Strange, but it seems some of my replies arrive about eight hours later than
I send them and some never get there.
Anyway, I have a question below:
> -----Original Message-----
> From: Andrew Rodney [SMTP:[EMAIL PROTECTED]]
> Sent: Thursday, January 11, 2001 3:01 PM
> To: Film Scanners; Bob Shomler
> Subject: Re: filmscanners: Fw: Color Profiles for Scanners
>
> on 1/10/01 7:54 PM, Bob Shomler at [EMAIL PROTECTED] wrote:
>
> > But if changes do expand into the larger gamut it might affect printed
> output.
>
> Taking a file in sRGB and converting it to Adobe RGB isn't going to expand
> the gamut of the file. It's fixed after becoming sRGB. You can't increase
> the color gamut simply by converting into a space that can hold a larger
> number of colors.
>
[Oostrom, Jerry] I wonder about this, are there spaces that can
hold a larger number of colors? If I see it as a 48bit image file I assume
the number of different colors to increase with a factor 2^24 in comparison
to a 24bit image file. Or is the number of bits only one of the upper limits
to the number of colors in a color space and will a color space never hold
more than say a number X of colors?
(After writing the stuff below I have to warn you: If you read on,
you risk getting a headache, I am totally confused here and don't even know
anymore what I am tyring to say or find out, I am getting some coffee now
and press send, if you read on get coffee and press delete. you have been
warned)
I assumed that the maximum number of colors in each of the commonly
used color spaces for photo files would actualy be infinite (X=infinite) and
only limited by the numbers of bits used. (Should I have assumed that image
files in smaller gamut color spaces do not use all available bits?)
I assumed that if you convert a binary image file from a limited
gamut space to a larger gamut space that would just decrease the number of
colors used in the file, because there is a much more limited range of
bit-values available to map colors from within the smaller gamut in the
larger gamut. As a result the used color gamut of the file would stay the
same, but the number of colors would have decreased, with the chance that
you get visible posterization if you use too few coding bits per pixel
(perhaps with 24 bits already).
Why do I ask this stuff (I am asking to myself too)?
If a space with a smaller gamut can hold only YY discrete colors and
another space with larger gamut can hold ZZ discrete colors would imply that
YY < ZZ then it would look to me that if I convert from the higher gamut
space to the lower gamut space I would have to map ZZ into YY colors, of
which even some of the ZZ colors cannot be mapped. This would always lead to
posterization, except if the image colors were originally all in the smaller
gamut range. There would also be no need for an image in the smaller gamut
color space to use more bits than needed to code YY colors. This is what I
am able to read from Andrew's reply, but I have the feeling it is not what
he intended.
If the colors are not discrete colors and the number of colors is in
fact 1 or infinite for any given gamut, then there would even be a sort of
posterization if you converted from the larger into the smaller space where
all colors of the image were already contained in the smaller gamut. (i.e.
you should see combing in the histogram of the image in the smaller gamut
space, because that smaller gamut space has larger resolution if coded in
the same number of bits as the larger gamut space (here my english really
gives up on me))
If I should never convert spaces, it becomes important to know which
gamut the scanner can actually cover and select a space in Vuescan that uses
the smallest gamut that can encompass the scanners gamut, instead of
choosing just any of the larger color gamut spaces. That was probably the
question that the originator of this thread started with and that was
probably answered long ago. 8-7
Jerry Confusestrom
