Efficient encoding of video blocks

Details Efficient encoding of video blocks Efficient encoding of video blocks

1998-12-22

2002-02-26

Chen, Wenpeng (Department: 2624)

Image analysis

Image compression or coding

Predictive coding

C382S239000, C375S240020, C375S240240

Reexamination Certificate

active

06351567

ABSTRACT:

FIELD
This invention relates to the compression of video signals, and more particularly it relates to detecting empty blocks in a video signal.
BACKGROUND
In a world wired for digital communication, the use of real time video encoders is becoming more common. For example, video encoders are used to prepare real time video images of exotic vacation spots for transmission to interested viewers having access to only a computer and a telephone line.
The process of encoding images in real time employs a great deal of computing power, and the computing power available to encode an image determines at least in part the amount of detail that can be included in the encoded image. For example, a thirty-two bit microprocessor running at 200 megahertz (MHZ) can successfully encode a 256×256 pixel real time video image, but to successfully encode a high resolution 1024×1024 pixel real time video image typically employs a sixty-four bit microprocessor running at 450 megahertz.
Various strategies have been developed to encode high resolution images while reducing the computing power employed. One strategy involves identifying video data blocks that are “empty” prior to encoding. A block is an array of pixels in a video frame. For example, in a video frame represented by a 1024×1024 array of pixels, a block within the video frame can be represented by an 8×8 array of pixels. An empty block is usually defined as a block that contains only zero-valued coefficients after a discrete cosine transform and quantization process are applied to the block. Such a block can be represented in a bitstream by a single bit indicating that the block is “empty.” If an empty block is identified prior to when the discrete cosine transform and quantization process are applied to the block, then the block is not encoded and the computing power normally employed to encode the block is saved. The saved computing power may be applied to encoding a higher resolution image or it may be applied to encoding real time video frames at a higher rate.
One approach to identifying empty blocks prior to encoding is to characterize each block by a single numerical value, and then to compare that numerical value to a fixed threshold value. The fixed threshold value is selected to roughly identify a value that separates empty blocks from non-empty blocks. If the numerical value associated with the block is less than the fixed threshold, then the block is assumed to be empty and is skipped. If the numerical value is greater than the fixed threshold, then the block is assumed to be non-empty and is encoded. A problem associated with this approach is that in order to avoid mischaracterizing a non-empty block as an empty block, the fixed threshold is set unnecessarily low and empty blocks still end up being encoded. This unnecessary encoding wastes computing power.
For these and other reasons there is a need for the present invention.
SUMMARY
In one embodiment of the present invention, a residual video block is received, and a probabilistic threshold is employed to predict whether the block is non-empty without encoding the block.


REFERENCES:
patent: 5737537 (1998-04-01), Gardos et al.
patent: 5847776 (1998-12-01), Khmelnitsky et al.
“Method for detecting all-zero DCT coefficients ahead of discrete cosine transformation and quantisation,” Zhou Xuan et al., Electronics Letters, vol. 34, No. 19, Sep. 17, 1998, pp. 1839-1840.*
“Video Codec for Audiovisual Services at p x 64 kbits”,International Telecommunications Union, Recommendation H.261,pp. 1-25, (1994).
Bist, A., et al., “Intelligent Pre-Quantization in Motion Compensated Video Coding”,Rockwell Semiconductor Systems,ITU-Telecommunications Standardization Sector, Study Group 16; Question Q.15/16, Expert's Group on Very Low Bitrate Visual Telephony, Tampere, Finland, 5 p., (1998).

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