JPH07220070A - Converter for multi-level image - Google Patents

Abstract

PURPOSE:To provide an image to be outputted as an image using available colors sufficiently and with high quality when an image with many colors is converted to the one with small colors. CONSTITUTION:A gradation number decision means decides the number of gradation of each color component based on the available number of colors. For example, when 256 available colors are prepared, the number of gradation of a red color component. a green color component, and a blue color component can be prepared by six, respectively. An optimum gradation number decision means finds the numof colors to be used in a conversion image when a color original image is converted based on the present number of gradation (1). and starts up an output image generating means by informing the number of gradation just before when the number of colors to be used exceeds the available number of colors (2), and stores the present number of gradation and increases the number of gradation when the former is less than the latter (3), then, returns processing to the above processing (1). The output image generating means converts the color original image based on the number of gradation informed from the optimum gradation number decision means. and generates an output image.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-tone image conversion device for converting an image expressed in a large number of colors into an image expressed in a small number of colors.

[0002]

2. Description of the Related Art FIG. 17 is a diagram showing the structure of a conventional multi-gradation image conversion device. In the figure, 1 is an input image file, 2 is an output image file, 3 is a conversion means, and 4 is a gradation determination means. File 1 stores the input image. The color of each pixel of the input image is, for example, R component (red component) of 0 to 255 gradations, 0 to 255
It is expressed by a G component (green component) of gradation and a B component (blue component) of 0 to 255 gradations.

File 2 stores the output image. The gradation number of each color component of the output image is fixed or given from the outside. The gradation determining means 4 determines the gradation to be used from the number of gradations for each color component. For example, each color component of the input image has 256 gradations from 0 to 255, and when converting it to 3 gradations, the gradations to be used are 0, 12 if they are evenly distributed.
It becomes 7,255. The conversion unit 3 converts the input image so that only the gradation determined by the gradation determination unit 4 is used.
In the case of converting to three gradations, one of 0, 127, and 255 is selected and replaced by the value of the point (pixel) of the input image.

FIG. 18 is a diagram showing a conversion operation flow of a conventional conversion device. In step S1, the input image is read from the file 1. In step S2, the number of gradations of each color component is obtained. Each color component is, for example, the above-mentioned three gradations.
In step S3, the gradation to be used is determined for each color component. The gradation used for each color component is, for example, 0,
127 and 255. In step S4, the color of each point is replaced. For example, the color of the input pixel is R component = 15, G
When the component = 100 and the B component = 240, the color of the pixel is converted to R component = 0, G component = 127, and B component = 255. In step S5, the image having the converted color is output to the file 2.

[0005]

As described above, in the format which is often used when a natural image or the like is handled by a computer,
The image is converted into an array of fine points (pixels), and the value of the color component is digitized at each point. In a typical example, three primary colors of green, red, and blue are used as color components, and each of them is digitized with 256 gradations. In this format, the color of each pixel is any one of about 16 million colors (256 × 256 × 256).

On the other hand, in the image display device of the computer which is generally used at present, the number of colors that can be displayed simultaneously is often limited. This is intended to improve display speed and save display memory. Some image display devices have a display memory that represents one pixel in 8 bits and a color lookup display that has 256 entries.
It has a table and can display any 256 colors out of about 16 million colors at the same time.

In this type of display device, it may not be possible to display the image in the above format as it is, so that the image is converted and the number of colors used is reduced to the number usable by the display device. Need to let. With conventional technology,
The number of gradations of each color component is reduced to the previously calculated number of gradations for display. For example, in the case of the above device, if each of the red, blue, and green components is converted into 6 gradations, only 216 colors are used at the maximum, so that display is possible.

The image converted by the conventional method has the color components of 256 gradations reduced to 6 gradations, so the image quality is remarkably deteriorated as compared with the original image, and it is not useful depending on the user's application. In many cases. However, it is burdensome to prepare a separate display device that does not limit the number of colors that can be displayed simultaneously.
There has been a strong demand for a device capable of displaying a high-quality image even in a general display device.

The present invention was created in view of this point, and when converting an image having a large number of colors into an image having a small number of colors and outputting the converted image, the colors usable by the output image are determined. The goal is to make sure you have a good quality product that you have used.

[0010]

FIG. 1 is a diagram for explaining the principle of the invention of claim 1. The multi-gradation image conversion device according to claim 1 is a conversion device for converting a multi-gradation color original image into an image having a number of colors within the usable number of colors, based on the number of usable colors. From the optimum gradation number determining means, which starts the operation after the gradation number is determined by the gradation number determining means, and the optimum gradation number determining means And an output image generating means for converting the color original image based on the gradation number to generate an output image, wherein the optimum gradation number determining means converts the color original image based on the current gradation number. The number of colors used in the converted image is calculated, and it is checked whether the number of colors used in the converted image exceeds the number of colors that can be used. If it exceeds, the number of gradations immediately before that is output image generation means. When the number of gradations is not exceeded, the current number of gradations is memorized and the number of gradations is increased. And it is characterized in that it is configured to perform processing to return to the process.

FIG. 2 is a diagram for explaining the principle of the invention of claims 2 and 3. The multi-gradation image conversion device according to claim 2 is a conversion device for converting a multi-gradation color original image into an image having a number of colors within a usable color number, and the multi-gradation color original image. Input image used color number measuring means for measuring the number of colors used in, an optimum gradation number determining means for starting operation after the color number is measured by the input image used color number measuring means, and an optimum gradation number And an output image generating means for converting the color original image to generate an output image based on the gradation number notified from the determining means. A new gradation number is estimated based on the number of colors available and the current number of gradations, the original color image is converted based on the estimated number of gradations, and the number of colors used in the converted image is calculated. Check if the number of colors used in is equal to the number of colors available, and if so, the current When the number of gradations is notified to the output image generation means and started, and the number of colors used in the converted image is not equal to the number of colors available, the number of colors used in the converted image exceeds the number of colors available. If the number of colors used in the converted image does not exceed the number of colors that can be used, the number of colors used in the converted image is the number of colors used immediately before. If the number of colors used in the converted image does not exceed the number of colors used immediately before, the output image generation means is notified of the number of gradations immediately before, and the colors are used in the converted image. When the number exceeds the number of colors used immediately before, the present number of gradations and the number of colors are stored, and the process is returned to the process of.

According to a third aspect of the present invention, there is provided a multi-gradation image conversion device for converting a multi-gradation color original image into an image having a color number within the usable color number. The number of colors used in the color original image is measured, and the number of gradations for each color component is also measured, and the number of colors and each color component are measured by the input image used color number measurement unit. An original color image is converted and output based on a combination of the optimum gradation number determining means for starting the operation after the gradation number is measured and the gradation number for each color component notified from the optimum gradation number determining means. And an output image generation means for generating an image, wherein the optimum gradation number determination means is configured to determine the current number of colors, the number of colors usable in the converted image, the current number of gradations for each color component, and the original color image. Estimate a new set of gradation numbers for each color component based on the gradation number for each color component Then, the original color image is converted based on the estimated set of gradation numbers for each color component, the number of colors used in the converted image is calculated, and it is determined whether the number of colors used in the converted image is equal to the number of usable colors. If they are equal, the set of gradation numbers for each current color component is notified to the output image generation means, the output image generation means is activated, and the number of colors used in the converted image is the number of usable colors. If it is not equal to, check whether the number of colors used in the converted image exceeds the number of colors that can be used. If it exceeds, return to the process of and the number of colors used in the converted image can be used. If the number of colors does not exceed the number of colors used in the converted image, check to see if the number of colors used in the converted image has exceeded the number of colors used immediately before. The output image generation means is notified of the set of gradation numbers for each color component of the If the number of colors to be used is exceeded, the present set of gradation numbers for each color component and the number of colors are stored, and the process is returned to the process.

FIG. 3 is a diagram for explaining the principle of the invention of claim 4. A multi-gradation image conversion device according to claim 4 is the multi-gradation image conversion device according to claim 1, 2 or 3, wherein the number of colors in the output image generated by the output image generation means can be used. If the number of colors is less than the number of colors, an output image correction means is provided for replacing the color of the pixel in the converted image corresponding to the pixel having a color that is frequently used in the color original image with the color of the pixel in the color original image. It is characterized by that.

[0014]

When the images converted by the conventional conversion device are analyzed and viewed, the number of colors actually used is less than the maximum number (product of each color component) in most images. For example, 6
When the gradation is reduced, a maximum of 216 colors may be used, but the number of colors included in the converted image is often several tens at most. Therefore, even if more than 6 gradations are actually used, the number of colors used is 2
It often does not exceed 56 colors.

Therefore, in the present invention, the number of colors included in the converted image is measured, and if there are still usable colors, the number of gradations is increased and conversion is tried again. By repeating this operation, the finally output image becomes a high quality image using the usable colors sufficiently.

In some cases, all the colors that can be used are not used even in the image that is finally output. In such a case, the surplus colors are replaced by colors that frequently appear in the color original image. Assigning and replacing corresponding points in the output image with that color results in a higher quality output image. In the present invention, a technique called dithering can be used together when converting an image. The combined use of the present invention and dithering techniques provides higher quality output than conventional dithering.

The operation of the converting device according to the first aspect of the present invention will be described. In the conversion device according to claim 1, the color original image is converted into an image having the number of gradations determined by the same method as the conventional method,
Check the number of colors used there. If there is still an excess in the number of colors, increase the number of gradations of any of the components and perform conversion again. This procedure is repeated, and when the number of colors in the converted image exceeds the number of usable colors, the image is converted and output.

The operation of the converting device according to the second aspect of the present invention will be described. In the conversion device according to the second aspect, first, the number of colors included in the color original image is checked, and the appropriate number of gradations of each color component is estimated using this number of colors. For example, if the red component has 256 gradations and 100 colors are used, it can be estimated that when the gradation is 128 gradations, half the 50 colors will be used.

Assuming that there are three color components, it can be estimated that when the number of gradations is changed by n times, the color used changes to the cube of n. Conversely, if the colors used are to be multiplied by m, the number of gradations of each of the red, blue, and green components should be multiplied by 1/3 of m. Conversion is performed using the number of gradations thus estimated. Compared with the conversion device according to the first aspect, the number of gradations for the next time can be estimated more appropriately, so that the result can be output in a short time. However, in the conversion device of claim 2,
In some cases, it is necessary to reduce not only the number of gradations but also the number of gradations. Note that this estimation method is not limited to the method described here, and if there is a more effective method depending on the nature of the image to be handled, it can be used.

The operation of the converter of claim 3 will be described. In the conversion device of the third aspect, when checking the number of colors, the number of gradations used for each color component is also checked at the same time. As a result, if the number of gradations used in any color component is less than the number of gradations assigned to that component, the number of unused gradations is used to determine the number of allocations of other components. Recalculate. For example, if only two gradations are used in the blue component, it is not necessary to allocate 6 gradations to all components, and 11 gradations can be allocated to red and green components (2 × 11 × 11 = 242). By doing so, useless allocation can be eliminated and the result can be output at higher speed.

The operation of the converter of claim 4 will be described. The conversion device according to claim 4, wherein when the number of colors used in the image obtained by any one of the above conversion devices is less than the number of colors that can be used, the surplus color is a color having a high appearance frequency in the original image. , And replace the corresponding points in the output image with the color.

[0022]

FIG. 4 is a diagram showing the configuration of the first embodiment of the present invention. In the figure, 1 is an input image file, 2 is an output image file, 3 is conversion means, 4 is gradation determination means,
Reference numeral 5 is a used color number measuring means, 6 is a gradation number determining means, 7 is a gradation number increasing means, 8 is a controlling means, and 9 is a storing means.

The means for carrying out the present invention can be realized by a computer and a program. In the first embodiment, the converting means 3, the gradation determining means 4, the used color number measuring means 5, the gradation number determining means 6, the gradation number increasing means 7, etc. correspond to a subroutine, and the control means 8 is a main routine. Equivalent to.

The maximum number of colors that can be used in the output image is given externally. The gradation number determining means 6 determines the number of gradations assigned to each color component from the maximum number of colors that can be used. For example, when the maximum number of colors that can be used is 256, the R component,
The number of gradations of the G component and the B component is 6, respectively. In this embodiment, all the components are treated equally, but the color components that have a great influence on the image may be prioritized. For example, the human eye is most sensitive to green, then red, and less sensitively to blue, so the number of gray levels for green is the highest, and the level for red is second. It is also possible to increase the number of tones and minimize the number of tones for blue.

The gradation determining means 4 is the same as the conventional one.
The gradation to be used is determined according to the given gradation number. 6
In the case of gradation, the gradation to be used is, for example, 0, 51, 10
2,153,204,255. The used color number measuring unit 5 measures the number of colors used in the converted image when the input image is converted so that only the gradation determined by the gradation determining unit 4 is used. The gradation number increasing means 7 increases the gradation number of any of the color components. In this embodiment, all the components are treated equally, but the color components that have a great influence on the image may be prioritized.

The storage means 9 stores the combination of the number of gradations, the number of colors, etc., which gives the best result. The control unit 8 requests the conversion unit 3, the gradation determination unit 4, the used color number measurement unit 5, the gradation number determination unit 6, and the gradation number increase unit 7 to perform processing, and reads / writes the storage unit 8. I do.
The conversion means 3 is the same as the conventional one.

FIG. 5 is a diagram showing an operation flow by the control means of the first embodiment. In step S1, the input image is read from the file 1. In step S2, the number of colors usable in the output image is obtained. In step S3, the gradation number determining unit 6 is called to obtain the gradation number assigned to each color component. Next, the gradation determining means 4 is called to determine the gradation based on the current number of gradations. In step S4, the number-of-used-colors measuring means 5 is called to obtain the number of colors used at the current number of gradations (gradation).

In step S5, it is checked whether or not the number of colors obtained in step S4 exceeds a predetermined value (for example, 256). If YES, the process proceeds to step S8, and if NO, the process proceeds to step S6. In step S6, the current number of gradations and the number of colors are stored in the storage unit 9. Step S
In step 7, the gradation number increasing means 7 is called to increase one of the gradation numbers. Next, the gradation determining unit 4 is called to obtain the gradation of the color component with the increased number of gradations. Then, the process returns to step S4.

In step S8, the stored gradation number is set in the communication area and the gradation determining means 4 is activated to obtain the gradation with the stored gradation number. In steps S9 and S10, the conversion means 3 is called to replace the color of each point of the input image, and the resulting image is output to the file 2.

FIG. 6 is a diagram showing an operation flow of the gradation number determining means of the first embodiment. In step S1, the 1/3 power of the number of usable colors is converted into an integer. In step S2, it is checked whether or not the result becomes 0. If it is not 0, the process proceeds to step S3, and if it is 0, the process proceeds to step S4. In step SS3, that value is set as the number of gradations. In step S4, an error is output and the conversion process is stopped.

FIG. 7 is a diagram showing an operation flow of the gradation number increasing means of the first embodiment. In step S1, the color component having the smallest number of gradations is obtained. In step S2, it is checked whether or not there are a plurality of color components obtained in step S1. If there is one, the process proceeds to step S3.
Go to 4. In step S3, the number of gradations of the color component is increased by one. In step S4, one of them is selected and the number of gradations of the selected color component is increased by one.

FIG. 8 is a diagram showing an operation flow of the used color number measuring means of the first embodiment. In step S1, flags are prepared and cleared for all possible colors. For example, when the number of gradations of the R component, the G component, and the B component is 6, and the used gradations are 0, 51, 102, 153, 204, 255, the possible color is the first color R = 0, G = 0, B = 0 2nd color R = 0, G = 0, B = 51 3rd color R = 0, G = 0, B = 102 ... 216th color R = 255, G = 255, B = 255. In step S2, each point of the input image is converted with the determined use gradation. In step S3, a flag added to the color used in the converted image is set. In step S4, the number of standing flags is counted.

FIG. 9 is a diagram showing the configuration of the second embodiment of the present invention. In the figure, 8'denotes a control means, 10 a gradation number estimating means, and 11 an input image used color number measuring means. The same reference numerals as those in FIG. 3 indicate the same items.

The maximum number of colors used in the output image is given externally. The input image used color number measuring means 11 performs the same operation as the used color number measuring means in the first embodiment, and measures the number of colors used in the input image. Gradation number estimating means 1
A value of 0 estimates the number of gradations of each color component from the number of colors used and the maximum number of colors that can be used.

The control means 8'determines the number of colors to be used based on the gradation number estimated by the gradation number estimating means 10 and repeats it until the best result is obtained. When the best combination is determined, the number of gradations is used to convert 3
And output the image obtained as a result of the conversion. The gradation determining means 4, the used color number measuring means 5, the converting means 3, and the storing means 9 are the same as those in the first embodiment.

FIG. 10 is a diagram showing an operation flow by the control means of the second embodiment. In step S1, file 1
Read the input image from. In step S2, the number of usable colors is calculated. The number of colors that can be used is 256, for example. In step S3, the input image used color number measuring means 11 is used.
Call to obtain the number of colors used in the input image.

In step S4, the gradation number estimating means 10 is called to estimate the gradation number of each color component. Next, the gradation determining means 4 is called to determine the gradation based on the estimated number of gradations. In step S5, the used color number measuring means 5 is called to obtain the number of colors used in the current number of gradations (gradation).

In step S6, it is checked whether the number of colors obtained in step S5 is maximum. If YES, step S
If NO, proceed to step S7. For example, if the number of colors available is 256, the maximum number is 256.
Becomes In step S7, it is checked whether the number of colors is over. If YES, then return to step S4, NO
In the case of, it progresses to step S8.

In step S8, it is checked whether or not the number of colors has updated its optimum value. If yes, then continue with step S9; if no, continue with step S10. For example, when the number of colors that can be used is 256, the number of colors obtained in step S5 immediately before is 200, and the number of colors obtained in step S5 this time is 2
In the case of 10, the best value has been updated. In step S9, the current gradation number and color number of each color component are stored. Then, the process returns to step S4.

In step S10, if the optimum value is not updated, the stored gradation number is set in the communication area and the gradation determining means 4 is activated to execute gradation based on the stored gradation number. To get When it is determined that the number of colors is the maximum number, the number of gradations at that time is set in the communication area and the gradation determining means 4 is activated, and the floor based on the number of gradations at the time when the maximum number is judged. Get the key. In steps S11 and S12, the conversion means 3 is called to replace the color of each point of the input image, and the image obtained as a result of the conversion is output to the file 2.

FIG. 11 is a diagram showing an operation flow of the gradation number estimating means of the second embodiment. In step S1, the number of colors available is divided by the number of colors currently used to obtain a quotient (denoted as D). For example, if the number of colors used in the input image is 10,000 and the number of colors available is 256,
Calculate 256/10000. Note that the target image is initially the input image and then the converted image.

In step S2, the quotient is the 1/3 power (D ^1/3 ) as a coefficient. In step S3, the gradation number of each color component is multiplied by a coefficient to be an integer. In step S4, it is checked whether the number of gradations is the same as the original number. If it does not change, the process proceeds to step S5, and if it does change, the process ends.

In step S5, it is checked whether the coefficient is larger than 1. If YES, proceed to step S7, N
In the case of O, the process proceeds to step S6. In step S6, one of the color components is reduced. In step S7, one of the color components is increased.

A third embodiment of the present invention will be described. The configuration of the third embodiment is the same as that of the second embodiment. Third
The input image used color number measuring means in the embodiment also measures the number of gradations of each color component used in the input image in addition to that in the second embodiment. The gradation number estimating means in the third embodiment uses the used colors, the maximum number of colors that can be used,
The number of gradations of each color component is estimated from the number of gradations of each color component used. The control means, the gradation determining means, the used color number measuring means, the converting means, and the storing means are the same as those in the second embodiment.

FIG. 12 is a diagram showing an operation flow of the gradation number estimating means of the third embodiment. In step S1, the number of colors that can be used is divided by the number of colors that are currently used, and the quotient (denoted as D) is used as a coefficient. For example, when the number of colors actually used in the input image is 786432 (1024 × 768) and the number of colors that can be used is 256, 256/78643
2 is a coefficient. The display screen is 1024 × 768 =
786432, and assuming that there are no pixels of equal value, the number of colors used in the input image is 786432.
32.

In step S2, the gradation number of each color component is multiplied by the coefficient to the 1/3 power to make it an integer. Assuming that the color component of the pixel of the color original image can take any value from 0 to 255, the initial value of the gradation number of each color component is 25.
It becomes 6,256,256. Coefficient is 256/78643
In the case of 2, the 1/3 power of the coefficient becomes 1 / 14.5, and when the gradation number of each color component of the input image = 256 is multiplied by 1 / 14.5 to be an integer, the gradation number of each color component is obtained. Becomes 17. In step S3, it is checked whether or not the number of gradations used in the input image is smaller. If YES, step S4
If NO, proceed to step S7. For example, in the input image, 1 out of 256 possible gradations of the R component
0 gradations are used, and R obtained in step S2
When the number of gradations of the component is 17, the number of gradations used in the input image is smaller.

In step S4, for color components having a smaller number of gradations used in the input image, the number of gradations of those color components is set to the number of gradations used in the input image. For example, of the 256 possible gradations of the R component in the input image, 10 gradations are used.
When the number of R component gradations obtained in 2 is 17, the number of R component gradations is set to 10. In step S5, the number of components to be changed is n. For example, when the number of gradations of the R component used in the input image is smaller than the number of gradations obtained in step S2 only for the R component, n is 2.

In step S6, the gradation number of the component to be changed is multiplied by the corrected coefficient to the power of 1 / n to be an integer. For example, the number of gradations that the R component can take is 256, and of the 256 gradations of the R component, the gradation that is actually used is 1.
When the number is 0 and the coefficient is 256/786432, the corrected coefficient is 256 ÷ 10 × 256 ÷ 7864.
32. Taking the square root of the corrected coefficient, it is 1/1
Becomes 1. When the gradation number 256 of the G component is multiplied by 1/11, and it is an integer, it becomes 23, and the gradation number 256 of the B component is 1/1.
Multiplying by 1 to make an integer gives 23. Therefore, the gradation number of the R component = 10, the gradation number of the G component = 23, and the gradation number of the B component = 23 are obtained.

In step S7, it is checked whether or not the original gradation number is different. If it changes, the process ends. If it does not change, the process proceeds to step S8. In step S8, it is checked whether the coefficient is larger than 1. If YES, the process proceeds to step S10, and if NO, the process proceeds to step S9. In step S9, the number of gradations of any component is reduced by 1. In step S10, the number of gradations of any component is increased by 1.

FIG. 13 is a diagram showing the operation flow of the used color number measuring means of the third embodiment. The operation flow of the input image used color number measuring means is the same as the operation flow of the used color number in FIG. 13, and when measuring the used color number in the input image, the gradation and the input image which can be used by the conversion means are measured. The same gradations that can be used in. In this way, the input image passes through the conversion means through.

In step S1, flags are prepared and cleared for all possible colors. For example, the number of gradations that the R component can take is 256, and the number of gradations that the G component can take is 25.
6, when the number of gradations that the B component can take is 256,
All possible colors are 256 x 256 x 256 = 1677
7216. Further, when the number of gradations that the R component can take is 6, the number of gradations that the G component can take is 6 and the number of gradations that the B component can take, the total number of possible colors is 6. ×
6 × 6 = 216.

In step S2, a flag is prepared for each gradation for each component and cleared. For example, when the gradation of the R component is 0, 1, ..., 255, a flag is prepared for each 0, 1 ,. The same applies to the G and B components.

In step S3, each point of the input image is converted with the determined gradation. For example, when converting 256 gradations to 6 gradations, it is assumed that 0 to 42 are converted to 0 43 to 84, 51 85 to 127 are 102 128 to 169, 153 170 to 212 are converted to 204 213 to 255, and 255 are converted to 255. . In such a case, R = 50,
Colors with G = 100 and B = 200 have R = 51 and G = 10.
2, the color is converted to B = 204. When measuring the number of colors used in the input image, 256 gradations of 0, 1, ..., 255 may be converted into 256 gradations of 0, 1 ,.

In step S4, a flag is set for the color used in the converted image (output image of the converting means). For example, in the converted image, R = 50, G = 10
Assuming that 0, B = 200 colors were used, then R
The flags corresponding to the colors of = 50, G = 100, B = 200 are set to 1. In step S5, a flag of the gradation used for each component is set. For example, R = 50, G = 10
Assuming that 0, B = 200 colors were used, then R
The flag of = 50 is set to 1, the flag of G = 100 is set to 1, and the flag of B = 200 is set to 1. In step S6, the number of standing flags is counted.

FIG. 14 is a diagram showing the configuration of the fourth embodiment of the present invention. In the figure, 8 ″ indicates a control unit, 12 indicates a used color frequency measuring unit, and 13 indicates a replacing unit. The same reference numerals as those in FIG. 9 indicate the same items. The number of colors used in the input image is counted, and the colors are arranged in order of appearance frequency.When the number of colors used in the image output by the conversion unit 3 is less than the maximum number, the replacement unit 13 has a surplus. The number of colors that are frequently used is calculated and the colors that are substituted in the output image are replaced. The control means 8 ″ is for converting the input image with the optimum number of gradations. After performing a series of processing, the used color frequency measuring means 12 is called, then the replacing means 13 is called, and the image replaced by the replacing means 13 is output to the file 2.

FIG. 15 is a diagram showing an operation flow of the used color frequency measuring means of the fourth embodiment. In step S1, counters are prepared and cleared for all possible colors. When the R component of the input image has 256 gradations, the G component has 256 gradations, and the B component has 256 gradations, the number of all possible colors is 256 ×.
It becomes 256 × 256 = 167777216. Step S
In 2, the value of the counter of the corresponding color is increased for each pixel of the input image. In step S3, each color is sorted by the value of the counter.

FIG. 16 is a diagram showing an operation flow of the replacing means of the fourth embodiment. In step S1, the number of colors still usable in the output image is obtained. For example, the number of colors that can be used is 2
56, and the number of colors used in the output image is 216
In this case, the number of colors that can still be used is 40. In step S2, the used color frequency of the input image is obtained, and the replacement color is set in descending order. In step S3, each pixel of the input image is examined, and if it is a color to be replaced, the value of the corresponding pixel of the output image is replaced. For example, R = 50, G = 100, B
= 200 is the color to be replaced and is the 10th color of the input image.
The color of the pixel in the 0th row and the 500th column is R = 50, G = 100, B
= 200, the 100th line, 5th line of the output image
Replace the color values in column 00 with R = 50, G = 100, B = 200.

[0058]

As is apparent from the above description, according to the present invention, the converted image has a larger number of colors used as compared with the image obtained by the conventional method, and the color whose value is close to that of the original image is obtained. Since it has been selected, the content closer to the original image can be expressed. Therefore, a good output result can be obtained with only a normal display device even for an image which conventionally requires another display device.

[Brief description of drawings]

FIG. 1 is a diagram illustrating the principle of the invention of claim 1;

FIG. 2 is a diagram for explaining the principle of the invention of claims 2 and 3.

FIG. 3 is a diagram illustrating the principle of the invention of claim 4;

FIG. 4 is a diagram showing a configuration of a first exemplary embodiment of the present invention.

FIG. 5 is a diagram showing an operation flow of the control means of the first embodiment.

FIG. 6 is a diagram showing an operation flow of a gradation number determining means of the first embodiment.

FIG. 7 is a diagram showing an operation flow of a gradation number increasing means of the first embodiment.

FIG. 8 is a diagram showing an operation flow of a used color number measuring means of the first embodiment.

FIG. 9 is a diagram showing a configuration of a second exemplary embodiment of the present invention.

FIG. 10 is a diagram showing an operation flow of the control means of the second embodiment.

FIG. 11 is a diagram showing an operation flow of a gradation number estimating means of the second embodiment.

FIG. 12 is a diagram showing an operation flow of a gradation number estimating means of a third embodiment.

FIG. 13 is a diagram showing an operation flow of a used color number measuring means of the third embodiment.

FIG. 14 is a diagram showing a configuration of a fourth exemplary embodiment of the present invention.

FIG. 15 is a diagram showing an operation flow of a used color frequency measuring unit of the fourth embodiment.

FIG. 16 is a diagram showing an operation flow of a replacing means of the fourth embodiment.

FIG. 17 is a diagram showing a configuration of a conventional conversion device.

FIG. 18 is a diagram showing a conversion operation flow of a conventional conversion device.

[Explanation of symbols]

 1 Input Image File 2 Output Image File 3 Converting Means 4 Gradation Determining Means 5 Number of Colors Measuring Means 6 Gradient Determining Means 7 Gradient Increasing Means 8 Control Means 8 ′ Control Means 8 ″ Control Means 9 Storage Means 10 gradation number estimating means 11 input image used color number measuring means 12 used color frequency measuring means 13 replacing means

Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location // H04N 1/60 1/46 H04N 1/40 D 1/46 Z

Claims (4)

[Claims] 1. A conversion device for converting a multi-gradation color original image into an image having the number of colors within the usable number of colors, wherein the number of gradations is determined based on the number of usable colors. Based on the number of gradations notified from the optimum number of gradations determining means, the optimum number of gradations determining means for starting the operation after the number of gradations is determined by the number of gradations determining means,
And an output image generating means for converting the color original image to generate an output image. The optimum gradation number determining means is a color used in the converted image when the color original image is converted based on the current gradation number. Calculate the number, check whether the number of colors used in the converted image exceeds the number of colors that can be used, and if it exceeds, notify the output image generation means of the number of gradations immediately before and start it. A multi-gradation image conversion device configured to store the current number of gradations, increase the number of gradations, and return to the process when the number of gradations is not exceeded. 2. A conversion device for converting a multi-tone color original image into an image having a color number within the usable color number, wherein the number of colors used in the multi-tone color original image is An input image used color number measuring means for measuring, an optimum gradation number determining means for starting operation after the color number is measured by the input image used color number measuring means, and a gradation notified from the optimum gradation number determining means Based on the number
And an output image generation means for converting the color original image to generate an output image, wherein the optimum gradation number determination means is based on the current number of colors, the number of colors usable in the converted image and the current number of gradations. , The new number of gradations is estimated, the original color image is converted based on the estimated number of gradations, the number of colors used in the converted image is calculated, and the number of colors used in the converted image is equal to the number of colors that can be used. If it is equal, the current number of gradations is notified to the output image generation means to start up. If the number of colors used in the converted image is not equal to the number of usable colors, the converted image is displayed. Check to see if the number of colors used in exceeds the number of colors that can be used. If it exceeds, return to the process of. If the number of colors used in the converted image does not exceed the number of colors that can be used, Check whether the number of colors used in the converted image exceeds the number of colors used immediately before, and determine the number of colors used in the converted image directly. If the number of used colors does not exceed the number of gradations used immediately before, the output image generation means is notified, and the number of used colors in the converted image exceeds the number of colors used immediately before. A multi-gradation image conversion device, which is configured to store the number of colors and the number of colors and return to the process. 3. A conversion device for converting a multi-tone color original image into an image having the number of colors within the usable color number, wherein the number of colors used in the multi-tone color original image is The operation is started after the color number and the gradation number for each color component are measured by the input image used color number measuring means for measuring and measuring the gradation number for each color component, and the input image used color number measuring means. An optimum gradation number determining means and an output image generating means for converting an original color image to generate an output image based on a set of gradation numbers for each color component notified from the optimum gradation number determining means. The optimum gradation number determining means is based on the current number of colors, the number of colors usable in the converted image, the current number of gradations for each color component, and the number of gradations for each color component in the color original image. Estimate the set of gradation numbers for each color component, and The original color image is converted based on the above, the number of colors used in the converted image is calculated, and it is checked whether the number of colors used in the converted image is equal to the number of colors that can be used. If the number of colors used in the converted image is not equal to the number of colors that can be used, the output image generating means is activated by notifying the output image generating means of a set of gradation numbers for each Check whether the number exceeds the number of colors that can be used, and if it exceeds, return to the process of. If the number of colors used in the converted image does not exceed the number of colors that can be used, Check whether the number of colors used exceeds the number of colors used immediately before, and if the number of colors used in the converted image does not exceed the number of colors used immediately before, output the set of gradation numbers for each color component immediately before. If the number of colors used in the converted image exceeds the number of colors used immediately before, the current colors are displayed. Stores sets and the number of colors of gradation number per minute, a multi-tone image, characterized in that it is configured to perform processing to return to the processing conversion apparatus. 4. A pixel in a converted image corresponding to a pixel having a frequently used color in a color original image when the number of colors in the output image generated by the output image generating means is less than the number of colors available. 4. The multi-gradation image conversion apparatus according to claim 1, further comprising an output image correction unit that replaces the color of 1. with the color of the pixel in the color original image.