Digital BW, The Print

> From: claudej1@... [mailto:claudej1@...]
>
> In a message dated 12/12/2003 3:23:42 PM Eastern Standard Time,
> DigitalBlackandWhiteThePrint@yahoogroups.com writes:
> Not true. With three channels of 8 bits, that's roughly equal to 9.5 bits,
> because the maximum value you can get by adding three 255's
> together is 765,
> which takes about 9.5 bits to represent.

> Not true either. The numbers multiply, they don't add. 256 x 256
> x 256 gives
> us 24 bits or 16.7+ million different values. Each bit double the
> numbers and can represent 1 stop.

No, THAT's not true. We're not talking about the number of possible
combinations of 24 bits, which is obviously over 16 million. We're talking
about the apparent resolution, meaning the number of apparent levels of
brightness you can perceive, or a colorimeter can measure. Believe me, with
three 8-bit color channels, equally weighted, the smallest change you can
see or measure when you change one bit isn't 1/16M of full scale, it's about
1/750 of full scale, because the brightness is roughly speaking based on the
sum of the three bytes, not their product. Since the gamma isn't generally
1, and since the three colors aren't perceived to be equally bright, the 750
figure isn't accurate, but it's more than 255 but probably averages out to
be somewhere around 750. It ain't 16M, or anything remotely like that.

--

Ciao,               Paul D. DeRocco
Paul                mailto:pderocco@...