DX JPEG Huffman decoder

Details DX JPEG Huffman decoder DX JPEG Huffman decoder

1996-11-25

1998-10-20

Williams, Howard L.

Coded data generation or conversion

Digital code to digital code converters

To or from number of pulses

341 67, H03M 740

Patent

active

058253122

ABSTRACT:
A low cost, high speed, JPEG Huffman code decoder. The entire gamut of Huffman codes is partitioned into groups, with each group being associated with it's own small look up table to minimize the overall memory requirements. The current Huffman code is stored in a register. For the disclosed embodiment there are N=4 memories with sizes 128, 256, 128 and 256 elements respectively. For the specific typical Huffman code set cited, the partitioning is: The code words in the first group have 7 bits or less and are decoded in the first memory. The next group has from 5 to 7 leading ones, where the first five 1's are masked out and the remaining bits are used to address the second memory. The remaining codes have at least eight leading ones. Here, the first eight ones are masked out and the remaining bits are used to address the last memory. (In this example, one of the memories is not used). Finally, the first eight bits are used in a selector to enable the correct memory so that a single correct output data word is output. The disclosed N=4 embodiment is designed to handle any custom JPEG Huffman code set. This concept can be extended to other memory partitions (a N=6 example is cited) that might provide some desirable memory vs logic switching tradeoffs.

REFERENCES:
patent: 5254991 (1993-10-01), Ruetz et al.
patent: 5325092 (1994-06-01), Allen et al.

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