[Bf-cycles] Color (un)premultiply

[Brecht Van Lommel]

Hi,

Right, it looks ok in this case, but it's not only about black
backgrounds, anything dark will tend to be more correct with the
option off.

But I just remembered that I can only turn this on once we refactor
the key/premul system, since otherwise this option would break other
cases where you're working with key alpha images. Maybe I should try
to tackle that refactor for 2.66.

Brecht.

On Wed, Dec 12, 2012 at 5:29 PM, Adriano Oliveira
<adriano.ufrb at gmail.com> wrote:
> As long as Blender internal compositor works right in linear, I think this
> is just a matter for those who need to compose outside.
> In real life, composing over black is rare. We are used to compose over
> other images or color gradients.
> If the behaviour of the option is correct, as it seams to me, I agree the
> default value should be ON.
>
>
>
> Em quarta-feira, 12 de dezembro de 2012, Brecht Van Lommel escreveu:
>
>> 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
>> >> >
>> >> > _______________________________________________
>> >> > Bf-cycles mailing list
>> >> > Bf-cycles at blender.org
>> >> > http://lists.blender.org/mailman/listinfo/bf-cycles
>> >> >
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>> >
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>
>
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>
> Adriano A. Oliveira
>
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