JP2005318257A - Motion picture encoder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a motion picture encoder capable of refreshing important MBs out of a plurality of MBs composing one screen efficiently. <P>SOLUTION: A position judging section 18-1 compares the number of a macroblock (MB number) notified from a block cut-out section 11 with the MB number of a macroblock (MB) stored in a table 18-2 and performing intra-encoding next, and notifies the comparison results to an intra-inter setting section 19. When the comparison results from the position judging section 18-1 indicates coincidence, the intra-inter setting section 19 sets intra-encoding method of MB otherwise sets inter-encoding method of MB. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

The present invention relates to a moving picture coding apparatus, and more particularly, to a moving picture coding apparatus that recovers deterioration in image quality caused by a transmission error due to insertion of an intra code.

  There are a predictive coding method and a transform coding method as a basic method of band compression coding of moving images. It is known that video signals have statistical properties, that is, there is a correlation between pixels within a frame and between pixels between frames, and high-efficiency encoding is performed using this property. .

  The predictive coding scheme is a scheme that uses the correlation in the time domain, and the transform coding is a scheme that uses the correlation in the frequency domain.

  As a predictive coding method, a motion compensated prediction method that encodes difference information from a predicted image obtained by motion compensated prediction is known.

  On the other hand, as a transform coding method, a block-by-pixel screen is transformed into the frequency domain by discrete cosine transform (DCT), and each obtained frequency component is quantized with a transform coefficient (DCT coefficient) and transmitted. To do.

  In recent years, a method in which both are combined is generally employed.

  For example, in the MPEG (Moving Picture Experts Group), which is a picture compression standardization group established under the international communication organization standard (ITU-T) H261, H263 and the International Organization for Standardization (ISO), 16 × 16 Encoding is performed in units of pixel blocks (hereinafter referred to as MB).

  In a general moving image encoding apparatus that employs the above-described method, intra-encoding in which input image data is encoded as it is without performing motion-compensated prediction, and a compensated predicted image stored in a frame memory, Inter code that calculates a motion vector from the input image data, forms a compensated prediction image that is the next screen from the motion vector and the above-described compensated prediction image, and calculates and encodes a difference image from the input image data Is done.

  By the way, since motion compensation prediction is performed in inter coding, the frame memory of the moving image coding apparatus has an image slightly different from the original image. Becomes a cause of deterioration of image quality.

  Therefore, in such a moving image encoding apparatus, the refresh by the intra encoding is periodically performed to prevent erroneous data from remaining and spreading.

In such refresh by intra coding, it is detected that the number of generated bits obtained when variable length coding is performed in MB units exceeds a predetermined value, and the number of times that the number of detections has reached a threshold value. Intra coding is performed on the image (see Patent Document 1).
JP 2001-169286 A

  However, a problem to be solved still remains in the method of refreshing image data by intra coding as described above.

  That is, in the above-described conventional method, since it is determined whether refresh by intra coding should be performed in units of MB, for example, intra coding is also performed on a plurality of peripheral MBs including MBs that require refresh. Although there are situations that should be performed, depending on the threshold value for determining whether or not to perform refresh by intra coding, a part of the MB that originally needs to be refreshed may be removed.

  Therefore, the present invention has been made to solve such a problem, and an object of the present invention is to make it possible to efficiently refresh an important MB among a plurality of MBs constituting one screen. To do.

  In order to achieve the above object, the moving picture coding apparatus according to the present invention is configured such that the order of performing intra coding in units of blocks is a spiral shape starting from one of a plurality of blocks constituting the frame. A table for arranging and storing the block numbers assigned to the blocks, a comparison unit for comparing the block numbers of the divided blocks and the block numbers stored in the table, and a result of comparison by the comparison unit; An encoding mode setting unit configured to set the encoding method for the block with the block number to intra encoding when the block number matches with the block number stored in the table; To do.

  According to the present invention, when performing intra refresh in units of macro blocks, it is possible to provide a reproduced image that does not cause a sense of incongruity by continuously refreshing macro blocks that form an important part of the image. .

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a block diagram showing a configuration of a moving picture encoding apparatus 1 according to the first embodiment of the present invention.

  In the figure, a moving image coding apparatus 1 includes a block cutout unit 11, a motion detection unit 12, a motion compensation unit 13, a discrete cosine transform (DCT) / quantization unit 14, an inverse discrete cosine transform (IDCT) / inverse quantum. It comprises a conversion unit 15, a variable length encoding unit 16, a frame memory 17, a refresh counter unit 18, an intra / inter setting unit 19, and a mode switching unit 20. The refresh counter unit 18 includes a position determination unit 18-1 and a table 18-2.

  The block cutout unit 11 divides the input screen into macro blocks (MB) made up of N × N (N is an arbitrary integer) and notifies the refresh counter 18 of the MB number assigned to this MB.

  The DCT / quantization unit 14 performs discrete cosine transform in units of blocks (MB) divided by the block cutout unit 11, and quantizes the obtained DCT coefficients.

  The variable length coding unit 16 performs variable length coding of the DCT coefficient quantized together with the mode information of the divided MB. That is, a short code is assigned to a signal with a high probability of occurrence, a long code is assigned to a signal with a low probability of occurrence, and an average code length is shortened.

  In the case of inter coding for performing motion compensation prediction, the motion detection unit 12 uses the image data stored in the frame memory 17 and the divided original image blocks, that is, the motion vector of the input screen, that is, one frame or more before. The direction and distance of movement are detected with reference to the values of neighboring pixels.

  The motion compensation unit 13 creates a predicted original image from neighboring pixels one frame or more before, using the pixel value stored in the frame memory 17 as a predicted value, corresponding to the motion vector detected by the motion detecting unit 12. In inter coding, a difference image is formed.

  The IDCT / inverse quantization unit 15 performs inverse quantization and inverse discrete cosine transform on the DCT coefficient data.

  In the frame memory 17, the predicted image created by the motion compensation unit 13 is added to the MB obtained by inverse quantization and inverse discrete cosine transform of the DCT coefficient, and motion compensated predicted image data of the next input screen is accumulated in units of one frame. The

  The table 18-2 stores the MB number to be subjected to intra coding, and the position determination unit 18-1 receives the MB number notified from the block cutout unit 11 and the MB number stored in the table 18-2. Is matched. Then, the refresh counter unit 18 outputs the determination result of the position determination unit 18-1 to the intra / inter setting unit 19.

  When the intra / inter setting unit 19 receives a signal indicating a match or mismatch based on the determination result of the refresh counter unit 18, the intra / inter setting unit 19 outputs an instruction signal for instructing the intra coding mode or the inter coding mode to the mode switching unit 20. To do.

  The mode switching unit 20 switches to either the intra coding mode or the inter coding mode according to the instruction signal from the intra / inter setting unit 19, that is, the contact S is set to A in the intra coding mode. In the inter coding mode, the contact is switched to B.

  The operation of encoding a moving image using the moving image encoding apparatus according to the first embodiment configured as described above will be described with reference to FIG.

  First, a screen input from an image input unit (not shown) is divided by the block cutout unit 11 into MBs composed of luminance information of 16 × 16 pixels and two color difference information of 8 × 8 pixels, and is output as block information. . At this time, the MB number of the divided MB is output to the refresh counter unit 18 (S201, S202).

  When the MB number is input to the refresh counter unit 18, the position determination unit 18-1 refers to the table 18-2 and determines whether the MB number of the MB to be encoded next is registered. The result is notified to the intra / inter setting unit 19 (S203).

Here, data relating to the order of MBs processed by intra coding registered in the table 18-2 will be described.
FIG. 3 shows an example of a table 18-2 in which the order of MBs to be intra-encoded is registered. The counter value 31 and the MB number of the MB to be intra-encoded are registered in association with each other.
The counter value starts from 0, and the maximum number of MBs included in one frame constituting a moving image is the maximum value. Each time MB is intra-encoded, the MB is incremented by 1 and the MB number of a new MB to be intra-encoded is determined. Will be.
That is, the position determination unit 18-1 corresponds to the MB number notified from the block cutout unit 11 and the counter value managed by the position determination unit 18-1, and the MB number to be intra-coded next matches. It is determined whether or not.

  Here, when it is detected that the MB number received by the position determination unit 18-1 from the block cutout unit 11 matches the MB number stored in the table 18-2 and designated for the next intra encoding, A signal (for example, 1-bit signal “1”) indicating that the MB numbers match is output.

  This output is received by the intra / inter setting unit 19 and is used to determine the encoding mode to be set. Here, since a signal indicating that they match is received, the intra / inter setting unit 19 instructs the mode switching unit 20 to set the MB coding mode to intra coding (S204).

  When the mode switching unit 20 receives an instruction to encode in the intra coding mode, the contact point S is set to the terminal A side. Here, since the output of the terminal A is 0, the MB output from the block cutout unit 11 is zero-difference (S205), that is, the state of the image data output from the block cutout unit 11 is a discrete cosine. This is input to the transform (DCT) / quantization unit 14.

  The DCT / quantization unit 14 performs a DCT operation on the input image data to obtain a DCT coefficient, and further, the obtained DCT coefficient is quantized (S206). The quantized MB image data is then subjected to variable length coding together with the coding mode information for each block in the variable length coding unit 16 (S207).

  The output of the DCT / quantization unit 14 is also input to the inverse discrete cosine transform (IDCT) / inverse quantization unit 15 for inverse quantization and inverse discrete cosine transform, and this result is added to the output of the mode switching unit 20. It is calculated and written in the frame memory 17 (S208).

  Here, since the intra coding mode is set in the mode switching unit 20, the output of the mode switching unit 20 is 0. Therefore, the output of the IDCT / inverse quantization unit 15 is written in the frame memory 17 as it is. Used as compensated prediction image data.

  On the other hand, if the position determination unit 18-1 determines that there is a mismatch in the process of S203, a signal (for example, 1-bit “0”) indicating that the MB numbers do not match is output. As a result, the intra / inter setting unit 19 instructs the mode switching unit 20 to set the encoding mode to inter encoding (S204).

  When receiving an instruction to set the encoding mode to inter encoding, the mode switching unit 20 sets the contact S to the terminal B side.

  In the inter coding, the motion detection unit 12 obtains a motion vector from the compensated prediction image data stored in the frame memory 17 and the MB of the input image data cut out by the block cutout unit 11 (S209). Thereafter, a predicted image is formed from the image data of one frame before stored in the frame memory 17, and a difference image from the MB of the image data output from the block cutout unit 11 is obtained (S210).

  Then, the difference image is input to the DCT / quantization unit 14 and subjected to DCT transform and quantization (S206). Subsequently, variable length coding (S207) and IDCT / inverse quantization (S208) are performed. ) Is executed.

  Here, since the inter coding mode is set by the mode switching unit 20, the output of the IDCT / inverse quantization unit 15 is added to the predicted image output from the motion compensation unit 13 and then added to the frame memory 17. Will be written on.

  The above processing is repeatedly executed every time MB is cut out from the input image data by the block cutout unit 11.

  Here, the order of MBs to be subjected to intra coding registered in the table 18-2 will be described more specifically.

  Normally, when MB is intra-encoded to refresh image data in units of MB, that is, when the correlation between frames becomes low, the MB is encoded by switching from inter encoding to intra encoding. The refresh process is performed while shifting from the upper left MB in the right direction, and this process is performed by shifting the lines. Here, however, intra-encoding is performed in a spiral shape around a predetermined MB. MB order is set.

FIG. 4 is a diagram showing the order in which intra coding is performed on a plurality of MBs constituting one frame in an easy-to-understand manner. In the state corresponding to the order shown in FIG. It is registered.
Referring to FIG. 4, the order of MB with MB number 48, MB with MB number 37, MB with MB number 38, and MB to be intra-coded is formed in a spiral from the MB with MB number 49. . The MB to be intra-encoded next to the MB with the MB number 0 is not the MB with the MB number 1 but the MB number with the MB number 10, which is the MB with the MB numbers 1 to 9 This is because intra coding has already been implemented.

  As described above, a plurality of MBs constituting image data are subjected to intra coding in a spiral shape starting from a certain MB, so that MBs adjacent to the specified MB in the frame can be continuously recorded. Since the image is refreshed, a visually important image portion can be quickly returned to an image with less disturbance.

In the above description, as shown in FIG. 4, it is assumed that refresh is performed on all MBs constituting one frame centering on a certain MB, but only a predetermined number of MBs centered on a predetermined MB. You may make it refresh.
FIG. 5 is a diagram showing an example of performing refresh for such a part of MBs. An MB with a MB number of 48 and a MB with a MB number of 37 starts from a MB with a MB number of 49 in the center of the screen. In the following, as indicated by the arrows, nine MBs having MB numbers up to 59 are refreshed.

  For example, when a moving person is arranged only in the center of the screen, such as a news program, the influence of distortion caused by encoding becomes larger in the central part than in the surrounding image data. By performing the refresh, it is possible to prevent image deterioration without deteriorating the transmission efficiency.

  Note that if only the center part of the screen is refreshed, the distortion generated in the surrounding MBs remains until the scene is changed. Therefore, after the partial refresh is performed a predetermined number of times, the entire screen is refreshed. Is preferred.

  FIG. 6 is a block diagram showing a configuration of a moving image encoding device 60 according to the second embodiment of the present invention. Note that description of parts common to FIG. 1 will be omitted, and different parts will be described in detail.

  In FIG. 6, the moving picture coding apparatus 60 includes a generated bit number extraction unit 61 and a refresh position setting unit 62, and the refresh start position and range registered in the table 63-2 of the refresh counter unit 63 are the refresh position setting unit. The point set by 62 is different from the configuration of the moving picture encoding apparatus 1 described in the first embodiment.

  Next, the operation according to the invention of the video encoding device 60 will be described with reference to FIG.

First, the input image is divided into MBs by the block cutout unit 11, and image data is output in MB units. At this time, the MB number assigned to the output MB is notified from the block cutout unit 11 to the refresh counter unit 63.
On the other hand, the output image data in units of MB is subtracted and then quantized by the DCT / quantization unit 14, and the quantized MB image data is encoded by the variable-length encoding unit 16 in each block encoding mode. Variable length coding is performed together with the information (S701).

  The generated bit number extraction unit 61 extracts the number of bits MB_bits generated in units of MB each time the variable length encoding unit 16 performs the variable length encoding process, and notifies the refresh position setting unit 62 of it (S702).

The refresh position setting unit 62 extracts MBs with a large code amount from MB_bits received in MB units from the generated bit number extraction unit 61, obtains the start position and range to be refreshed from the next frame, and sets them in the table 63-2. (S703).
The refresh start position and range can be obtained as follows, for example.

First, the determination of the generated MB with a large amount of code is performed by comparing a predetermined threshold with the amount of code generated in units of MB. The threshold used at this time is a value determined by the system designer in consideration of the transmission capacity and the importance of the image.
Then, a rectangular area including the MB in which the code amount exceeding the threshold is generated is obtained, this area is set as the refresh range, and the MB at the center position is set as the refresh start position.

  When the start position and range of the MB to be refreshed are determined in this way, the MB number to be spirally refreshed in order from the MB number of the MB that is the starting point of the refresh is registered in the table 63-2 in correspondence with the counter value. Is done.

  In addition to this, the MB with the largest generated code amount is obtained, and the freshness is determined with respect to a range specified in advance around this MB, for example, a total of nine MBs composed of upper and lower 2 MB and left and right 2 MB. It does not matter if it is given.

  When the information about the MB to be refreshed is registered in the table 63-2, the refresh is performed based on this information from the next frame.

  That is, when the block cutout unit 11 divides the screen to be input next into MB units, the MB number of the MB to be output to the subsequent stage is notified to the refresh counter unit 63. The MB number registered in the table 63-2 and the MB number registered in the table 63-2 are compared according to the value indicated by the counter, and a signal indicating match / mismatch is notified to the intra / inter setting unit 19 (S704).

  The intra / inter setting unit 19 controls to set the coding mode to intra coding when a signal indicating coincidence is received, and to set the coding mode to inter coding when a signal indicating mismatch is received. (S705).

  In this way, by determining the MB to be refreshed every time one frame is encoded, the image quality can be improved efficiently, and distortion due to encoding can be removed in order from the important part of the image. Become.

1 is a block diagram showing a configuration of a moving image encoding apparatus according to Embodiment 1 of the present invention. 5 is a flowchart illustrating processing for performing intra coding in units of blocks according to the first embodiment of the invention. The figure which shows the structure of the table which memorize | stores the order which carries out intra encoding. The figure which shows the process which the block which comprises a flame | frame carries out intra encoding helically. The figure which shows the process which carries out intra coding helically with respect to a part of block which comprises a flame | frame. The block diagram which shows the structure of the moving image encoder which concerns on Example 2 of this invention. The flowchart which shows the process which sets the block which performs intra encoding which concerns on Example 2 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,60 ... Moving picture encoding device 11 ... Block extraction part 12 ... Motion detection part 13 ... Motion compensation part 14 ... Discrete cosine transform (DCT) and quantization part 15 ... · Inverse discrete cosine transform (IDCT) · Inverse quantization unit 16 ··· variable length encoding unit 17 ··· frame memory 18 and 63 ··· refresh counter units 18-1 and 63-1 ··· position determination unit 18-2, 63-2 ... Table 19 ... Intra / inter setting unit 61 ... Generated bit amount extraction unit 62 ... Refresh position setting unit

Claims (3)

In a moving image encoding apparatus that divides a frame constituting a moving image into blocks and performs encoding in units of blocks,
A table for arranging and storing the block numbers assigned to the blocks so that the order of performing intra-coding in units of blocks becomes a spiral starting from one of a plurality of blocks constituting the frame;
A comparison unit that compares a block number of the divided block with a block number stored in the table;
As a result of the comparison by the comparison unit, when the block number matches the block number to be intra-encoded stored in the table, the encoding mode setting unit sets the encoding method for the block with the block number to intra-encoding. A video encoding apparatus comprising: The moving picture coding apparatus according to claim 1, wherein the block to be subjected to intra coding stored in the table is a rectangular area composed of a part of blocks constituting the frame. . In a moving image encoding apparatus that divides a frame constituting a moving image into blocks and performs encoding in units of blocks,
A table for arranging and storing the block numbers assigned to the blocks so that the order of performing intra-coding in units of blocks becomes a spiral starting from one of a plurality of blocks constituting the frame;
A generated bit amount extraction unit that extracts a code amount when encoded in units of blocks;
Based on the output of the generated bit amount extraction unit, a block for performing intra encoding is obtained, and a refresh position setting unit set in the table;
A comparison unit that compares a block number of the divided block with a block number stored in the table;
As a result of the comparison by the comparison unit, when the block number matches the block number to be intra-encoded stored in the table, the encoding mode setting unit sets the encoding method for the block with the block number to intra-encoding. A video encoding apparatus comprising:

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