Digital BW, The Print

the bottom line really is that you have plenty of data to create a 
good 8 or 16 bit _depth_ image from a rgb image file.  The fact is 
that you can combine them in such away as to yeild a huge number of 
different b&w reditions of a scene after you capture the image, a 
small subset of which will appear similar to commercially available 
b&w film... the others are left for the creative adventurer.

mark

PS  the channels do get mixed so black is 0.0 and white is 3x256 for 
a 24-bit color file going to b&w which then is scaled to your final 
image depth (ie. Paul is correct).

--- In DigitalBlackandWhiteThePrint@yahoogroups.com, "Paul D. 
DeRocco" <pderocco@i...> wrote:
> > From: claudej1@a... [mailto:claudej1@a...]
> >
> > 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@i...