JPS6318787A - Encoder for orthogonal transformation - Google Patents

Abstract

PURPOSE:To lower a transmission speed without deteriorating the transmission quality of a moving picture by accumulating absolute values of the difference between the frames of the orthogonal transformation signal of a picture signal for every area obtained by dividing a block into the plural areas and encoding only the orthogonal transformation signal or the difference between the frames in the area having a larger accumulated value. CONSTITUTION:A decision circuit 12 compares the accumulated value for every area of the absolute value of the difference between the frames from an accumulation circuit 11 with a prescribed threshold and controls a switch circuit 5 so as to be closed only during a period when the accumulated value of the absolute value of the inputted difference between the frames exceeds the threshold. Therefore, from the switch circuit 5, only a signal in the area in which the accumulated value of the absolute value of the difference between the frames to the orthogonal transformation of a preceding frame outputted from a frame memory 8 on the orthogonal transformation signals of the respective blocks from an orthogonal transformation circuit 4 exceeds the threshold value is outputted. Thus, the orthogonal transformation signal selected in the switch circuit 5 is transmitted to a transmission path 7 through a buffer memory 6 in a constant bit rate, inputted to the frame memory 8 and the contents of the frame memory 8 are rewritten.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to an orthogonal transform encoding device that orthogonally transforms and encodes an image signal.

(Prior Art) Orthogonal transform encoding techniques such as Hadamard transform and cosine transform are known as one of high-efficiency encoding techniques for image signals. Image signals have statistically strong spatial correlation, so when orthogonal transformation is applied, energy is concentrated in low-order components. Conventional orthogonal transform encoding takes advantage of these properties of image signals to allocate a larger number of bits to the lower-order components (corresponding to low-frequency components on the frequency axis) of the orthogonal transform signal, and The next component is encoded by allocating a smaller number of bits to reduce the average number of pits.

However, in the conventional orthogonal transform encoding method, when attempting to transmit a moving image signal at a lower bit rate, it is necessary to reduce the number of bits per block, resulting in a significant deterioration of image quality.

Furthermore, the fact that image signals have a large spatial correlation is only statistically true, and in reality, there are image signals that have a small correlation. In the conventional orthogonal transform encoding method, the image quality deteriorates significantly for such image signals with low correlation.

Furthermore, in the conventional orthogonal transform encoding method, the high-order components (corresponding to high frequency components) of the orthogonal transform signal are encoded with a small number of bits, so the blurring of the image is noticeable, especially in the case of a still image.

(Problems to be Solved by the Invention) As described above, in the conventional orthogonal transform coding method, it is difficult to reduce the transmission speed without deteriorating the transmission quality of moving images, and There is a problem in that the image quality tends to deteriorate in the case of still images.

The present invention provides an orthogonal transform code that can effectively reduce the transmission speed without deteriorating the transmission quality of moving images, and that can also provide good image quality for images with low spatial correlation and image signals of still images. The purpose is to provide a device for converting

[Structure of the Invention] (Means for Solving the Problems) The present invention calculates the difference between frames for orthogonally transformed signals obtained by orthogonally transforming an image signal block by block, and calculates the absolute value of the difference between frames. The block is divided into multiple regions and accumulated for each region.

Then, only the orthogonal transformed signals or interframe differences in regions where the cumulative value of the absolute values of interframe differences for each region is larger are encoded.

(Function) If only the region in which the cumulative value of the absolute value of the inter-frame difference for each region of the orthogonal transform signal is larger is encoded, the main information of the video will be lost when transmitting the image signal of the video. Therefore, the amount of data per block decreases. Furthermore, even in images with low spatial correlation, information on images in regions with large inter-frame differences is transmitted at a predetermined bit rate, so deterioration in image quality can be suppressed.

Furthermore, for still images, for example, if a method is adopted in which only the orthogonal transform signal of the area where the cumulative value of the absolute value of the inter-frame difference is the largest is encoded, the area from the area with the larger cumulative value of the absolute value of the inter-frame difference to the region with the lowest cumulative value The information is transmitted sequentially, and finally the image signals of all areas and all blocks are sent at the same bit rate.

(Embodiment) FIG. 1 is a block diagram showing the configuration of an orthogonal transform encoding device according to an embodiment of the present invention.

In FIG. 1, the image signal input to input terminal 1 is A
After being converted into a digital signal of an appropriate number of bits, for example 8 bits, by the /D converter 2, the signal is input to the block dividing circuit 3. The block dividing circuit 3 has a built-in frame memory, and divides the digital image signal inputted from the A/D converter 2 into blocks each consisting of, for example, 8×8 64 pixels.

The orthogonal transform circuit 4 orthogonally transforms the image signal inputted from the block dividing circuit 3 for each block. As the method of this orthogonal transformation, Hadamard transform, cosine transform, and other known methods can be arbitrarily selected.

The orthogonal transform signal output from the orthogonal transform circuit 4 is input to the buffer 6 through the switch circuit 5, and after being converted into an encoded image signal of a constant bit rate by the buffer memory 6, it is sent to the transmission line 7.

The switch circuit 5 is controlled by the output of a determination circuit 12, which will be described later, and selects a region in which the cumulative value of the absolute value of the inter-frame difference is larger for each region among the orthogonal transform signals inputted from the orthogonal transform circuit 4 for each block, e.g. It is for selecting only the signals in the area where the cumulative value exceeds a predetermined threshold value, and together with the buffer 6 constitutes a selective encoding means.

That is, the orthogonal transformed signal of the area selected by the switch circuit 5 is input to the subtracter 9 via the frame memory 8,
Here, the difference from the orthogonal transform signal output from the orthogonal transform circuit 4 is obtained. This uses the orthogonal transform signal output from the orthogonal transform circuit 4 as the signal of the current frame, and the frame memory 8
This corresponds to determining the difference between the two frames by using the orthogonal transformed signal output from the previous frame as the signal of the previous frame.

The information on the inter-frame difference of the orthogonal transformed signal thus obtained by the subtracter 9 is input to the area dividing circuit 10, and the block dividing circuit 3 divides the block into areas which are units obtained by further dividing the block into a plurality of parts. The inter-frame differences of the orthogonal transformed signal divided into a plurality of regions by the region dividing circuit 10 are input to the accumulation circuit 11, and the absolute values are accumulated for each region.

That is, the sum of the absolute values of the inter-frame differences for each region is determined.

The cumulative value of the absolute value of the inter-frame difference outputted from the accumulating circuit 11 for each region is inputted to the determining circuit 12 .

The determination circuit 12 is, for example, a comparison circuit, and compares the cumulative value of the absolute value of the inter-frame difference for each region from the accumulating circuit 11 with a predetermined threshold value, and determines whether the cumulative value of the absolute end of the inputted inter-frame difference exceeds the threshold value. The switch circuit 5 is controlled to close only for the period exceeding the period. As a result, from the switch circuit 5, among the orthogonal transform signals of each block from the orthogonal transform circuit 4, the cumulative value of the absolute value of the inter-frame difference from the orthogonal transform of the previous frame output from the frame memory 8 exceeds the threshold value. Only the signals in the selected area are output. The orthogonal transformed signal thus selected by the switch circuit 5 is sent to the transmission line 7 at a constant bit rate via the back 7 memory 6, and is also input to the frame memory 8, and the contents of the frame memory 8 are rewritten. .

FIG. 2 is a diagram showing an example of region division by the region division circuit 10, in which (x, y) is output from the orthogonal transformation circuit 4.
A 1nxn-order orthogonal transformed signal of -(1,1) to (m,n) is divided into six regions indicated by A-F.

For example, if a cosine transformation is used as the orthogonal transformation, it is desirable that the area A-F be divided by a line extending from the upper left to the lower right on the (x, y) plane as shown in the figure. At this time, the upper left area A is the lowest order, B, C
,...F, the order becomes higher as it moves to the lower right.

In the above-described orthogonal transform encoding device based on the present invention, only the region where the cumulative value of the absolute value of the inter-frame difference for each region of the orthogonal transform signal is larger, for example, the region where the cumulative value is present (FA (exceeding i & Therefore, compared to the conventional orthogonal transform coding method in which the orthogonal transform signal of the entire block is always encoded and transmitted, the amount of data per block is reduced and transmission can be performed at a lower bit rate. In this case, when transmitting the image signal of a moving image, information in areas with low spatial correlation will be lost, but key information for the moving image, that is, information in areas with large interframe differences, will be lost. Since the data is transmitted with a sufficient number of bits without any additional processing, deterioration in image quality can be minimized.

Further, even if the overall spatial correlation is low in an image, the information of the image in the area where the inter-frame difference is large is transmitted at a predetermined bit rate, so deterioration in image quality can be suppressed to a small level.

Note that the present invention is not limited to the above-mentioned embodiments; for example, in the embodiment, only orthogonal transformed signals in regions where the cumulative value of the absolute value of inter-frame differences exceeds a predetermined threshold are encoded; Only the orthogonal transform signal in the region where the cumulative value of the absolute value of is the maximum may be encoded. In that case, in addition to the orthogonal transform signal of the region where the cumulative value of the absolute value of the inter-frame difference is the largest, the orthogonal transform signal of the lowest-order region (region A in Figure 2), which is important as an image signal, is also encoded. It is also effective to do so.

be.

In this way, if the method is used to encode the orthogonal transform signal of the region where the cumulative value of the absolute value of the inter-frame difference is the largest, information will be transmitted sequentially from the region where the cumulative value of the inter-frame difference is the largest for the still image, In the end, the image signals of all regions and all blocks are sent at the same bit rate, so much higher image quality can be obtained compared to the orthogonal transform encoding method of Jumei.

Further, in the above embodiment, the orthogonal transformed signal is encoded and transmitted, but the inter-frame difference of the orthogonal transformed signal may be encoded and transmitted.

Furthermore, the method of dividing blocks into regions can be modified in various ways other than the example shown in FIG.

In addition, the present inventors have proposed a method in which orthogonal transform signals are compared block by block between frames, and only the orthogonal transform signal (or inter-frame difference) of a block with a larger inter-frame difference is encoded. Although proposed as No. 72973, the present invention can also be implemented in combination with the system of this earlier application.

[Effects of the Invention] According to the present invention, orthogonal transform coding can reduce the transmission speed without deteriorating the transmission quality of moving images, and can improve the image quality of images with low correlation and still images. equipment can be provided.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of an orthogonal transform encoding device according to an embodiment of the present invention, and FIG. 2 is a diagram showing an example of region division of an orthogonal transform signal in the same embodiment. 1... Image signal input terminal, 2... A/D converter, 3
...Area dividing circuit, 4...Orthogonal transformation circuit, 5...
Switch circuit, 6... Buffer, 7... Transmission line, 8
...Frame memory, 9...Subtractor, 10...@
Area division circuit, 11...accumulation circuit, 12...judgment circuit.

Claims (4)

[Claims] (1) means for orthogonally transforming an image signal block by block; means for determining inter-frame differences of the orthogonally transformed signals obtained by this means; means for accumulating for each region divided into regions, and selectively only orthogonal transformed signals or interframe differences of regions where the cumulative value of the absolute value of interframe differences for each region obtained by this means is larger. An orthogonal transform encoding device comprising: selective encoding means for encoding. (2) A patent characterized in that the selective encoding means encodes only the orthogonal transformed signal or the interframe difference in a region where the cumulative value of the absolute value of the interframe difference exceeds a predetermined threshold. An orthogonal transform encoding device according to claim 1. (3) The selective encoding means encodes only the orthogonal transformed signal or the interframe difference in a region where the cumulative value of the absolute value of the interframe difference is the largest. The orthogonal transform encoding device according to item 1. (4) The selective encoding means encodes only the orthogonal transform signal or the interframe difference in the region where the cumulative value of the absolute value of the interframe difference is the largest and the lowest order region. An orthogonal transform encoding device according to claim 1.