[Bf-cycles] Color (un)premultiply

[Brecht Van Lommel]

Hi,

As far as I know, the new color management changes in 2.64 should not
introduce any extra fringes compared to before. If that's the case it
would be interesting to understand why.

This option is definitely a color management option though, and
affects compositing as well, I don't think it's correct to place it in
the Film panel. The exposure option in the film panel will be removed
eventually, it's a separation option but it should really be using the
color management settings instead. Maybe it should be there anyway,
but ideally we could find a better way to communicate things rather
than duplicating the option, or maybe the default value should be
changed.

In any case, the unpremultiply option is something that should be
avoided when possible, there is no right way to use it, depends a bit
on the image what looks best, but the result will be subtly wrong
either way. Ideally you should never do color space conversion on an
image that has an alpha channel, which means working in linear float
color space and only doing the color space conversion at the very end
when everything is composited together. Though it's not always
possible to set up an entirely correct color pipeline with external
tools involved.

Brecht.

On Wed, Dec 12, 2012 at 3:34 PM, Adriano Oliveira
<adriano.ufrb at gmail.com> wrote:
> Since 2.64 I've problems with transparency finges when editing render
> outside Blender.
> Last week I discover the "Color unpremultiply" option and every thing is
> fine again.
>
> I supose that many others like me are having hard times dealing with
> premultiplied fringes due to new Color Management been so far from render
> options.
>
> My proposal is to merge Color Management in the FILM slider at Render
> Options.
> At least, "Color unpremultiply" option should be near TRANSPARENCY option,
> even if it is repeated in Color Management, like Exposure seams to be.
>
> Adriano A. Oliveira
>
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