KR20040035014A - Method for moving picture decoding - Google Patents

Abstract

PURPOSE: A moving picture decoding method is provided to decide information on scan direction in an encoder from information on decoded blocks, without deciding information on an added intra mode option by decoding, thereby preventing an error of a scan direction caused by a channel bit error. CONSTITUTION: A compressed moving picture bit stream is decoded to decide information on a picture header, a GOB(Group Of Blocks) header and a macroblock header of a video frame(S601). The macroblock header information of the decoded video frame and information on blocks configuring the macroblock are decided(S602). Intra mode option information inserted in the macroblock header information is decided, and a coefficient of previously decoded and stored blocks is decided to perform intra mode decoding for the decoded video frame according to the intra mode option information(S603). An encoding scan direction in an encoder is decoded according to the coefficient of the previously stored blocks to perform decoding in a decoder in the same scan direction as the encoder(S604). And if an error is generated in the previously decoded and stored blocks, decoding is performed through motion predictive compensation by using the intra mode information inserted in the header information of the decoded macroblock(S605).

Description

How to decode video {METHOD FOR MOVING PICTURE DECODING}

The present invention relates to a video decoding method. More specifically, when intra mode decoding a compressed video bitstream transmitted through a wireless network, an image quality is improved by preventing an error in a scanning direction due to an error of decoded intra mode information. It relates to a video decoding method that can be.

The current and future communication environments are rapidly changing beyond the distinction between wired and wireless areas and regional countries. In particular, future communication environments, such as IMT-2000, require users as well as video and audio. The trend is to build an environment that provides various information in real time or comprehensively.

In addition, the development of the personal mobile communication system is not only a voice communication in the cellular phone or PCS, but also to transmit text information as well as to access the Internet wirelessly using a personal mobile communication terminal, or to watch videos on TV It is being developed to transmit the data.

In particular, a digital television system that processes a video into digital data, transmits the data in real time, receives the video, and displays the video, and the video transmitted in real time is becoming an essential element in a personal portable terminal using the IMT2000.

In the related art, the portable terminal transmits and receives only human voice. However, due to the development of multimedia and the development of digital information processing technology, various information such as voice and video can be transmitted.

Above all, this technology has been commercialized. First of all, the analog video signal is subjected to special digital processing such as quantization and variable length encoding, and then included in the digital information and transmitted. The development of video compression technology, which allows abundant information transmission and reception, contributed greatly.

Recently, with the development of digital signal processing technology, methods of compressing and transmitting a large amount of video information through a limited bandwidth transmission channel have been developed. However, if an error occurs on the transmission channel, the quality of the reconstructed image is greatly reduced. Occurs.

At this time, error concealment techniques have been studied to recover near to the original image by supplementing the lost information from the neighboring information that is normally restored without using an error correction code to maximize the limited bandwidth.

In particular, in the case of an MPEG (Moving Picture Experts Group), if an error occurs, all information until the next sync signal is found is lost. In addition, since the motion compensation encoding technique is used, the influence of the damaged portion is continued over the subsequent frames.

The present invention is an IMT-2000 video terminal that applies an optimized motion decision value and an intra mode compression algorithm to a hardware accelerator structure that enables fast encoding and quality improvement of video data. Motion decision value of MPEG compression method, which is generally used for wireless image communication, is the most important because it has the largest amount of computation and directly affects the quality and the amount of bits.

Therefore, many studies on motion judgments have been made continuously, and recently, the motion judgments have the same image quality and bit rate as the full search using the diamond search pattern, and are most commonly used. A three step search method is used.

FIG. 1 is a diagram for describing a state of intra encoding a video bitstream according to the related art.

When a video signal is applied, the encoder encodes the video signal by discrete cosine transform, quantization, or the like. The current coding is performed by comparing a DC voltage and an AC voltage to the pixels of the blocks constituting the image frame. The prediction value of the pixels of the block is determined.

Usually, the DC voltage value represents a screen component having the same value in the entire region of the video image, and quantization is performed for the entire common portion of the image block, and the AC voltage value is zigzag scan along the pixels constituting the block. The quantization is performed by a scan, an alternate horizontal scan, and an alternate vertical scan.

In this way, the image blocks are encoded by horizontally scanning macro blocks horizontally in a GOB unit in the horizontal direction in the H.263 + standard. Therefore, the decoder decodes the video bitstream encoded in this manner in the same direction as the scan direction of the macroblocks encoded by the encoder.

However, in the enhanced intra mode of the H.263 + standard, the above-described various scan schemes are encoded by applying various scan schemes inconsistently according to each option.

Therefore, when the video frame to be decoded is an intra mode, as shown in the drawing, the DC and AC values are obtained in advance by using the picture header information of the decoded video frame and the header information of the macro block. Then, decoding is performed by obtaining prediction values of adjacent blocks.

As shown in the figure, in general, the values of the upper block and the next side block of the block constituting the macro block of the image frame are predicted and decoded, and scanned in the horizontal direction.

However, the scan direction in which the pixels of the currently decoded block in the macro block are decoded based on the predicted block is based on the intra mode information inserted into the macro block header information. Scan and decode.

When the decoded video frame is in the inter mode, motion compensation is performed. The motion compensation is performed by using the motion vector value of the previous video frame and the difference vector transmitted from the encoder.

The decoding of the intra mode image frame by the decoder may include pixels arranged in the vertical direction of the X block among blocks included in the macro blocks existing in the GOB unit at the same position of the block A included in the adjacent macro block. The motion compensation is performed by obtaining a reference motion vector from the existing pixels. The compensating scan order of the respective pixels constituting the block is obtained from the intra mode information included in the macro block information, as described above.

Similarly, pixels arranged in the horizontal direction of the X block are compensated for motion by obtaining a reference motion vector from pixels located in the horizontal direction of the C block present in the macro block.

Accordingly, the motion compensation of the 8 * 8 blocks X, Y, C, and D in the macro block is obtained by obtaining a motion vector from pixels of blocks present at the same position as blocks adjacent to the left and upper sides. The scan order of decoding the respective pixels of the block to compensate for the motion prediction while performing the scan is performed according to the intra information included in the macro block.

2 is a diagram illustrating header information of a macroblock generally included in an image frame.

As shown in FIG. 2, when the encoder encodes a video signal, information (COD: Coded Macroblock Indication) for distinguishing between an intra mode and an inter mode, information on a macroblock type, and each color difference signal Macroblock type & coded block pattern for chrominance (MCBPC) representing coded block pattern information, and intra mode information including intra mode option information enhanced in the H.263 + standard and coding scan direction information of pixels constituting the block (Intra_Mode) ), A macroblock mode for B-blocks (MODB) indicating a macroblock mode for a B picture frame, a coded block pattern for B-blocks (CBPB) indicating a coding block pattern for a block of a B picture frame, and a luminance signal Coded block pattern for luminance (CBPY) for coding block pattern, DQUANT (Differential values for Quantizer I) for difference information of quantized values nformation).

The decoder detects the presence or absence of option information added from the header information of the decoded macroblock, and if there is option information, performs decoding according to the information inserted in the option information. Otherwise, it uses the MCBPC information to determine the macro information and The encoding information is determined and decoding is performed.

3 is a diagram illustrating a prediction mode value included in intra mode information of FIG. 2.

As shown in FIG. 3, macroblock type & coded block pattern for chrominance (MCBPC) included in header information of a macroblock includes macroblock type information of a decoded image frame, color difference information signals of respective blocks, and encoded information. Have In general, the decoder decodes the macroblocks by determining the MCBPC information inserted when the encoder encodes the information. When the enhanced intra mode option is added in the H.263 + standard, the encoder encodes the information processed by the special option. Insert in addition to macro header information.

When encoding an intra mode image frame, if encoding is performed according to a method of predicting an intra image such that coding efficiency, calculation amount, complexity, and system situation are matched, the macroblock header information of the encoded image frame is added to each prediction mode. Insert intra information.

In other words, when the DC value of the block is only 0, the entropy-encoded value is 0, and when the direct-current and AC pixel values in the vertical direction are 1, the entropy encoding is 10, and the direct-current and AC pixel values in the horizontal direction are set. In the case of 2, entropy coding was set to 11.

4A to 4C are diagrams illustrating a scan method according to a prediction mode information value of the prior art.

As shown in FIG. 4A, the encoder scans the pixels included in the block according to the prediction mode value in FIG. 3. When the prediction mode value is 0 and the VLC value is 0, the encoding is zigzag-scanned. If the prediction mode value is 0 in the intra mode information from the macroblock header information when decoding at the decoder, the decoding is determined as being encoded according to the zigzag method.

Similarly, when the prediction mode value is 1, the encoder encodes the image block according to an optional horizontal scan method as shown in FIG. 4B, and inserts the macroblock header information into the decoder to encode the information. send. The decoder determines the prediction mode information by determining interla information of the decoded macroblock, and performs intra decoding according to an optional horizontal scan method.

As shown in FIG. 4C, when the prediction mode value is 2, since the pixels of the blocks are encoded by the encoder according to the selective vertical scan method, the decoder may decode the information included in the intra mode information of the macroblock header information. Check and decode the blocks according to the selective vertical scan method.

However, as described above, when the encoder encodes a video signal in the video bit stream and the decoder reads from the header information of the macro block at the time of decoding, the decoder applies to the video bit stream transmitted through the wireless network. If an error occurs, there is a problem that can not determine whether the error.

As a result, the scanning method decoded and the encoder coded by the encoder are different from each other, thereby degrading image prediction efficiency and degrading image quality.

The present invention relates to an error detection for a scanning scheme included in macro block header information for improved intra coding due to channel error when an image bitstream is transmitted through an IMT-2000 wireless network. It is an object of the present invention to provide a video decoding method capable of preventing a deterioration in image quality due to a scan direction error by applying a decoding scheme applied by an encoder to a decoder without using intra mode information among header information.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram for explaining a state of intra encoding a video bitstream according to the related art.

2 is a diagram illustrating header information of a macroblock generally included in an image frame.

FIG. 3 illustrates a prediction mode value included in intra mode information of FIG. 2. FIG.

4A to 4C are diagrams illustrating scan methods according to prediction mode information values of the prior art.

5 is a diagram for explaining a mode of intra coding a video bitstream according to the present invention;

6 is a diagram for explaining a method of decoding macroblock information in which an error occurs in accordance with the present invention;

* Description of the symbols for the main parts of the drawings *

COD: Coded Macroblock Indication

MCBPC: Macroblock type & Coded block pattern for chrominance

MODB: Macroblock mode for B-blocks

CBPB: Coded Block pattern for B-blocks

CBPY: Coded block pattern for luminance

DQUANT: Differential values for Quantizer Information

In order to achieve the above object, a video decoding method according to the present invention,

Decoding the compressed video bitstream to determine picture header information, GOB header information, and macroblock header information of an image frame;

Determining macro block header information of the decoded video frame and information of blocks constituting the macro block;

Determining intra mode option information inserted in the macro block header information;

Determining coefficient values of previously decoded and stored blocks for intra mode decoding according to the intra mode option information according to the intra mode option information; And

Determining the encoding scan direction performed by the encoder according to the coefficient values of the stored previous blocks, and accordingly decoding in the same scan direction as the encoder by the decoder.

Herein, the encoder selects and encodes one of a zigzag scan method, an optional horizontal scan method, and an optional vertical scan method according to the intra mode option information, and inserts the intra frame inserted into the macro block header information. Previously stored blocks referred to for intra mode decoding according to the mode option information are characterized in that the previous next block and the previous upper block of the current decoding block.

If an error occurs in previously decoded and stored blocks referred to to determine the encoding scan direction of the encoder, motion prediction compensation is performed using intra mode information inserted in header information of the decoded macroblock. It is characterized in that the decoding.

According to the present invention, an error occurs due to a channel bit error when scan direction information encoded according to an enhanced intra coding scheme, which is an optional information added to the H.263 + standard that compresses and reproduces a video, is transmitted through a wireless network. In order to prevent this, the decoder scans the encoder as it is, so that the image quality deterioration due to the scan direction error can be prevented.

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

5 is a diagram for explaining a mode of intra coding a video bitstream according to the present invention.

An encoder using the H.263 + standard for encoding video signals adds an enhanced intra-mode encoding option to achieve better image quality. When the DCT conversion of the video signal at the encoder, the encoding scan method is expressed differently according to the improved prediction mode. In the intra mode encoding process, the scan method is classified and encoded, and then inserted into the macro block header information and transmitted to the decoder in the form of an image bitstream.

When decoding the video bitstream, the decoder first determines the video frame header information, the header information of the macro block, and the like, and performs appropriate decoding according to the respective information.

However, since decoding is performed after decoding from an image bitstream transmitted to the decoder, there is a problem that information decoded by the decoder and information encoded by the encoder are not the same due to channel bit errors during transmission.

In particular, the H.263 + standard allows 17 options to be added to improve picture quality. Among them, in the enhanced intra mode coding method, encoding is performed by appropriately selecting a scanning method of blocks encoded by an encoder. Information about a scan method is inserted into macroblock header information included in an image bitstream and transmitted.

Therefore, in the present invention, instead of simply scanning the intrablock option information inserted in the decoded macroblock header information in the decoder, the previous block B referred to by the block in the intramode decoding process as shown in FIG. ) And the coefficient of the immediately next block A in the reverse direction of decoding.

The direction of decoding the macroblocks (X, Y, C, D) in the GOB unit is the same, but the scan direction in which the pixels in the block are encoded does not use the intra mode information in the decoded macroblock header information, and is an actual encoder. The decoding is performed according to the encoding scan scheme performed by the NOR.

Accordingly, in the decoder, when decoding, the encoding scan scheme is performed by the encoder regardless of the decoded intra information without decoding the image bitstream and using the intra information in the header information of the macro block by decoding the image bitstream. Is applied as it is during decoding.

In this case, since an error in the scan direction does not occur, there is an effect of improving the screen quality displayed during decoding.

6 is a diagram for describing a method of decoding macroblock information in which an error occurs according to the present invention.

As illustrated in FIG. 6, when a decoder receives a video signal encoded by an encoder, the decoder decodes a compressed video bitstream. (S601) When a video frame is decoded from the decoded video bitstream, the video is decoded. In the frame, picture header information and GOB header information are decoded in the case of the h.263 + standard, and then macroblock header information is decoded (S602).

The video frame is encoded and decoded into a series of streams. Before decoding the blocks of the decoded video frame by the decoder, such header information is analyzed to determine the picture header type, macro block type, Determine additional option information.

When the encoder encodes the blocks of the image frame by determining the macro block header information included in the image frame, the encoder adds an option to variously change the encoding scan direction to improve the intra mode. It is determined from the intra mode information included in the macro block header information.

Header information of the macroblock includes coded macroblock indication (COD), macroblock type & coded block pattern for chrominance (MCBPC), option information Intra_Mode information for improving intra mode, macroblock mode for B-blocks (MODB), Coded Block Pattern for B-blocks (CBPB), Coded Block Pattern for Luminance (CBPY), Differential Values for Quantizer Information (DQUANT), Motion Vector Data (MVD), and Motion Vector Data (MVD _2-4 ) And MVDB (Motion vector data for B-macroblock), followed by data information on blocks constituting the macroblock.

The intra mode option information (Intra Mode) is decoded and the decoder is not decoded, and decoding is performed using neighboring blocks that are previously decoded and stored.

The scan direction for encoding in the encoder is determined by using coefficient values of the previous next block of the current decoding block and the upper neighboring block of the current decoding block (S603).

When an error occurs in the intra mode information included in the macroblock header information to be decoded, the determination is difficult. Therefore, the decoder determines the scan direction to be encoded by the encoder from the neighboring blocks of the current block to be decoded. Regardless of the intra mode option information, the encoding scan direction performed by the encoder is used as it is (S604).

However, when decoding the current decoding block along the encoding direction in the same direction as the encoder, the stored coefficient values of the previous blocks are used as described above, but an error occurs in the previous blocks used. Intra-mode option information included in the macro header information of the decoded video frame is used without correction in the scan direction encoded by the encoder using the error block.

Therefore, in the present invention, when decoding an image bitstream encoded by an encoder, intra mode option information is added to obtain high quality image quality in the h.263 + standard. The scan direction is included in each mode information and transmitted.

Since the option information included as described above is transmitted through the wireless network, a channel error occurs. When such an error occurs, the decoder cannot accurately determine whether an error exists.

However, the present invention does not use the decoded intra mode option information, but rather encodes the encoding scan direction information performed by the encoder from the previous block and encodes the encoder from the previous block despite the intra mode option information decoded in the macro block header information. The decoding is performed using the scan direction information.

As described in detail above, the present invention does not determine additional intra mode option information for realizing improved image quality among image bitstream information transmitted through the IMT-2000 wireless network, but decoded block information. Since the scan direction information is determined by the encoder from the scan direction error, the scan direction error due to the channel bit error can be prevented.

As a result, the decoding efficiency can be improved and the image quality deterioration caused by the scan error can be prevented.

The present invention is not limited to the above-described embodiments, and various changes can be made by those skilled in the art without departing from the gist of the present invention as claimed in the following claims.

Claims (4)

Decoding the compressed video bitstream to determine picture header information, GOB header information, and macroblock header information of an image frame; Determining macro block header information of the decoded video frame and information of blocks constituting the macro block; Determining intra mode option information inserted in the macro block header information; Determining coefficient values of previously decoded and stored blocks for intra mode decoding according to the intra mode option information according to the intra mode option information; And And determining the encoding scan direction performed by the encoder according to the coefficient values of the stored previous blocks, and decoding the same in the same scan direction as the encoder by the decoder. The method of claim 1, And encoding the blocks of the image frame by selecting one of a zigzag scan method, an optional horizontal scan method, and an optional vertical scan method according to the intra mode option information. The method of claim 1, And the previously stored blocks referred to for intra mode decoding according to the intra mode option information inserted in the macro block header information are the previous next block and the previous upper block of the current decoding block. The method of claim 1, When an error occurs in previously decoded and stored blocks referred to to determine the encoding scan direction of the encoder, decoding through motion prediction compensation is performed using intra mode information inserted in header information of the decoded macroblock. Video decoding method characterized in that.