Re: Erroneous color transformations with Apple CMM
Re: Erroneous color transformations with Apple CMM
- Subject: Re: Erroneous color transformations with Apple CMM
- From: Klaus Karcher <email@hidden>
- Date: Wed, 27 Jan 2010 09:38:50 +0100
Marco Ugolini wrote:
In a message dated 1/26/10 2:53 PM, Klaus Karcher wrote:
The image was processed in a linear workflow -- assigning anything else
but a profile with gamma 1 is simply inappropriate. The main part of the
image gets almost black if you assign a profile with gamma 2 or higher.
Not in my own test: assigning AdobeRGB (gamma 2.2) makes the very darkest
measurable point in the image appear like L* 38, and near-neutral -- L* 38
is not what I would consider to be "near black", though it is indeed a
dark-looking cloud, as I suspect it would be in the actual scene.
Just add a gradient from let's say RGB 5 5 5 to RGB 20 20 20 to the image.
The profile was made from an underexposed shot while the photo is
overexposed.
I have chosen this image as it is a good visual demonstration for the
bugs I seemingly found.
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.
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
Klaus
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