KR0178243B1 - Error detection method of h. 263 image bit stream - Google Patents

Abstract

The present invention provides a reconstructed method for effectively detecting an error in a reconstructed H.263 image bit stream by using a level (LEVEL) value of transform coefficient (TCOEF) information included in block data on the reconstructed image bit stream. TECHNICAL FIELD The present invention relates to an error detection method in a video bit stream. To this end, the present invention relates to detecting an LEVEL value in TCOEF information included in a block in a video bit stream reconstructed into an original signal before being coded through a decoding means, and assigning the same. If the bit string for the LEVEL value in the TCOEF information is a value not specified in the H.263 Recommendation Specification, i.e. 1000 0000 or 0000 0000, then an error is detected in the block of the recovered video bit stream. Accordingly, the present invention provides a method for concealing and reconstructing a previous picture immediately adjacent to a time axis previously stored in a corresponding GOB data unit in a current picture including a block in which an error is detected in a LEVEL value in TCOEF information when an error occurs through error concealment and recovery means. By performing error concealment and recovery using the corresponding GOB data in, it is possible to effectively perform error detection and error concealment and recovery in the reconstructed video bitstream of the H.263 picture.

Description

H (263) Error Detection Method in Video Bit Stream

1 is a schematic block diagram of a decoding system suitable for applying an error detection method in an H.263 video bit stream according to the present invention.

2 is a diagram illustrating a process of detecting an error occurring in an H.263 video bit stream using an MCBPC value in a macro block according to an exemplary embodiment of the present invention, and performing error concealment and recovery based on the error detection result. One flowchart.

* Explanation of symbols for main parts of the drawings

100: system multiplexed decoding block 200: video decoding block

300: error detection block 400: error concealment and recovery block

500: frame memory

The present invention provides a video signal compression-coded based on the H.263 algorithm established by the International Telecommunication Union (ITU) for realizing very low bit rate video transmission, such as video telephony and video conferencing systems. The present invention relates to a technique for detecting an error during restoration, and more particularly, to an error detection method suitable for detecting an error that may occur in an H.263 video bit stream restored to an original signal through a receiver video decoding system.

As is well known in the art, the transmission of discrete video signals can maintain better image quality than analog signals. When a video signal composed of a series of image frames is represented in digital form, a considerable amount of transmission data is generated. However, since the usable frequency range of the conventional transmission channel is limited, in order to transmit a large amount of digital data, it is necessary to compress the data to be transmitted and reduce its transmission amount.

On the other hand, various compression techniques mainly used for encoding video signals in H.261, which is mainly used for communication media, and MPEG-1 algorithm, which is suitable for storage media, and MPEG-2 algorithm, which is suitable for video media, include stochastic encoding techniques and Hybrid coding combined with temporal and spatial compression is known to be the most efficient.

Most of the hybrid coding techniques, which are one of the above coding techniques, use motion compensated DPCM (differential pulse code modulation), two-dimensional DCT (discrete cosine transform), quantization of DCT coefficients, VLC (variable modulation coding), and the like. Here, the motion compensation DPCM determines a motion of the object between the current frame and the previous frame, and predicts the current frame according to the motion of the object to generate a differential signal representing the difference between the current frame and the predicted value. These methods are described, for example, in Staffan Ericsson's Fixed and Adaptive Predictors for Hybrid Predictive / Transform Coding, IEEE Transactions on Communication, COM-33, NO.12 (Dec. 1985), or A motion Compensated Interframe Coding from Ninomiy and Ohtsuka. Scheme for Television Pictures, IEEE Transactions on Communication, COM-30, NO.1 (January 1982).

In general, the DPCM / DCT hybrid coding scheme as described above has a target bitrate of Mbps, and may be a CD-ROM, a computer, a home appliance (such as a digital VCR), a broadcast (HDTV), etc. It is mainly concerned with MPEG-1, 2 and H.261 coding algorithms related to high bit rate encoding, which mainly consider only the statistical characteristics of the block-by-block motion in the image, which has already been completed by the World Standards Organization.

On the other hand, in recent years, due to the improvement and spread of PC performance, the development of digital transmission technology, the realization of high-definition display device, the development of memory device, various devices such as home appliances can process and provide image information with huge data. In order to meet this demand, the transmission of audio-video data through existing low-speed transmission paths (eg, PSTN, LAN, mobile network, etc.) with a bit rate of kbps and a limited capacity to meet these demands. There is a need for new coding techniques with high compression rates for storage to storage.

Therefore, at present, there is a need for a standard of a coding scheme for realizing additional compression that can be realized in a video telephony and a video conferencing system, and according to the needs of the times, subjective picture quality is considered important based on recent human visual characteristics. The development of low bit rate video encoding technique for MPEG-2 corresponding to MPEG-2 standard and low bit rate video encoding technique for H.263 corresponding to H.261 has been actively developed. The present invention here relates to an error detector method in the H.263 algorithm.

On the other hand, when transmitting a video signal, the transmitting side compresses and encodes the image signal in the buffer of the output side in order by taking into account the spatial and temporal correlation of the video signal in block units or pixel units through the above-described encoding technique. The video data, i.e., the bit stream, will be transmitted to the decoding system on the receiving side via the transmission channel at a desired bit rate in response to the channel requirements.

Next, in the decoding system on the receiving side, the bit stream of the compressed coded video received through the transport channel is converted into the original signal before the coded coded video data using a technique such as IVLC, inverse quantization, or IDCT. The recovered video bit stream may be recovered and concealed such as a transmission error that may occur during transmission, and then provided to the display side for display through a monitor. The error recovery and concealment schemes are not actively adopted by the H.261 algorithm, but the H.263 algorithm is more aggressive in consideration of the fact that bit strings are transmitted in the ATM (Asynchronous Transfer Mode) transmission network. Recovery and concealment techniques are provided.

In addition, in the video encoding method using the H.263 algorithm, even if only one bit is damaged in the bit stream of the video frame, the image quality deterioration in the substantially reconstructed video can be greatly affected. Therefore, detecting an error portion on the bit stream of the reconstructed image frame on the receiving side can be said to be a very important process for applying an effective error recovery and concealment technique.

Accordingly, the present invention has been made in view of the above-mentioned point, and the present invention relates to a H.263 video bit stream reconstructed by using a level (LEVEL) value of transform coefficient (TCOEF) information included in block data on the reconstructed video bit stream. An object of the present invention is to provide an error detection method in a reconstructed video bit stream that can effectively detect an error of.

In order to achieve the above object, the present invention provides an original signal before encoding using a decoding means including techniques of IVLC, inverse quantization, and IDCT for the encoded H.263 video bit stream separated through the system multiplexing decoding block. 10. A method for detecting an error in a decoding system which performs error concealment and recovery based on an error signal generated when an error signal is generated in the restored video bit stream, and then provides it to a display side. A first step of inputting an image bit stream to continuously perform codeword searches for a plurality of pieces of information included in each block data to search for codewords for transform coefficient information having a predetermined length; A second step of checking whether the retrieved TCOEF information is a codeword having a variable length or a codeword having a fixed length; A third step of checking whether the searched TCOEF information is a codeword having a fixed length, as a result of the check in the second step, whether the LEVEL value of the searched TCOEF information is a predetermined prescribed bit string; If it is determined in the second step that the searched TCOEF information is a codeword having a variable length or the LEVEL value of the searched TCOEF information is the preset prescribed bit string, the error signal is not generated. A fourth step of providing the restored picture bit stream to the display side without the error concealment and recovery; A fifth step of generating the error signal to provide error concealment and recovery means if it is determined that the LEVEL value of the retrieved TCOEF information is not the preset prescribed bit string; And error concealment and recovery in the bitstream section in which an error occurs among the reconstructed video bitstreams based on the generated error signal, and the error concealment and recovered video bitstreams obtained as a result are displayed on the display side. An error detection method of an H.263 video bit stream provided by a sixth step is provided.

The other objects and various advantages of the present invention will become more apparent from the preferred embodiments of the present invention described below with reference to the accompanying drawings by those skilled in the art.

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

First, according to a draft published in 1995 by the International Telecommunication Union (ITU), the image data hierarchy of H.263 is based on the picture layer, the GOB layer, and the macro block layer. block layer and block layer.

In the above hierarchical structure, the picture layer is screen data for one screen, and the data of each picture constituting the picture layer is composed of picture header information followed by GOB data, and the GOB has a CIF (common intermediate format) format. ) Consists of screen data that is divided into 12 screens of one screen, and is divided into screen data that is divided into three in the case of quarter CIF (QCIF) in which the number of pixels in the horizontal and horizontal directions is half of the CIF, and the data of each GOB is followed by the GOB header information followed by It consists of macro block (MB) data.

In addition, the macro block layer MB is composed of macro block header information followed by block data, and one block in the block layer is composed of four luminance blocks and two color difference blocks, and each block data of the block layer is It consists of 8-bit fixed length DC coefficient for INTRA block (INTRADC) information and variable length TCOEF (transform coefficients) information. Herein, the present invention aims to detect an error in a reconstructed video bit stream using a LEVEL value having a fixed length included in TCOEF information having a variable length in a block.

On the other hand, the TCOEF information included in the block layer and applied to the actual error detection in the present invention and representing the conversion coefficient has a structure of LAST, RUN, and LEVEL according to the recommended standard of H.263. Here, LAST of 0 means that there are more nonzero coefficients in the block, and 1 means that this coefficient is the last nonzero coefficient in the current block. In this case, RUN indicates how many consecutive zero coefficients immediately before the current nonzero coefficient, and LEVEL indicates the value of the encoded nonzero coefficient. Combinations that appear frequently among these values are represented by variable length codes, and other combinations are represented by a total length of 22 bits of fixed length code consisting of ESCAPE codeword 0000 11 followed by 1 bit LAST, 6 bit RUN, and 8 bit LEVEL. .

In the present invention, as described above, an error in a block is detected by using a LEVEL value of TCOEF information having a fixed length.

Table 1 below shows a 6-bit fixed length table for RUN, and Table 2 shows an 8-bit fixed length table for LEVEL.

By the way, as can be seen from the above Table 2, when analyzing the 8-bit fixed length LEVEL value included in the TCOEF information having a variable length presented, according to the recommended standard of H.263, the bit You can see that it can't have 0000 0000 or 1000 0000 as its value.

Accordingly, the present invention checks the information values of the bit strings corresponding to the LEVEL values in the TCOEF included in the block data in the H.263 video bit stream restored to the original signal through the decoding system using such a condition (or fact). In other words, it is intended to detect a position where an error occurs, and to conceal and recover an error portion of an error portion in an image bit stream section based on the error detection result. That is, if a bit string in the form of 0000 0000 or 1000 0000 appears in the part corresponding to the TCOEF information value in the block included in the reconstructed video bit stream of H.263, an error has occurred.

Next, a process of detecting an error that can occur on the video bit stream of the H.263 algorithm according to the present invention using the ELVEL value in the TCOEF information having the fixed length as described above will be described.

1 is a schematic block diagram of a decoding system suitable for applying an error detection method in an H.263 video bit stream according to the present invention. As shown in the figure, a typical decoding system includes a system multiplexed decoding block 100, an image decoding block 200, an error detection block 300, an error concealment and recovery block 400, and a frame memory 500. do.

In FIG. 1, the system decoding block 100 performs a function of synchronizing and separating information such as compressed coded video, voice, and text provided from a coding system of a transmitting side (not shown) through a transport channel. In this case, the separated voice and text information is provided to the audio and text information decoding block (not shown), and the video information in the form of a bit stream is provided to the video decoding block 200 through the line L11.

In addition, the video decoding block 200 restores the compressed video bitstream according to the specification determined in the standard of H.263 to the original signal before the encoding. For the video data of the intra picture or the inter picture, As is well known in the art, a video bit stream for an original signal is generated by reconstructing a compressed coded video bit stream using techniques such as IVLC, inverse quantum, IDCT, and motion compensation prediction. Is provided to the error detection block 300 via line L13 and at the same time to the error concealment and recovery block 400 via line L15.

On the other hand, the error detection block 300 detects an error in the video bit stream of the reconstructed intra picture or inter picture on the line L13, and in particular, TCOEF information having a fixed length included in the block data on the video bit stream according to the present invention. The position where the error occurred in the reconstructed video bit stream is detected by using the LEVEL value in the detected error information, wherein the detected error position information is an error concealment through the line L17 as a control signal for error concealment or recovery in the reconstructed video bit stream. And recovery block 400.

As mentioned above, the LEVEL value in the TCOEF information to be used for error detection in the present invention is represented by 8-bit fixed-length codewords, as shown in Table 2 above.

Further, as can be seen from Table 2 above, when analyzing the LEVEL value in the TCOEF information included in the block layer and used for error detection in the present invention, according to the recommended standard of H.263, 0000 0000 or 1000 It can be seen that the bit string of the 0000 type cannot come. In the present invention, by using these conditions, by checking the bit string values corresponding to the LEVEL value in the detected TCOEF information, the image reconstructed based on the check result An error occurrence in the bit stream will be detected. That is, in the error detection block 300 according to the present invention, an error occurs when a bit string of 0000 0000 and 1000 0000 appears in the portion corresponding to the LEVEL value in the TCOEF information in the block included in the reconstructed video bit stream of H.263. Will be detected.

Therefore, the error detection block 300 detects the LEVEL value in the TCOEF information included in the block data on the reconstructed video bit stream provided from the video decoding block 200 through the line L13, and the detection information value is 0000 0000 or 1000. If it is determined whether the detected information value is a 0000 0000 or 1000 0000 bit value after checking whether the bit string is in the 0000 form, an error signal (e.g., an error signal indicating that an error has occurred in the corresponding block of the restored video bit stream) For example, a logic signal of 1 or 0) is generated and provided to the error concealment and recovery block 400.

As a result, in the error concealment and recovery block 400, the corresponding GOB data of the restored picture including the currently input block (the block in which the error occurred in the LEVEL value of the TCOEF information) is stored in the frame memory 500. Errors will be concealed through techniques such as replacing the corresponding GOB data of the previous picture. In this case, the error concealment and recovery block 400 performs error concealment on the entire GOB data having the block in which the error occurred in the LEVEL value without performing error concealment on the data of only the block in which the error has occurred in the LEVEL value. This is because the block in which the occurrence of an error in the current LEVEL value is detected is not known at which position of the GOB data. Therefore, error concealment and recovery are performed on the entire GOB data including the block in which the occurrence of an error in the LEVEL value is detected.

Next, according to the present invention, an error is detected in a video bit stream reconstructed using the LEVEL value in the TCOEF information included in the block data, and error concealment and recovery are performed based on the detection result. It demonstrates in detail with reference to the flowchart of FIG.

First, in the error detection block 300, if a reconstructed video bit stream on the line L13 provided from the above-described image decoding block 200, that is, a bit stream for the reconstructed current picture is input (step 210), the current input is received. A codeword search is performed on the codewords of the corresponding information in each block of the bit stream of the picture, that is, the INTRADC information having a fixed length of 8 bits and the TCOEF information having a variable length (step 220).

Then, in step 230, the codeword retrieved in step 220 is checked, and if the codeword currently retrieved is not a codeword for the TCOEF information to be searched for error detection according to the present invention, TCOEF information The codeword retrieval step 220 is repeated until a codeword for is retrieved, and if it is determined that the currently retrieved codeword is a codeword for TCOEF information to be retrieved, the process proceeds to step 240. Proceed. At this time, the retrieved TCOEF information is a codeword having a variable length, as described above.

Next, in step 240, it is checked whether the TCOEF information is represented by a fixed length codeword, that is, whether the ESCAPE codeword starts with 0000 011, and the check result here indicates that the TCOEF information is a fixed length code. If it is determined that it is not represented by a word, the process proceeds to step 250, i.e., the error detection block 300 of FIG. Error concealment and recovery block 400 of FIG. Accordingly, the error concealment and recovery block 400 will provide the restored picture bit stream input to the display side, which is not shown in the following stage, without applying the error concealment and recovery technique.

On the other hand, if it is determined in the step 240 that the TCOEF information is represented by a fixed length codeword, in the error detection block 300 of FIG. 1, the bit string corresponding to the LEVEL value of the TCOEF information is H. 263 It is checked whether or not it is a bit value specified in the recommendation (step 260). That is, in step 260, it is checked whether the bit string corresponding to the LEVEL value in the TCOEF information is any one of the bit values among the bit values as shown in Table 2 above.

At this time, whether the bit string corresponding to the LEVEL value of the TCOEF information is a value other than the value corresponding to the value defined in the H.263 recommendation through the step 260, that is, the LEVEL value of the TCOEF information. The reason for checking whether the bit string is 1000 0000 or 0000 0000 not specified in the H.263 Recommendation is as described above, in accordance with the Recommendation of H.263, 1000 in the bit string corresponding to the LEVEL value of TCOEF information. This is because a bit value in the form of 000 or 0000 0000 cannot come. That is, a bit value in the form of 1000 0000 or 0000 0000 comes to the portion corresponding to the LEVEL value of the TCOEF information, indicating that an error has occurred in a corresponding block of the reconstructed video bit stream.

Therefore, when it is determined in the step 260 that the bit string of the part corresponding to the LEVEL value of the retrieved TCOEF information is not a bit value in the form of 1000 0000 or 0000 0000, the process proceeds to step 250 described above. Proceed. Accordingly, the error concealment and recovery block 400 of FIG. 1 will provide the recovered image bit stream input to the display side, not shown in the following stage, without applying the error concealment and recovery technique as described above.

On the other hand, if it is determined in step 260 that the bit string of the portion corresponding to the LEVEL value of the retrieved TCOEF information is a bit value in the form of 1000 0000 or 0000 0000 rather than the value specified in the H.263 Recommendation, The error detection block 300 of FIG. 1 generates an error plug value 1 on the line L17 (step 270), and the error plug signal of the logic signal 1 value on the line L17 generated as described above is returned to the error concealment and recovery block 400. FIG. Is provided.

As a result, when the error concealment and recovery block 400 receives an error signal having a value of 1 from the error detection block 300 described above, the error concealment and recovery block 400 is on the reconstructed image bit stream currently input from the image decoding block 200 through the line L15. Error concealment and recovery is performed on the GOB data containing the block in which the error occurred in the LEVEL value of the TCOEF information in which the error occurrence is confirmed (step 280). For example, the error concealment and recovery block 400 replaces the corresponding GOB data of the currently reconstructed picture picture with corresponding GOB data in the immediately preceding picture on the time axis stored in the frame memory 500. Will conceal the error.

At this time, an error concealment is performed on the data of only the corresponding block in which the error occurs in the LEVEL value of TCOEF information. The reason why the data is replaced with GOB data is that it is not known at which position of the GOB data the block in which the occurrence of an error in the LEVEL value of the TCOEF information is detected is present. Therefore, error concealment and recovery are performed on the entire GOB data including the block in which the occurrence of an error is detected. Therefore, the error concealment and recovery block 400 applies an error concealment and recovery technique to the reconstructed image bitstream, thereby transferring the bit stream of the reconstructed image picture from which the error has been recovered to the display side, not shown in the next step. Will be provided.

Therefore, according to the present invention, the error detection block 300 will detect continuous error occurrence for all blocks included in one entire video bit stream restored through the above-described process. Error occurrence detection for the reconstructed picture bit stream of the input picture will be performed by successive error detection.

As described above, according to the present invention, when an error occurs in the video bit stream encoded according to the algorithm of H.263 and then restored on the receiver side, the error is included in the video bit stream to conceal or recover the generated error. By using the LEVEL value in the TCOEF information of the block data to be detected, it is possible to effectively detect the occurrence of errors in the H.263 video bit stream accompanying the deterioration of the image quality in the playback video and to conceal and recover the errors using the same.

Claims (9)

An encoded H.263 video bit stream separated through a system multiplexed decoding block is restored to an original signal before being encoded using decoding means including techniques of IVLC, inverse quantization and IDCT, and the restored video bit stream. A method of detecting an error in a decoding system which performs error concealment and recovery based on an error signal generated when an error signal is generated in the present invention and then provides the display to the display, wherein the restored image bit stream is inputted into each block data. Performing a codeword search on a plurality of pieces of information included in a row to search for codewords for transform coefficient (TCOEF) information having a predetermined length; A second step of checking whether the retrieved TCOEF information is a codeword having a variable length or a codeword having a fixed length; A third step of checking whether the searched TCOEF information is a codeword having a fixed length, as a result of the check in the second step, whether the LEVEL value of the searched TCOEF information is a predetermined prescribed bit string; If it is determined in the second step that the searched TCOEF information is a codeword having a variable length or the LEVEL value of the searched TCOEF information is the preset prescribed bit string, the error signal is not generated. A fourth step of providing the restored picture bit stream to the display side without the error concealment and recovery; A fifth step of generating the error signal to provide error concealment and recovery means if it is determined that the LEVEL value of the retrieved TCOEF information is not the preset prescribed bit string; And error concealment and recovery in the bitstream section in which an error occurs among the reconstructed video bitstreams based on the generated error signal, and the error concealment and recovered video bitstreams obtained as a result are displayed on the display side. The error detection method of the H.263 video bit stream comprising the sixth step provided to the. The method of claim 1, wherein the codeword check in the second step is performed by detecting an ESCAPE codeword. 3. The method of claim 2, wherein the ESCAPE codeword is 0000 011. The error in the H.263 video bit stream according to claim 1 or 2, wherein the error signal generated based on the detected TCOEF information value is a plug signal having a logic value of 0 or 1. Detection method. 2. The method of claim 1, wherein the undefined bit string is 1000 0000 or 0000 0000. The method of claim 1, wherein the error detection in the reconstructed video bit stream is performed in units of blocks. The method of claim 6, wherein error concealment and recovery in the reconstructed video bit stream are performed in one GOB data unit of a current input picture including a block in which an error is detected in the LEVEL value of the TCOEF information. An error detection method in an H.263 video bit stream. 8. The method of claim 7, wherein error concealment and recovery of the corresponding GOB data in the current picture including a block in which an error has been detected in the LEVEL value of the TCOEF information is directly on the time axis previously stored in the error concealment and recovery block. An error detection method in an H.263 video bit stream, which is performed by using corresponding GOB data in an adjacent previous picture. 10. The apparatus of claim 8, wherein the corresponding GOB data including a block in which an error occurrence is detected in a LEVEL value of TCOEF information in the current picture is replaced with corresponding GOB data in the previous picture for error concealment and recovery. Error detection method in H.263 video bit stream.