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List:       kde-kimageshop
Subject:    exposure and gamma
From:       Boudewijn Rempt <boud () valdyas ! org>
Date:       2012-06-05 7:12:59
Message-ID: 201206050912.59527.boud () valdyas ! org
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So yesterday after a day of frantic hacking on the "lut-docker" I finally discovered \
that we're not using the mechanism I thought we were using for showing \
gamma/exposure...

Basically, we have two mechanisms in place:

* a glsl shader fragment for the opengl canvas
* a visitor to set exposure as a property on profiles that are used by ctlcs \
colorspaces.

The glsl shader only works with colorspaces that are marked as supporting hdr, and I \
guess the ctlcs colorspaces aren't marked as hdr to avoid the shader kicking in and \
doing the same transform twice.

The visitor approach means the entire image is recomposited as soon as the exposure \
changes. It is also used by the color selection selection system to automatically \
transform a selected color to work with the current exposure \
(http://blog.cberger.net/2007/12/01/painting-in-hdr-with-krita/, \
http://cyrille.diwi.org/images/kritablog/krita-painting-hdr.mpeg).

Now that we're trying to use lcms instead of ctlcs, the profile route won't work \
anymore, so we need something new.

I'm going to try this:

* for painting: when setting fg/bg color on the canvas resource provider, transform \
those for the gamma/exposure settings so painting on hdr works as it did.

* for display: 
** opengl: try to beat the shader back into working state and pass it the gamma \
                settings as a variable.
** qpainter: use the gamma/exposure setting to create an lcms transform and apply \
that when generating the prescaled image.

Anything I've missed here?
-- 
Boudewijn Rempt
http://www.valdyas.org, http://www.krita.org, http://www.boudewijnrempt.nl
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