Reduced complexity IDCT decoding with graceful degradation

Abstract

Data compressed according to a lossy DCT-based algorithm, such as the MPEG or MPEG2 algorithms, is decompressed according to a dynamically-selected set of DCT coefficients, with unused coefficients masked out. A macroblock of the data exhibiting little motion is decompressed with a small subset of DCT coefficients, while a macroblock exhibiting more motion is decompressed using a larger subset of DCT coefficients up the full set of DCT coefficients. Average computational complexity is thus kept low, enabling the use of inexpensive equipment, while degradation is minimized.

1 . A method of decoding DCT-encoded blocks of a data signal, the method comprising: 
 (a) predetermining a plurality of subsets of DCT coefficient positions;    (b) receiving a set of DCT coefficients obtained from DCT-encoding a corresponding portion of a data signal;    (c) selecting one of said subsets of DCT coefficient positions according to a value of a predetermined one of the received DCT coefficients;    (d) performing IDCT decoding on the selected subset of DCT coefficients to recover a representation of the corresponding portion of the data signal; and    (e) repeating steps (b), (c), and (d) for successive sets of DCT coefficients.    
     
     
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         8 . Apparatus for decoding DCT-encoded blocks of a data signal, the apparatus comprising: 
 a data store for storing a predetermined plurality of subsets of DCT coefficient positions;    a receiver for receiving a set of DCT coefficients obtained from DCT-encoding a portion of said data signal;    computation means for:    selecting one of said subsets of DCT coefficient positions according to a value of a predetermined one of the received DCT coefficients; and    performing IDCT decoding on the selected subset of DCT coefficients to recover a representation of the corresponding portion of the data signal; and    control logic for routing successive sets of DCT coefficients through the receiver and computation means.    
     
     
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