KR20040095399A - Weighting factor determining method and apparatus in explicit weighted prediction - Google Patents

Abstract

PURPOSE: A method for determining a weighting factor in a weighting prediction is provided to control a sample pixel value of a prediction block obtained by performing a motion compensation and a motion prediction, and to approximate to a sample value of an original block, thereby minimizing a residue error. CONSTITUTION: A device performs a motion compensation and a motion prediction for all blocks within a slice(S410). The device decides a reference picture with which a block of a picture to be encoded is predicted, and groups blocks having the same reference picture(S420). The device calculates the number of pixels by group(S430), and sets an offset(S440). Depending on a value for setting the offset, the device calculates a weighting factor(S450).

Description

Weighting factor determining method and apparatus in explicit weighted prediction

The present invention relates to encoding / decoding of video data, and more particularly, to a method and apparatus for determining a weighting factor of a prediction sample in video prediction.

With the advent of digital TV and DVD-Video, broadcast and home entertainment services have changed significantly. Various application services provided by such broadcasting services and home entertainment services are made possible by standardization of video compression technology. Among the standards for video compression technology, MPEG4-visual enabled Internet-based video application services, and ITU-T's H.263 standard is widely used in videoconferencing systems.

MPEG4-visual and H.263 are standards based on video compression. Moving Picture Experts Group (MPEG) and Video Coding Experts Group (VCEG) involved in these standards are higher-quality and lower-bitrate than MPEG4 and H.263. The next step was to establish a standard for the next level of technology that would allow more compression while supporting streaming video.

After the completion of the H.263 standard, ITU-T's Video Coding Experts Group (VCEG) worked on the H.263 version 2 standard, which added additional functionality to H.263, and a new standard for low-bit rate video communications. Started research on. The new standard for low bit rate video communication is named ITU-T H.26L. In addition, ISO's Video Experts Group (MPEG) recognizes the importance of this new standard and has formed a joint video team (JVT) with ITU-T's Video Coding Experts Group (VCEG) to build the H.26L model. The study began to set international standards. The standard thus defined is ISO MPEG4 Part 10, that is, ITU-T H.264. The official name of this standard is MPEG-4 Advanced Video Coding (AVC), but is better known as H.264.

1 is a block diagram of an H.264 encoder.

The H.264 encoder largely includes a prediction block 110, a transform and quantization block 120, and an entropy coding block 130.

The prediction unit 110 performs inter prediction and intra prediction. Interprediction refers to performing block prediction of a current picture by using a reference picture stored in a buffer by performing decoding and deblocking filtering. That is, prediction is performed by using information between pictures. To this end, a motion estimation block 111 and a motion compensation block 112 are provided. Intra prediction refers to performing prediction using pixel data of a block adjacent to a block to be predicted in a picture that has already been decoded.

The transform and quantization unit 120 transforms, predicts, and compresses the prediction samples obtained by performing the prediction in the prediction unit 110. The entropy coding unit 130 performs encoding on the quantized video data in a predetermined manner to form an H.264 bitstream.

2 is a block diagram of an H.264 decoder.

The H.264 decoder receives the bitstream encoded by the H.264 encoder, performs entropy decoding, inverse quantization and inverse transformation, and performs decoding using reference picture information on which motion compensation or intra prediction is performed.

The weighted sample prediction process described in the H.264 standard is used for the main profile and the extended profile of H.264, and is obtained by performing motion compensation and motion prediction. Sample values are adjusted using weighting factors. That is, the weighting factor is used to minimize the residual value obtained by subtracting the predicted pixel value from the original pixel value of the sample to be predicted.

The weighted sample prediction process described above includes a default mode, an explicit mode, and an implicit mode. In the explicit mode, the weighting factor used in the weighted sample prediction process is calculated and selected directly in the encoder, so that the selected weighting factor is specified and used in slice units.

3 is a flowchart of a weighting factor selection process in explicit mode.

A DC value (dc_org) of a picture to be encoded is calculated (S310). In operation S320, DC values (dc_ref [0], ... dc_ref [n]) of n reference pictures, which the picture uses as reference, are calculated. The reference picture is obtained after performing motion compensation and motion prediction. The DC value is the sum of the pixel values of the reference picture. Then, the weights W [0], ... W [n] and the offsets O [0], ... O [n] are calculated using the calculated DC values (S330). In other words, W [n] = dc_org [n] / dc_ref [n], O [n] = 0.

In other words, the total DC value of the current picture to be encoded is obtained, the total DC value of the reference picture is obtained, and the weight W is calculated using the ratio of two DC values. Each reference picture has a parameter consisting of a weight and an offset. The offset is set to 0 for all reference pictures and the weight is calculated.

The weighting factor of the reference picture in H.264 AVC video encoding is to increase encoding efficiency in interprediction. However, conventionally, only the ratio of the DC value between two calculated pictures is used as described with reference to FIG. 3. That is, since only the overall average value of the DC values is used, it is effective only when there is a simple DC difference between the reference picture and the current picture to be encoded. Otherwise, the compression efficiency may not be high or worse. There is this.

An object of the present invention is to provide a method and apparatus for determining a weighting factor for a reference picture in an explicit mode of H.264 AVC.

1 is a block diagram of an H.264 encoder.

2 is a block diagram of an H.264 decoder.

3 is a flowchart of a weighting factor selection process in explicit mode.

4 is a flowchart of the weighting factor determination method of the present invention.

5 is a block diagram of the weighting element determination device of the present invention.

In order to achieve the above object, in the weighting factor calculation method according to the present invention, in the weighting factor calculation method when performing block prediction using a weighting factor, (a) blocks in a picture to be predicted are the same. Grouping blocks having a reference picture together; And (b) calculating weights and offsets for minimizing an error between a pixel value of a block belonging to each group, multiplying a pixel value of a corresponding reference picture by a predetermined weight, and adding an offset to each grouped block. It includes a step.

In addition, the error is preferably a mean square error.

According to an aspect of the present invention, a weighting factor calculation apparatus includes: a block grouping performing unit for grouping blocks in a picture to be predicted with blocks having the same reference picture; And a weighting factor for calculating a weight and an offset for minimizing an error between a pixel value of a block belonging to each group and the pixel value of a corresponding reference picture by a predetermined weight and minimizing an offset for each of the grouped blocks. It includes a calculation unit.

In order to achieve the above object, the present invention provides a computer-readable recording medium recording a program for executing the method on a computer.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings.

4 is a flowchart of the weighting factor determination method of the present invention.

In the present embodiment, a case where one reference picture is used in the explicit mode, that is, (PredFlagL0 xor PredFlagL1) == 1 will be described. PredFlagL0 and PredFlagL1 are flags related to the use of the reference picture.

First, motion compensation and motion prediction are performed on all blocks (macro blocks or subblocks) in the slice (S410). By performing motion compensation and motion prediction, the reference picture can be known. Then, it is determined which reference picture the block in the picture to be encoded is predicted with, and blocks having the same reference picture are grouped together (S420). Next, the number N of pixels for each group is calculated (S430), and an offset is set (S440). According to which value the offset is set, the weighting factor is calculated using one of two methods described below (S450).

If the pixel of the original picture to be predicted is O _i and the pixel of the reference picture corresponding thereto is r _i , the mean square error is calculated by Equation 1 below.

Here, W means weight and O means offset. The first method of calculating the weight W and the offset O that minimizes the above-described equation 1 is to set the offset O to 0 and calculate the weight W.

In other words, when the offset is set to 0, Equation 1 is partially differentiated with respect to W as in Equation 2. Then, the weight W as in Equation 3 can be obtained.

In the second method, the offset is set as in Equation 4, and the partial derivative is made as in Equation 3 to obtain a weight as in Equation 5.

5 is a block diagram of the weighting element determination device of the present invention.

The weight factor determining apparatus includes a block grouping unit 510, an offset setting unit 520, and a weight calculator 530. The offset setting unit 520 and the weight calculator 530 are referred to as the weighting factor calculator 540.

The block grouping performing unit 510 groups the blocks in the picture to be predicted with blocks having the same reference picture. The weighting factor calculator 540 multiplies the pixel values of the blocks belonging to each group by the grouped blocks, and multiplies a pixel weight of the pixel corresponding to the reference picture by a predetermined weight and minimizes an error between the weights. Calculate and offset.

The offset setting unit 520 sets the offset to 0 or sets it as in Equation 4 described above. The weight calculation unit 530 substitutes the offset set by the offset setting unit 520 into the above-described Equation 1, and calculates the weight by an equation such as Equation 3 or Equation 5 below.

The invention can also be embodied as computer readable code on a computer readable recording medium. The computer-readable recording medium includes all kinds of recording devices in which data that can be read by a computer system is stored. Examples of computer-readable recording media include ROM, RAM, CD-ROM, magnetic tape, floppy disk, optical data storage, and the like, and may also be implemented in the form of a carrier wave (for example, transmission over the Internet). Include. The computer readable recording medium can also be distributed over network coupled computer systems so that the computer readable code is stored and executed in a distributed fashion.

So far I looked at the center of the preferred embodiment for the present invention. Those skilled in the art will appreciate that the present invention can be implemented in a modified form without departing from the essential features of the present invention. Therefore, the disclosed embodiments should be considered in descriptive sense only and not for purposes of limitation. The scope of the present invention is shown in the claims rather than the foregoing description, and all differences within the scope will be construed as being included in the present invention.

As described above, the present invention has the effect of increasing the encoding efficiency by minimizing the residual error in the explicit mode during the weighted sample prediction process described in the H.264 AVC standard. That is, by adjusting the sample pixel value of the prediction block obtained by performing the motion compensation and the motion prediction to approximate the sample value of the original block, there is an effect of minimizing the residual error to increase the encoding efficiency of the encoder.

Claims (11)

In the weighting factor calculation method when performing block prediction using a weighting factor, (a) grouping blocks within a picture to be predicted with blocks having the same reference picture; And (b) calculating weights and offsets for minimizing an error between a pixel value of a block belonging to each group and the pixel value of a corresponding reference picture by a predetermined weight and minimizing an offset for each grouped block; Weighting element calculation method comprising the step. The method of claim 1, The error is a weighted factor calculation method, characterized in that the mean square error. The method of claim 2, The mean square error is calculated by the following equation. Here, N is the total number of pixels of the blocks belonging to each group, o _i is the pixel value of the block belonging to each group of the picture to be encoded, r _i is the pixel value of the corresponding reference picture. The method of claim 3, And setting the offset to zero and calculating the weight. The method of claim 4, wherein The weighting factor W is calculated by the following equation. The method of claim 3, The offset O is calculated by the following equation. The method of claim 6, The weight W is calculated by the following equation. A block grouping performing unit for grouping blocks in a picture to be predicted with blocks having the same reference picture; And For each of the grouped blocks, a weighting factor calculation for calculating weights and offsets that minimizes an error between a pixel value of a block belonging to each group and a pixel value of a corresponding reference picture by multiplying a predetermined weight and adding an offset. Weighting element calculation device comprising a. The method of claim 8, wherein the weighting factor calculator An offset setting unit that sets an offset to a predetermined value; And And a weight calculation unit for calculating a weight based on the set offset value. The method of claim 9, wherein the offset is Set to 0, or calculated by the following equation. A computer-readable recording medium having recorded thereon a program for executing the method according to any one of claims 1 to 7.