Pulse or digital communications – Bandwidth reduction or expansion – Television or motion video signal
Reexamination Certificate
1996-06-24
2001-04-24
Britton, Howard (Department: 2713)
Pulse or digital communications
Bandwidth reduction or expansion
Television or motion video signal
C375S240200, C375S240120
Reexamination Certificate
active
06222886
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a compressed video decoder. More specifically, the present invention relates to a compression-based reduced memory video decoder, with substantially lossless compression.
2. Description of the Related Art
The most popular video encoders in present use utilize motion compensated prediction, followed by transmission of a compressed error signal, as a means of efficient compression. Some encoders use forward prediction (past reference), while other decoders use both forward and backward (future reference) prediction. The standard MPEG-1 and MPEG-2 class of video encoders use both of these two types of predictions.
The implication for a video decoder is that it must maintain a copy of these reference pictures in order to decode the picture that referenced them. An MPEG decoder, for example, must have sufficient memory to store the decoded version of at least two reference pictures, in addition to a display buffer consisting of the current picture being decoded and displayed.
A standard MPEG-2 video decoder includes a channel buffer, a variable length decoder (VLD), an inverse quantization (IQ) means, an inverse discrete cosine transform (IDCT) means, a motion compensator, an anchor frame storage, and a display memory.
In the related device, the total memory space includes memory to store incoming coded data, channel buffer, and sufficient memory in anchor frame storage to store at least two reference pictures, in addition to the display memory.
Requiring this amount of memory is disadvantageous, because memory space is expensive and accounts for the largest percentage of the cost of a video decoder.
SUMMARY OF THE INVENTION
The present invention is intended to overcome the above mentioned disadvantages in the related art by reducing the amount of memory space required in a compressed video decoder.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
Accordingly, the present invention broadly relates to a method and apparatus for decoding compressed video data, comprising the steps of receiving compressed video data in a channel buffer, decompressing the compressed video data and transferring the decompressed video data to a display memory, recompressing a portion of the decompressed video data as intraframe data to be used as an anchor frame, storing the intraframe data in a compressed anchor frame storage, motion compensating the intraframe data, selecting a reference picture from the intraframe data, and decompressing a region of interest of the reference picture.
The present invention further foresees a potential difficulty with recompressing a portion of the decompressed video data. If the compression is lossy, prediction drift will occur, introducing distortion and inaccuracies in the decoded picture.
Accordingly, the present invention further comprises a method and apparatus for receiving compressed video data having a quantization matrix, a quantizer scale, and a field/frame coding type, decompressing the compressed video data, recompressing a portion of the compressed video data as intraframe data to be used as an anchor frame, the recompression using a discrete cosine transform, the quantizer matrix, the quantizer scale, and the field/frame coding type, and storing the intraframe data in a compressed anchor frame storage, motion compensating the intraframe data, and selecting a reference picture from the intraframe data. The above recompression technique is substantially lossless.
The present invention further relates to compressed video decoders comprising means for performing the above-stated steps.
The teachings of the invention further can be applied to reducing the memory space of a display buffer.
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Britton Howard
Diep Nhon T.
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Kabushiki Kaisha Toshiba
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