference to first to third embodiments.

(First embodiment)
FIG. 2 is a functional block diagram of the image processing apparatus according to the first embodiment of the present invention.
As shown in FIGS. 1 and 2, the control unit 11a according to the present embodiment performs color conversion on the input color value of the target image to a corresponding output color value and obtains it as a temporary output color value (color conversion). The processing means) 110 and a value corresponding to the minimum resolution of the temporary output color value are set for each color component forming the temporary output color value, or each combination constituted by not setting is generated as a modulation difference. A modulation difference generation unit (modulation difference generation unit) 111 and a color value modulation unit (color value modulation unit) 112 that performs modulation to add or subtract a randomly selected modulation difference to the temporary output color value Prepare as a block.

The color conversion processing unit 110 includes RGB to CMYK conversion means 1100 that converts a color corresponding to the color value (RGB value) of each pixel of the input image into a color value (CMYK value) in a reproducible output format.
Specifically, an LUT (Look Up Table) that is represented in a three-dimensional orthogonal grid by grid points corresponding to the correspondence between RGB values and CMYK values is prepared in advance, and the RGB values of the target pixel are referred to this LUT. As a result, color conversion is performed to the corresponding CMYK values. For RGB values located at coordinates between grid points, corresponding CMYK values are obtained by a known interpolation operation.
The color value related to each grid point is defined as an integer, and the color value related to each grid point is converted to an integer by performing fractional fraction processing or the like.
In this way, it is possible to reduce the load on the memory and calculation compared to the case where decimal values are included.
The output color values after color conversion (CMYK values) that have not yet been modulated are called temporary output color values (temporary CMYK values).

The modulation difference generation unit 111 includes a modulation amount candidate generation unit 1110, a modulation amount setting unit 1111, a random number generation unit 1112, and a modulation addition switch 1113.
The modulation amount candidate generation unit 1110 sets a value corresponding to the minimum resolution for each channel of the temporary output color value or sets each combination formed by not setting as a modulation difference (modulation amount) candidate. Generate.
For example, a group of combinations in which “1” or “0” is set for each channel of {C, M, Y, K} is a modulation difference. That is, the modulation difference includes the following 2 ⁴ = 16 patterns.
{0,0,0,0}, {0,0,0,1}, {0,0,1,0}, {0,0,1,1}, {0,1,0,0}, {0,1,0,1}, {0,1,1,0}, {0,1,1,1}, {1,0,0,0}, {1,0,0,1}, {1,0,1,0}, {1,0,1,1}, {1,1,0,0}, {1,1,0,1}, {1,1,1,0}, {1,1,1,1}
Also, by setting “1”, “−1”, and “0” for each channel, 3 ⁴ = 81 modulation differences can be created.
The modulation amount candidate generation unit 1110 stores the generated modulation difference.

The modulation amount setting unit 1111 randomly selects one modulation difference from the modulation differences generated by the modulation amount candidate generation unit 1110.
For example, the correspondence between the 16 kinds of modulation differences and the numerical value or numerical range of the random numbers that can be generated by the random number generation means 1112 is stored, and the modulation difference corresponding to the random number actually obtained from the random number generation means 1112 is stored in this manner. Obtained from the correspondence.
The modulation amount setting unit 1111 outputs the selected modulation difference to the color value modulation unit 112.

The modulation addition switch 1113 sets whether or not to perform modulation in accordance with a user setting operation.
The modulation addition switch 1113 outputs the setting signal to the color value modulation unit 112.

The color value modulation unit 112 includes a final CMYK value setting unit 1120 that performs inherent modulation on the temporary output color value.
Specifically, modulation is performed by adding or subtracting the modulation difference input from the modulation difference generation unit 111 to the temporary CMYK value acquired by color conversion by the color conversion processing unit 110.
As a result, for example, when adding a modulation difference randomly selected from the 16 modulation differences, C, M, Y, and K are individually added to the temporary CMYK values, or , The value is maintained as it is. When the modulation difference is subtracted, the temporary CMYK values are subtracted by 1 from C, M, Y, and K, or are maintained as they are.
When the 81 types of modulation differences are used, a temporary CMYK value is added to C, M, Y, and K individually by adding a modulation difference randomly selected from them, or 1 Subtracted or maintained as is.
The output unit 12 (output unit) outputs a target image based on the color value after being modulated in this way.

Note that when the signal indicating that the modulation is not performed is input from the modulation addition switch 1113, the color value modulation unit 112 can control itself so as not to perform the modulation.
In this case, the color value modulation unit 111 outputs the temporary output color value (temporary CMYK value) after color conversion to the output unit 12 as it is, and the output unit 12 outputs the target image based on the temporary CMYK value. .
In this case, for example, when there is no merit of performing modulation until sacrificing image quality, for example, it is not assumed that pseudo contours are generated, when reduction in compression rate due to discontinuity of the same color value is not desired, etc. This is convenient when modulation is not desired.

Also, any of the C, M, Y, and K values of the temporary CMYK values is 0 (minimum value in the range of color values 0 to 255) or 255 (maximum value in the range of color values 0 to 255). In such a case, control may be performed so that no modulation is performed only on the color value of the channel. That is, modulation can be performed only when the temporary CMYK value is 1 to 254.
In this way, for example, when the modulation difference is subtracted when the temporary output color value is 0, an error in which the final output color value cannot be performed (a negative value) can be prevented in advance.
By performing such modulation according to the provisional output color value, it is effective in that a subsequent error measure such as correcting the output color value to a feasible value can be omitted.
For the same reason, when the temporary output color value is 0 to a predetermined value (for example, 127) or less, a randomly selected modulation difference is added, and the temporary output color value exceeds the predetermined value (128). ˜255), it is also possible to perform modulation to reduce the randomly selected modulation difference.

As described above, according to the image processing apparatus 1 (control unit 11a) according to the first embodiment of the present invention, the modulation difference generation unit 111 sets values corresponding to the minimum resolution of the temporary CMYK values to C, M, Temporary CMYK values obtained by generating a plurality of modulation differences that are set for each of the Y and K color components or not being set, and the color conversion unit 112 performs color conversion by the color conversion processing unit 110 On the other hand, modulation which adds or subtracts a modulation difference selected at random is applied.
For this reason, as a result of changing the output color value to a minute and irregular color value, it is possible to effectively prevent the occurrence of a pseudo contour due to the continuation of the same color value.
In addition, since the color value is modulated based on the value corresponding to the minimum resolution of the output color value, it is possible to solve both the trade-off problem of preventing the occurrence of the pseudo contour and reducing the image quality.
That is, according to the image processing apparatus 1 according to the present embodiment, it is possible to effectively prevent the generation of a pseudo contour while maintaining the image quality.

(Second embodiment)
Next, the image processing apparatus 1 according to the second embodiment of the present invention will be described.
FIG. 3 is a functional block diagram of the image processing apparatus according to the present embodiment.
As shown in FIG. 3, the image processing apparatus 1 according to the present embodiment is different from the first embodiment in that the control unit 11b includes a color conversion processing unit 110, a modulation difference generation unit 111, and a color value modulation unit 112. It is the same. However, the control unit 11b of the present embodiment is different in that the color value modulation unit 112 further includes a modulation channel selection unit 1121.
For this reason, the following will mainly describe items related to the modulation channel selection means 1121, and a detailed description of the other components will be omitted.

The modulation channel selection unit 1121 selects a part or all of the color components forming the temporary output color value according to the selection operation by the user.
Specifically, as shown in FIG. 4, (i) when only K channels are modulated (first mode), (ii) when only CMY channels are modulated (second mode), (iii) all CMYK channels are modulated. In some cases (third mode), a mode corresponding to the selected channel is provided so that the user can select any mode by a certain operation.
When the modulation channel is selected by the mode selection, a switching control signal including identification information of the selected channel is output to the final CMYK value setting unit 1120, and the final CMYK value setting unit 1120 receives the modulation target signal from the identification information. A channel is specified and only the temporary output color value of that channel is modulated.

Further, by outputting a control signal including identification information to the modulation amount candidate generating unit 1110 and controlling to generate only the modulation difference of the selected channel, it is possible to modulate only a specific channel as a result. .
For example, when the first mode is selected, the modulation amount candidate generation unit 1110 generates a group of combinations in which “1” or “0” is set for only the K channel as a modulation difference. As a result, the following two modulation differences are generated.
{0,0,0,0}, {0,0,0,1}
When the second mode is selected, the modulation amount candidate generation unit 1110 generates a group of combinations in which “1” or “0” is set for each of the C, M, and Y channels as a modulation difference. As a result, the following 2 ³ = 8 modulation differences are generated.
{0,0,0,0}, {0,0,1,0}, {0,1,0,0}, {0,1,1,0}, {1,0,0,0}, {1,0,1,0}, {1,1,0,0}, {1,1,1,0}

The modulation amount setting unit 1111 randomly selects one modulation difference from these modulation differences, and the color value modulation unit 112 (final CMYK value setting unit 1120) sets the selected modulation difference as a temporary output color value. Add or subtract.
In this case, only the temporary output color value of the selected color component is modulated, and as a result, the color value that has been modulated and the temporary output color value of the color component that has not been modulated are used. Thus, the target image is output.

As described above, according to the image processing apparatus 1 according to the second embodiment of the present invention, the control unit 11b includes the modulation channel selection unit 1121, and the user can appropriately select a desired modulation method. I am doing so.
Therefore, for example, when it is desired to avoid hue modulation, it is possible to perform modulation only in the brightness direction by selecting the first mode in which modulation is not performed for the CMY channels.
In addition, when a change in graininess is not desired or a large change in brightness is not desired, a desired modulation can be performed by selecting a second mode in which modulation is not performed for the K channel.
Accordingly, it is possible to provide the image processing apparatus 1 that has the same operational effects as the first embodiment and is further excellent in user convenience.

(Third embodiment)
Next, an image processing apparatus 1 according to the third embodiment of the present invention will be described.
FIG. 5 is a functional block diagram of the image processing apparatus according to the present embodiment.
As shown in FIG. 5, the image processing apparatus 1 according to the present embodiment is the same as the above-described embodiments in that the control unit 11 c includes a color conversion processing unit 110, a modulation difference generation unit 111, and a color value modulation unit 112. It is. However, the control unit 11c of this embodiment is different in that the modulation difference generation unit 111 further includes a maximum modulation width setting unit 1114, a modulation width setting unit 1115, and a maximum modulation width mode setting unit 1116.
For this reason, hereinafter, these means of the modulation difference generation unit 111 will be mainly described, and detailed description of other components will be omitted.

The maximum modulation width setting unit 1114 sets the maximum modulation width according to the user's setting operation.
The modulation width setting means 1115 sets the modulation width r based on the maximum modulation width and the ratio of the temporary output color value to the maximum value.
The modulation amount candidate generation unit 1110 sets or does not set a value corresponding to the minimum resolution for each color component forming the temporary output color value within the range of the modulation width set by the modulation width setting unit 1115. Are generated as modulation differences.

For example, when the maximum modulation width is an integer value of ± n, the modulation difference ΔM for each channel when the maximum modulation width is applied is ΔM = {− n, −n + 1, −n + 2 ,,,-2, -1,0,2 ,,, n-1, n}. Therefore, when n = 6, the modulation difference for each channel when the maximum modulation width is applied is {−6, −5, −4, −3, −2, −1,0,1, 2,3,4,5,6}.
Here, the maximum value of the temporary output color value is Cv-max, the temporary output color value is Cv-i, and the ratio ρ [Cv-i] of Cv-i in Cv-max is expressed by the following equation (1). Ask.
ρ [Cv-i] = (Cv-i / Cv-max) (1)
In addition, a logarithmic curve equation or an S-shaped curve equation can be used instead of the linear form as in equation (1).

The modulation width r to be changed according to the temporary output color value is obtained by using the following equation (2) that multiplies the maximum modulation width by ρ [Cv-i] and rounds off the decimal value. it can.
r = Round [ρ [Cv-i] * n] (2)
Therefore, the modulation difference ΔM [ρ] for each channel when the modulation width is r is ΔM [ρ] = {− r, −r + 1, −r + 2 ,, − 2, −1,0,1 , 2 ,,, r-1, r}.
For example, when n = 6, Cv-i = 127, and Cv-max = 255, since ρ [127] = 127/255, r = Roundd [ρ [127] * 6] = 3.
That is, when Cv-i [127], the modulation difference for each channel is {-3, -2, -1,0, 1, 2, 3}. For this reason, if the temporary output color value is {127, 127, 127, 127}, the modulation amount candidate generation unit 1110 generates a modulation difference including 7 ⁴ = 2401 combinations.
The modulation amount setting unit 1111 randomly selects one modulation difference from these modulation differences, and the color value modulation unit 112 adds or subtracts the selected modulation difference to modulate the temporary output color value. I do.

As described above, according to the image processing apparatus 1 of the present embodiment, the control unit 11c further includes the maximum modulation width setting unit 1114 and the modulation width setting unit 1115, and is within the minimum resolution range (−1 to +1). Unlike the above-described embodiment in which the modulation is uniformly performed, the modulation width is extended to a range in which the image quality is not deteriorated depending on the temporary output color value.
That is, in view of the fact that the effect of modulation on image quality differs depending on the actual temporary output color value and the range that the temporary output color value can take, the larger the temporary output color value, the larger the modulation width is set, and the temporary output color value is smaller. As the modulation width is set to be smaller, the allowable range of modulation is widened.
For this reason, not only the same effect as the above-described embodiment can be achieved, but also the modulation can be varied, and the generation of the pseudo contour can be more effectively suppressed as compared with the above-described embodiment.

As shown in FIG. 5, the maximum modulation width according to the various modes selected by the user can be set by adding the maximum modulation width mode setting means 1116 to the configuration.
Specifically, based on the results obtained from prior surveys and experiments, several modes are set based on the impressions and sensations that humans feel, and the maximum modulation width corresponding to each mode is linked and registered. .
For example, the `` detection limit mode '' in which the modulation width used in the limit of whether the image quality etc. has changed due to modulation is linked as the maximum modulation width, or the difference in image quality etc. can be recognized by applying modulation, A “tolerance mode” in which the modulation width used at the limit that a human can endure is linked as the maximum modulation width can be exemplified.
For this reason, when using the image processing apparatus 1 according to the present embodiment, an appropriate maximum modulation width can be set flexibly and easily, and user convenience can be improved.

(Image processing program)
Next, the image processing program will be described.
The color conversion processing function, modulation difference generation function, color value modulation function, and the like of the computer (image processing apparatus) in the above embodiment are realized by an image processing program stored in a ROM or the like.
The image processing program is read by a computer control means (CPU or the like) to send commands to each component of the computer, and each means (color conversion processing means, modulation difference generation means, color value modulation) corresponding to each function. Means, output means).
As a result, the functions are realized by the cooperation of the image processing program that is software and each component of the computer that is hardware resources.

Note that the image processing program for realizing the above functions can be stored in a computer-readable recording medium such as an external storage device and a portable recording medium in addition to being stored in a ROM of the computer.
The external storage device is a memory expansion device that incorporates a recording medium such as a CD-ROM (Compact Disc-Read Only Memory) and is externally connected to the image processing apparatus 1. On the other hand, the portable recording medium is a recording medium that can be mounted on a recording medium driving device (drive device) and is portable, and refers to, for example, a flexible disk, a memory card, a magneto-optical disk, and the like.

The image processing program recorded on the recording medium is loaded into the RAM of the computer and executed by the CPU. By this execution, each function of the above-described embodiment is realized.
Further, when the image processing program is loaded by the computer, the image processing program held by another computer can be downloaded to its own RAM or external storage device using a communication line. The downloaded program can also be executed by the CPU to realize the functions of the above-described embodiment.

Thus, the present invention can also be implemented by a program.
Therefore, by installing the image processing program in another device, it is possible to configure an apparatus that exhibits the same operational effects as the image processing apparatus 1 according to the present embodiment.

The image processing apparatus and the image processing program of the present invention have been described with reference to the embodiments. However, the present invention is not limited to the above-described embodiments, and various modifications can be made. Yes.
For example, the present invention can be applied to image forming apparatuses other than printers and MFPs.
In the above-described embodiment, the RGB to CMYK conversion unit 1100 performs the color conversion processing via the one-stage LUT in which the input color value and the output color value are directly associated with each other. The present invention is not limited to this mode, and the configuration of the LUT, the color conversion process, and the like are not particularly limited as long as the output color value of the image processing apparatus 1 can be obtained as a result.
For example, as shown in FIG. 6, the color conversion processing of RGB values (input color values) and CMYK values (output color values) is divided into several stages via an LUT that performs color conversion to XYZ space or Lab space. Can also be done.

  The present invention can be applied to color-compatible image forming apparatuses such as printers and MFPs.

1 image processing apparatus 10 input unit 11 control unit 110 color conversion processing unit 1100 RGB to CMYK conversion unit 111 modulation difference generation unit 1110 modulation amount candidate generation unit 1111 modulation amount setting unit 1112 random number generation unit 1113 modulation addition switch 1114 maximum modulation width setting unit 1115 Modulation width setting means 1116 Maximum modulation width mode setting means 112 Color value modulation section 1120 Final CMYK value setting means 1121 Modulation channel selection means 12 Output section

Claims (6)

Color conversion processing means for color-converting an input color value of a target image into a corresponding output color value and obtaining a temporary output color value;
Modulation difference generating means for generating a value corresponding to the minimum resolution of the temporary output color value for each color component forming the temporary output color value or generating each combination constituted by not setting as a modulation difference When,
Color value modulation means for performing modulation to add or subtract the modulation difference selected at random to the temporary output color value;
And an output unit that outputs the image based on the color value after the modulation. The color value modulating means includes
The image processing apparatus according to claim 1, wherein the modulation is not performed when the temporary output color value is a minimum value or a maximum value in a range of the color value. The color value modulating means includes
When the temporary output color value is less than or equal to a certain value, modulation is performed to add the modulation difference to the temporary output color value. When the temporary output color value exceeds the certain value, the modulation difference is The image processing apparatus according to claim 1, wherein the subtracting modulation is performed. In accordance with a selection operation, comprising color selection means for selecting part or all of the color components forming the temporary output color value,
The color value modulating means includes
Performing the modulation only on the temporary output color value of the selected color component;
The output means includes
The output of the image is performed based on the color value subjected to the modulation and the provisional output color value of the color component not subjected to the modulation. The image processing apparatus described. Maximum modulation width setting means for setting the maximum modulation width according to the setting operation;
A modulation width setting means for setting a modulation width based on the maximum modulation width and a ratio of the temporary output color value at the maximum value; and
The modulation difference generation means includes
A value corresponding to the minimum resolution is set for each color component forming the provisional output color value within the range of the modulation width, or each combination configured by not setting is generated as the modulation difference. The image processing apparatus according to claim 1, wherein the image processing apparatus is characterized. Computer
Color conversion processing means for color-converting an input color value of a target image into a corresponding output color value to obtain a temporary output color value;
Modulation difference generating means for generating a value corresponding to the minimum resolution of the temporary output color value for each color component forming the temporary output color value or generating each combination constituted by not setting as a modulation difference ,
Functions as color value modulation means for performing modulation to add or subtract the modulation difference selected at random to the temporary output color value, and output means for outputting the image based on the color value after modulation. An image processing program characterized in that

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