JP2001357393A - Method for converting picture data - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a picture data converting method by which the number of color scheme table numbers is reduced in a color scheme table while reducing the deterioration of image quality and the size of whole image data is reduced even when a conversion processing is performed from original image data into image data which is constituted by a general purpose color scheme table relying on a display device, etc. SOLUTION: A color scheme table numbers among the plurality of numbers being the index of the color scheme table of original image data, where the usage frequency of original image data in image data is prescribed times, e.g. >=1 times, is extracted and re-constituted as the new color scheme table. Then new image data is constituted by using the color scheme table.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for converting image data, and more particularly to a method for converting image data composed of general-purpose color tables independent of individual image data by reducing the number of color table numbers in the color table. The present invention relates to an image data conversion method for converting image data.

[0002]

2. Description of the Related Art Conventionally, when converting into image data composed of a color table, a method of determining the color table depends on a method of determining according to a color appearing in the image data and a display device. There was a method using a general-purpose color table.

A method of determining a color table according to colors appearing in image data is, for example, to first arrange color information appearing in pixel data representing each pixel of original image data in descending order of appearance frequency, and to arrange the color information in the color table from the top. By selecting an appropriate number as a table number, a color arrangement table of new image data is obtained.

When a general-purpose color table is used, colors constituting the color table are determined by a display device or the like, and a color table cannot be created according to individual image data. A color arrangement table is configured to include a wide range of colors in advance so as to be able to cope with the above. Then, for the color table determined in this way, it is determined which color table number of the color table corresponds the color information of each pixel of the original image data to. For example, the method disclosed in Japanese Patent Application Laid-Open No. 08-278776 is a method using the latter general-purpose color table, and the original image data is configured by combining R, G, and B of each color with 5, 9, and 5 gradations. The conversion is performed using a color table of all 225 colors.

[0005]

Among the above-mentioned conventional conversion methods, in the method of determining a color scheme table according to image data, the number to be selected is adjusted to reduce the number of color scheme table numbers in the color scheme table to some extent. However, in the method using a general-purpose color table that is determined depending on the display device and the like and does not depend on the type of individual image data, the number of color table numbers in the color table is determined in advance. The data size of the portion representing the color scheme table cannot be reduced, and the entire size of the image data increases, and when transmitting and receiving image data by communication or the like, there is a problem that the communication time increases and the communication cost increases. . There is also a method of selecting a small number of color table numbers in advance as a general-purpose color table in order to reduce the number of color table numbers in the color table. There is a problem that it is difficult to reproduce the color of the image data and the quality of the converted image data is deteriorated.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and a first object of the present invention is to reduce the deterioration of image quality even when a general-purpose color table is used. This is to reduce the number of numbers. A second object is to reduce the size of the entire image data.

[0007]

According to a first aspect of the present invention, there is provided an image data conversion method comprising the steps of converting a first image data composed of a first color table into a color table number which is an index of the first color table. The first image data whose frequency of use in the pixel data is equal to or greater than a predetermined value is extracted and reconstructed as a second color table, and the second image data constructed using the second color table Is converted to

According to a second aspect of the present invention, in the first aspect, the predetermined value of the use frequency is 1.

A third aspect of the present invention is the image data conversion method according to the first aspect, wherein the first color table is a general-purpose color table.

According to a fourth aspect of the present invention, in the image data conversion method according to the first aspect, the number of the second coloration table numbers is changed to the first coloration table number.
Is limited to a predetermined number or less, which is smaller than the number of color scheme table numbers in the color scheme table.

According to a fifth aspect of the present invention, there is provided the image data conversion method according to the third aspect, wherein the third image data in an arbitrary format is converted into image data composed of the general-purpose coloration table, and this is converted into the first image data. It is characterized by the following.

According to a sixth aspect of the present invention, in the fourth aspect, if the number of coloration table numbers is reduced with respect to the second image data, the size of a portion representing each pixel data is correspondingly reduced. The compression is performed using a compression method that reduces the size.

[0013]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

Embodiment 1 FIG. 1 is a block diagram illustrating an outline of an apparatus used for implementing the image data conversion method according to the first embodiment. This device has a central processing unit 1, a program memory 2, a data memory 3, and a bus 4 connecting these to each other. The central processing unit 1 operates according to a computer program stored in the program memory 2. At that time, data is written to or read from the data memory 3.

The operation of the central processing unit 1 in the present embodiment is enumerated as follows. The central processing unit 1
The original image data supplied from the outside and its coloration table are read and written in the data memory 3. The central processing unit 1 also reads the original image data and the color table written in the data memory 3 and examines the image data of each pixel to determine which color table number in the color table represents. These are summed up by the number of pixel data of the image data, and the summation result is stored in the data memory 3. The central processing unit 1 further rearranges the colors of the color arrangement table in descending order of appearance frequency based on the information on the appearance frequency of each color of the color arrangement table that has appeared, and stores the rearranged colors in the data memory 3. The central processing unit 1 further extracts those whose appearance frequency is one or more times and stores them in the data memory 3. The central processing unit 1 further reassigns the color arrangement table numbers in the order in which the colors have been rearranged (in the order of appearance frequency), and stores them in the data memory 3 as a new color arrangement table. The central processing unit 1 further calculates pixel data of each pixel of the original image data,
The color table number of the original color table is replaced with a new color table number and stored in the data memory 3. The central processing unit 1 further configures new image data by adjusting additional information other than the above, and stores the new image data in the data memory 3.

FIG. 2 is a flowchart showing a processing procedure of the image data conversion method according to the first embodiment. FIG.
Shows an example of original image data to be converted.

In FIG. 3, reference numeral 11 denotes the entirety of the original image data, reference numeral 12 denotes a color scheme of the image data 11, and reference numeral 13 denotes pixel data representing information on actual pixels of the image data. FIG.
BM as a format of image data using a color scheme such as
There are a P format, a GIF format, a PNG format, a TIF format, and the like, and depending on the format, other additional information such as a data format identification flag, the size of the entire image data, a header size, etc. are included. ing.

One row of the color scheme table 12 includes a color scheme table number (the left column described as No.) which is an index of the color scheme table 12, and
It is composed of data representing the elements of each color information of red, green and blue. In the actual image data format, the color scheme table number of the color scheme table 12 is specified in the data as a number, or simply a red,
A set of green and blue data is arranged, and the information of which color table number and which color information is shown in the order from the top in the color scheme table of this set. Red, green, and blue data are represented in 24-bit color with 8 bits for each color.
Each is represented by an integer value between 0 and 255. For example, in the color scheme table 12 of the original image data 11, the elements of the second “No. 1” of the color scheme table number are red = 90, green = 123, and blue = 123, and the entire color scheme table 12 has eight reds and greens. , A set of blue. The pixel data 13 representing the color information of each pixel of the image data 11 is represented by a color scheme number in the color scheme 12. For example, the upper left pixel of the pixel data 13 of the image data 11 is represented as “2”, which means that the color of this pixel is the color scheme number No. of the color scheme 12. The actual colors are red = 165, green = 16, blue = 4 with reference to the color scheme table 12.
It turns out that it is the color represented by 9.

Although the pixel data 13 of the image data 11 is described in FIG. 3 as being 5 pixels in width and 7 pixels in height in the same manner as the actual image data, the pixel data 13 is simply arranged in a color arrangement table in the actual image data format. 11 is a sequence of numbers representing the coloration table number 11, and the image width information and the image height information may be described in another place in the image data 11.

A case where the original image data shown in FIG. 3 is processed and converted according to the procedure shown in FIG. 2 will be described below.
FIG. 4 is a diagram showing a conversion process, and FIG. 5 is a diagram showing data after conversion.

First, in the process ST1 of FIG. 2, the color arrangement table 12 included in the original image data 11 is extracted.

Next, in the process ST2 of FIG. 2, the pixel data of the original image data is examined, the color table number indicating the color of each pixel data is determined, and the number of pixel data of each color table number in the entire image is totaled. I do. Table 14 in FIG. 4 shows a totaling result of the image data 11 for a total of 35 pixels which is the entire pixel data 13. To the right of each color table number, the frequency of appearance (the number of applications to the number of applications) of the color table number in the pixel data 13 is shown. 0, 3 No. No. 1; No. 2; No. 3 and No. 3 No. 4, two No. 4 No. 5, 0, No. 6 and no. 7 is 0.

Next, in the process ST3 of FIG. 2, the colors of the color arrangement table are rearranged in descending order of appearance frequency based on the information on the appearance frequency of each color arrangement table number of the totaled color arrangement table. Table 15 in FIG. 4 shows the result of rearranging the colors of the tabulated coloration table in descending order of appearance frequency. At this time, the coloring table number No. 5 and No. 5 7 indicates that the appearance frequency in the pixel data is 0, which means that the pixel data is registered in the color scheme table but is not used once in the actual pixel data 13 of the original image data 11.

Next, in the process ST4 of FIG. 2, those having an appearance frequency of one or more are extracted.

Next, in process ST5 of FIG. 2, the color arrangement table numbers are changed. That is, in Table 15, numbers are assigned in the order of the appearance frequency of each color (in the order rearranged in Table 15), instead of the color arrangement table number representing each color. Table 16 in FIG. 4 shows the result of rearranging the extracted colors (each represented by a color scheme table number) in the arrangement order (order of appearance frequency).

Next, in process ST6 of FIG. 2, the color table number of the pixel data of the image data is changed. That is, the color table number of the new color table is assigned instead of the color table number of the original color table. FIG. 5 shows new image data generated based on Table 16 in FIG. 4 by the process ST6. In the figure, reference numeral 17 denotes new image data, 18 denotes a new color scheme, and 19 denotes new pixel data.

Next, in process ST7 of FIG. 2, additional image information other than these is adjusted to form new image data.

In FIG. 4 and FIG. 5, each color is rearranged in the order of the number of appearances and numbered, but this is not always necessary. For example, a color arrangement table number whose appearance frequency is 0 is excluded. Otherwise, they may be arranged in the order of the color table numbers in the original color table, and the color table numbers may be renumbered.

Comparing the original image data 11 of FIG. 3 with the new image data 17 of FIG. 5, the number of color table numbers in the converted color table 18 is larger than the number of color table numbers in the converted color table 12. Few. That is, in the illustrated example, the original image data 11
There is a color arrangement table 12 of which the appearance frequency in the pixel data is 0 (color arrangement table numbers No. 5 and No. 7 in the color arrangement table of the original image data) in the color arrangement table 12 of FIG.
The number of color scheme table numbers 8 is reduced. As described above, if pixel data of the original image data which is not used even once exists in the color table of the original image data, the number of the color table numbers of the new color table is reduced accordingly. If the number of color arrangement table numbers can be reduced, the area in which the distribution color table is described becomes smaller, so that the size of the entire image data can be reduced.

In the case where the original image data 11 uses a specific color table depending on the display device or the like, the colors defined by the color table can be normally changed by the display device regardless of the format of the color table in the image data. When display is possible, the colors included in the new color scheme are all colors included in the color scheme of the original image data as described above, so that the new image data can be normally displayed on this display device. it can. For example, a color table of 216 colors that expresses red, green, and blue in six gradations is used in browser software on the Internet.
Embodiment 1 of the present invention is effectively used as long as colors can be displayed irrespective of the format of a color table of image data.

Embodiment 2 FIG. 6 is a flowchart showing the processing of the image data conversion method according to the second embodiment of the present invention. FIG. 6 shows ST21 to ST21 in FIG.
This is an added step of T23. In the first embodiment, the number of color table numbers in the color table of the new image data after conversion is automatically determined based on the contents of the original image data and the color table, but in the second embodiment, the number of the color table in the new image data is changed. The number of color arrangement table numbers is determined in advance.

Hereinafter, a case where the original image data shown in FIG. 3 is processed and converted according to the procedure shown in FIG. 6 will be described.
It is assumed that the number of color table numbers in the color table in the new image data is determined to be "4" in advance. FIG. 7 and FIG.
FIG. 9 is a diagram showing a process of conversion, and FIG. 9 is a diagram showing image data after conversion.

The processing up to the processing ST4 in FIG. 6 is the same as that in FIG. That is, first, the color table 12 of the original image data 11 is extracted (ST1), the color table indicating the color of each pixel data is determined, and the pixel of each color table number in the entire pixel data 13 (composed of 35 pixels) is determined. Aggregate the number of data (ST
2). The tabulation results are shown in Table 31 of FIG. Next, the colors are rearranged in descending order of appearance frequency (ST3). The rearranged result is Table 32 in FIG. Then, ones having an appearance frequency of one or more times are extracted, and the extracted colors are renumbered in the arrangement order (the order of appearance frequency) (ST4). Table 33 (FIG. 7) shows the result of the rearrangement of the coloring table numbers.

Next, in process ST21, the number of color table numbers of the target color table in the new image data and the process S
Compare with the number extracted in T4.

In the example shown in the figure, the number of color table numbers in the target color table, ie, the number of colors 4, and the number of color table numbers in the table 33 obtained by extraction up to the processing ST4 in FIG. 6, ie, the colors Is compared with the number 6 (ST21), the number of colors “6” in Table 33 is larger.

If it is determined in the process ST21 that the number extracted up to the process ST4 is larger, the process ST2 is executed.
In step 2, further extraction is performed up to the number of colors in the target color table.
That is, four targets are selected and extracted in descending order of the appearance frequency of the table 33 extracted in the process ST4. The result is shown in Table 34.
It is.

The result is used as a new color table. Processing ST
Colors that have not been extracted in spite of the appearance frequency being one or more in step 22 are assigned to any color in the color scheme table extracted in step ST22. Hereinafter, this assignment method will be described.

FIG. 8 shows a method of the assignment. In the process ST22 of FIG. 6, the one extracted from the table 33 of FIG. 0 to No. Nos. 4 to No. 3 and those not extracted are No. 3. 4 and no. 5 two. In the pixel data 13 of the original image data 11, the No. 4 and no. The pixel data represented by No. 5 is represented by No. 5, respectively.
0 to No. For example, a method of using a distance between two pieces of color information to determine which of the three pieces of color information is assigned will be described. The distance D between the two pieces of color information A and B is defined as the sum of the squares of the differences between the red, green, and blue data. That is, red, green, and blue color information Ar, Ag, Ab, and B of two pieces of color information A and B.
When A = (Ar, Ag, Ab) B = (Br, Bg, Bb) as a set of r, Bg, and Bb, the distance D between the two pieces of color information A and B is given by the following equation. Ask. Distance D (A, B) = (Ar-Br) ² + (Ag-Bg) ²
+ (Ab-Bb) ²

This equation is referred to as No. 4 and no. Table 36 shows the result applied to No. 5. No. The color of No. 4 is red = 117, green = 237, blue = 184. 0 to No. The distance D is obtained for each of the three. No.
No. 4 is No. 0 to No. No. 3 out of 4 out of 4 Since the distance to D.2 is minimum at D = 17446, No. 2 4 is determined to have the least effect on the quality of the image data. Therefore, No. The pixel data represented by No. 4 is No. 4. 2
And convert. Similarly, No. When four distances D are obtained for No. 5 as well, No. 0 is minimized.
The pixel data represented by No. 5 is No. 5. Convert to 0.

It should be noted that in FIG. 4 as No. 4. 2
No. No. 5 to No. 5. Although the process ST22 in FIG. 6 is performed by replacing the value with 0, the dithering process such as the pattern dither or the error diffusion method may be performed at the time of the replacement in order to obtain an area gradation expression using a new coloration table. Good.

On the other hand, if the number of the color arrangement table numbers in the target color arrangement table is larger in the processing ST21, the processing ST23 is executed.
In step (1), for example, zero data (red = 0, green = 0, blue = 0) is added by a required number to the table extracted up to the processing ST4 to obtain a target number, which is used as a new color table.

Note that, depending on the format of the image data, it is impossible to take an arbitrary size exceeding a certain limit. In this case, the number of the target color table numbers is limited to the number of the limit. For example, in GIF format image data, since the number of color scheme table numbers in the color scheme table is up to 256,
No more can be specified.

In step ST5 and subsequent steps, the pixel data 13 is converted based on the new color table created in step ST22 or ST23 in the same manner as in the first embodiment, and new image data 37 (FIG. 9) is obtained. Is configured.

That is, the color arrangement table 38 of the new image data 37 is obtained by using the table 34 created through the processes of FIGS.
make. The pixel data 39 of the new image data 37 is formed by changing the color table number of the pixel data 13 of the original image data 11 based on the color table 38 of the new image data 37. Then, necessary conversion of other additional information and the like is performed to obtain new image data 37 (FIG. 9) (ST
7).

Comparing the original image data 11 in FIG. 3 with the new image data 37 in FIG. 9, the number of color table numbers in the color table 38 after conversion is smaller than the number of color table numbers in the color table 12 before conversion. . In particular, the number of the color scheme table numbers of the new color scheme table 38 is determined to be 4 in the above example, but since this value can be arbitrarily reduced as needed, the color scheme table 1 of the original image data 11
It is possible to select so that the number of color arrangement table numbers in the color arrangement table 38 of the new image data 27 is always smaller than the number of color arrangement table numbers of 2. If the number of color scheme numbers in the color scheme can be reduced,
The size of the entire image data can be reduced. If you want to further reduce the overall size of the converted image data,
What is necessary is just to reset the number of color table numbers in the color table of the new image data after the conversion, and repeat the process of converting the target color table into image data. Also, the assignment of the color table numbers performed when the number of the color table numbers is reduced is changed to an optimum value, or a dither process is performed in some cases, so that deterioration in image quality can be reduced.

Embodiment 3 FIG. 10 illustrates an image data conversion method according to the third embodiment. FIG. 10 is obtained by adding processing ST41 to the method of the second embodiment shown in FIG.

The method shown in FIG. 10 is applied when the original image data is image data represented without using a color table or image data constituted by a color table different from the target color table. In the process ST41, the image data represented without using the color table or the image data composed of the color table different from the target color table is converted into the image data composed of the target color table.

In the case where the original image data is image data represented without using a color table, the conversion is performed by, for example, using the pixel data of each pixel as described in FIG. 8 in the second embodiment. It is only necessary to determine which color table number of the table corresponds to. Further, in order to perform conversion from image data composed of a coloration table different from the target coloration table, for example, an image composed of the target coloration table is first converted into image data represented without using the coloration table, and then converted. The conversion into image data without using the color scheme table is performed by converting the pixel data of each pixel represented by the color scheme table into red, green, and blue color information indicated by the color scheme table. Can be realized by replacing After the conversion into the image data composed of the target color table, the color table is taken out from this, and new image data is constructed in the same manner as in FIG.

In FIG. 10, after further extracting up to the size of the target coloration table in the process ST22, those not extracted are assigned to any of the extracted ones. As shown in FIG. 11, a new color table determined from the original image data expressed without using the color table to the processing ST5 is as follows:
In the process ST42, a conversion process from the original image data to the image data composed of the target color table may be performed.
That is, with respect to the color table generated up to the process ST5, FIG.
0, using the data of the original image instead of ST7.
By directly converting to image data using a new coloration table by performing dither processing or the like, an image closer to the original image can be obtained.

In the process ST41, from the original image data,
When converting to image data represented using a color table, if the color table is created according to the original image data, the colors included in the color table are selected so as to be included in the original image data, There are not many colors that are included in the color scheme but not included in the pixel data portion of the image data. However, when the process ST41 is performed on a specific color table depending on the display device or the like, the color table is determined in advance so as to correspond to various image data. It is common to make it universal. On the other hand, since the original image data may be biased toward a specific color depending on the content, it is highly possible that a color not included in the original image data exists in the color arrangement table. Therefore, in this case, if the processing of FIG. 10 including the processing ST41 is applied, the number extracted up to the processing ST4 is already smaller than the number of the coloration table numbers of the coloration table of the original image data, and the quality of the image data is less deteriorated. . Therefore, any original image data can be converted to new image data of a color table composed of colors represented by a specific color table, and the new image data has a small number of color table numbers in the color table and the size of the entire image data is small. The image quality is small and there is little deterioration.

Embodiment 4 FIG. FIG. 12 illustrates an image data conversion method according to the fourth embodiment. FIG. 12 is obtained by adding a compression process ST43 to the method of the second embodiment shown in FIG.

For this compression, a compression method is used, in which the smaller the number of color scheme table numbers, the smaller the size of the pixel data.

As a format of image data using such a compression method, there is a GIF format and the like.
Embodiment 4 will be described using a compression method of the IF format. GIF format image data is a type of image data represented using a color scheme, and an area representing pixel data in each pixel is compressed by the LZW method. In the LZW compression method, when the same data arrangement is present in the pixel data portion, the first data that appears first is registered in a temporary dictionary used for compression. The data size is compressed as indicated by an index representing. First, all the color arrangement table numbers of the color arrangement table are registered as indices of the dictionary, and thereafter, the arrangement of the pixel data is sequentially registered. For example, when the index is 256 bits and the number is represented by 8 bits, the index used for compression starts with 9 bits, and when it exceeds the maximum number that can be expressed by 9 bits, it is expressed by the next 10 bits. Increase the number of bits of the indicator. Since the data to be compressed is described by arranging the data corresponding to the number of bits currently used for the index, if the number of bits used for the index is small, the data after compression becomes small. Therefore, if the number of color scheme table numbers in the color scheme table is small, the number of bits of the index at the time of starting compression is small, and the size for describing this is small, so
The data size after compression of the pixel data can be reduced. As described above, when the number of color table numbers in the color table is reduced, not only the size describing the color table becomes smaller, but also the size describing the pixel data by compressing the new image data after the conversion. Therefore, the effect of reducing the size of the entire image data when the number of color arrangement table numbers in the color arrangement table is reduced can be increased. Therefore, when the upper limit of the data size that can be displayed by the display device is set, new image data is configured with a color scheme table having a larger number of color scheme tables, even if the converted data size is the same. Thus, it is possible to reduce the deterioration of the quality of the image data due to the decrease in the number of the coloring table numbers in the coloring table.

In the above-described first to fourth embodiments, in the process ST4, one having an appearance frequency of 1 or more is once extracted, but one having an occurrence frequency of 2 or more is extracted. Is also good. In this case, as described with reference to FIG. 8, another color, for example, the color with the shortest distance, may be assigned to the color of the coloration table number having an appearance frequency of 1 or more.

[0055]

Since the present invention is configured as described above, it has the following effects.

According to the first aspect of the present invention, it is possible to obtain second image data in which the number of color table numbers in the color table is equal to or less than the number of color table numbers in the first image data. If there is even one color table number whose appearance frequency is less than the predetermined value, the number of the color table numbers of the color table obtained after the conversion is smaller than that of the first image data. When the colors defined by a specific color scheme table can be displayed normally regardless of the format, the size of the entire image data can be efficiently reduced, and the communication time when transmitting and receiving image data by communication or the like can be reduced. It can be shortened and communication costs can be reduced.

According to the second aspect of the present invention, the number of color table numbers in the color table is equal to or smaller than the number of color table numbers in the color table of the original image data with the same image quality as the first image data. Image data can be obtained, and if there is even one color table number having an appearance frequency of 0 in the first image data, the number of color table numbers in the color table obtained after the conversion is equal to the first image data. Less than the data.

According to the third aspect of the present invention, when the original image uses a general-purpose color table, the number of color table numbers in the color table is equal to or less than the number of color table numbers in the first image data. Certain second image data can be obtained.

According to the fourth aspect of the present invention, when the display device has an upper limit of the data size that can be displayed, the data size is controlled so that the number of color table numbers in the color table is equal to or less than the upper limit. can do. Therefore, even if the first image data cannot be displayed on the display device, the converted second image data can be adjusted so that the converted second image data can be displayed. Can be eliminated.

According to the fifth aspect of the present invention, when converting arbitrary image data into image data composed of a general-purpose coloration table depending on a display device or the like, simply converting the third image data (original image data) Can be displayed on the display device even if the data size exceeds the upper limit of the display device and cannot be displayed on the display device if converted to image data (second image data) composed of this general-purpose color table. Since the third image data can be adjusted to an appropriate size, convenience is improved.

According to the invention of claim 6, when the number of coloration table numbers in the coloration table is reduced, the size of the entire image data can be further reduced. Therefore, when the upper limit of the data size that can be displayed by the display device is set, new image data is configured with a color scheme having a larger number of color scheme tables even if the data size after conversion is the same. It is possible to reduce the influence on the quality of the image data due to the reduction in the number of the coloration table numbers in the coloration table, and it is possible to display the second image data of higher quality.

[Brief description of the drawings]

FIG. 1 is a block diagram schematically showing an apparatus used for implementing an image data conversion method according to a first embodiment of the present invention.

FIG. 2 is a flowchart illustrating an image data conversion method according to the first embodiment.

FIG. 3 is a diagram illustrating an example of original image data used in the image data conversion method according to the first embodiment;

FIG. 4 is a diagram illustrating a color table conversion process in the image data conversion method according to the first embodiment;

FIG. 5 is a diagram illustrating new image data after conversion by the image data conversion method according to the first embodiment;

FIG. 6 is a flowchart showing an image data conversion method according to the second embodiment of the present invention.

FIG. 7 is a diagram illustrating a color table conversion process in the image data conversion method according to the second embodiment;

FIG. 8 is a diagram illustrating a process of assigning a color of a color table number that has not been extracted to a color of an extracted color table number in the image data conversion method according to the second embodiment;

FIG. 9 is a diagram illustrating new image data after conversion by the image data conversion method according to the second embodiment;

FIG. 10 is a flowchart showing an image data conversion method according to Embodiment 3 of the present invention.

FIG. 11 is a flowchart illustrating another image data conversion method according to the third embodiment.

FIG. 12 is a flowchart illustrating an image data conversion method according to a fourth embodiment of the present invention.

[Explanation of symbols]

1 central processing unit, 2 program memory, 3 data memory, 11 original image data, 12 color scheme,
13 pixel data, 17 image data, 18 color scheme table, 19 pixel data, 37 image data, 38
Color scheme, 39 pixel data.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5B057 AA11 CA01 CA08 CB01 CB08 CE16 CH07 5C077 MP01 MP08 PP32 PP37 PP43 PQ12 PQ19 PQ20 PQ23 RR21 SS06 5C079 HB11 LA02 LB02 MA04 NA03 NA10 PA01 PA02 PA03

Claims (6)

[Claims] 1. A method according to claim 1, wherein the frequency of use of the first image data in the pixel data of the color image table number, which is an index of the first color image table, is determined from the first image data composed of the first color image table. An image data conversion method of extracting data having a predetermined value or more, reconstructing the extracted data as a second coloration table, and converting the data into second image data configured using the second coloration table. 2. The image data conversion method according to claim 1, wherein the predetermined value of the use frequency is 1. 3. The image data conversion method according to claim 1, wherein the first color table is a general-purpose color table. 4. The image data conversion method according to claim 1, wherein the number of said second color table numbers is limited to a predetermined number which is smaller than the number of color table numbers of said first color table. . 5. The image data according to claim 3, wherein the third image data in an arbitrary format is converted into image data composed of the general-purpose color table, and the converted image data is used as the first image data. Conversion method. 6. The method according to claim 1, wherein the second image data is compressed using a compression method that reduces the number of coloration table numbers and accordingly reduces the size of a portion representing individual pixel data. The image data conversion method according to claim 4, wherein