JPH0714212B2 - High efficiency encoder - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-efficiency coding apparatus for image information.

PRIOR ART Predictive coding is often used as a method for highly efficient coding of image information. Predictive coding is the difference between the sample value and the predicted value (prediction error) when the predicted value for the sample value of the pixel is calculated from the pixels adjacent to the pixel when the pixel is coded.
Is to be encoded. In general, in image information, adjacent pixels have approximately the same sample value, and therefore the difference between the predicted value and the sample value is a very small value, and large compression is possible.
Further, by using variable length coding, short code words (small bits) are assigned when the difference between the predicted value and the sample value is small, and long code words (large bits) are assigned when the difference is large. Becomes

FIG. 4 shows an example of variable length coding of an image consisting of 64 pixels in total of 8 pixels in the horizontal direction and 8 pixels in the vertical direction. The numbers in FIG. 4 represent the number of bits when each pixel is variable length coded. Here, one screen has a total of 203 bits. Therefore, if the transmission amount per screen is set to 208 bits, all the images in FIG. 4 can be transmitted.

By the way, in the variable-length coding, the code length is different for each pixel, and therefore, if an error occurs in the transmission path and a codeword having an incorrect code length is reproduced, all the pixels thereafter may be erroneously decoded. Therefore, when the transmission path error cannot be ignored, a method is used in which the screen is divided into small blocks and variable length coding is performed for each block to stop the influence of the transmission path error in block units.

Problems to be Solved by the Invention In FIG. 5a, one screen is divided into eight blocks A to H, and one line is one block. Therefore, when the image of FIG. 4 is subjected to variable length coding by division as shown in FIG. 5a, the number of bits of each block becomes 16 to 43 bits. Here, if the number of bits of each block is limited to 26 bits (26 bits = 208 bits / 8), the D, E, and F blocks lack the number of bits, and part of the codeword cannot be transmitted. As a result, the image quality in the shaded area in FIG. 5b is greatly degraded. In this way, in a general image, the code length greatly changes for each line,
Image quality is degraded. On the contrary, if the transmission amount per block is increased in order to prevent the deterioration of image quality, the compression rate will deteriorate.

Further, in the conventional division as shown in FIG. 5A, when an error in block units occurs due to a transmission path error, there is a possibility that one line is erroneous, resulting in a large visual deterioration in image quality.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a high-efficiency coding apparatus that solves the above problems.

Means for Solving the Problems The high-efficiency encoding device of the present invention obtains the difference between the predicted value obtained from the pixel adjacent to the pixel and the sample value of the pixel for one screen of image information for one screen. Of the quantized value generating means for quantizing by means of the quantized value and the quantized value for one screen obtained by the quantized value generating means, which are distant in the same block and do not exist on the same horizontal and vertical straight lines. It is characterized by comprising block generating means for making a block so that a value is included, and variable length coding means for variable length coding the quantized value in the block obtained by the block generating means.

Effect According to the present invention, even if a part of the screen is extremely changed, the quantized value of that part is distributed to the whole block, so that a large quantized value is concentrated in a specific block. There is nothing to do. As a result, the dispersion of the code length of each block in each block becomes small, and only the image quality of some blocks does not deteriorate. Further, even if an error occurs in the transmission line and becomes an error in block units, the error is dispersed in the screen, and the deterioration of the image quality is reduced.

Embodiment FIG. 1a shows a block diagram of a high-efficiency coding apparatus according to an embodiment of the present invention.

1a, 1 is an input part of the apparatus, 2 is a prediction error generator for generating a prediction error, 3 is a quantizer, 4 is a blocker, 5 is a variable length encoder, and 6 is an output part. Shows.

In the apparatus of FIG. 1a, the sample value of the image is input from the input part 1 to the prediction error generator 2, the prediction error obtained by this is quantized by the quantizer 3, and further divided by the blocker 4 into blocks. To do. The divided quantizers are variable-length coded by the variable-length encoder 5 so that each block has a constant length and output to the output unit 6.

The device of FIG. 1a can be modified as shown in FIG. 1b. In FIG. 1 b, 7 is an input part, 8 is a prediction error generator for generating a prediction error, 9 is a quantizer, 10 is a variable length encoder, 11 is a blocker, 12 is a block length controller, 13
Indicates the output part.

In the apparatus of FIG. 1b, the sample value of the image is input from the input part 7 to the prediction error generator 8, the prediction error obtained by this is quantized by the quantizer 9, and the variable length coder 10 changes the variable length. Encode. Variable length coded codeword is a blocker
It is divided into blocks at 11, and is outputted to the output portion 13 by the block length controller 12 so as to have a constant length in block units.

Now, the prediction error generators 2, 8 and the quantizer shown in FIGS.
3, 9 and variable length encoders 5 and 10 are the same as those used in the conventional variable length predictive encoder, and various methods can be applied. However, in FIG.
Since 11 is after the variable length encoder 10, it is necessary to calculate the number of transmission bits of each block up to that time using the block 12 and feed it back to the variable length encoder 10. Further, the block length controller 12 can be easily configured by a counter or the like.

The blockers 4 and 11 of FIGS. 1a and 1b will now be described. As a simple construction method of the blocker, the quantized value input from the quantizer is first read into the RAM, and the output address is controlled to be distributed to the blocks.

Here, the specific content of blocking will be described. FIG. 2a is a first example of blocking. FIG. 2A shows that one screen is divided into eight blocks A to H, and each block is encoded while cyclically shifting from the top line to the bottom line by 3 pixels for each line. It shall be. When the image shown in FIG. 4 is divided into blocks as shown in FIG. 2a, the number of bits of each block is 23 to 29 bits, which is more dispersed than the conventional example (16 to 43 bits) shown in FIG. 5a. Is getting smaller. This is because the property that large quantized values and small quantized values continuously appear in a specific area of an image disappears because adjacent pixels are dispersed into a large number of blocks by this block formation. is there. Therefore, the portion deteriorated by limiting one block to 26 bits as shown in FIG. 2b is reduced to almost half as compared with the conventional example of FIG. 5b. Further, for the same reason, a large amount of deterioration does not concentrate on a specific block, so that the deteriorated portion concentrates on the lower end of the screen as shown in FIG. 2b. Since human vision is insensitive to deterioration at the edges of the screen, deterioration of image quality can be visually prevented. Furthermore, even if block-based errors occur due to transmission line errors, the errors are dispersed on the screen, so the deterioration of image quality is less noticeable.

The second example of blocking is a modification of the variable length coding order for each block in the first example of blocking. FIG. 3A is an explanatory diagram of the variable length coding of this block formation. Here, variable length coding is performed so that the quantized value for the pixel in the shaded portion of FIG. 3A is coded last. Therefore, as can be seen from FIG. 2a, the two codewords encoded at the end of each block except the C block are the third codeword.
Collect in the shaded area in Figure a. Therefore, the number of bits in one block
The part that deteriorates when limited to 26 bits is also concentrated on the right and bottom edges of the screen as shown in FIG. 3b. As described above, in the second example, the deteriorated portion is further concentrated toward the edge of the screen as compared with the first example, so that the deterioration of the image quality is less noticeable visually. Further, in the variable length coding, the influence of the transmission path error concentrates on the latter half of the block due to the loss of word synchronization, but in the present embodiment, the latter half of the block comes toward the edge of the screen, so that the image quality deterioration is less noticeable.

Although the two blocking examples have been described above, a number of other methods can be considered for the blocking and coding order of the present invention. Further, although the present invention has been described by using predictive coding, it can be applied to other high efficiency coding methods. Furthermore, the present invention can be used for screens having any number of pixels other than the embodiment.

EFFECTS OF THE INVENTION As described above, according to the present invention, the property that large codewords concentrate in some blocks when an image is variable-length coded is improved, so that the area where the image quality deteriorates as a whole. Becomes smaller. At the same time, the influence of the transmission path error is dispersed in the screen to make it inconspicuous, and the deterioration of the image quality is concentrated near the edge of the screen, so that the deterioration of the image quality can be visually prevented. As described above, by using the present invention, it is possible to significantly reduce the drawbacks of variable-length coding, and its practical effect is great.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention, FIG. 2 is an explanatory diagram of a first blocking example of the present invention, and FIG. 3 is an explanatory diagram of a second blocking example of the present invention. FIG. 4 is an explanatory diagram of variable length coding, and FIG. 5 is an explanatory diagram of a conventional example. 2 ... Prediction error generator, 3 ... Quantizer, 4 ... Blocking device, 5 ... Variable length encoder.

Claims (3)

[Claims] 1. Quantized value generation means for quantizing image information for one screen for each pixel by obtaining a difference between a predicted value obtained from a pixel adjacent to the pixel and a sample value of the pixel; Block generation means for dividing the quantized values for one screen obtained by the quantized value generating means so that the quantized values that are distant and do not exist on the same horizontal and vertical straight lines are included in the same block; And a variable length coding means for variable length coding the quantized value in the block obtained by the block generating means, the high efficiency coding device. 2. The high efficiency code according to claim 1, wherein the variable length coding means performs variable length coding on the quantized values in the block according to the order in which the quantized values are generated. Device. 3. The variable-length coding means performs variable-length coding such that the quantized values for pixels near two sides sandwiching the corner where the pixel to be quantized last on the screen is present are finally coded. The high-efficiency coding device according to claim 1.