[Bf-committers] regarding color correction and images

[Dahlia Trimble]

I would think that there would be precision losses and possibly color gamut
clipping on successive conversions to/from linear and srgb color space. This
may not be visible if internal formats have a high precision, such as 32 bit
floats for each pixel color, but if they are stored as low precision such as
8 bit integers, then you would see visible steps in color gradients which
would become worse with each conversion.

2011/5/26 Ρυακιωτάκης Αντώνης <kalast at gmail.com>

> Hi everyone, as part of my GSOC I started working on a certain bug that has
> to do with color correction and image/projection painting, In particular,
> strange colors/fringes appear when painting in image/texture projection
> mode. After testing it seems that the correct behavior occurs by first
> converting brush color from srgb to linear rgb, doing the painting and then
> converting back to srgb for display. Converting brush colors to linear rgb
> is fairly easy, however there are complications when it comes to images.
>
> Currently there is no color correction applied to texture images before
> they
> are sent for display, with one exception: Float textures, when doing
> projection painting are sent for display color-corrected. What this means
> is
> that Imbuf->rect is filled with color corrected values.
>
> This is all fine and well but it implies that Imbuf's used for rendering
> must be linearized before rendered or used in calculations by GLSL shaders.
> Is this already happening (based on Imbuf->profile flag?) or am I risking
> breaking something by storing sRGB values in Imbuf->rect?
>
> A search for IB_PROFILE_SRGB shows a result in pipeline.c that indicates
> that, at least for rendering purposes this is accounted for. Is this also
> true for GLSL?
>
> Another consideration is performance: If Imbuf->rect stores sRGB values
> then
> these will have to be converted again to linear rgb when texture painting,
> lowering performance.
> Another option is to store linear values in Imbuf->rect but upload sRGB
> values to OpenGL. This is better performance-wise and feasible but again,
> values must be converted back to linear in GLSL.
>
> Any suggestions observations and thoughts are really welcome, since I
> haven't got too much experience with all the different parts of the code
> and
> time is precious.
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