Pulse or digital communications – Bandwidth reduction or expansion
Reexamination Certificate
1999-10-01
2004-09-07
An, Shawn S. (Department: 2613)
Pulse or digital communications
Bandwidth reduction or expansion
C375S240100, C375S240110, C375S240120, C375S240030, C375S240180, C375S240250, C348S397100, C348S398100, C348S408100, C382S234000, C382S238000, C382S240000
Reexamination Certificate
active
06788740
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention is directed, in general, to video encoding systems and, more specifically, to an encoding system and a decoding system for streaming video data.
BACKGROUND OF THE INVENTION
Real-time streaming of multimedia content over data networks, including the Internet, has become an increasingly common application in recent years. A wide range of interactive and non-interactive multimedia applications, such as news-on-demand, live network television viewing, video conferencing, among others, rely on end-to-end streaming video techniques. Unlike a “downloaded” video file, which may be retrieved first in “non-real” time and viewed or played back later in “real” time, streaming video applications require a video transmitter that encodes and transmits a video signal over a data network to a video receiver, which must decode and display the video signal in real time.
Scalable video coding is a desirable feature for many multimedia applications and services that are used in systems employing decoders with a wide range of processing power. Scalability allows processors with low computational power to decode only a subset of the scalable video stream. Another use of scalable video is in environments with a variable transmission bandwidth. In those environments, receivers with low-access bandwidth receive, and consequently decode, only a subset of the scalable video stream, where the amount of that subset is proportional to the available bandwidth.
Several video scalability approaches have been adopted by lead video compression standards such as MPEG-2 and MPEG-4. Temporal, spatial and quality (e.g., signal-noise ratio (SNR)) scalability types have been defined in these standards. All of these approaches consist of a base layer (BL) and an enhancement layer (EL). The base layer part of the scalable video stream represents, in general, the minimum amount of data needed for decoding that stream. The enhanced layer part of the stream represents additional information, and therefore enhances the video signal representation when decoded by the receiver.
For example, in a variable bandwidth system, such as the Internet, the base layer transmission rate may be established at the minimum guaranteed transmission rate of the variable bandwidth system. Hence, if a subscriber has a minimum guaranteed bandwidth of 256 kbps, the base layer rate may be established at 256 kbps also. If the actual available bandwidth is 384 kbps, the extra 128 kbps of bandwidth may be used by the enhancement layer to improve on the basic signal transmitted at the base layer rate.
For each type of video scalability, a certain scalability structure is identified. The scalability structure defines the relationship among the pictures of the base layer and the pictures of the enhanced layer. One class of scalability is fine-granular scalability. Images coded with this type of scalability can be decoded progressively. In other words, the decoder may decode and display the image with only a subset of the data used for coding that image. As more data is received, the quality of the decoded image is progressively enhanced until the complete information is received, decoded, and displayed.
The proposed MPEG-4 standard is directed to video streaming applications based on very low bit rate coding, such as video-phone, mobile multimedia/audio-visual communications, multimedia e-mail, remote sensing, interactive games, and the like. Within the MPEG-4 standard, fine-granular scalability (FGS) has been recognized as an essential technique for networked video distribution. FGS primarily targets applications where video is streamed over heterogeneous networks in real-time. It provides bandwidth adaptivity by encoding content once for a range of bit rates, and enabling the video transmission server to change the transmission rate dynamically without in-depth knowledge or parsing of the video bit stream.
An important priority within conventional FGS techniques is improving coding efficiency and visual quality of the intra-frame coded enhancement layer. This is necessary to justify the adoption of FGS techniques for the compression of the enhancement layer in place of non-scalable (e.g., single layer) or less granular (e.g., multi-level SNR scalability) coding methods.
Many video coding techniques have been proposed for the FGS compression of the enhancement layer, including wavelets, bit-plane DCT and matching pursuits. At the MPEG-4 meeting in Seoul, Korea in March 1999, the bit-plane DCT solution proposed by Optivision was selected as a reference. The bit-plane coding scheme adopted as reference for FGS includes the following steps at the encoder side:
1. residual computation in the DCT domain, by subtracting from each original DCT coefficient the reconstructed DCT coefficient after base-layer quantization and dequantization;
2. determining the maximum value of all of the absolute values of the residual signal in a video object plane (VOP) and the maximum number of bits n to represent this maximum value;
3. for each block within the VOP, representing each absolute value of the residual signal with n bits in the binary format and forming n bit-planes;
4. bit-plane encoding of the residual signal absolute values; and
5. sign encoding of the DCT coefficients which are quantized to zero in the base-layer.
These coding steps are reversed at the decoder side. It is important to notice that the current implementation of the bit-plane coding of DCT coefficients is done independently of the base-layer (coding) information. The quantized base-layer DCT coefficients, which are employed for the residual layer computation in the DCT domain, are the only information of the base-layer that is re-used for the compression of the enhancement layer. However, additional base-layer information that could be used to further compress the enhancement layer data is unused.
There is therefore a need in the art for improved encoders and encoding techniques for use in streaming video systems. In particular, there is a need for encoders and decoders that use base-layer information to increase the efficiency of the encoding and decoding of enhancement layer data. More particularly, there is a need for encoding techniques that use base-layer information to eliminate as much redundant information as possible from the enhancement layer data. There is a further need for decoding techniques that are able to use the base-layer information to predict as much enhancement layer data as possible.
SUMMARY OF THE INVENTION
To address the above-discussed deficiencies of the prior art, it is a primary object of the present invention to provide a new technique for improving the coding efficiency of an enhancement layer compression scheme. The present invention proposes a technique for enhancing the coding efficiency of the bit-plane compression scheme of, for example, the residual DCT coefficients currently adopted as a reference within the MPEG-4 standard. However, it is important to realize that the proposed improvements are not limited to the DCT transform. Those skilled in the art will readily understand that the principles of the present invention may also be successfully, applied to other transforms (e.g., wavelets) for the compression of the base and enhancement layer. However, in the descriptions that follow, DCT coefficients are employed for illustration purposes only.
The proposed algorithm employs base-layer quantization parameters to predict a range of the residual DCT coefficients (i.e., a maximum number of significant bit-planes for each residual coefficient) and to avoid the unnecessary transmission of certain zero-valued bit-planes of the DCT coefficients.
While the adopted FGS scheme eliminates most of the temporal dependencies between consecutive enhancement-layer frames by adopting a motion-compensation prediction-based scheme at the base-layer, unexploited redundancies still remain at the enhancement-layer level. Using base-layer coding information, certain characteristics of the enhancement-layer (residual) DCT coef
Chen Yingwei
Radha Hayder
van der Schaar Mihaela
An Shawn S.
Koninklijke Philips Electronics , N.V.
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