[argyllcms] Re: Profile input white not mapping to output white

  • From: Ben Goren <ben@xxxxxxxxxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Fri, 23 Nov 2012 15:19:16 -0700

On 2012-11-23, at 1:12 PM, Iliah Borg wrote:

> It has to do with both, and more with raw processing and the way you shoot 
> than with anything else. But you are not listening.

Well, what's got me confused is two-fold.

First, the TIFF that I'm feeding to Argyll has no weird color shifts and looks 
like a typical linear raw camera file -- confirmed by the samples in the .ti3 
and by tagging the linear output with something like sRGB.

Second, the profile works very well for the chart itself, including the 
lightest and darkest patches. Running profcheck gives this:

[9.578221] I13: 0.005281 0.004926 0.004770 -> 3.851130 7.556675 -4.587199 
should be 0.077060 0.022064 -0.034357
[3.318288] N18: 0.530850 0.539870 0.522690 -> 96.132563 0.082416 0.822188 
should be 99.354158 -0.236898 0.093899

So, what's got me utterly confused is how the profile can go from R=135 G=138 
B=133 => L=96 a=0 b=1 (and a very well-behaved response below that) to 
R=G=B=255 => L=97 a=108 b=-51.

What could possibly account for that *very* hard turn in the profile after 
L=96, *especially* when everything below that is so close to perfect?

It just doesn't make sense to me. What's causing Argyll to extrapolate that, 
though it left off almost perfectly on the neutral axis with L=96 and almost 
perfectly balanced channels, and lacking anything beyond that, that that it 
should suddenly make everything whiter than that not white but cyan?

It seems to me that, if you were going to manufacture input data that you would 
expect to result in a straightforward input profile, you'd manufacture pretty 
much the data that's in that .ti3. So where's the difference between my .ti3 
and a non-screwed-up-.ti3? Which patches are leading Argyll astray?



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