Pixel translations

[Akira Hatakeyama]

Greetings.

Subject Pixel translations
       Apr 11, 12:39pm, Ho-Kuo Chan wrote:
] Hi,
] 	I was looking at the code for the pixel format translations and there
] is something I can't quite figure out (I'm hoping Wez or Jonathan can
] help me with this). Let's say the server is at 24 bpp in BGR888 and the
] client wants 8 bpp in BGR233. If we use three separate tables in the
] server, then the server will translate 8 bit blue to 2 bit blue, 8 bit
] green to 3 bit green and 8 bit red to 3 bit red. I would think that this
] would work out to an even distribution, eg: for blue, 8 bit input values
] from 0 to 63 would translate to 0 in 2 bits, 64 to 127 -> 1, 128 to 191
] ->2 and 192 to 255 -> 3. However, after analysing the code, I see that
] in fact, the distribution is actually: 0 to 42 -> 0, 43 to 127 -> 1, 128
] to 212 -> 2 and 213 to 255 -> 3. The results are similar to other
] translations (eg: 8 bit primary colour input to 3 bit primary output, 8
] bit to 5 bit, etc). I would think that an equally distributed
] translation would result in a more true image. Can anyone explain?

How about <http://www.inforamp.net/~poynton/Poynton-color.html>?
Gamma FAQ and Color FAQ will help you.

-- 
Akira Hatakeyama	E-Mail: akira "at" sra.co.jp
   http://www.sra.co.jp/people/akira/index.html
chigasaki-minami, tsuzuki ward, yokohama, japan
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