KR100557047B1 - Method for moving picture decoding - Google Patents

Abstract

The present invention discloses a video decoding method capable of preventing image quality deterioration by improving size information error of a video format generated when transmitting and receiving compressed video information using a communication device using a wireless network. According to an exemplary embodiment of the present invention, there is provided a method of receiving an image data signal, decoding the received image data and determining the size of the decoded image data, and comparing the determined image data with QCIF to determine whether the image data is smaller than the QCIF. Determining whether GOB header information exists in an image frame if the decoded image size information is smaller than the QCIF; and if GOB header information exists in the image frame, whether the GFID information in the GOB has the same value Determining whether the GFID information of the decoded image frame is the same as the GFID information value and the GFID information in the GOB of the previously decoded image frame; And if the GFID information of the previously decoded image frame and the GFID information in the GOB of the currently decoded image frame are the same, decoding using the image size information of the previous image format.

Video, CIF, GOB, Error, GFID, Video Format

Description

How to decode video {METHOD FOR MOVING PICTURE DECODING}

1 is a block diagram showing the structure of a video decoder according to the prior art.

2 is a diagram illustrating commonly used image format standard values.

3 is a view for explaining a problem when an image format error appears in the decoding process according to the prior art.

4 is a diagram illustrating header information of a picture frame generally coming in a bitstream state.

5 illustrates GOB header information of a picture frame used in the present invention.

6 is a flowchart illustrating a method of correcting an image format error in a video decoding process according to the present invention.

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

1: buffer section 3: VLD

5: error detection / recovery unit 7: inverse quantization unit

9: reverse DCT 10: display unit

12: motion compensator (MC) 15: image frame memory

The present invention relates to a video decoding method, and more particularly, to improve video quality by correcting an image format size information error generated when video data is transmitted and received through multiple paths in a system for transmitting and receiving video data wirelessly, such as IMT-2000. And it relates to a video decoding method that can be efficiently decoded.

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, but 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 makes it possible to send and receive rich amounts of information, greatly contributed.

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), when 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.

When the encoded video bitstream is decoded by the decoder, it is necessary to correctly decode according to the information inserted at the time of encoding so as to realize high quality image quality.

1 is a block diagram showing the structure of a video decoder according to the prior art.

As shown in FIG. 1, when the encoded image data enters the decoder unit in the form of a bit stream, decoding is performed in a processing step opposite to encoding performed by an encoder in order to restore the original image.

Therefore, the decoder for decoding the compressed video bitstream includes a buffer unit 1 that temporarily stores the data amount of the received image bit stream and a bit stream stored in the buffer unit 1 to reproduce the image. Variable Length Decoding (VLD 3) for decoding and an error detection / reconstruction unit for error detection, motion vector restoration and image reproduction in the image bitstream decoded from the variable length decoder (3) ( 5) and an inverse quantization unit for performing inverse quantization and inverse discrete cosine transform in the opposite direction of the compression method implemented by the encoder for reproducing the image in the error detection / recovery unit (7). ) And an Inverse Discrete Cosine Transform (9), a Motion Compensation (MC 12) for compensating for the motion vector reconstructed by the error detection / recovery unit (5), and The image consists of a frame memory 15 for storing the previous image from the display section 10 to display.

The process of reproducing the compressed video by the decoder having the above structure is as follows.

The analog video signal is encoded by Discrete Cosine Transform and Quantization in an encoder, and then variable length encoding is performed to differentiate the bit length according to the frequency of information. It is transmitted to the outside in the compressed video bit stream state.

The video information compressed by the encoder is received by the other terminal, transmitted to the internal codec, and then decoded by the decoder. The decoder stores the image information transmitted first in the buffer unit 1 to temporarily store the image information. The compressed video bitstream stored in the buffer unit 1 converts the value, length, etc., of the compressed bitstream by the variable length decoder 3 into two-dimensional encoding, and then detects the error / The restoration unit 5 detects a motion vector value and whether an error occurs.

Then, the compressed image applied from the error detection / recovery unit 5 is reconstructed in the opposite direction as when the encoder is compressed by the encoder. The inverse quantization unit 7 performs inverse scan and inverse quantization, and then performs inverse discrete cosine transformer (IDCT) 9 (103) for IDCT conversion.

The video signal, which has been subjected to the Inverse Discrete Cosine Transform, is input to the adder 11, in which the reconstructed video frame is an intra mode image that is first started or a previous video frame. After determining whether or not the existing Inter Mode image is present, in the case of the intra mode image, since the previous image does not exist, prediction is performed in an internal frame of the image, and then the display unit 10 reproduces the image.

In case of determining the inter mode, a previously decoded image exists, and thus, a motion vector is determined by determining a degree of motion from the decoded image. After the motion vector is extracted, a difference value is obtained by a motion compensator 12 to compensate for the movement of the currently decoded image, thereby compensating the currently decoded image.

The motion compensator 12 obtains and decodes a difference of motion vectors extracted from the error detection / recovery unit 5 from the image frame memory 15 storing a previous image frame reproduced by the display unit 10. Compensate the video.

Therefore, the motion compensator 12 transmits the difference obtained by subtracting the current motion vector value from the previous video frame to the adder 11, and when the compressed bitstream is an inter mode in which the previous video frame exists, The image is reproduced by adding the inverse DCT values.

The reconstructed image frame is divided into macroblock units, and the data of each macroblock includes a motion vector as it is decoded, and these motion vectors indicate a predetermined direction. Video compression technology reduces the compression rate by taking a macro block of a previous video frame and restoring the current video frame by using the motion vector.

2 is a diagram illustrating a commonly used image format standard value.

As shown in FIG. 2, in general, image size information of a video signal format using a wireless communication terminal is reproduced by formatting the CIF and the size of QCIF reduced to 1/4. When the video is formatted, the size of the video is encoded while the encoder is encoding, and when the decoder is decoded, the size of the video is conveyed together with information indicating that the size of the video is restored to a certain range, and the decoder restores the video information encoded by the encoder. Display in size.

Accordingly, an encoder or a decoder formats an image within an allowable image size, and when encoding, the image size information is processed as a bit signal and transmitted together with the image bitstream.

In particular, IMT 2000 also uses an auxiliary QCIF, which is a smaller image size than QCIF. Accordingly, the auxiliary QCIF and QCIF are provided by a communication terminal that transmits and receives the video. The image size is represented by the number of luminance pixels along the x-axis and the luminance lines along the y-axis, and two color difference blocks are provided in the vertical direction of the macro block. The color difference block also has luminance pixels in the x-axis and luminance in the y-axis. Expresses size in number of lines.

Sub QCIF is 128 * 96 color difference block 64 * 48 size, QCIF is 176 * 144 color difference block 88 * 72, CIF is 352 * 288 color difference block 176 * 144, 4CIF is 704 * 576 color difference block 352 * 288, The 16CIF has a size of 1408 * 1152 chrominance blocks 704 * 576.

Such information is generally included in picture header information, and when decoding, such image size information is recognized and decoded.

However, the decoding method according to the related art decodes and displays the video bitstream compressed by the decoder according to the image format information inserted in the encoder. When an error occurs in the process of transmitting and receiving the image format information, the image quality is deteriorated. Cause.

For example, as follows.

3 is a diagram illustrating a problem when an image format error appears in a decoding process according to the prior art.

As shown in FIG. 3, in a communication device such as IMT2000, a size of an image frame decoded by a decoder according to various sizes of an image frame encoded by an encoder is generally decoded to a size of an auxiliary QCIF and a QCIF.

Therefore, when the digital information about the image format size information indicates that "001" represents auxiliary QCIF, "010" represents QCIF, "011" represents CIF, "100" represents 4CIF, and "101" represents 16CIF. If the information of the stream is transmitted and added to display in the decoder at QCIF of "010", but the channel error is changed to "011", "100", "101" etc. which are not provided by the decoder, memory allocation and decoding processing is performed. Many problems occur on the back.

In addition, the image memory access and processing in the decoder is impossible to be displayed after decoding or displayed in other image formats, resulting in deterioration of image quality.

The present invention can be decoded while correcting the error of the image size information caused by a channel error when transmitting and receiving video information using a wireless network in the decoder to perform an efficient decoding operation, while preventing video quality degradation The purpose is to provide a method.

In order to achieve the above object, a video decoding method according to the present invention,
Receiving an image data signal;
Decoding the received image data and determining the size of the decoded image data;
Determining whether the image data having the size is smaller than the QCIF by comparing QCIF;
Determining whether GOB header information exists in an image frame when the decoded image size information is smaller than the QCIF;
Determining whether GFID information in the GOB has the same value when there is GOB header information in the video frame;
If the GFID information of the decoded video frame is the same, determining whether the GFID information value is equal to the GFID information in the GOB of the previously decoded video frame; And
And if the GFID information of the previously decoded image frame and the GFID information in the GOB of the currently decoded image frame are the same, decoding using image size information of the previous image format.

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Here, when the image size information is larger than QCIF compared with the image size information and QCIF information of the currently decoded image format, the image size information of the currently decoded image format is limited to QCIF and decoded, and the currently decoded image When there is no GOB header information in the format image frame, it is determined whether the image size information of the previous image format and the image size information of the currently decoded image format are the same.

If the image size information of the previous image format and the image size information of the currently decoded image format are the same, the image size information of the currently decoded image format is decoded as it is, and the image size information and the current decoding of the previous image format are decoded. If the video size information of the video format is different, the video size information may be obtained from the PSC information of the video data to be decoded and then decoded.

In addition, when the GFID information belonging to the GOB header information of the currently decoded video frame has different values, the GFID information is corrected to have the same value, and the criterion for correcting the same value among the GFIDs in the GOB is the same value among the GFID information. It is determined that most of these errors are correct and the value is corrected to a GFID value. If the GFID information in the GOB header information of the currently decoded video frame is the same as the GFID information in the GOB header information of the previous video frame, If the GFID information in the GOB header information of the decoded video frame is different from the GFID information in the GOB header information of the previous video frame, the picture header information and the GOB information of the decoded video frame are different. And correcting using the macro block information.

According to the present invention, there is an advantage of preventing image quality degradation by efficiently correcting and decoding an image size information error of an image format generated by multiple paths when transmitting and receiving video information wirelessly, as in IMT2000.

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

4 is a diagram illustrating header information of a picture frame generally coming in a bitstream state.

As shown in FIG. 4, the video coded by the encoder has picture header information, GOB information, macro block information, and the like as follows.

PSC {Picture Start Code (22 bits)} as a code indicating the beginning of a compressed bitstream video, TR {Temporal Reference (8 bits)} indicating a time-series reference number of each video frame, and a decoded video. PTYPE {Picture Type Information (Variable Length)} indicating information that can identify a picture type of a frame, PQUANT {Quantizer Information (5 bits)} indicating information of a picture frame quantized by an encoder, and the current multi-point being continued. Continuous Presence Multipoint and Video Multiplex (1 bit)} for video multiplex, Picture Sub-Bitstream Indicator (2 bits)}, and TRB for time reference for B picture in P picture and B picture frames {Temporal Reference for B-pictures in PB-frames (3/5 bits)}, and DBQUANT {Quantization information for B-pictures in P-picture and B-picture frame] PB frames (2 bits)}, PEI {Extra Insertion Information (1 bit)} which specifies whether there is user data thereafter as a picture layer, and PSUPP {Supplemental Enhancement Information (0/8/16. bits)}, GOB (Group Of Black) and ESTUF {Stuffing (Variable length)}, EOS {End Of Sequence (22 bits)}, PSTUF {Stuffing (Variable length) )}.

Based on the picture header information of the compressed video, decoding is performed in the decoder system of FIG. 2 to reproduce the compressed video in the encoder.

5 is a diagram illustrating GOB header information of a picture frame used in the present invention.

As shown in FIG. 5, a video bitstream compressed by an encoder has a plurality of video frames continuing in a time-series direction, and in a predetermined format and condition in a compressed direction when the video header information is decoded by inserting picture header information for each video unit. To be displayed.

In general, when an image comes in a bitstream form, one unit video includes a plurality of image frames, and picture header information, as described with reference to FIG. 3, is inserted into each image frame.

Here, the image frame is divided into a plurality of GOBs in the vertical direction, respectively. GOB information of the image frame is composed as follows.

A plurality of macro blocks in the direction are constituted by another small unit of information unit of picture header information of an image frame. GSTUF {Group Stuffing (Variable length)}, GBSC {Group of Block Start Code (17 bits)}, GN {Group Number (5 bits)}, GSBI {GOB Sub-Bit stream Indicator (2 bits)} , GFID {GOB Frame ID (2 bits)}, GQUANT (Group of Quantizer Information (5 bits)) and a macro block. Although not clearly shown in the figure, the macro block is divided into four blocks again and has two color difference values in the longitudinal direction.

 In the present invention, a picture type is determined using picture header information in a decoding operation, and the GOB information of each image frame is referred to to determine whether the picture type is information changed by an error.

In other words, instead of using only data corresponding to one by using error correction, image quality is improved by more accurately identifying and correcting an error generated by using data corresponding to two data.

Therefore, among the picture header information included in the video compression bitstream, the GFID exists in the GOB. The GFID represents a frame ID in the GOB, and has a fixed length of 2 bits. The GFID in the GOBs in one image frame All the same.

Therefore, if the picture type {PTYPE: Picture Type Information (Variable Length)} of the previous video frame is the same as the current video frame to be decoded, the picture type of the picture header should be the same, and the GFID value in each GOB should be the same. If the picture type is the same but the GFID value in each GOB is different, a channel error occurs and the picture type is changed and it is determined based on the GFID and corrected.

If there is no GOB header information, since there is no data for comparing and determining picture errors, it is determined whether intra mode or inter mode is used to decode a macroblock that follows.

6 is a flowchart illustrating a method of correcting an image format error in a video decoding process according to the present invention.

As shown in FIG. 6, the picture header information and the GOB header information of FIG. 4 and FIG. 5 are compared and judged to determine whether or not an image format information is an error. I could do it.

When the compressed image data through the wireless network communication channel is received in the form of a bitstream, the buffer unit of the decoder temporarily stores before decoding and decodes variable length encoding.

Here, the present invention is a decoding method for correcting an error that occurs when decoding the size information of the image format of the image frame.

The video size of the video format is decoded from the video bitstream (S601) and compared with the QCIF, which is the video format size used in the IMT2000 communication network (S602).

If the image size of the decoded image frame is not larger than QCIF, it determines that the image format information has an error when received by the decoder and proceeds to correct it (S603).

First, it is determined whether GOB header information is present in the decoded video frame (S603). If header information exists, it is determined whether GFID information in each GOB has the same value (S604, S605). In this case, when the GFID values are not equal, the correction is made to be the same. Generally, the correction is made according to a large number of GFID values (S613).

Then, after all of the GFID information in the GOB is the same or corrected, the GFID values in the previous image frame GOB are compared with the GFID value in the GOB of the image frame currently being decoded from the memory of the previous image frame (S607). ). If the GFID value of the previous video frame and the GFID of the currently decoded video frame are the same, the image size information of the previous video frame is corrected to the image size of the current video frame (S608).

However, if the GFID of the previous video frame and the GFID value of the currently decoded video frame are not the same, the previous video format cannot be used and the picture format of the current video frame cannot be clearly determined that an error has occurred. The picture header information of the previous video frame is compared and corrected (S614).

If the size of the video frame is larger than the video size information QCIF of the current video frame to be decoded, the video format of the video frame to be decoded is limited to QCIF (S609).

In addition, if the video format of the decoded current video frame is not larger than QCIF, it is determined whether there is GOB header information. If there is no GOB header information, the video size information of the previous video format is determined by determining the video size information of the previous video frame. The comparison is the same (S610).

Here, when the image size information of the previous video frame and the image size information of the current decoded video frame are the same, it is determined that no error occurs in the image size of the current decoded video frame and the decoded current video format is used. S611).

However, when the image size information of the previous image format and the current decoded image format is different, the image size information is obtained from the image size information of the current image format and the PSC information of the following picture header information. The image size information having a low error occurrence rate is selected and used by comparing the information with the size information of the currently decoded image frame (S613).

As described in detail above, the present invention has the advantage that the decoding can be performed while correcting the image size information error during decoding due to the channel error of the video bitstream in the IMT-2000 wireless network.

In addition, there is an effect that can improve the image quality does not occur during the decoding operation.

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 (9)

Receiving an image data signal; Decoding the received image data and determining the size of the decoded image data; Determining whether the image data having the size is smaller than the QCIF by comparing QCIF; Determining whether GOB header information exists in an image frame when the decoded image size information is smaller than the QCIF; Determining whether GFID information in the GOB has the same value when there is GOB header information in the video frame; If the GFID information of the decoded video frame is the same, determining whether the GFID information value is equal to the GFID information in the GOB of the previously decoded video frame; And And if the GFID information of the previously decoded video frame and the GFID information in the GOB of the currently decoded video frame are the same, decoding using the image size information of the previous video format. The method of claim 1, And comparing the image size information of the decoded image format and the QCIF information if the image size information is larger than QCIF, and decoding the image size information of the decoded image format to QCIF. The method of claim 1, And if there is no GOB header information in the video frame of the decoded video format, determining whether the video size information of a previous video format and the video size information of the decoded video format are the same. The method of claim 3, wherein And when the image size information of the previous image format is the same as the image size information of the currently decoded image format, decoding using the image size information of the currently decoded image format as it is. The method of claim 3, wherein And when the image size information of the previous image format and the image size information of the currently decoded image format are different, obtain image size information from PSC information of the image data to be decoded next, and decode the image size information. The method of claim 1, And if GFID information belonging to the GOB header information of the currently decoded video frame has different values, correcting them to have the same value. The method of claim 6, The criterion of correcting the same value among the GFIDs in the GOB is that the most identical value among the GFID information determines that there is no error and corrects the value to the GFID value. The method of claim 1, And if the GFID information in the GOB header information of the currently decoded video frame and the GFID information in the GOB header information of the previous video frame are the same, the video format of the previous video frame is used as it is. delete

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