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I am attempting to write JPEG decompression program. With...

<< Back to: JPEG image compression FAQ, part 1/2

Question by TxITGuy
Submitted on 8/21/2003
Related FAQ: JPEG image compression FAQ, part 1/2
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I am attempting to write JPEG decompression program.  With the information I have found on the Internet, I have:
* successfully parsed the entire file
* retrieve the image dimensions, color component count, related tables, etc.
* extracted and rebuilt both Quantization tables
* extracted the raw data for all four Huffman tables (including the 16 bytes of symbol length data for each table).

Two items have me stumped though ... and don't seem to have any practical documentation on the Internet.

1.  How do I recreate the original Huffman tree from the symbol length data?

2.  Once I decompress the bit stream, how to I apply the values in the Quantization Tables to the image data?  I think I need use the Inverse Discrete Cosine Transform, which takes two inputs.  After that, I'm just guessing.

Thanks,
Ben


Answer by Korejwa
Submitted on 5/11/2004
Rating:  Rate this answer: Vote
Buy a copy of the "ISO DIS 10918-1" JPEG standard.  It includes flow charts that show you how to construct a Huffman tree from a DHT marker.  There is not enough free information on the web to go any further than you have gone.  (unless you study existing sourcecode)  You need the actual standard.

 

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