JP2004040446A - Image-coding device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image-coding device that can more efficiently code images in without visual nonconformities. <P>SOLUTION: A reference image generating section 131 generates reference images of a plurality of predictive modes. An error-evaluating value calculating section 132 calculates a first error evaluating value. A reference image generating section 134 generates a reference image, based on the incidental information of an adjacent macro block. Another error evaluating value calculating section 135 calculates a second error-evaluating value, by using the reference image generated by the reference image generating section 134 and an input image. Prediction mode discriminating sections 133 and 136 discriminate a prediction mode, based on the first and second error evaluating values. When the discriminated prediction mode is a mode for generating a reference image, based on the incidental information of the adjacent macro block, the incidental information of the present macro block is replaced by the incidental information of the adjacent macro block. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a video encoding device that encodes a video signal by MPEG2.
[0002]
[Prior art]
In BS digital broadcasting, which started broadcasting in December 2000, a video signal is compressed by MPEG2 and broadcasted. Even terrestrial digital broadcasting scheduled to start broadcasting in 2003, broadcasting using MPEG2 is performed. In MPEG2, data compression is performed on the basis of temporal correlation and spatial correlation of video, and human visual characteristics.
[0003]
Since terrestrial digital broadcasting is operated in a narrower frequency band than BS digital broadcasting due to the limitation of frequency band allocation, operation at a low bit rate is assumed. Also, as a future broadcasting system, it is essential to transmit HDTV or simultaneously transmit a plurality of channels to increase the number of channels in order to make the broadcasting system attractive to a viewer.
[0004]
By the way, what is actually defined in MPEG2 is only the format at the time of decoding, and the video encoding device may perform encoding in accordance with the MPEG2 standard. Therefore, the encoding method (encoding algorithm) by the video encoding device has a very high degree of freedom, and the data amount and the image quality at the time of encoding are determined by the performance of the video encoding device itself.
[0005]
It is well known that a video encoding device includes a motion vector detection unit and a motion compensation prediction unit. The conventional motion compensation prediction unit is configured as shown in FIG. As shown in FIG. 3, the motion compensation prediction unit includes a reference image generation unit 31 that generates a reference image of each prediction mode, an error evaluation value calculation unit 32 that calculates an error evaluation value of each prediction mode, and a mode determination unit. 33 and an accompanying information holding unit 38.
[0006]
The reference image generator 31 receives the motion vector output from the motion vector detector (not shown) and the local decoded image. The reference image generation unit 31 generates a reference image for each prediction mode based on the input motion vector and the locally decoded image. The error evaluation value calculation unit 32 extracts a prediction block from the input reference image for each prediction mode and calculates an error evaluation value while obtaining a difference from the input image. The error evaluation value for each prediction mode calculated by the error evaluation value calculation unit 32 is input to the mode determination unit 33.
[0007]
The mode determination unit 33 determines the prediction mode based on the error evaluation value for each prediction mode input from the error evaluation value calculation unit 32. The incidental information output from the mode determining unit 33 is input to and held in the incidental information holding unit 38. The additional information output from the additional information holding unit 38 is supplied to a variable length encoding unit (not shown). In addition, the mode determination unit 33 supplies a predicted image according to the prediction mode to a subtracter (not shown) for obtaining a difference from the input image.
[0008]
In this way, the motion compensation prediction unit determines whether or not to use the input motion vector and how to use it, and determines the motion vector used for encoding, the prediction mode, the frame macroblock Supplementary information consisting of the type of / field macroblock is supplied to the variable length coding unit.
[0009]
[Problems to be solved by the invention]
A conventional video encoding device multiplexes encoded data and incidental information. Video signals have spatial correlation, and adjacent macroblocks often have exactly the same incidental information. Even in such a case, the conventional encoding device generates and transmits the additional information for each macroblock, and as a result, there is a problem that the encoding efficiency is low.
[0010]
The present invention has been made in view of such a problem, and an object of the present invention is to provide a video encoding device that can perform encoding more efficiently and without any visual defects.
[0011]
[Means for Solving the Problems]
The present invention provides a video encoding apparatus having a motion vector detection unit (12) for detecting a motion vector and a motion compensation prediction unit (13), in order to solve the above-mentioned problems of the conventional technology. A first reference image generation unit (131) configured to generate a reference image in a plurality of prediction modes based on the motion vector and the locally decoded image encoded and decoded in the video encoding device; A first error evaluation value calculation unit (132) for calculating a first error evaluation value using the reference images of the plurality of prediction modes and an input image, and additional information of an adjacent macroblock adjacent to the current macroblock. A second reference image generation unit (134) for generating a reference image, and a second error evaluation value calculated using the reference image and the input image generated by the second reference image generation unit Second error evaluation A calculation unit (135); a prediction mode determination unit (133, 136) for determining a prediction mode based on the first error evaluation value and the second error evaluation value; If the additional information holding unit (138) for storing information and the prediction mode determined by the prediction mode determining unit are modes for generating a reference image based on additional information of an adjacent macro block, the current macro block And a supplementary information replacing means (137) for replacing the supplementary information with the supplementary information of an adjacent macroblock and outputting the supplementary information.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a video encoding device according to the present invention will be described with reference to the accompanying drawings. FIG. 1 is a block diagram showing an example of the overall configuration of a video encoding device according to the present invention, and FIG. 2 is a block diagram showing an embodiment of a main part of the video encoding device according to the present invention.
[0013]
First, an example of the overall configuration of the video encoding device of the present invention will be described. In FIG. 1, a video signal to be encoded is input to a buffer memory / preprocessing unit 1. Specifically, the buffer memory / preprocessing unit 1 has a configuration in which a preprocessing unit that performs a filtering process, a downsampling process, and the like is provided at a subsequent stage of the frame buffer.
[0014]
The video signal of the n-th frame once stored in the buffer memory / preprocessing unit 1 is input to the subtracter 2 for each macroblock. A macroblock is a unit used for motion compensation prediction, and is composed of 16 × 16 or 16 × 8 pixels in MPEG2. The subtracter 2 calculates the difference between the locally decoded data of the (n−i) th or (n + j) th (i, j ≠ 0) frame, which is stored in a frame memory 11 described later and motion compensated and predicted by the motion compensation prediction unit 13. Take. This eliminates temporal redundancy.
[0015]
The output of the subtracter 2 is input to a discrete cosine transform unit (DCT) 3 and converted into a frequency-domain signal, and further input to a quantization unit 4 and quantized (bit-converted). The output of the quantization unit 4 is input to the variable length coding unit 5.
[0016]
The output of the quantization unit 4 is also input to the inverse quantization unit 8 and is inversely quantized. Then, the output of the inverse quantization unit 8 is input to the inverse discrete cosine transform unit (IDCT) 9 and returned to the state before the discrete cosine transform. The output of the inverse discrete cosine transform unit 9 is input to the adder 10. The adder 10 adds the output of the inverse discrete cosine transform unit 9 and the locally decoded data (locally decoded image) output from the motion compensation prediction unit 13, and supplies the addition result to the frame memory 11.
[0017]
The motion vector detection unit 12 detects a motion vector based on the output of the buffer memory / preprocessing unit 1 and the output of the frame memory 11, and supplies the motion vector to the motion compensation prediction unit 13.
[0018]
The incidental information output from the motion compensation prediction unit 13 and the quantized signal output from the quantization unit 4 are input to the variable length coding unit 5 and are variable length coded. The output of the variable length coding unit 5 is input to a multiplexer (MUX) 6. The multiplexer 6 performs multiplexing so that the output of the variable-length encoding unit 5 has a data structure conforming to the MPEG2 standard. Further, the code amount control unit 7 sets coefficients necessary for the quantization in the quantization unit 4 based on the information from the multiplexer 6 so that the data amount of the encoded data per unit time falls within an appropriate range. .
[0019]
Next, a specific configuration and operation of the motion compensation unit 13 will be described with reference to FIG. As shown in FIG. 2, the motion compensation prediction unit 13 includes a reference image generation unit 131 that generates a reference image of each prediction mode, an error evaluation value calculation unit 132 that calculates an error evaluation value of each prediction mode, and a mode discrimination. Unit 133, a reference image generation unit 134 that generates a reference image based on the additional information of the adjacent macroblock, an error evaluation value calculation unit 135 that calculates an error evaluation value, a mode determination unit 136, and an additional information update unit 137 and an additional information holding unit 138.
[0020]
The motion vector output from the motion vector detection unit 12 and the locally decoded image output from the frame memory 11 are input to the reference image generation unit 131. The reference image generation unit 131 generates a reference image for each prediction mode based on the input motion vector and the locally decoded image. Each prediction mode is as shown below.
[0021]
In the case of an I picture, it is an intra-coded macroblock (Intra MB), and in the case of a P picture, it is Intra MB, a forward prediction motion compensation macroblock (Forward MC MB), or a forward interframe prediction macroblock. (No MC MB). In the case of a B picture, it is an Intra MB, a Forward MC MB, a backward prediction motion compensation macroblock (Backward MC MB), or a bidirectional prediction motion compensation macroblock (Average MC MB).
[0022]
The error evaluation value calculation unit 132 extracts a prediction block from the input reference image for each prediction mode and calculates an error evaluation value while obtaining a difference from the input image. The error evaluation value for each prediction mode calculated by the error evaluation value calculation unit 132 is input to the mode determination unit 133. The mode determination unit 133 determines the prediction mode based on the error evaluation value for each prediction mode input from the error evaluation value calculation unit 132.
[0023]
The supplementary information of the adjacent macroblock is input from the supplementary information holding unit 138 to the reference image generation unit 134. The adjacent macroblock is most preferably the macroblock to the left of the current macroblock. The reference image generation unit 134 generates a reference image based on the incidental information (prediction mode, motion vector, type of frame macroblock / field macroblock) of the input adjacent macroblock and the locally decoded image in the frame memory 11. I do.
[0024]
The error evaluation value calculation unit 135 calculates an error evaluation value based on the reference image output from the reference image generation unit 134 while obtaining a difference from the input image. The error evaluation value calculated by the error evaluation value calculation unit 135 is input to the mode determination unit 136. The mode determination unit 136 determines a prediction mode based on the error evaluation value input from the error evaluation value calculation unit 135 and the prediction mode input from the mode determination unit 133, and subtracts a prediction image of the prediction mode from the subtractor 2 To supply.
[0025]
Here, if the determined prediction mode is the same prediction mode as the adjacent macroblock, the incidental information updating unit 137 replaces the incidental information of the current macroblock with the incidental information of the adjacent macroblock. The additional information holding unit 138 stores and holds the additional information of the current macroblock and the additional information of the adjacent macroblock. The additional information output from the additional information holding unit 138 is supplied to the variable length coding unit 5.
[0026]
As described above, when the supplementary information of the current macroblock is the same as the supplementary information of the adjacent macroblock, and all the coefficients after the processing in the DCT unit 3 and the quantization unit 4 are 0, the current macroblock has a variable length. The encoding unit 5 determines that the block is a skip macro block. If it is determined that the macroblock is a skipped macroblock, the variable-length encoding unit 5 outputs the macroblock without adding the additional information of the macroblock.
[0027]
This makes it possible to reduce the code amount for the additional information. Even when it is not determined that the macroblock is a skipped macroblock, since the difference between the motion vectors is 0, the amount of code for the motion vector can be reduced, and the efficiency of variable-length coding in the variable-length coding unit 5 is improved. Further, according to the rules of MPEG2, in a decoding device, for a macroblock having no supplementary information, the supplementary information of the immediately preceding macroblock is used as it is, and the decoding is performed without adding the supplementary information as described above. This does not affect the reproduced image. Therefore, it is possible to perform more appropriate encoding even with a limited data amount.
[0028]
【The invention's effect】
As described above in detail, the video encoding device of the present invention provides a motion compensation prediction unit that performs a plurality of predictions on the basis of a motion vector and a locally decoded image encoded and decoded in the video encoding device. A first reference image generation unit for generating a reference image of the mode, a first error evaluation value calculation unit for calculating a first error evaluation value using the reference images of the plurality of prediction modes and the input image, A second reference image generation unit that generates a reference image based on incidental information of an adjacent macroblock adjacent to the macroblock, and a reference image generated by the second reference image generation unit and an input image. A second error evaluation value calculation unit that calculates a second error evaluation value; a prediction mode determination unit that determines a prediction mode based on the first error evaluation value and the second error evaluation value; Stores incidental information of adjacent macroblock If the prediction mode determined by the additional information holding unit and the prediction mode determination unit is a mode for generating a reference image based on the additional information of the adjacent macroblock, the additional information of the current macroblock is added to the adjacent macroblock. Since the configuration includes the additional information replacing means for replacing the additional information with the additional information and outputting the information, it is possible to perform the encoding more efficiently and without any visual defect.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an example of the overall configuration of the present invention.
FIG. 2 is a block diagram showing an embodiment of a main part of the present invention.
FIG. 3 is a block diagram showing a conventional example.
[Explanation of symbols]
REFERENCE SIGNS LIST 1 buffer memory / preprocessing unit 2 subtracter 3 discrete cosine transform unit 4 quantizer 5 variable length encoder 6 multiplexer 7 code amount controller 8 inverse quantizer 9 inverse discrete cosine transform unit 10 adder 11 frame memory 12 Motion vector detection unit 13 Motion compensation prediction unit 131, 134 Reference image generation unit 132, 135 Error evaluation value calculation unit 133, 136 Mode discriminating unit 137 Additional information updating unit (additional information replacement unit)
138 Additional information storage unit

Claims (1)

In a video encoding device having a motion vector detection unit that detects a motion vector, and a motion compensation prediction unit,
The motion compensation prediction unit,
A first reference image generation unit that generates a reference image in a plurality of prediction modes based on a motion vector and a locally decoded image encoded and decoded in the video encoding device; A first error evaluation value calculation unit that calculates a first error evaluation value using the reference image and the input image;
A second reference image generation unit that generates a reference image based on incidental information of an adjacent macroblock adjacent to the current macroblock;
A second error evaluation value calculation unit that calculates a second error evaluation value using the reference image generated by the second reference image generation unit and the input image;
A prediction mode determining unit that determines a prediction mode based on the first error evaluation value and the second error evaluation value;
An additional information holding unit that stores additional information of the current macroblock and adjacent macroblocks;
When the prediction mode determined by the prediction mode determination unit is a mode for generating a reference image based on the additional information of the adjacent macroblock, the additional information of the current macroblock is replaced with the additional information of the adjacent macroblock. A video encoding device, comprising: an additional information replacing unit that outputs.

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