[argyllcms] Re: help with camera profile

  • From: Ben Goren <ben@xxxxxxxxxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Sun, 29 Jul 2012 14:45:42 -0700

On 2012-07-29, at 12:55 PM, Iliah Borg wrote:

>> If I try to do the same with the 7D profile, the error gets higher (27
>> as peak) and even after removing 3 patches it stays to 17. The "bad"
>> patches are always orange/yellow.
> it might depend on the output colour space and how they get their. I mean, 
> have you checked for clipping?

Iliah's excellent point deserves a bit of expansion. For example, sRGB is only 
big enough to encode 96% of the ColorChecker gamut, and only 83% of the Digital 
ColorChecker gamut. Indeed, there isn't a single standard reference chart that 
sRGB can entirely encode without clipping:


If you follow the link on that page to his ColorChecker calculator, you'll see 
that the cyan patch needs a negative red value in sRGB. I don't think it's 
quite enough to account for a double-digit DE error, but I can't do that kind 
of math in my head...besides which, the classic ColorChecker orange / yellow 
patches are well within the sRGB gamut.

If you don't want any clipping in any of the standard charts, there're only two 
working spaces to pick from: the oversized ProPhoto RGB, and Bruce's own Beta 
RGB. If you're using Adobe products, your only choice for color space after raw 
conversion to avoid clipping is ProPhoto, since it doesn't support Beta RGB. 
Canon's Digital Picture Professional doesn't even give you that choice. As they 
say, your mileage not only may vary, but it's pretty much guaranteed to....



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