clipka wrote:
> No, basically the JPEG compression quality is a non-discrete value;

JPEG compression quality isn't even defined as a number. Each 8x8 block on 
the image can pick how much of the quality to throw away. (For example, I 
wrote one compressor way back in the dark ages that would compress a block 
less if the average color was close to skin-tone.)

It's not a number. It's an entire 8x8 matrix for each 8x8 block of the 
image. That said, most programs take the number you give it and translate it 
into an appropriate 8x8 block. The open source library (originally used in 
cjpeg and djpeg) used a 0..100 scale. On this scale, 95..100 give you a 
range of pixels that are usually spot-on, or off by one out of 255 each, but 
a huge change in the size (3x? 10x?) for stepping from 95 to 100.

There's also the possibility of having multiple huffman tables, or an 
optimized huffman table, or a simple huffman table. Nobody does the simple 
huffman table any more, but back when a jpeg compression took ten seconds or 
so, not going thru it twice to recalculate the huffmans was sometimes 
worthwhile.

-- 
Darren New, San Diego CA, USA (PST)
   Linux: Now bringing the quality and usability of
   open source desktop apps to your personal electronics.

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