KR100212543B1 - Method for detecting error of bit stream for intra frame in mpeg-2 algorithm - Google Patents

Abstract

The present invention provides an error detection method for a bit stream in which an error in a bit stream of an MPEG-2 intra frame reconstructed using macro block type information included in macro block data on a bit stream of an image intra frame can be effectively detected. To this end, the present invention is to check whether the bit stream of the video frame reconstructed to the original signal before being encoded by the decoding means is an intra frame; If it is determined that the result is an intra frame, the codeword for the macro block address increment having a predetermined bit value that is currently input is skipped; Detect whether an input codeword subsequent to the codeword for this skipped macroblock address increment is a codeword for the macroblock type; As a result of the check in this codeword detection step, it is checked whether or not the detected macroblock type information value is an information value corresponding to the intra frame; If it is determined that the detected macroblock type information value is an information value corresponding to an intra frame, an error signal is not generated. If it is determined that the detected macroblock type information value is not an information value corresponding to an intra frame, an error signal is determined. Generate to provide error concealment and recovery means; Performing error concealment and recovery in the bit stream of the intra frame by performing error concealment and recovery in the bit stream section in which the error occurred in the bit stream of the recovered intra frame based on the generated error signal. Error occurrence detection and error concealment and recovery in the bit stream of two intra frames can be effectively performed.

Description

MPEG-Error detection method in bit stream of 2 intra frames

1 is a schematic block diagram of a decoding system suitable for applying an error detection method in a bit stream of an MPEG-2 intra frame according to the present invention.

2 is a diagram for detecting an error occurring on a bit stream of an intra frame using macro block type information included in a macro block according to a preferred embodiment of the present invention, and performing error concealment and recovery based on the error detection result. Flowchart showing the process.

* 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 relates to a technique for detecting an error in reconstruction of a video signal encoded by compression based on an MPEG-2 algorithm capable of realizing high-definition television (HDTV). More particularly, the present invention relates to an original signal through a receiver video decoding system. An error detection method suitable for detecting a possible error in a bit stream of an MPEG-2 intra frame reconstructed as

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 a digital form, a considerable amount of transmission data is generated, particularly in the case of high-definition television (HDTV). 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 the amount of transmission.

Therefore, in order to reduce the amount of data transmitted when transmitting a video signal, the transmitting system encodes and compresses the encoded video signal using the spatial and temporal correlation of the video signal and then compresses the encoded video signal through the transmission channel. To the decryption system.

As is well known in the art, MPEG-1, which only handles progressive scanning images, and whose transmission rate is approximately 1.5 Mbps, is primarily suitable for storage media. In contrast, MPEG-2 is seen as an extension of H.261, which is primarily intended for communications media, and MPEG-1, which is suited for storage media, but is widely used in a wide range of media, such as communications, computers, consumer electronics, and broadcasting. It is an algorithm that can be applied and exchanged information. Unlike MPEG-1, MPEG-2 has the advantage that it can handle progressive scanning and interlaced scanning. . The present invention relates to an error detection technique in a bit stream occurring under such an MPEG-2 algorithm.

On the other hand, as the various compression techniques mainly used for encoding video signals in the MPEG-1 and MPEG-2 algorithms described above, a hybrid encoding technique combining a stochastic encoding technique and a temporal and spatial compression technique is known to be the most efficient. .

Most of the hybrid coding schemes, one of the above-described coding schemes, in particular, the hybrid coding scheme used in the MPEG-2 algorithm, include motion compensated DPCM (differential pulse code modulation), two-dimensional discrete cosine transform (DCT), quantization of DCT coefficients, VLC (variable length coding) or the like is used. 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 prediction 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 (1985, December), or A motion Compensated Interframe from Ninomiy and Ohtsuka. Coding Scheme for Television Pictures, IEEE Transactions on Communication, COM-30, NO.1 (January, 1982).

Therefore, 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 image signal in block units or pixel units through the above-described encoding technique. The image data, i.e., the bit stream, will be transmitted to the decoding system at the receiving side via the transmission channel at the 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. Such error recovery and concealment schemes are not actively provided by the MPEG-1 algorithm, but the MPEG-2 algorithm is more aggressive in consideration of the fact that bit strings are transmitted in an ATM (Asynchronous Transfer Mode) transmission network. Recovery and concealment techniques are provided.

On the other hand, in the video encoding method using the MPEG-2 algorithm, even if only one bit is damaged in the bit stream of the video frame, it may have a significant effect on the image quality deterioration in the substantially restored picture. Therefore, detecting the occurrence of an error on the bit stream of the video frame is a very important process for applying an effective error recovery and concealment technique.

Accordingly, the present invention has been devised in view of the above, and effectively avoids errors in the bit stream of the MPEG-2 intra frame reconstructed using the macro block type information included in the macro block data on the bit stream of the video intra frame. It is an object of the present invention to provide a method for detecting an error in a recovered bit stream.

In order to achieve the above object, the present invention is encoded using decoding means including techniques of IVLC, inverse quantum and IDCT for video bit streams of encoded MPEG-2 intra frames separated through system multiplexed decoding blocks. Restoring to the original original signal and detecting the error signal generation position on the bit stream to conceal and recover the error generated when the error occurs on the bit stream of the restored intra frame through error concealment and recovery means. The method may include: checking whether a corresponding frame is an intra frame by inputting a bit stream of the reconstructed video frame; Skipping a codeword for a macro block address increment having a predetermined bit value currently determined as an intra frame as a result of the check in the frame checking step; Detecting whether an input codeword subsequent to the codeword for the skipped macroblock address increment is a codeword for the macroblock type; Checking whether the detected macroblock type information value is an information value corresponding to the intra frame, as a result of the check in the codeword detection step; If it is determined in the information value checking step that the detected macro block type information value is an information value corresponding to the intra frame, the error signal is not generated and the detected macro block type information value is the intra signal. Generating an error signal and providing the error concealment and recovery means if it is determined that the information value is not corresponding to a frame; And performing error concealment and recovery in a bit stream section in which an error occurs in the bit stream of the restored intra frame on the basis of the generated error signal. To provide.

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.

As is well known in the art, the MPEG-2 video data hierarchy consists of a sequence layer, a group of picture (GOP) layer, a picture layer, a slice layer, a macro block layer and a block layer.

In the above hierarchical structure, the sequence layer is composed of one or a plurality of GOPs in which the sequence header information and the image rate are the same, and the GOP layer is encoded by the intra coding mode without taking a difference (error signal). It consists of an intra coded picture, a forward predictive coded picture (P), and a bidirectionally predictive coded picture (B picture).

In addition, the picture layer is an image frame constituting one screen, and is composed of one or a plurality of slices, and the slice layer is composed of one or a plurality of macro blocks successive to the scanning line of the image, and the macro block layer is composed of four luminance blocks. And a macro block having two color difference blocks and determining which to use as prediction data which is reference image data which takes a difference (error signal). Substantially, such a macro block layer is intended to be pursued by the present invention. It is used for error detection in the video bit stream.

In more detail, the macro block type information values included in each macro block in the macro block layer are classified into two types according to the quantization scale, one of which uses the previous quantization scale as it is, and the other of which corresponds to the corresponding macro block. In this case, a new quantization scale is applied. The MPEG-2 Algorithm Recommendation prescribes the macroblock type information value as 1 in the former case and macroblock type information value as 1 in the latter case. Detailed data of this macro block layer will be described later in detail. Finally, the block layer is composed of 8x8 lines / pixels separated by luminance or color difference, which block is used as a unit of DCT.

Meanwhile, according to the present invention, a macroblock layer to be used for detecting an error on a bit stream of an intra frame has the following data information.

1) MBE (macroblock escape): Escape code information of the macro block address, which is used only when the MBAI is 33 or more, and has a length of 11 bits.

2) MBAI (macroblock address increment): VLC indicating the number of previously skipped macro blocks + 1, information indicating the number of macro blocks + 1 from the left end of the image, having a length of 1-11 bits. In case of intra frame, it must be defined as 1

3) MBT (macroblock type): VLC encoding information indicating a coding mode of a macroblock, having a length of 1-9 bits, and having an intra frame having two types (1 or 1) defined according to a quantization scale.

4) Spatial temporal weight code (STWC): Information indicating the upsampling method of the lower layer screen in temporal scalability, and has a length of 2 bits.

5) FrMT (frame motion type): Predictive type information about a frame, MBT uses prediction, and exists only when frame predictive frame DCT (FPFD) is zero (0) in a frame structure. Has the length of

6) FiMT (field motion type): As a prediction type information for a field, MBT uses prediction and exists in the case of conditions other than FrMT, and has a length of 2 bits.

7) DT (DCT type): Information indicating whether the DCT is in the frame mode or the field mode. The information is added only when the DCT data is present and has a length of 1 bit.

8) QSC (quantizer scale code): Information about the quantization step size of a macro block, and has a length of 5 bits.

9) MVFS (motion vertical field select): In case of field prediction, information indicating which field of a reference image is predicted from and has a length of 1 bit.

10) MHC (motion horizontal code): Information indicating that the difference between the horizontal component of the motion vector for the macroblock and the previous motion vector is encoded by VLC, and has a length of 1-11 bits.

11) MHr (motion horizontal r): Information used with MHC and has a length of 1-8 bits.

12) DH (DMV horizontal): In the case of dual prime prediction, this is VLC information indicating a horizontal difference vector and has a length of 1-2 bits.

13) MVC (motion vertical code): Information indicating that the difference between the vertical component of the motion vector for the macroblock and the previous motion vector is encoded by VLC, and has a length of 1-11 bits.

14) MVr (motion vertical r): Information used with MVC and has a length of 1-8 bits.

15) DV (DMV vertical): In the case of dual prime prediction, this is VLC information indicating a vertical difference vector and has a length of 1-2 bits.

16) CBP (coded block pattern) 420: Indicates CBP information when the color difference format is 4: 2: 0, and has a length of 3-9 bits.

17) CBP 1 (coded block pattern 1): Information added to CBP 420 when the color difference format is 4: 2: 2, and has a length of 2 bits.

18) CBP 2 (coded block pattern 2): Information added to CBP 420 when the color difference format is 4: 4: 4, and has a length of 6 bits.

Next, a process of detecting an error that can occur on the bit stream of an intra frame in the MPEG-2 algorithm using the specific information of the macro block layer having the above-described data information will be described.

Figure 1 shows a schematic block diagram of a decoding system suitable for applying an error detection method in a bit stream of MPEG-2 intra frames 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 multiplexing 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 transmission 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 a video bit stream that has been compression-coded according to a specification determined in the MPEG-2 standard to an original signal before being encoded. For video data of an intra frame or an inter frame, As is well known in the art, it is possible to reconstruct a compressed coded video bit stream using techniques such as IVLC, inverse quantization, IDCT, and motion compensation prediction to generate a video bit stream for the original signal. It is provided to the error detection block 300 via line L13 and simultaneously to the error concealment and recovery block 400 via line L15.

On the other hand, in the error detection block 300, an error is detected in the video bit stream of the reconstructed intra frame or inter frame on the line L11, and in particular, the macro block type included in the macro block layer on the bit stream of the intra frame according to the present invention. The error value is detected in the reconstructed video bit stream using the information value, and the detected error position information is an error concealment and recovery through the line L17 as a control signal for error concealment or recovery in the generated bit stream. Provided to block 400.

As mentioned earlier, the macroblock type information value for an intra frame is a value of 1 or 1 as specified in the MPEG-2 Recommendation, i.e. 1 value if the macroblock uses the previous quantization scale as it is. If a macro block applies a new quantization scale, it should have a value of 1.

Accordingly, in the error detection block 300, a macro block escape (MBE) information value (not required for an intra frame) and a 1-11 bit length having an 11-bit length data value detected on the bit stream of the intra frame. Macro Block Address Increment (MBAI) information value with data value (Must be specified as 1 for intra frame) Check the following Macro Block Type (MBT) information value and check that the value is other than 1 or 1 If it is determined to have an error signal (e.g., a logic signal of 1 or 0) indicating that an error has occurred in the corresponding macro block on the restored intra frame bit stream, the error concealment and recovery block 400 described below is generated. To provide. As a result, in the error concealment and recovery block 400, the slice data of the restored intra frame including the currently input macro block (macro block in which the error occurred) is stored immediately in the frame memory 500 in the corresponding intra frame. Errors will be concealed through techniques such as replacing the corresponding slice data on the spatial axis of the frame. In this case, the error concealment and recovery block 400 performs error concealment on all of the slice data having the macroblock in which an error occurs without performing error concealment on data of only the corresponding macroblock in which an error occurs. This is because it is not possible to know in which position of the slice data the macroblock in which the current error occurrence is detected is present. Therefore, error concealment and recovery are performed on the entire slice data including the macro block in which the occurrence of an error is detected.

Next, when the current input frame is an intra frame, the error detection block 300 detects an error in the bit stream of the intra frame using the macro block type information value included in the macro block, and the detection result. The process of performing error concealment based on will be described 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 frame is input (step 210), the current input is received. It is checked whether the frame is an intra frame (step 220).

If it is determined in step 220 that the current frame is not an intra frame, that is, an inter frame, the error detection block 300 generates an error plug value 0 (ie, a logic signal) (step 270). Error concealment and recovery block 400 to be provided. Accordingly, the error concealment and recovery block 400 may provide the reconstructed image bit stream provided from the image decoding block 200 through the line L15 to the display side, which is not shown in the next stage, without applying the error concealment and recovery technique. will be.

On the other hand, if it is determined in step 220 that the current frame is an intra frame, the next codeword, i.e., 1-11 bits of macro block address increment (MBAI) information value (Intra in MPEG-2) Skip the codeword with a value of 1 for the frame (step 230), and then the process proceeds to step 240.

In this case, the reason for not checking (or skipping) the macro block escape (MBE) information value existing in front of the macro block address increment (MBAI) information value of the macro block layer in the above step 230 is the macro block address. This is because the macro block escape (MBE) information value is included in the macro block layer only when the increment information MBAI value is 33 or more. That is, in the case of the intra frame, the macro block address increment (MBAI) information value must be 1 as specified, since the macro block escape (MBE) information value cannot be included in this case.

Next, in step 240, it is checked whether the codeword of the currently input bit stream is a codeword for a macro block type (MBT) information value, and the current codeword inputted as a result of the check in this step 240 If is determined not to be a codeword for the macro block type (MBT) information value, then processing proceeds to step 270 described above. Accordingly, the error concealment and recovery block 400 will provide the bit stream of the recovered intra frame that is input without the application of the error concealment and recovery technique to the display side, not shown in the next stage.

On the other hand, if it is determined in step 240 that the input codeword is a codeword for the macroblock type information value, the error detection block 300 corresponds to the case where the corresponding codeword value is an intra frame again. Whether the macroblock type information value is 1 (if the old quantization scale is used as it is) or 1 (if the new quantization scale is applied to the macroblock). 250, if it is determined in the step 250 that it is not the information value of the codeword for the corresponding macroblock type, the process proceeds to the step 270 described above to perform the subsequent process as described above. will be.

On the other hand, if it is determined that the information value of the codeword for the macro block type is 1 or 1 as a result of the check in the step 250, the error detection block 300 generates an error plug value 1 (step 260). The error plug signal of the logic signal 1 value thus generated is provided to the error concealment and recovery block 400.

As a result, the error concealment and recovery block 400, if an error signal is input from the error detection block 300 described above, on the bit stream of the restored intra frame currently input from the image decoding block 200 via the line L15. Error concealment and recovery is performed on the slice data including the macro block where the occurrence of the error is confirmed (step 280). For example, the error concealment and recovery block 400 replaces the corresponding slice data of the restored intra frame that is currently input with the corresponding slice data in the immediately preceding intra frame on the time axis stored in the frame memory 500. The technique will conceal errors. In this case, the reason for replacing the corresponding slice data of the previous frame to conceal the error of all the slice data having the macro block in which the error occurs without performing error concealment on the data of only the corresponding macro block in which the error occurs is the current error. This is because it is not possible to know in which position of the slice data the macroblock in which occurrence has been detected is present. Therefore, error concealment and recovery are performed on the entire slice data including the macro block in which the occurrence of an error is detected.

As described above, according to the present invention, when an error occurs in the bit stream of the intra frame video encoded according to the algorithm of MPEG-2 and then reconstructed at the receiver, an image frame is used to conceal or recover the generated error. By using the macro block type information in the macro block included in the bit stream of the video stream, error occurrence detection and error concealment and recovery using the bit stream of the MPEG-2 intra frame accompanied by deterioration of image quality in the playback image can be effectively performed. Can be.

Claims (3)

The video bit stream of the encoded MPEG-2 intra frame separated through the system multiplexing decoding block is restored to the original signal before being encoded by using decoding means including the techniques of IVLC, inverse quantum and IDCT, and error concealment. And detecting an error signal generation position on the bit stream to conceal and recover an error generated when an error occurs on the bit stream of the restored intra frame through recovery means, wherein the bit stream of the recovered video frame is detected. Checking whether the corresponding frame is an intra frame by inputting a; Skipping a codeword for a macro block address increment having a predetermined bit value currently determined as an intra frame as a result of the check in the frame checking step; Detecting whether an input codeword subsequent to the codeword for the skipped macroblock address increment is a codeword for the macroblock type; Checking whether the detected macroblock type information value is an information value corresponding to the intra frame, as a result of the check in the codeword detection step; If it is determined in the information value checking step that the detected macro block type information value is an information value corresponding to the intra frame, the error signal is not generated and the detected macro block type information value is the intra signal. Generating an error signal and providing the error concealment and recovery means if it is determined that the information value is not corresponding to a frame; And performing error concealment and recovery in a bit stream section in which an error occurs in the bit stream of the restored intra frame on the basis of the generated error signal. . The method of claim 1, wherein the macro block type information value has a bit value of 1 or 1. The error detection method of claim 2, wherein the error signal generated based on the detected macroblock type information value is a plug signal having a logic value of 0 or 1. Way.