[argyllcms] Re: Shadow detail problem
- From: Leonard Evens <len@xxxxxxxxxxxxxxxxxxxxx>
- To: argyllcms@xxxxxxxxxxxxx
- Date: Fri, 01 Feb 2008 13:02:08 -0600
On Fri, 2008-02-01 at 12:21 -0600, Dave Wagner wrote:
>
> Here is what I am doing, I create a black (rgb 0,0,0) image in gimp
> and then select a rectangle and bump it one rgb level at a time until
> I can see a difference between it and the background. With just the
> calibration loaded (.cal file or vcgt tag, it is visibly different at
> 3,3,3 or 4,4,4 (of 255 for 8-bit in gimp). With the CMM loaded, it
> isn't visibly different until 21,21,21.
I haven't really been following this discussion, but do I understand
that you are trying to use a gray scale with 256 steps? That doesn't
seem to make much sense. To illustrate, at one point, for my setup at
the time, essentially uncalibrated, I came up with the following Ansel
Admas Zone System numbers in the 0..255 scale:
O 0, I 25, II 50, III 75, IV 100, V 130, VI 165, VII 195, VIII 225, IX
245, X 255
This is only a rough approximation, but it gives you some idea of what
this means in terms of ordinary photography.
If 0 is pure black, I is supposed to represent the first zone above
black but still not high enough to show shadow detail. It seems to me
to be able to recognize subtle differences of the kind you describe at
the bottom of the scale is beyond what the normal eye can perceive.
But maybe I just misunderstand the whole discussion.
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