JP2863026B2 - Motion compensation prediction method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a motion compensation prediction method, and more particularly, to a motion compensation prediction method used for efficiently coding an interlaced image signal such as a television (TV) signal. Regarding improvement.

[0002]

2. Description of the Related Art One of techniques for efficiently encoding a moving image is a motion compensation prediction method using block matching. In this method, the amount of motion of an image is obtained for each small area called a block, and the value of past image data shifted by the amount of motion is used as the predicted value of the current image data.

Conventional techniques using such a motion compensation prediction method for an interlaced scanned image signal include the following: (a) Only the temporally previous field is used, and both the horizontal and vertical directions are used. Method of compensating for motion (b) Using only two previous fields in time,
Method for compensating for both horizontal and vertical motions (c) Simple combination of the above method (a) and the above method (b) (for example, (b) performed after (a)), switching and using for each block There are known methods.

[0004]

SUMMARY OF THE INVENTION In the prior art,
In the motion compensated prediction using the field immediately before (b), the difference between the sampling time of the pixel in the block used for prediction and the pixel in the current block is
This is about twice that of the motion compensation prediction using the field immediately before (a). Therefore, (b) is inferior to the motion than (a), and the prediction efficiency is reduced in the moving area.

On the other hand, adjacent two
In the two fields, the positions of the lines in the other fields do not coincide two-dimensionally. Therefore,
In the immediately preceding field, no pixel exists at the same position as the pixel of the current field, whereas in the two preceding field, a pixel exists at exactly the same position. Therefore, in the still region and the horizontally moving region, (a) is (B) The prediction efficiency is further reduced.

On the other hand, in the motion compensation prediction combining (a) and (b) of (c), efficient prediction is always performed to compensate for the reductions in the prediction efficiency of (a) and (b). Although it can be performed, the type of motion vector representing the amount of motion and the amount of calculation for obtaining the amount of motion are twice as large as those in each of (a) and (b).

An object of the present invention is to solve the above-mentioned problems in the conventional motion compensation prediction methods, and to provide the same kind of motion vector and the same amount of calculation as (a) and (b), and as much as (c). Another object of the present invention is to provide a motion-compensated prediction method capable of realizing the prediction efficiency.

[0008]

In order to achieve the above object, according to the present invention, when the immediately preceding field is used for prediction, motion compensation is conventionally performed in both horizontal and vertical directions. When the previous field is used for prediction, motion compensation is performed only in the horizontal direction.

[0009]

According to the present invention, the motion compensation prediction using the immediately preceding field is mainly used in the area including the vertical motion, and the two previous fields are mainly used in the still area and the horizontally moving area. Since the used motion compensated prediction is used, almost the same prediction efficiency as the conventional method (c) can be obtained.
Further, since the motion compensation when using the two previous fields is limited to only the horizontal direction, the amount of calculation for determining the motion vector type and the motion vector is the same as the conventional (a),
It is only slightly increased as compared with the method (b).

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a block diagram showing one embodiment of the present invention. In the figure, a motion compensation predictor 11 obtains a motion compensation prediction value in both the horizontal and vertical directions by using a temporally previous field.
The motion compensation prediction value is obtained only in the horizontal direction using the previous field. The comparator 13 inputs the current image field of the input terminal 1 and the predicted value of the motion compensation predictors 11 and 12, and sets the switch 14 so that the smaller predicted value of the sum of absolute values of prediction errors is selected for each block. Switch. Other configurations are basically the same as those of the conventional (c).
Is the same as

An image signal is input to an input terminal 1, and a subtracter 2 selects a motion compensation predictor 1 selected by a switch 4.
One or twelve predicted values can be reduced. The output difference signal of the subtracter 2 is subjected to discrete cosine transform by the discrete cosine transformer 3, and the transform coefficient is quantized by the quantizer 4. The quantized coefficients are variable-length coded by the variable-length encoder 5 and output from the output terminal 15, pass through the inverse quantizer 6, the inverse discrete cosine transformer 7, and are added by the adder 8. The predicted value of the motion compensation predictor 11 or 12 selected by the switch 14 is added to become a reproduced value. The reproduction value is stored in the field memory 9 and used in the motion compensation prediction as data one field before in the motion compensation prediction unit 11.
At the same time, the data is further stored in the reproduction value field memory 10 one field before, and is used in the motion compensation prediction as data two fields before in the motion compensation prediction unit 12. The predicted value by the motion compensated predictor 11 and the predicted value by the motion compensated predictor 12 are input to the comparator 13. In the comparator 13,
The switch 14 is switched so that the smaller of the absolute value sums of the prediction errors is selected for each block that is a unit of motion compensation.

FIGS. 2 and 3 show a motion vector search method in the motion compensation predictor 11 and the motion compensation predictor 12, respectively.

The motion compensation predictor 11 uses the immediately preceding field for motion compensation prediction. The search range (one block) is ± 14.5 pel in the horizontal direction and ± 14.5 lines in the vertical direction as shown in FIG. is there. The motion vector search method in the motion compensation predictor 11 is as follows. First, it is assumed that the first step is performed for 35 points indicated by “●” around (0, 0), and as a result, (12, 8) is selected. Next, as the second step, it is assumed that (14, 10) has been selected with respect to (12, 8) and 24 points indicated by “○”. Finally, as a third step, the value between pixels is obtained by linear interpolation, and the calculation is performed for eight points indicated by “x” around (14, 10), and the coordinates of the finally selected point Becomes a motion vector. Therefore, the number of motion vector searches in the motion compensation predictor 11 is 35 + 24 + 8 = 67 (1) The type of motion vector is (14.5 × 2 × 2 + 1) × (10.5 × 2 × 2 + 1) = 2537 (2) It is.

On the other hand, the motion-compensated predictor 12 uses the previous two fields for motion-compensated prediction, and the search range is as shown in FIG.
Is ± 14.5 pel only in the horizontal direction as shown in FIG. The number of motion vector searches is: 7 + 4 + 2 = 13 (3) The type of motion vector is 14.5 × 2 × 2 + 1 = 59 (4) Therefore, the total number of vector searches is 8
0 and the type of motion vector is 2596.

The coding characteristics of the above-described motion compensation prediction method according to one embodiment of the present invention were obtained by computer simulation. The used images are two types of “image 1” and “image 2”. "Image 1" is a landscape in a forest (many tree branches)
This is a scene where the camera is tilted (moved in the vertical direction) with respect to. "Image 2" is a scene of playing table tennis,
Camera zoom out (SC1), camera still (SC1)
2), camera pan (horizontal movement) (SC3),
3 scenes. The coding rate is 9.6
Mbit / s.

For comparison, conventional (a),
The following experiments corresponding to (b) and (c) were also performed. (A ') Using only the previous field in time,
Prediction that performs motion compensation of ± 14.5 pel in the horizontal direction and ± 10.5 lines in the vertical direction (b ′) Using only the two fields before in time,
Prediction for performing motion compensation of ± 14.5 pel in the horizontal direction and ± 10.5 lines in the vertical direction (c ′) Combination of the above method (a ′) and the above method (b ′), both of which are ± 14.5 pel in the horizontal direction, Vertical direction ± 1
Prediction that performs motion compensation of 0.5 line and switches adaptively for each block

The types of motion vectors and the number of motion vector searches in each motion compensation prediction method are as shown in FIG. That is, the types of motion vectors and the number of searches in (a ′) and (b ′) are as shown in equations (1) and (2), respectively, and are twice as large in (c ′).

FIGS. 5A and 5B show experimental results of each motion compensation prediction method. FIG. 5A corresponds to "picture 1" and FIG. 5b corresponds to "picture 2". As is clear from FIG. 5, in SC1 of “image 1” and “image 2”, the SN ratio of (a ′) is improved by 0.5 to 1 dB as compared with (b ′), Conversely, in SC2 and SC3 of “image 2”, the SN ratio is reduced by 2 to 4 dB. On the other hand, in the method according to the present invention, the same performance as that of the superior characteristic in (a ′) and (b ′) is always obtained, and the same performance as that of (c ′) is always obtained. Have been.

[0020]

As described above, according to the present invention,
In motion-compensated prediction for interlaced image coding, the same prediction efficiency can be obtained with a calculation amount and a type of motion vector that are about half that of the conventional prediction method (c).

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing one embodiment of the present invention.

FIG. 2 is a diagram showing a motion vector search method in the motion compensation predictor 11 of FIG.

FIG. 3 is a diagram showing a motion vector search method in the motion compensation predictor 12 of FIG.

FIG. 4 is a diagram collectively showing types of motion vectors and the number of times of motion vector search in each motion compensation prediction performed by experiments according to the present invention and the conventional method.

FIG. 5 is a diagram showing experimental results.

[Explanation of symbols]

 Reference Signs List 1 input terminal 2 subtractor 3 discrete cosine transformer 4 quantizer 5 variable length encoder 6 inverse quantizer 7 inverse discrete cosine transformer 8 adder 9, 10 field memory 11, 12 motion compensation predictor 13 comparator 14 Switch 15 Output terminal

Claims (1)

(57) [Claims] When encoding an image signal in which one frame is composed of two fields by interlaced scanning, the image is divided into a plurality of blocks, and the amount of motion of the image is obtained for each block. A motion-compensated prediction method in which a value of past image data shifted by the same amount is used as a prediction value of current image data, and an (N-1) -th field is used to predict a pixel value of an N-th field. And (N-2) th field are used, and these are selectively switched based on the prediction error value for each block, and the (N-1) th field is used for prediction. Motion compensation is performed in both horizontal and vertical directions, and when the (N-2) th field is used for prediction, motion compensation is performed only in the horizontal direction. Method.