Re: Erroneous color transformations with Apple CMM
Re: Erroneous color transformations with Apple CMM
- Subject: Re: Erroneous color transformations with Apple CMM
- From: Marco Ugolini <email@hidden>
- Date: Wed, 27 Jan 2010 14:13:29 -0800
- Thread-topic: Erroneous color transformations with Apple CMM
In a message dated 1/27/10 12:38 AM, Klaus Karcher wrote:
> Just add a gradient from let's say RGB 5 5 5 to RGB 20 20 20 to the image.
Done. I see a neutral-looking gradient. What does that show, or prove?
> In the meantime it turns out that what you see in the image seems to be
> not related to what's happening in my numerical examples (apparently the
> unusual primaries in the profile exceed the numerical range Apple's
> CMM is able to deal with and as the profile is not fully ICC-compliant,
> I shouldn't blame the Apple CMM for the oddities). So I'd suggest to
> close this case an concentrate on the numerical examples.
As for the primaries, this 3D graph shows their charming nuttiness when
compared to ProPhoto RGB, which is already a VERY wide-gamut profile:
<http://tinyurl.com/ybtacbn>
As one who lived through the 60s, I must say that it looks very psychedelic
-- but, to be fair, those primaries seem to live in some region far beyond
the twilight zone, and clearly cannot possibly reflect a real-world device
like the camera whose behavior the profile to which they are associated is
supposed to be describing.
So, it's good to have established that the profile is not fully
ICC-compliant, as I had suspected.
> It is still about errors up to Delta E 27 with fully ICC-compliant ICC
> profiles!
>
> Rgamma: 2.234375
> Ggamma: 2.234375
> Bgamma: 2.234375
> Red: X: 0.478958, Y: 0.275146, Z: 0.049362
> Green: X: 0.350143, Y: 0.618881, Z: 0.130112
> Blue: X: 0.135101, Y: 0.105972, Z: 0.105972
>
> Number of tests: 100000
>
> Delta E avg / max lapack: 0.00 / 0.02
> Delta E avg / max float Lab: 1.24 / 9.18
> Delta E avg / max fixed: 1.25 / 9.18
> Delta E avg / max float XYZ: 5.40 / 27.29
I don't follow what exactly these numbers are measuring. What is the
procedure? What is being compared? And which DeltaE formula?
Marco Ugolini
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