[Bf-cycles] Color (un)premultiply

[Brecht Van Lommel]

Right, if you composite it over a black it will be correct result with
the option off, for anything else it's a matter of which result looks
less wrong. In this case having the option on looks better. Maybe
that's true in most cases, then we should change the default.

Brecht.

On Wed, Dec 12, 2012 at 4:27 PM, Adriano Oliveira
<adriano.ufrb at gmail.com> wrote:
> See exemple atached:
>
> Render with transparency and saved as TIF 16bits RGBA.
> Composed in Photoshop over a red BG.
>
> Adriano A. Oliveira
>
>
> 2012/12/12 Brecht Van Lommel <brechtvanlommel at pandora.be>
>>
>> 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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>> >
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