Television – Bandwidth reduction system – Data rate reduction
Reexamination Certificate
1997-10-31
2002-04-09
Kostak, Victor R. (Department: 2711)
Television
Bandwidth reduction system
Data rate reduction
C348S558000, C370S474000
Reexamination Certificate
active
06369855
ABSTRACT:
NOTICE
(C) Copyright 1996 Texas Instruments Incorporated. A portion of the disclosure of this patent document contains material which is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent disclosure, as it appears in the Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever.
FIELD OF THE INVENTION
This invention generally relates to audio-visual systems and integrated circuits used therein, and more particularly, to improved audio-visual systems and improved integrated circuits used therein.
BACKGROUND OF THE INVENTION
Currently, digital television DSS/DVB signals are transmitted in an MPEG format. In the MPEG format, the signals are transmitted in the form of data packets, with each packet including a useful signal or data and a header signal or data containing information about the contents of the useful signal or data.
Such a digital signal generally consists of packets of various types, such as audio data packets, video data packets and packets containing information pertaining to the program transmitted.
In general, the decoding of such digital signals takes place in a decoder in a reception station, which identifies and selects, in the incoming signals, desired audio and video data packets and then decodes these packets to form data trains, of the audio and video types, respectively. The audio data trains are decoded by means of an audio decoder for forming an analog acoustic signal. Similarly, the video data trains are used to form an image as well as chrominance and luminance signals.
There are known devices for the identification of packets. These devices extract a piece of data from each header signal, which is representative of the type of the corresponding useful signal. They include a means for storing reference data in a memory, at addresses each corresponding to one packet type, and a means for comparing the piece of data extracted from each header signal with said reference data (stored in the memory) then delivering to a data processing unit for further processing, an address signal indicating the nature of the corresponding packet. The processing unit then selects the identified packets for decoding and for forming corresponding data trains.
For this type of identification device, the comparison between the piece of data extracted from the header signal and the reference data stored in memory is conducted successively; that is, at a transition of a synchronization clock, an extracted piece of data is compared to a reference piece of data.
However, since the transmission rate of the packets is very high, the packet being identified must be stored, for example, in a memory of the FIFO type, associated with a piloting circuit and then further processed by the data processing unit.
Consequently, this type of identification device is relatively slow, requires a large number of components, and requires a large amount of memory and/or local storage buffers.
International standardization committees have been working on the specification of the coding methods and transmission formats for several compression algorithms to facilitate world wide interchange of digitally encoded audiovisual data. The Joint Photographic experts Group (JPEG) of the International Standards Organization (ISO) specified an algorithm for compression of still images. The ITU (formerly CCITT) proposed the H.261 standard for video telephony and video conference. The Motion Pictures Experts Group (MPEG) of ISO specified a first standard, MPEG-1, which is used for interactive video and provides a picture quality comparable to VCR quality. MPEG has also specified a second standard, MPEG-2, which provides audiovisual quality of both broadcast TV and HDTV. Because of the wide field of applications MPEG-2 is a family of standards with different profiles and levels.
The JPEG coding scheme could be in principal also used for coding of images sequences, sometimes described as motion JPEG. However, this intraframe coding is not very efficient because the redundancy between successive frames is not exploited. The redundancy between succeeding frames can be reduced by predictive coding. The simplest predictive coding is differential interframe coding where the difference between a current pixel of the present frame and the corresponding pixel of the previous frame is quantized, coded and transmitted. To perform such interframe prediction a frame memory for storing one or more frames is required to allow for this pixel by pixel comparison. Higher efficiency than the simple differential interframe coding can be achieved by a combination of discrete cosine transform (DCT) and interframe prediction. For so-called hybrid coding the interframe difference, which is similar to JPEG, is obtained, DCT coded and then transmitted. In order to have the same prediction at both the receiver and transmitter the decoder is incorporated into the coder. This results in a special feedback structure at the transmitter which avoids coder-decoder divergence.
Variable word length coding results in a variable bit rate which depends on image content, sequence change, etc. Transmission of the coded information over a constant rate channel requires a FIFO buffer at the output to smooth the data rate. The average video rate has to be adjusted to the constant channel rate. This is performed by controlling the quantizer according to the buffer content. If the buffer is nearly full, the quantization is made more sever and thus the coded bitrate is reduced. Conversely, if the buffer is nearly empty, the quantization is relaxed.
In general, the MPEG coding use a special predictive coding strategy. The coding starts with a frame which is not differentially coded; it is called an Intraframe (I). Then prediction is performed for coding one frame out of every M frames. This allows computation of a series of predicted frames (P), while “skipping” M-1 frames between coded frames. Finally, the “skipped” frames are coded in either a forward prediction mode, backward prediction mode, or bi-directional prediction mode. These frames are called bi-directionally interpolated (B) frames. The most efficient prediction mode, in terms of bitrate, is determined by the encoder and its selected mode is associated with the coded data. Thus the decoder can perform the necessary operations in order to reconstruct the image sequence. A main difference between MPEG-1 and MPEG-2 is that MPEG-1 has been optimized for non-interlaced (progressive) format while MPEG-2 is a generic standard for both interlaced and progressive formats. Thus, MPEG-2 includes more sophisticated prediction schemes.
In more detail, motion pictures are provided at thirty frames per second to create the illusion of continuous motion. Since each picture is made up of thousands of pixels, the amount of storage necessary for storing even a short motion sequence is enormous. As higher and higher definitions are desired, the number of pixels in each picture grows also. This means that the frame memory used to store each picture for interframe prediction also grows; current MPEG systems use about 16 megabits (MB) of reference memory for this function. Fortunately, lossy compression techniques have been developed to achieve very high data compression without loss of perceived picture quality by taking advantage of special properties of the human visual system. (A lossy compression technique involves discarding information not essential to achieve the target picture quality to the human visual system). An MPEG decoder is then required to reconstruct in real time or nearly real time every pixel of the stored motion sequence; current MPEG decoders use at least about 16 MB of frame memory for reconstruction of frames using the encoded interframe prediction data.
The MPEG standard specifies both the coded digital representation of video signal for the storage media, and the method for decoding to achieve compatibility between compression and decompression equipment. The standard supp
Benbassat Gerard
Chae Brian O.
Chauvel Gerard
Chiang Y. Paul
Giani Mario
Brady III W. James
Kostak Victor R.
Laws Gerald E.
Telecky , Jr. Frederick J.
Texas Instruments Incorporated
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