JPH02185187A - Encoding method for video signal - Google Patents

Abstract

PURPOSE:To easily attain the special reproduction in both transmission and recording systems by selecting periodically one frame from plural frames, encoding a signal by the in-frame encoding system and encoding a difference signal between a frame and one preceding frame. CONSTITUTION:A switch 7 is changed over to encode a difference between a video signal of a picture element to be encoded and a prediction signal obtained from one picture element memory 4 storing information of one just preceding picture element. Moreover, a difference between a refreshed signal and a signal of preceding frame is encoded. Thus, a signal encoded/decoded by the one picture element memory 4 at the refresh is switched an input video signal by a switch 12 and a difference with the preceding frame signal in the frame memory 3 is calculated by a subtractor 5. The encoded result is arranged in a buffer memory 11 in matching with the read sequence at the decoding together with the code word by the in-frame encoding and outputted.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to interframe coding of video signals and interframe coding.
The present invention relates to a video signal encoding method that facilitates special playback in intra-frame adaptive encoding.

BACKGROUND OF THE INVENTION In a video signal such as a conventional television signal, the time difference between two consecutive frames is small, so it is thought that there is little change in the image between these frames.

Interframe coding aims to improve efficiency by utilizing the correlation between frames. Usually, the difference signal between two consecutive frames is quantized, encoded, and transmitted, and the receiving side converts the frame into It reproduces television signals by accumulating the difference values between them.

In addition to this method, motion compensation, inter-frame/intra-frame adaptive coding, etc. have been devised to prevent a sudden increase in the difference value due to motion.

Problems to be Solved by the Invention However, in conventional interframe coding, or interframe or intraframe adaptive coding, differences in the time axis direction are taken, so it is generally difficult to easily perform special playback. Ta.

For example, to display a still image at an arbitrary time,
It is necessary to go back and decode the original signal portion from which interframe differences are taken. Here, the original signal part is PC
Refers to the part that is refreshed using intra-frame coding, such as m-coding, which is relatively less affected by deterioration and error propagation. In many cases, it is rare that only the original signal is encoded for one frame, so each part in one frame is traced back to the original signal part, and the decoded signal for one frame is decoded based on that part. need to be collected.

At this time, if the time gap between each original signal part is large, the discontinuity between the decoded signals of each part will also be large, which may cause deterioration in image quality.

Further, even if decoding is possible, it is impossible to search and trace back to the original signal part without any information in advance, in terms of the scale of the computing device and the memory capacity.

In addition to still images, high-speed playback, slow playback, reverse playback, etc. are possible. In the case of slow playback, there are almost the same problems as in the case of still images, and image quality is at stake. The method for realizing reverse playback is itself difficult. In other words, to go back from a certain point in time, basically all you have to do is subtract the difference signal from the previous frame (the next frame in the reverse playback direction), but you can also read it in the reverse order of transmission. Therefore, it is necessary to store previous codewords, which poses problems in terms of equipment scale. This problem can be easily solved by recording systems, especially those that allow backward searches and those that allow random access.

In addition to the above problems, in the conventional method, there is no part in the reverse direction that corresponds to the original signal portion from which the difference is taken, making reverse reproduction impossible.

In view of this, an object of the present invention is to provide a video signal encoding method that can easily perform special playback in both transmission and recording systems.

Means for Solving the Problems The invention as claimed in claim 1 is a method of periodically selecting one frame out of a plurality of frames in interframe coding and interframe and intraframe adaptive coding using the correlation between frames of a video signal. , the frame is encoded using an intra-frame encoding method that has less influence of propagation of image quality deterioration due to at least code errors than inter-frame encoding, and
The invention according to claim 2 is characterized in that a difference signal between the frame and one frame before the frame is encoded. When converting one frame of screen into m lines*
Divide into a plurality of blocks of n lines, select one or more blocks per frame periodically so as to go around once every several frames, and measure the influence of propagation of image quality deterioration due to at least code errors on the blocks. The present invention is characterized in that encoding is performed using an intra-frame encoding method in which the number of blocks is smaller than that of inter-frame encoding, and that a difference signal between the block and a block at the same position one frame before the block is encoded.

Effect: By the above means, the present invention periodically obtains a decoded signal containing no inter-frame differences for one frame every several frames, thereby making it easy to perform special playback such as still playback, slow-speed playback, etc. . Furthermore, by separately preparing the difference between the decoded signal that does not include the interframe difference and the signal one frame before that, it becomes possible to go back in time from that point, making it easy to perform reverse playback. can.

Embodiment A first embodiment of the present invention will be described with reference to FIGS. 1 and 2. FIG. 1 is a diagram for explaining the encoding method in this embodiment. In the figure, 1 is an A/D converter, 2 is a clock generation circuit, 3 is a frame memory (interframe predictor), 4 is a 1-pixel memory (intraframe predictor), 5 is a subtracter, 6 is an adder, 7.12 is a switch, 8 is an encoder, 9 is an encoding control circuit, 10 is a decoder, and 11 is a buffer memory.

The difference between the input video signal converted into a digital signal by the A/D converter 1 and the predicted signal obtained from the frame memory 3 storing the video signal of the previous frame is calculated by the subtracter 5, and the difference is calculated by the encoder 8. Encoded by This result is temporarily stored in the buffer 1 memory 11 and then output, and is also decoded by the adder 6 and decoder 10, stored in the corresponding position on the frame memory 3, and used for predicting the next frame. .

Further, a synchronization signal is separated from the input video signal, and various control clocks synchronized with this signal are generated by the clock generation circuit 2.

In response to this clock, the encoding control circuit 9 switches to intra-frame encoding for one frame out of a plurality of predetermined frames and performs refreshing. Specifically, by switching the switch 7, the difference between the video signal of the pixel to be encoded and the predicted signal obtained from the 1-pixel memory 4, which stores the information of the previous 1 pixel in the memory, is encoded. become The increase or decrease in the amount of data due to differences in encoding is handled by buffer memory 1.
Absorb by 1.

In this embodiment, the difference between the refreshed signal and the previous frame signal is further encoded. Therefore, during refresh, the signal encoded and decoded by the 1-pixel memory 4 is switched to the input video signal by the switch 12, and the difference between the signal and the signal of the previous frame in the frame memory 3 is calculated by the subtracter 5. The encoded data is output after being arranged in the buffer memory 11 in accordance with the reading order at the time of decoding, together with the code word obtained by intra-frame encoding.

FIG. 2 is a diagram for explaining the decoding method in this embodiment. In the figure, 13 is a buffer memory, 14 is a clock generation circuit, 15 is a decoding control circuit, 16 is a decoder, 17 is a frame memory, 18 is a 1-pixel memory, 1
9.22.23 is a switch, 20 is an adder, 21 is a D/
It is an A converter.

The code word that has passed through the transmission path is stored in the buffer memory 13.
and then sent to the decoder 16. The decoded signal is output after being converted by the D/A converter 21, and is also stored in the frame memory 17 or the 1-pixel memory 18.

Normally, the switch 19 is connected to the frame memory F side and performs interframe decoding, but the decoding control circuit 1
5 switches the switch 19 to the 1-pixel memory 18 side and performs intra-frame decoding.

Immediately after this, the switches 22 and 23 are switched to store the difference between the refreshed signal sent and the signal of the previous frame in the frame memory 17 in preparation for a reverse playback request.

The difference described above is generally not used for decoding during normal playback, but is effective during special playback. That is, the difference value from the previous frame is also encoded in the refresh signal (therefore, it is easy to go back and perform reverse playback).

When playing back still images, by tracing back to the nearest refresh frame and displaying it, it is possible to obtain still images with less deterioration in image quality.

During slow playback, the same frame is repeated several times, but by increasing the refresh frame repetition rate within a range where screen discontinuities are not noticeable, it is possible to obtain slow images with less noticeable deterioration in image quality than before. can.

During high-speed playback, by reading the refresh frame or a portion thereof while changing the range depending on the playback speed, playback can be performed without using interframe decoding, and increases in memory size and calculation scale can be suppressed.

FIG. 3 is a diagram showing the encoding method in the second embodiment of the present invention. In the figure, 1 is an A/D converter, 2
is a clock generation circuit, 3 is a frame memory (inter-frame predictor), 4 is a 1-pixel memory (intra-frame predictor), 5
．． 25 is a subtracter, 6.26 is an adder, 12.29 is a switch, 8.27 is an encoder, 24 is an encoding control circuit, 1
0.28 is a decoder, and 11 is a buffer 1 memory.

Normally, the switch 29 is off, and the results of intraframe encoding are not sent to the buffer memory 11. Also,
Here, it is also possible to prevent the encoding control circuit 24 from performing intraframe encoding itself. Although this increases the complexity of control, it has advantages in terms of processing speed, etc.

As in the first embodiment, intraframe encoding is performed for one frame for each predetermined plurality of frames.

For this purpose, switch 29 is turned on. Furthermore, switch 12
By switching from the input signal side to the intraframe predicted signal, that is, the decoded signal side of intraframe coding, it is possible to encode the difference between the refresh signal obtained by intraframe coding and the signals of all frames thereof. This embodiment requires an extra encoder, decoder, etc. compared to the first embodiment, but
It is more practical because intra-frame encoding and inter-frame encoding can be performed in parallel. Furthermore, it is possible to perform different encoding on inter-frame differences and intra-frame differences.

In the first and second embodiments, the encoding control circuit 9.24
By changing the algorithm of the decoding control circuit 15, refreshing performed in units of one frame can be changed to be performed in blocks of m pixels*n pixels. These will be referred to as third and fourth embodiments of the present invention, respectively. The encoding control circuit 9.24 and the decoding control circuit 15 are
It is necessary to manage the block addresses so that one refresh cycle takes several frames. Normally, the address information of the refresh block is also transmitted, but
By providing block address generation means in advance on both the encoding side and the decoding side as in No. 1-131988, it is possible to eliminate the need for transmitting block addresses.

The third and fourth embodiments have a difference of 1 from the first and second embodiments.
By distributing the number of pixels that are refreshed each time, it is possible to suppress a sudden increase in information during refresh, and improve the image quality of the frames before and after the refresh.

Furthermore, the fourth embodiment in particular can be easily applied to inter-frame and intra-frame adaptive coding.

This is shown in FIG. 4 as a fifth embodiment of the present invention. Fourth
This embodiment requires an error accumulation device 30, 311, a comparator 32, and a switch 33 compared to the embodiment.

Error accumulator 30.31 performs interframe encoding and intraframe encoding for each block.
The comparator 32 calculates the error of both encodings for one block accumulated in
The encoding result with the smaller error is sent to the buffer memory 11 together with the code code used for determining the method during decoding. This makes it possible to perform inter-frame and intra-frame adaptive coding. There are various error calculation methods and comparison methods at this time, but the present embodiment is not limited to these methods.

In this embodiment, the inter-frame difference is calculated only for the periodic refresh portion, but if the increase in the amount of information is within the allowable range, the inter-frame difference may be encoded for all the inter-frame encoded portions. good. Alternatively, the difference may be adaptively encoded so that it falls within the allowable range of the buffer memory 11. Here, we used the same method for encoding the normal interframe difference and interframe difference encoding added to refresh, but by setting one more encoder and one more decoder,
It is also possible to change the encoding method and bit number allocation for the above two types of inter-frame differences.

The present invention can be configured in various ways other than those shown in the above embodiments.

For example, in the above embodiment, a simple method that does not include motion compensation has been described, but the present invention does not rely on an algorithm for interframe coding or interframe or intraframe adaptive coding; A similar effect is achieved when . Also,
Although the intra-frame encoding method is based on prediction based on one immediately preceding pixel, prediction based on the values of several surrounding pixels may also be used. In this case, the intra-frame predictor and its decoding memory require memory for several pixels instead of one pixel memory. Furthermore, in the second embodiment, it is also possible to use coding that does not use prediction for the intraframe coding portion. For example, in the case of simple PCM encoding, one pixel memory 4
, subtractor 25, and adder 26 are no longer necessary.

Effects of the Invention According to the present invention, by using the above-described means, a decoded signal containing no inter-frame differences can be obtained periodically every several frames, thereby making it easy to perform still, slow and high-speed reproduction. Furthermore, by separately preparing a decoded signal that does not include interframe differences and the difference between the signal one frame before that, it becomes possible to go back in time from that point, making it easy to perform reverse playback. be able to.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a video signal encoding method in the first and third embodiments of the present invention, FIG. 2 is a block diagram showing a video signal decoding method in the same embodiment, and FIG. FIG. 3 is a block diagram showing the video signal encoding method in the second and fourth embodiments of the present invention, and FIG. 4 is a block diagram showing the video signal encoding method in the second and fourth embodiments of the present invention.
FIG. 2 is a block diagram showing a video signal encoding method in the embodiment. 316. Frame memory, 4, 1 pixel memory, 5
．． 25 , , Subtractor , 6.2B , , Adder , 7.1
2.19.29.33. ,,switch,8.27. ,,
Encoder, 911. Encoding control circuit, 10.16.28
゜1. Decoder, 30.31. ,,error accumulator, 32
゜0. Comparator.

Claims (4)

[Claims] (1) In interframe coding and interframe/intraframe adaptive coding that utilize the correlation between frames of a video signal, one frame is periodically selected from among multiple frames, and the image quality deterioration due to at least a code error is selected for the frame. A method of encoding a video signal, characterized in that encoding is performed using an intra-frame encoding method in which the influence of propagation is less than that of inter-frame encoding, and that a difference signal between the frame and one frame before it is encoded. (2) In interframe coding and interframe and intraframe adaptive coding that utilize the correlation between frames of a video signal, one frame of screen is divided into multiple blocks of m lines * n lines. One or more blocks per frame are periodically selected so as to go around every few frames, and the blocks are subjected to an intra-frame encoding method that has less influence of propagation of image quality deterioration due to code errors than inter-frame encoding. 1. A method for encoding a video signal, comprising encoding a difference signal between the block and a block at the same position one frame before the block. (3) When encoding the difference signal between the selected frame and the frame before it, a certain threshold is set, and if it is less than the threshold, the bits necessary for encoding are at least more than the threshold. 2. The video signal encoding method according to claim 1, wherein switching is performed adaptively so as to reduce the number of video signals. (4) When encoding the difference signal between the selected block and the block at the same position one frame before it, a certain threshold is set, and if it is less than that threshold, it is at least more than the threshold. 3. The method of encoding a video signal according to claim 2, wherein the switching is performed adaptively so that the number of bits required for encoding is further reduced.