Re: SANE & exposure times
Didier Carlier (Didier.Carlier@sema.be)
Fri, 30 Jul 1999 11:24:26 +0200
ewald@pobox.com said:
> The main use is for scanning negatives. For negatives, density of blue
> is ~3x that of red, and that of green is ~2x that of red (hence the
> orange color of the negative mask). So if you scan with 1:1:1 exposure
> time, the green channel will only use 1/2 of it's full range. In other
> words, you have lost one bit of what is basically your luminance. The
> blue channel is filled for only 1/3 and this poor blue definition can
> also be very visible to the human eye.
>
> All this can be solved by scanning with a 1:2:3 exposure so that the
> full range of all channels is utilized.
If I look at the RGB values after a scan of a negative, the values of all
channels go from 0 to 255, so I'm not quite sure of what you are trying to do.
Putting the multiple scan issue aside you can't get more than 8 bits of
resolution per channel so that you don't loose definition on the blue channel,
you loose dynamic range.
I.e. you do not extract the clearer blue details, but you do keep the full 8 bit
color resolution for the dynamic range that was scanned.
Am I missing something here ?
Didier
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