JPH02291775A - Image block encoding system - Google Patents

Abstract

PURPOSE:To prevent meshed block borders which cross each other at right angles from appearing in a decoded image by making one of lateral and longitudinal block border into a constant-length straight line and the other block border into a stepwise straight line which is shifted longitudinally and laterally or slanting curve. CONSTITUTION:Picture elements pij (i=1-4, j=1-4) constitute one block B. Namely, each part encircled with a thin solid line shows one block and respective blocks each consists of four picture elements longitudinally and four picture elements laterally, i.e., what is called 4X4 picture-element constitution. Here, the lateral block border is made into the constant-length straight line, the longitudinal block border is shifted right by one picture element, and all blocks are shifted in the same direction. Consequently, the number of picture elements in each block is equal to the number of picture elements in a conventional rectangular block, so processing in a block after division is performed similarly to conventional processing. Further, the block borders are never in an orthogonal meshed shape.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an image block encoding method, and in particular, it divides an image into a plurality of blocks and encodes each block. An image block encoding method is known as one of the image encoding methods.

This image block encoding method generally divides an image into multiple rectangular blocks of the same size, arranges each divided block regularly in a grid pattern, and performs encoding for each block. .

In addition to the above, the basic idea is to divide a given image into a plurality of rectangular blocks of the same size, and randomly move the distribution of blocks in the horizontal direction for each vertical block row. A floating block encoding method that encodes blocks configured in this way has been proposed [Nakajima et al. Zheng. Angoin: “Image quality Q-improvement method in block coding method”, Institute of Electronics, Information and Communication Engineers technical research report IE87-76>.

Furthermore, what about the given image? ! An octagonal block encoding method has also been proposed in which the blocks are made into octagons rather than rectangular blocks of the same size, and each divided octagonal block is encoded (Nakajima, Chung, Angoin: ""Otagonal Block Coding Method", 1986 Institute of Electronics, Information and Communication Engineers Spring National Conference D-82).

[Problem to be solved by the invention]

However, in the general block encoding method in which the rectangular blocks are regularly arranged in a case f shape, the decoded image has orthogonal mesh-like block boundaries that do not exist in the original image. Because the encoding and decoding processes are performed independently for each block, changes in brightness or color that do not exist in the original image appear linearly along the boundaries between these adjacent blocks, which is difficult to see in the human visual sense of the contours of figures. The image quality of the decoded image is significantly degraded due to the enhancement effect (Mach effect).

In addition, in the floating block encoding method described above,
Of the orthogonal mesh-like block boundaries that do not exist in the original image, the zigzag-shaped ones do not appear, but the T-shaped ones do, so the effect of improving image quality is low. It was necessary to provide the horizontal movement distance.

Furthermore, in the octagonal block encoding method described above,
Since orthogonal mesh-like block boundaries that do not exist in the original image do not appear, image quality deterioration due to the sharpening effect is reduced, but there are always blocks with different shapes among the blocks that include the edges of the image. Therefore, encoding and
In the decoding process, a plurality of processing procedures are necessarily performed for each block shape.

The present invention has been made in view of the above points, and uses a conventional method for encoding/decoding processing, and solves the problem that orthogonal mesh-like block boundaries that do not exist in the original image appear in the decoded image. The purpose is to provide a solved image block coding method.

[Means to solve the problem]

In order to achieve the above object, the present invention has a flow chart configuration as shown in FIG. That is, when an image is input (step 11), the number of pixels constituting a block is determined (step 12), the image is divided into a plurality of blocks (step 14), and each block is encoded (step 14). Steps 15 and 16) In the image block encoding method, the present invention divides the image into blocks after determining the shape of the blocks as shown in Step 13.

Here, the shape of the block in step 13 is such that one of the block boundaries in the horizontal and vertical directions is a straight line of a constant length, and the other block boundary is divided by the number of pixels in the vertical direction according to a predetermined rule. It is distinctive in that it has a step-like straight line or oblique curved shape that is shifted in the horizontal and vertical directions.

[Effect]

In the present invention, the shape of the block is such that one of the block boundaries in the horizontal and vertical directions is a straight line with a constant shape, and the other block boundary is divided by the number of pixels f in the vertical and horizontal directions according to a predetermined rule. Since the block is a step-like straight line or diagonal curve that is shifted by the block, the number of pixels within the block is the same as when the block is rectangular.

Furthermore, the spatial frequency can be increased because the block boundaries do not become perpendicular to each other and the number of pixels forming the block boundary length is smaller than the number of pixels forming the sides of the block.

(Example) Fig. 2 shows an explanatory diagram of the block shape of the first example of the present invention.
4) are pixels and constitute one block B. That is, in the figure, each part surrounded by a thick solid line indicates each block, and each block has a so-called 4x4 pixel configuration, with 4 pixels in the vertical direction and 4 pixels in the horizontal direction.

In this embodiment, the horizontal block boundary is a straight line of a constant length, the vertical block boundary is shifted one pixel at a time in the right h direction,
In addition, the block shape is such that all blocks are shifted in the same direction.

Note that the actual image exists within the rectangular area surrounded by the solid line and does not exist in the dashed line at the right end, but for processing purposes, the image in the asterisk area at the left end is assumed to exist in the dashed line. (The same applies to the cases of FIGS. 3 to 5, which will be described later).

FIG. 3 shows a block shape explanatory diagram of a second embodiment of the present invention. In the figure, each part surrounded by a thick solid line indicates each block, and each block has a configuration of 4×4 pixels.

In this example, the horizontal block boundary is a straight line of a constant length,
It shifts the block boundaries in the vertical direction one pixel at a time.
The direction of shifting is alternated for each block in the direction.
, FIG. 4 shows a block shape explanatory diagram of a third embodiment of the present invention. In the figure, each part surrounded by a thick solid line extends to each block, and each block has a configuration of 4x4 pixels.

In this example, the horizontal block boundary is a straight line of a constant length,
The vertical block boundary is curved 2 pixels → 1 pixel → 0
This shows an example of a block shape in which the position of each block is the same, and the size is the same as that of a pixel.

Furthermore, the block shape of the fourth embodiment of the present invention is shown in FIG. In this embodiment, each block size is 4×4 pixels, as in the first to third embodiments described above.

Furthermore, each block has the shape shown surrounded by a thick solid line in Fig. 5, and the horizontal block boundary is a straight line of a constant length.
Also, the vertical block boundaries are curved for 2 pixels, 1 pixel,
O pixels and f are shifted, and the order of shifts for each block in the vertical direction is crossed n [divided into 1 block shape, . In this way, in the first to fourth embodiments described above, each block is 4 x 4 pixels, and the block size is the same as that of the conventional block encoding method when divided into 4 x 4 pixel rectangular blocks. Therefore, in each embodiment, the processing within the block after division may be the same as the conventional method for rectangular blocks.

Also, the number of pixels (second
In the case of the figure, "1") is smaller than the number of pixels composing the vertical side of the block "4" and has a higher spatial frequency, so in conventional decoded images, changes in brightness or color that do not exist in the original image occur. Deterioration in image quality due to the Mach effect, which occurs due to linear appearance along orthogonal mesh block boundaries, is reduced.

It should be noted that the present invention is not limited to the above-described embodiment, and the same effect can be obtained even if the horizontal direction and vertical direction in FIGS. 2 to 4 are reversed. Furthermore, when the block size is large, various modifications such as shifting each block in a quadratic curve are possible.

〔Effect of the invention〕

As described above, according to the present invention, since the number of pixels in each block is the same as the number of pixels in a conventional rectangular block, the processing in the divided block can be performed in the same way as in the case where the block is rectangular. (In other words, the conventional rectangular block encoding method can be used for the encoding/decoding process), and the block boundaries do not form an orthogonal mesh shape, making it possible to increase the spatial frequency. Therefore, it is possible to reduce image quality deterioration due to the Mach effect, which occurs when changes in brightness or color that do not exist in the original image appear linearly along orthogonal mesh block boundaries in conventional decoded images. It has certain characteristics.

[Brief explanation of drawings]

FIG. 1 is a diagram for explaining the principle of the present invention, and FIGS. 2 to 5 are diagrams for explaining the block shape of each embodiment of the present invention. 11-16...Step, B...Block.

Claims (1)

[Claims] In an image block encoding method in which an image is divided into a plurality of blocks each consisting of a fixed number of pixels and each block is encoded, one of the block boundaries in the horizontal and vertical directions is Divide into blocks with a straight line of a certain length and a stepped straight line or diagonal curve with the other block boundary shifted vertically and horizontally by the number of pixels according to a predetermined rule, and perform encoding. An image block encoding method characterized by: