Re: [Libjpeg-devel-6x] 12bit jpeg and std_huff_tables

[Frank W. <war...@po...>]

Tom Lane wrote:
> Frank Warmerdam <war...@po...> writes:
>> The std_huff_tables() function has a comment reading:
> 
>> /* Set up the standard Huffman tables (cf. JPEG standard section K.3) */
>> /* IMPORTANT: these are only valid for 8-bit data precision! */
> 
>> So, my question is, does anyone know appropriate comparable tables to use
>> for 12bit images?
> 
> AFAIK the JPEG committee never did propose any default Huffman tables
> for 12-bit mode :-( ... that's why libjpeg is set up to forcibly compute
> a table in that mode.

Tom,

Thanks.

I have successfully developed a huffman table that seems to work ok
for a variety of 12 bit images.  I basically picked a reference image,
computed the symbol histogram, and added "1" to each bucket in the
histogram and computed an optimal table based on that.  I don't know how
good this is, but at least it works and saves me a preprocessing pass
which is difficult in the context of libtiff.

I have prepared a patch for this, and attached it to a new ticket.  I
would appreciate feedback on it before I apply it.

http://sourceforge.net/tracker/?func=detail&aid=2809979&group_id=159521&atid=812162

Best regards,
-- 
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I set the clouds in motion - turn up   | Frank Warmerdam, war...@po...
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