JPH0451688A - Motion compensating interframe coding device - Google Patents

Abstract

PURPOSE:To improve picture quality by executing interframe coding for a block for which intraframe coding was decided to be executed as well by correcting that decision if the motion vector of a coding block is the same as the motion vector of an adjacent circumferential block. CONSTITUTION:A first coding system deciding part 9 to decide either to interframe-code or intraframe-code the block to be coded, and a second coding system deciding part 21 to correct the decided result of the first coding system deciding part 9 are provided. Then, the motion vector of the coding block is compared with the motion vector of the adjacent circumferential block by the second coding system deciding part 21, and if the motion vector of the coding block is the same as the motion vector of the adjacent circumferential block, the interframe coding is executed for the block for which the intraframe coding is decided to be executed as well. Thus, the deterioration of the picture quality to be caused by the mixing of the block to be interframe-coded and the block to be intraframe-coded at the flat part of a picture at the time of the parallel movement of the whole picture can be prevented, and the picture quality can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a motion compensated M-frame intercoding device for video signals.

BACKGROUND OF THE INVENTION In recent years, with the development of video encoding technology, motion compensated predictive interframe encoding devices have been developed as high-efficiency encoding devices for color video images used in video telephones, video conferencing systems, CD-ROMs, digital VTRs, etc. is being developed. For example, Sakae Okubo: ``Standardization trends in video conferencing/telephone coding'' PSCJ89 Image Coding Lecture pp. 43-48.
A motion-compensated predictive interframe coding device is known.

Hereinafter, a conventional motion compensated predictive interframe coding device will be described with reference to FIG. In FIG. 2, 51 is an input terminal into which an input video signal is input, and 53 is a motion vector calculator that compares the image signal of the encoded block of the current frame with the reproduced image signal of the previous frame to calculate the motion vector of the encoded block. 54 is an image memory unit that stores the reproduced image signals of the current frame and the previous frame; 58 is a motion compensation prediction unit that performs motion compensation prediction for the reproduced image signal of the previous frame; and 60 is an intraframe code for the block to be encoded. 64 is a prediction error calculation unit that calculates a prediction error by calculating the difference between the original picture signal and the prediction signal of the coding block; 66 is a coding method control signal; 68 is an orthogonal transformation section that orthogonally transforms the signal to be orthogonally transformed; and 70 is a quantization section that quantizes orthogonal transformation coefficients. , 73 is a quantization step size calculation unit that calculates a quantization step size, 74 is a code memory unit that temporarily stores transmission frames, 76 is an inverse orthogonal transformation unit that performs inverse orthogonal transformation of quantized orthogonal transformation coefficients, and 78 is a current A reproduced image calculation section a that calculates a reproduced image of a frame; 82 is a prediction error encoding section that encodes a prediction error through a channel; a diagonal symbol represents a motion vector encoder that encodes a motion vector through a channel; 86;
89 is a multiplexer unit that configures a transmission frame from a prediction code and a motion vector code, and 89 is an output terminal that outputs a transmission signal.

The operation of the above configuration will be explained below.

The video signal, which is converted into a digital signal by an analog-to-digital conversion circuit (not shown) and divided into blocks of M pixels in the horizontal direction and N lines in the vertical direction, is sent to the input terminal 51.
The input video signal 52 is inputted as the input video signal 52.

The motion vector calculation unit 53 calculates the input video signal 52 and the reproduced video signal 5 of the previous frame stored in the image memory unit 54.
5 and calculates the motion of the encoded block as a motion vector, which is output as a motion vector signal 56. At the same time, the motion vector calculation unit 53 uses the evaluation value at the time of motion vector calculation to determine whether motion compensation prediction is valid or invalid for the encoded block, and outputs the result as a motion compensation prediction control signal to the motion vector signal 56. do. Therefore, the motion vector signal 56
A motion vector and a motion compensated prediction signal are superimposed on each other. The motion compensation prediction unit 58 (1) performs motion compensation prediction on the reproduced video signal 55 of the previous frame using a motion vector when the motion compensation prediction control signal instructs to enable motion compensation prediction; When the compensation prediction control signal instructs invalidation of motion compensation prediction, the reproduced video signal 55 of the previous frame is output as is as the prediction signal 63.

The encoding method determining unit 60 determines whether intra-frame encoding or inter-frame encoding is effective based on the input video signal 52 and the prediction signal 63 on a block-by-block basis, and outputs the result as an encoding method control signal 61. By switching the encoding method between the intra-frame encoding method and the inter-frame encoding method on a block-by-block basis, the following improvements can be made compared to the case where encoding is performed using only the inter-frame encoding method.

(1) When a scene change occurs, intra-frame encoding is selected, so the image quality after the scene change can be improved. (
2) When a large movement of the moving object occurs, a background area hidden behind the moving object appears, and in this case, intra-frame encoding is selected, so that the image quality can be improved.

In addition, in the storage media encoding method used for CD-ROMs, etc., in order to realize the editing function and reverse playback function of the reproduced image, a frame in which all blocks are intra-frame encoded at a fixed frame period (this frame , [referred to as a Refresh Frame J], and the insertion of the refresh form can be realized by providing an intra-frame encoding device to the motion-compensated predictive inter-frame encoding device.

The prediction error calculation unit 64 performs a difference calculation between the input video signal 52 of the encoded block and the prediction signal 63, and outputs the result as a prediction error signal 65.

The switch unit 66 selects the input video signal 52 as the signal 67 to be orthogonally transformed when the Q) encoding method control signal 61 selects intraframe encoding, and (2) when the encoding method control signal 61 selects intraframe encoding. When interframe coding is selected, the prediction error signal 65 is selected as the signal 67 to be orthogonally transformed.

The orthogonal transform unit 68 performs orthogonal transform on the signal 67 to be orthogonally exchanged, removes high correlation between neighboring pixels of the signal 67 to be orthogonally transformed, and calculates orthogonal transform coefficients 69.

As the orthogonal transform method, in the case of multiple transforms, discrete cosine transform is used, which has high transform efficiency and is practical for hardware implementation.

The quantization unit 70 uses the quantization step size 71 to
The orthogonal transform coefficient 69 is quantized and the orthogonal transform quantized coefficient 72 is
Calculate.

The quantization step size calculation section 73 includes a code memory section 74.
Quantization step size 71 is calculated from residual code amount 75 within.

The inverse orthogonal transform unit 76 performs inverse orthogonal transform on the orthogonal transform quantization coefficient 72 and calculates an orthogonally transformed signal 77 containing a quantization error.

The switch unit 66 (1) selects the numerical value rOJ signal 80 as the reproduction image calculation signal 79 when the encoding method control signal 61 selects intraframe encoding, and (2) selects the numerical value rOJ signal 80 as the reproduction image calculation signal 79. 61 selects interframe coding, the predicted signal 63 is used as the reproduced image calculation signal 79.
Select.

The reproduced image calculation unit 78 adds the orthogonally transformed signal 77 containing the quantization error and the reproduced image calculation signal 79 to calculate a reproduced image 81 of the encoded block.

The image memory 54 stores the reproduced image signal 81 of the current frame and outputs the reproduced image signal 55 of the previous frame. The prediction error encoding unit 82 encodes the orthogonal transform quantization coefficient 72, the quantization step size 71, and the encoding method control signal 61, and calculates the prediction error code 83. The quantization step size 71 is encoded only when the value of the quantization step size 71 changes.

The motion vector encoding unit 84 encodes the motion vector 56 and calculates a motion vector code 85. Multiplexer section 8
6 calculates a transmission frame 87 in a predetermined format from the prediction error code 83 and the motion vector code 85.

The code memory unit 74 temporarily stores the transmission frame 87,
It is output from an output terminal 89 as a transmission code 88 in synchronization with a clock signal input from an external source (not shown). At the same time, the code memory unit 74 calculates the amount of codes remaining in the memory as the remaining code amount 75.

Problems to be Solved by the Invention Although the motion compensated predictive interframe coding method can achieve high coding efficiency, it has the following problems.

Whether to perform intraframe encoding or interframe encoding for each block is determined by the following method using the predicted pixel value of the encoded block and the pixel value of the encoded block based on the motion compensation control signal. There is.

Let the size of the encoded block be MXN, the predicted pixel value of the encoded block be P (M, N), and the pixel value be S (M, N).

VA R=p(P (X, Y) −S (X,
Y)"/ (MxN) to calculate VAR (the root mean square of the error between the input pixel value and the predicted pixel value) and VAROR (the variance of the input pixel values) and perform intra-frame encoding or inter-frame encoding according to the following criteria. Determine whether to encode.

If VAR<=64, then interframe coding; if VAR>=64, then intraframe coding; if VAR<VAROR, then interframe coding; therefore, VA R, VA RORK, J:
7v - In a part where there are many blocks where a decision is made near the boundary whether to perform intra-frame encoding or inter-frame encoding, the blocks that perform intra-frame encoding and the blocks that perform inter-frame encoding will be mixed.

In particular, when the entire screen is translated (panning) with a size larger than a certain value, if there is a block that is intra-frame encoded surrounded by inter-frame encoded blocks on a flat part of the screen. This may cause image quality deterioration.

In view of the above-mentioned problems, the present invention examines whether the motion vector of a block subjected to intra-frame encoding is the same as the motion vector of neighboring adjacent blocks in the conventional method, and detects whether the encoded block is the same when panning occurs. The purpose of this is to correct the decision to perform intra-frame encoding and perform inter-frame encoding when the block is in the center of the frame, thereby improving image quality.

Means for Solving the Problem To achieve this object, the present invention provides means for converting a video signal from analog to digital, and for converting one frame or field of the digitized input video signal into blocks of a defined size. A means for dividing, a means for calculating a motion vector representing the motion of a television screen image for each block, and a means for determining whether or not to perform motion compensation for the coded block using the motion vector based on the interframe difference value. motion compensation determining means for determining and outputting the result as a motion compensation control signal; means for accumulating motion vectors of the encoded block and surrounding blocks adjacent to the encoded block; and pixels of the input video signal of the encoded block. and a means for calculating a prediction error value as a difference between the predicted pixel value and the predicted pixel value based on the motion compensation control signal; a first encoding method determining means for determining whether to perform intra-frame encoding and outputting it as an encoding method control signal; a motion vector of a block determined to be intra-frame encoding by the first encoding method determining means; The motion vectors of adjacent blocks are compared, and if the number of blocks that can be imaged with matching motion vectors is at least k (a positive integer of 8 or less), the first encoding method control signal is corrected, and the interframe code is means for orthogonally transforming an input video signal or prediction error value to calculate an orthogonal transform coefficient; and a quantum controller for calculating a quantization step size from the amount of generated code. quantization step size determining means, means for quantizing orthogonal transform coefficients using the quantization step size and calculating quantized orthogonal transform coefficients, means for encoding the quantized orthogonal transform coefficients, and quantized orthogonal transform coefficients. An inverse quantization means that performs inverse orthogonal transform to calculate an inverse quantized signal, and an encoding method control signal determines whether the pixel value used when calculating the reproduced pixel value is the predicted pixel value or the numerical value "0". an image reproduction means for calculating a reproduced image from a predicted pixel value or numerical value "0" and an inverse quantization signal; an image storage means for accumulating the reproduced image; and a motion vector code for encoding a motion vector. The device is configured to provide means for converting the information.

Effect of the Invention With the above configuration, the present invention corrects the determination even in a block that is determined to undergo intra-frame encoding when the motion vector of the encoded block is the same as the motion vector of an adjacent surrounding block. By performing interframe coding, it works to improve image quality.

EXAMPLE Hereinafter, an example of the present invention will be described with reference to the drawings. FIG. 1 shows motion compensation in one embodiment of the present invention≠
FIG. 2 is a block diagram of a side interframe encoding device.

In FIG. 1, 1 is an input terminal into which an input video signal is input, and 3 is a motion vector of the coded block and a motion compensation prediction control signal by comparing the picture signal of the coded block of the current frame and the reproduced picture signal of the previous frame. a motion vector calculation unit that calculates
Reference numeral 4 denotes an image memory unit that stores reproduced picture signals of the current frame and the previous frame; 7 denotes a motion compensation prediction unit that performs motion compensation prediction on the reproduced picture signal of the previous frame; and 9 performs interframe encoding of blocks to be encoded. 21 is a first encoding method determining unit that determines whether to perform intra-frame encoding, and a second encoding method determining unit that corrects the determination result of the first encoding method determining unit based on the motion vector of the encoded block and the motion vectors of surrounding blocks. 13 is a prediction error calculation unit that calculates a prediction error by calculating the difference between the original picture signal and the predicted signal of the coding block; 15 and 16 are used to determine the signal to be orthogonally transformed by the coding method control signal; 17 is an orthogonal transformation unit that performs orthogonal transformation; 19 is a quantization unit that quantizes orthogonal transformation coefficients; and 22 is a quantization step that calculates the quantization step size. 28 is a code memory unit that temporarily stores transmission frames; 30 is an inverse orthogonal transform unit that performs inverse orthogonal transform on quantized orthogonal transform coefficients;
4 is a reproduced image calculation unit that calculates a reproduced image of the current frame;
36 is a prediction error encoding unit that encodes a coding method control signal, a prediction error, and a quantization step size through a channel; 38 is a motion vector encoder that encodes a motion vector through a channel; 40
43 is a multiplexer unit that configures a transmission frame from a prediction code and a motion vector code, and 43 is an output terminal that outputs a transmission signal.

The operation of the above configuration will be explained below.

The video signal is converted into an analog-to-digital signal by a signal processing section not shown in FIG.

Next, the motion vector calculation section 3 compares the input video signal 2 with the reproduced image 5 of the previous frame read out from the image memory section 4, calculates a motion vector, and outputs it as a motion vector signal 6. At the same time, the motion vector calculation unit 3 uses the evaluation value at the time of motion vector calculation to determine whether motion compensation prediction for the encoded block is valid or invalid, and outputs the result as motion compensation prediction control information to the motion vector signal 6. do. Therefore, the motion vector signal 6 has a motion vector and a motion compensated prediction signal superimposed thereon.

The motion compensation prediction unit 7 performs motion compensation prediction using the motion vector when performing motion compensation prediction using the motion vector signal 6 on the reproduced image 5 of the previous frame at the same position as the encoded block, and does nothing when not performing motion compensation prediction. Then, the predicted pixel signal 8 is output.

The first encoding method determining unit 9 determines which of the interframe encoding method and the intraframe encoding method is effective, based on the input video signal 2 and the prediction error signal obtained from the predicted pixel signal 8 in block units. The determination is made and the result is output as the first encoding method control signal 1o. Next, the second encoding method determination unit 21 outputs the first encoding method control signal 10 as it is as the second encoding method control signal 44 for the encoded block determined to be subjected to interframe encoding. For blocks that are determined to undergo intra-frame encoding, the motion vector of the encoded block and the motion vectors of surrounding blocks are compared from the motion vector signal 6, and the motion vectors of the encoded block and the motion vectors of surrounding blocks are compared, and the number of blocks that can be imaged as a match is equal to or greater than the number of blocks that can be imaged. (k is a positive integer of 8 or less), the first encoding method control signal 10 is corrected to perform interframe encoding, and the result is output as the second encoding control signal 44. The prediction error calculation unit 13 calculates the difference between the input video signal 2 and the prediction signal 8 of the encoded block, and outputs the result as a prediction error signal 14. Switch part 1
5 selects the input video signal 2 as the signal 16 to be orthogonally transformed when the first encoding method control signal selects intraframe encoding, and (2) selects the input video signal 2 as the signal 16 to be orthogonally transformed. If interframe coding is selected for the control signal,
The prediction error signal 14 is selected as the signal 16 to be orthogonally transformed.

The orthogonal transform unit 17 performs orthogonal transform on the signal 16 to be orthogonally transformed, removes high correlation between neighboring pixels of the signal 16 to be orthogonally transformed, and calculates orthogonal transform coefficients 18 .

As the orthogonal transform method, in many cases, discrete cosine transform is used, which has high transform efficiency and can be implemented in hardware.

The quantization unit 19 quantizes the orthogonal transform coefficients 18 with a quantization step size of 20, and calculates an orthogonal transform quantized signal 29.

The switch unit 16 includes (1) a second encoding method control signal 44;
selects intraframe encoding, selects the numerical value “0” signal 33 as the reproduced image calculation signal 32, and (2
) When the second encoding method control signal 44 selects interframe encoding, the predicted signal 8 is selected as the reproduced image calculation signal 32.

The reproduced image calculation unit 34 adds the signal 31 containing the quantization error and the reproduced image calculation signal 32 to calculate a reproduced image 35 of the encoded block. The image memory 4 stores the reproduced image signal 35 of the current frame, and stores the reproduced image signal 5 of the previous frame.
Output.

The prediction error encoding unit 36 encodes the encoding method control signal 44, the quantization step size 20, and the orthogonal transform quantization coefficient 29, and calculates the prediction error code 37.

The motion vector encoding unit 38 encodes the motion vector signal 6 of the block subjected to motion compensation prediction and calculates a motion vector code 39.

The multiplexer unit 40 calculates a transmission frame 41 in a predetermined format from the prediction error code 37 and the motion vector code 39.

The code memory unit 28 temporarily stores the transmission frame 41,
It is output from an output terminal 43 as a transmission code 42 in synchronization with a clock signal input from an external source (not shown). At the same time, the code memory unit 28 calculates the amount of codes remaining in the memory as the remaining code amount 23.

As is clear from the above description, according to this embodiment, the second
The encoding method determining unit 21 compares the motion vector of the encoded block with the motion vector of the adjacent peripheral block, and if the motion vector of the encoded block is the same as the motion vector of the adjacent peripheral block, the intra-frame code is used. By performing interframe encoding on blocks that have been determined to be encoded, when the entire screen is moved in parallel, blocks that undergo intraframe encoding and blocks that undergo interframe encoding coexist in flat areas of the screen. This prevents the deterioration of image quality caused by this and improves the image quality.

In the above explanation, the judgment is corrected for blocks determined to be intra-frame encoded, and whether or not to perform inter-frame encoding is determined based on the motion vector of the encoded block and the motion of surrounding blocks adjacent to the encoded block. Although an example has been shown in which the determination is made based on the number of matching vectors, the determination may be made based on the number of matches.

In addition, in the above explanation, an example was shown in which the motion vector is inspected using the reproduced image of the previous frame and the current image of the current frame. Vectors may also be detected.

Effects of the Invention As described above, the present invention relates to the determination of inter-frame coding/intra-frame coding, and for a coding block determined to be subjected to intra-frame coding, the motion vector of the coding block and the adjacent surrounding blocks are determined. The motion vector of the encoded block is compared with the motion vector of the adjacent surrounding block, and if the motion vector of the encoded block is the same as the motion vector of the adjacent surrounding block, the motion vector of the encoded block is temporarily stored. By correcting the decision to perform encoding and providing means for performing interframe encoding, blocks that perform intraframe encoding on flat areas on the screen and interframe encoding can be used when the entire screen moves in parallel. It is possible to prevent the deterioration of image quality that would occur due to the coexistence of blocks that perform this, and to improve the image quality.

[Brief explanation of drawings]

FIG. 1 is a block diagram of a motion-compensated predictive inter-frame encoding device according to an embodiment of the present invention, and FIG. 2 is a block diagram of a conventional motion-compensated predictive inter-frame encoding device. 1.51... Input terminal, 3, 53... Motion vector calculation unit, 4.54... Image memory unit, 7.58... Motion compensation unit, 60... Encoding method determination unit, 9 . . . first encoding method determination unit, 21 . . . second encoding method determination unit, 1
3.64...Prediction error calculation unit, 15. 16.66・
- Switch section, 17.68... Orthogonal transformation section, 19.
70... Quantization section, 22.73... Quantization step size calculation section, 28.74. Code memory section, 28.74
... code memory section, 30.76... inverse orthogonal transform section,
34.78 Reproduction image calculation section, 36.82... Prediction error encoding section, 38, 84. Motion vector encoding section, 40.8
6... Multiplexer section, 43.69... Output terminal.

Claims (1)

[Claims] Means for converting a video signal from analog to digital; means for dividing one frame or one field of a digitized input video signal into blocks of a predetermined size; and means for converting a television image into blocks of a prescribed size for each block. means for calculating a motion vector that is motion; and determining whether or not to perform motion compensation for a coded block using the motion vector based on an interframe difference value, and outputting the result as a motion compensation control signal. a motion compensation determining means; a means for accumulating motion vectors of the encoded block and peripheral blocks adjacent to the encoded block; and a pixel value of an input video signal of the encoded block and a predicted pixel value based on a motion compensation control signal. means for calculating the difference between the two as a prediction error value, and determining whether to perform interframe encoding or intraframe encoding for each block based on the prediction error value and the pixel value of the input video signal, and controlling the encoding method. A first encoding method determining means outputs a signal, and a motion vector of a block determined to be intra-frame encoded by the first encoding method determining means is compared with a motion vector of an adjacent block, and a motion vector is determined. If there are k or more blocks (k is a positive integer of 8 or less) that can be considered to match, the first encoding method control signal is corrected and changed to perform the interframe encoding method. Coding method control signal correction means; means for orthogonally transforming the input video signal or prediction error value to calculate orthogonal transform coefficients; quantization step size determining means for calculating the quantization step size from the generated code amount; A means for quantizing orthogonal transform coefficients using a quantization step size and calculating the quantized orthogonal transform coefficients, a means for encoding the quantized orthogonal transform coefficients, and an inverse orthogonal transform for the quantized orthogonal transform coefficients, and a means for calculating the quantized orthogonal transform coefficients. an inverse quantization means for calculating a quantized signal; a switching means for switching whether a pixel value used when calculating a reproduced pixel value is a predicted pixel value or a numerical value "0" according to the encoding method control signal; A motion device comprising: an image reproduction means for calculating a reproduced image from a predicted pixel value or numerical value "0" and a dequantized signal; an image storage means for accumulating the reproduced image; and a motion vector encoding means for encoding a motion vector. Compensated interframe coding device.