JP3740376B2 - Computer screen image encoding method, execution program thereof, and recording medium recording the execution program - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention transmits screen information displayed in real time between a plurality of computers connected to a network, for example, in a system that performs cooperative work while sharing materials displayed on the computer screen. The present invention relates to an efficient computer screen image encoding method used in the present invention.
[0002]
[Prior art]
In the conventional image encoding method, it is encoded with a relatively small number of colors, which can be said to be a feature of a graphical user interface (GUI) displayed on a computer screen. A typical image coding method has not been considered.
[0003]
[Problems to be solved by the invention]
For this reason, the conventional image coding method described above is used for a system that performs collaborative work among a plurality of computers connected to a network, for example, by sharing images displayed on a computer screen or images such as a GUI. In this case, these images are encoded with a relatively small number of colors, and even though there are many uniform color areas, it takes time to encode and decode, and the displayed screen information is transmitted in real time. It was difficult to do.
[0004]
Accordingly, an object of the present invention is to provide a technique for efficiently encoding screen information in order to transmit screen information displayed on a computer in real time.
[0005]
[Means for Solving the Problems]
In order to solve the above problems, the present invention obtains a histogram by quantizing the pixel values of an image constituting a computer screen into a plurality of gradations, and each of the resulting gradations is included in that gradation. Calculate the average of the pixel values for the pixels, and use this average value as the color table value for that gradation. After calculating the color table values for all the gradations, create a color table by expressing it with an index based on the histogram. After generating the color table and dividing the entire image into several blocks, the pixel value is expressed for each block by an index that refers to the color table value, and a histogram is created. to allocate the procedure to sort the order of appearance frequency of the pixel, a short code in descending order of the frequency of occurrence of pixels that are changed column header And having a procedure for variable length coding the pixels expressed in the index for each of the blocks.
[0007]
Alternatively, in the computer screen image encoding method described above, in the procedure of variable-length encoding the pixel represented by the index for each block, the index for each divided block is assigned to each pixel value of the color table. It is characterized by reallocation corresponding to the index.
[0008]
Alternatively, in the computer screen image encoding method described above, in the procedure of variable-length encoding the pixel expressed by the index for each block, each pixel having the index for each block is run-length encoded. Features.
[0009]
Alternatively, in the computer screen image encoding method described above , in the procedure of performing the run length encoding on each pixel having the index, the allocated encoded code is added to the encoded data encoded by the run length. Therefore, the variable length coding is performed.
[0010]
Or it has the procedure in said computer screen image coding method, It was set as the program for making a computer perform the said procedure, It is characterized by the above-mentioned.
[0011]
Alternatively, a program for causing a computer to execute the procedure in the above computer screen image encoding method is recorded on a computer-readable recording medium.
[0012]
In the present invention, in consideration of the fact that there are many areas where the data, GUI, etc. displayed on the computer screen are expressed with a small number of colors and that there are many areas expressed with uniform colors. Thus, an efficient encoding method is provided by performing variable length encoding or combining variable length encoding and run length encoding.
[0013]
That is, in the present invention, by dividing the image of the computer screen into blocks and rearranging the indexes corresponding to the pixel values in the order of appearance frequency for each block, and then performing variable length coding, the pixel values that appear in the entire image are obtained. Even if the number of allocated indexes increases, the number of allocated indexes is decreased locally to increase the encoding efficiency. This is because it is considered that many pixels having the same index are gathered locally.
[0014]
Also, the index value itself does not become a large value by allocating or reallocating the index for each block. For example, in an image having a size of 800 × 600, when all pixels have different index values, 480000 index values appear, but if this is divided into blocks of size 40 × 40, 1600 Only the second index value appears. As a result, the code amount can be suppressed as the size of the target image increases.
[0015]
Furthermore, when quantization is performed to reduce the code amount, the value of the color table that is actually defined is set to the average value of the pixel values assigned to the histogram, so that the image can be compared with simple quantization. So that the reproducibility of the is high.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings. In the present invention, intra-frame coding is performed on a screen (frame) basis.
[0017]
FIG. 1 is a configuration diagram of encoded data of screen information generated in the embodiment of the present invention. As shown in FIG. 1A, the overall encoded data configuration includes a header portion 11, a color table 12, and block information 13. The header portion 11 includes information such as the size of the original image and the data length of the encoded data. The color table 12 includes color information used in this image. This color information includes an index number and three color values of RGB. As shown in FIG. 1B, the block information 13 includes a block header section 14, a color table reference index table 15, and an index value 16 of each pixel. The block header portion 14 includes information such as the size of the block image and the data length of the block information.
[0018]
FIG. 2 is a flowchart illustrating an example embodiment of a method for creating the color table 12. First, the input image is quantized according to the number of color gradations of the input image and the data length expected for the encoded data to be transmitted. In this embodiment, description will be made assuming that an input image is quantized into a 24-bit image and is quantized into a 12-bit image.
[0019]
For all pixels in one screen, the pixel value represented by 24 bits (8 bits for each color of R, G, B) is linearly quantized to 12 bits (4 bits for each color of R, G, B). A histogram is obtained, and for each of the 4096 (2 to the 12th power) gradations obtained as a result, an average of pixel values is calculated for pixels included in the gradation, and this average value is used as a color table value for the gradation. . Thereby, the reproducibility of an image becomes high compared with simple quantization. After calculating the color table values for all the gradations, an index number is assigned based on the histogram, and a color table indicating the correspondence between the index number and RGB values is created. Thereby, since the index number is not assigned to the gradation that does not include any pixel, the code amount can be reduced.
[0020]
FIG. 3 is a flowchart showing an image encoding method when pixels are encoded for each block after the entire image is divided into several blocks.
[0021]
First, the pixel values of all the pixels in the block are replaced with index numbers indicating the color table values (hereinafter referred to as color index numbers), and a histogram is created. This histogram is rearranged in the order of pixel appearance frequency, and an intra-block index number is assigned. A table indicating the allocation, that is, a table indicating the correspondence between the index number in the block and the color index number is the color table reference index table 15. Then, variable length coding is performed by assigning short coding codes in descending order of appearance frequency to the intra-block index numbers.
[0022]
Next, run-length encoding is performed on each pixel value represented by the intra-block index number. Here, in the run-length encoding, when pixels having the same intra-block index number are consecutive, the consecutive number is called a run, and the same continuous intra-block index number is represented by the run and the intra-block index number. That means.
[0023]
Next, variable length encoding is performed on the run-length encoded data in accordance with the encoding code assigned to the intra-block index number, that is, in the order of appearance frequency. The above encoding process in the block is applied to all blocks in the screen.
[0024]
In the encoding method according to the above-described embodiment, for each block, the intra-block index number is first subjected to variable length encoding (1), and then the pixels having the intra-block index number are run-length encoded (2). Then, an example in which the maximum efficiency is obtained by performing variable-length coding (3) after that is shown. However, in the present invention, only (1) is executed in each coding process, or (1) It is also possible to increase the encoding efficiency by executing only and (2) in combination.
[0026]
Furthermore, it is needless to say that the processing procedure described with reference to FIGS. 2 and 3 can be configured by a computer program and the program can be executed by the computer. Record it on a computer-readable storage medium, for example, FD (floppy disk (registered trademark)), MO, ROM, memory card, CD, DVD, removable disk, etc., save it, provide it, or distribute it. It is also possible to provide or distribute the program through a network such as the Internet.
[0027]
【The invention's effect】
According to the present invention, in addition to the effect of improving the reproducibility of the image as compared with simple quantization and the effect of reducing the amount of codes , the screen information of computers such as data and GUI can be efficiently encoded. As a result, the screen information to be transmitted is reduced, the computer screen information can be transmitted in real time, and the update frequency of the screen information displayed on the receiving computer can be increased. Thereby, for example, the quality of collaborative work performed by sharing screen information such as materials and GUIs can be improved.
[Brief description of the drawings]
FIGS. 1A and 1B are configuration diagrams of encoded data of screen information in an exemplary embodiment of the present invention. FIG. 2 is a flowchart of a color table creation process in the exemplary embodiment of the present invention. FIG. 3 is a flowchart of a block image encoding process in the embodiment of the present invention.
DESCRIPTION OF SYMBOLS 11 ... Header part 12 of the encoded data of the whole image information ... Color table 13 associating an index value allocated to each pixel with RGB color ... Block information 14 showing image information for each block ... Block header part 15 ... Color table index Color table reference index table 16 for associating a value with an intra-block index value assigned to each pixel in the block.

Claims (5)

Quantize the pixel values of the image that composes the computer screen into a plurality of pixels to obtain a histogram, and calculate the average of the pixel values for the pixels included in the gradation for each of the resulting multiple gradations. A procedure for generating a color table for creating a color table by expressing an index based on the histogram after calculating a color table value for all the gradations with the value as a color table value for the gradation,
After dividing the entire image into several blocks, a pixel value for each block is expressed by an index referring to the color table value, a histogram is created, and the histogram is rearranged in order of appearance frequency of pixels;
A computer screen image encoding method comprising: a step of variable-length encoding the pixels represented by the index by assigning short codes in descending order of the appearance frequency of the rearranged pixels. In the procedure of variable-length encoding the pixel represented by the index for each block,
The computer screen image encoding method according to claim 1, wherein the index for each of the divided blocks is reassigned in association with an index assigned to each pixel value of the color table. In the procedure of variable-length encoding the pixel represented by the index for each block,
The computer screen image encoding method according to claim 1, wherein each pixel having the index for each block is run-length encoded. It has the procedure in the computer screen image coding method of any one of Claim 1- Claim 3 ,
An execution program for a computer screen image encoding method, characterized in that the program is a program for causing a computer to execute the procedure. A program for causing a computer to execute a procedure in the computer screen image encoding method according to any one of claims 1 to 3 ,
A recording medium recording a computer screen image encoding method execution program recorded on the computer-readable recording medium.

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