Re: [Gimp-developer] Don't make an architectural mistake based on a groundless premise

On 10/07/2014 07:32 PM, Simone Karin Lehmann wrote:
In babl/unbounded sRGB world your input space and output space differ
in a very important aspect to the PCS space unbounded sRGB:
unbounded sRGB can have values < 0 or > 1, input and output don't.
Whereas in ICC / XYZ world input, output and PCS have well defined boundaries,
namely 0 and 1 and well defined clipping, so everything is 0 <= x <= 1.

Display-referred editing does require bounded RGB channel values and will require an incredible amount of hacks to work within the proposed "sRGB as PCS" architecture.

This picture illustrates why gamma slider adjustments only make sense when done on display-referred channel values:

The image on the left is a ProPhotoRGB image. The image in the middle was given a Levels gamma slider adjustment in the ProPhotoRGB color space. Results are normal and expected. The image on the right was converted to unbounded sRGB and given the same Levels gamma slider adjustment. Results are quite abnormal and unexpected.

This article explains why gamma slider adjustments requires values that are bounded by the range 0.0 to 1.0:

Gamma slider adjustments should be added to the official list of editing operations that require a hack in order to work in "sRGB as PCS".

With respect,
Elle Stone

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