JP2537242B2 - Motion compensation motion vector coding method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Outline] The present invention relates to a motion compensation motion vector coding method in which an input motion vector of a detected input screen is variable-length coded by an entropy coder and then transmitted. For the purpose of reducing the number, a memory for accumulating a predetermined plurality of the input motion vectors, a codebook storing a plurality of motion vector patterns obtained in advance, the input motion vector and the motion vector patterns are provided. A matching determination circuit that selects a motion vector pattern having the smallest error by comparison and sends the index to the entropy coder.

[Industrial applications]

The present invention relates to an image coding system, and more particularly to a motion compensation motion vector coding system in which a detected input motion vector of an input screen is variable-length coded by an entropy coder and then transmitted.

In recent image transmission such as video conferencing, various proposals have been made from the viewpoint of realizing a low bit rate by compressing the transmission amount as much as possible in order to effectively use the transmission line and reduce the terminal cost. However, the so-called block matching type motion compensation method, which detects the motion of the transmission screen and obtains the difference signal by compensating the prediction screen by the amount of the motion and further quantizing and transmitting the difference signal, is in the limelight. Is coming.

[Conventional technology]

FIG. 11 shows a well-known coding system with motion compensation, which was announced at the Institute of Electronics and Communication Engineers on April 5, 1984, for example.

In the figure, 11 is a quantizer, 12 is a frame memory, 13 is a variable delay device, and 14 is a motion detector. In this method, as shown in FIG. 12, input screen block x (I, J) Absolute value of pixel-by-pixel difference between the same position on the reference screen stored in the frame memory 12 and the surrounding blocks y (i, j) | x (I, J) -y (i, j) | Is taken by the motion detector 14 and accumulated for one block, and the accumulated value Block is predicted to be the closest to the screen block before moving, that is, the predicted block is delayed by the amount moved by the variable delay unit 13 and the difference with the next input screen block is obtained. The quantizer 11 quantizes and sends out to the transmission path. At the same time, the prediction screen is stored in the frame memory 12 (via an inverse quantizer (not shown)) and is used to determine the next prediction block. Then, the detected amount of motion of the block (hereinafter, referred to as a motion vector value) is separated from (or together with) the coding circuit of the quantized output of the quantizer 11 by the entropy coder (coding circuit) shown in FIG. ) Send to receiver via 10.

The receiving side reproduces the original screen from the received signal according to the motion detection information.

[Problems to be solved by the invention]

In the above conventional motion compensation motion vector entropy coder as shown in FIG. 13, a set of a motion vector in the X-axis (vertical axis) direction and a motion vector in the Y-axis (horizontal axis) direction (V _(X , V _Y ) is appropriately variable-length coded and transmitted individually to the receiving side, so although individual motion vectors can be accurately transmitted, the smaller the size of the block for motion compensation becomes, There is a problem that the amount of information increases due to motion compensation.

Therefore, the present invention aims to reduce the amount of information transmitted by a motion compensation motion vector in a motion compensation motion vector encoding system in which an input motion vector of a detected input screen is variable length coded by an entropy coder and then transmitted. To aim.

[Means for solving problems]

FIG. 1 conceptually shows a motion compensation motion vector encoding system according to the present invention for achieving the above object. 1 is a memory for accumulating a predetermined plurality of input motion vectors, and 2 is a preset memory. The codebook 3 storing the obtained plurality of motion vector patterns compares a predetermined plurality of input motion vectors stored in the memory 1 with the motion vector patterns stored in the codebook 2 and the error is minimized. Is a matching determination circuit that selects the motion vector pattern of and sends the index to the entropy coder 10.

[Action]

In the motion compensation motion vector encoding method of the present invention shown in FIG. 1, the motion of the input screen with respect to the prediction screen is stored in the memory 1 as the input motion vector. The memory 1 stores a predetermined plurality of input motion vectors. Further, the codebook 2 stores a plurality of motion vector patterns obtained in advance in the X-axis direction and the Y-axis direction of the input motion vector. The matching determination circuit 3
The plurality of input motion vectors stored in the memory 1 and the plurality of motion vector patterns stored in the codebook 2 are compared, and the motion vector pattern with the smallest error, that is, the distortion is selected from among these, and its index is entropy. Send to Coder 10. The entropy coder 10 encodes the index into a variable length code, sends it to the transmission path, and sends it to the receiving side.

As described above, the motion vector pattern in the codebook that is closest to the X-axis direction vector and the Y-axis direction vector due to a plurality of combinations of input motion vectors, that is, the motion vector pattern closest to the group of input motion vectors has a small amount of information. It is transmitted in the form of an index.

〔Example〕

Embodiments of the motion compensation motion vector encoding method according to the present invention will be described below.

FIG. 2 shows an embodiment in which the motion compensation motion vector coding system of the present invention shown in FIG. 1 is incorporated into a motion compensation coding system. In this embodiment, the motion detector 1 is used. The input motion vectors detected in step 1 are stored in the memory 1 by a predetermined number. The matching determination circuit 3 compares the motion vector pattern stored in the codebook 2 with the X-axis direction and Y-axis direction vectors of the input motion vector, selects the motion vector pattern having the smallest error, and sets its index to the entropy coder 10. To the receiving side via.

The index of the selected motion vector pattern is also input to the demultiplexer 5, and the index is used in the cobook 2
To obtain the motion vector pattern, and apply it to the variable delay unit 13. Thereby, the variable delay unit 13 shifts the previous screen in the frame memory 12 to generate a prediction screen.

Here, since various examples can be considered for the motion vector pattern stored in the codebook 2, those examples will be described below together with the input motion vector.

FIGS. 3 (a) and 3 (b) show motion vector patterns stored separately in the X-axis direction and the Y-axis direction in the codebook 2, and n _x vectors are collected for the X-axis direction. motion vector pattern could Te is m _x number (each 1 to m _x is each of the index of the motion vector pattern) is prepared, motion vector pattern collection n _y number of vectors in the Y-axis direction is m _y (1 to m _y are each indexes of the motion vector pattern) are prepared. These motion vector patterns are obtained in advance and stored, but even if n _x = n _y and m _x = m _y , n _x ≠ n _y , m _x ≠ m _y
May be. However, when n _x = n _y , it is not necessary to separate the code book 2 for the X-axis direction and the Y-axis direction, and in that case, the pattern configuration is the same as that shown in FIG.

With such determine the motion vector pattern codebook 2, and correspondingly, the number of the input motion vectors stored in the memory 1 X-axis direction input V _x is n _x pieces, Y-axis direction input
V _y is automatically set to n _y .

FIG. 5 shows an embodiment in which actual numbers are applied to the embodiment of the code book of FIG. 4, and in this embodiment,
Matching is performed by setting n _x = n _y = 3 and _collecting three vectors in the X-axis direction and three vectors in the Y-axis direction.

Further, FIG. 6 shows an input motion vector and an embodiment in which it is stored in the memory 1. However, the input motion vectors may be stored in the memory 1 as they are and rearranged by the matching determination circuit as shown in FIG.

Next, an embodiment of the judgment operation in the matching judgment circuit 3 will be described with reference to the flow chart shown in FIG.

First, the input motion vector is V _I (n) (n is the number of dimensions), and the code of the motion vector pattern of codebook 2 is V _O (n,
m) (m is the number of codes, which is the number of indexes), and variables for determination are D, R, and IDX (index) (step S1 in FIG. 7).

As an initial value, R = ∞ (however, ∞ means the maximum value that the cumulative value D can take), J (count) = 0, D = 0, I
= 0 (step S2). Then, in step S3, J
Is incremented by "1".

In step S4, I is incremented by "1" and the absolute value error (represented by ABS) between V _I (I) and V _O (I, J) is calculated, and the value obtained by adding D to this is added. As D
Repeat steps S4 and S5 until J reaches n. As a result, as shown in FIG. 4, for each of the motion vector values 1 to n of the motion vector pattern of the index “1”, the error with the X-axis direction vector (or Y-axis direction vector) of the input motion vector is accumulated. To do.

When the index "1" ends, R and D are compared (step S6 in the same step), and if D has not reached R, R
= D and set the current cumulative value D to the previous cumulative value D and ID
With X = J (step S7), steps S3 to S8 are repeated until J = m. As a result, the error is accumulated for each of the m motion vector patterns, and since the steps S6 and S7 provide the IDX that gives a smaller D, the motion vector that gives the smallest error (distortion) is finally obtained. The pattern index is selected and sent to the entropy coder 10.

It should be noted that, in step S4 for obtaining the error, the square error (V _I (I) −V _O (I, J)) ² may be used instead of the absolute value.

8 (a) and 8 (b) are the same as FIG. 3 except that n _x = 3,
An example of the codebook when n _y = 7 is shown,
FIG. 9 shows an example of an input motion vector corresponding to this.

The reason why the number of motion vector patterns in the X-axis direction and the Y-axis direction is changed in this way is that the horizontal motion is usually larger than the vertical motion in a video conference and the like. In this case, as shown in the figure, only three X-axis direction vectors of the input motion vector are processed, and waiting for input may occur (in order to prevent this, a buffer should be provided to wait until seven are accumulated). However, since seven Y-axis direction vectors are processed together, no input waiting occurs.

Unlike the above, FIG. 10 shows an embodiment in which the codes in the X-axis direction and the Y-axis direction are not separately stored, but the codes in both directions are paired and stored together. For the motion vector, both the X-axis direction vector and the Y-axis direction vector are subjected to the arithmetic processing of FIG. 7 at the same time.

On the receiving side, the reverse operation is performed to reproduce the motion vector.

That is, a motion vector pattern (the same codebook as the transmission side is prepared for the reception side) is extracted by the transmitted index, and this motion vector pattern is calculated in the number of dimensions (the number of vectors of the motion vector pattern). It is sufficient to perform motion compensation by using the same motion vector for n).

Therefore, only the index of the matched motion vector pattern needs to be sent from the transmitting side to the receiving side.

〔The invention's effect〕

As described above, according to the motion compensation motion vector encoding method according to the present invention, a plurality of motion vector patterns are prepared, a predetermined number of input motion vectors and an error that minimizes the error are selected, and only the index is selected. Since it is configured to transmit, a predetermined number of input motion vectors can be represented by one pattern, and although some distortion occurs, the amount of information is small and extremely efficient encoded transmission can be realized.

[Brief description of drawings]

FIG. 1 is a block diagram showing the principle of a motion compensation motion vector coding system according to the present invention, and FIG. 2 is an embodiment of a motion compensation coding system incorporating the motion compensation motion vector coding system according to the present invention. 3 is a block diagram showing an example of a codebook used in the present invention, FIG. 6 is a diagram showing an example of processing of an input motion vector, and FIG. 7 is a matching judgment. FIG. 8 is a flow chart for explaining the arithmetic operation of the circuit, FIG. 8 is a diagram showing an embodiment of a codebook used in the present invention, FIG. 9 is a diagram showing an embodiment of processing of an input motion vector, and FIG. FIG. 11 is a diagram showing an embodiment of a codebook used in the present invention, FIG. 11 is a block diagram showing an example of a conventionally known motion compensation coding system, and FIG. 12 is a diagram for explaining the principle of motion compensation. Figure 13 encodes a conventional motion vector Shows the entropy coder is. In FIG. 1, 1 ... Memory, 2 ... Codebook, 3 ... Matching determination circuit, 10 ... Entropy coder. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (5)

(57) [Claims] 1. A motion compensating motion vector coding system for variable-length coding and transmitting a detected input motion vector of an input screen by an entropy coder (10), and a memory for accumulating a predetermined plurality of the input motion vectors. (1), a codebook (2) that stores a plurality of motion vector patterns determined in advance, and a motion vector pattern that minimizes the error is selected by comparing the input motion vector and the motion vector pattern. Then, a motion compensation motion vector encoding method comprising: a matching determination circuit (3) for sending the index to the entropy coder (10). 2. The code book (2) has a Y-axis direction and a Y-axis direction.
The motion vector pattern is stored separately in the axial direction, and the matching judgment circuit (3) divides the input motion vector into a set of values in the X-axis direction and a set of values in the Y-axis direction. The motion-compensated motion vector coding method according to claim 1, which is used for comparison with a vector pattern. 3. The motion compensation motion vector coding method according to claim 2, wherein the number of respective values of the motion vector pattern divided in the X-axis direction and the Y-axis direction is different. 4. The code book (2) has a Y-axis direction and a Y-axis direction.
The motion vector patterns divided in the axial direction are stored as a pair, and the matching determination circuit (3) forms a pair with a value in the X axis direction and a value in the Y axis direction of the input motion vector. The motion compensation motion vector encoding method according to claim 2, which is used for comparison. 5. The codebook (2) has a Y-axis direction and a Y-axis direction.
The motion vector pattern common to the axial direction is stored, and the matching determination circuit (3) divides the input motion vector into a set of values in the X-axis direction and a set of values in the Y-axis direction. The motion compensation motion vector encoding method according to claim 2, which is used for comparison with a vector pattern.