Ive <"ive### [at] lilysoftorg"> wrote:
> On 04.07.2010 15:06, Ive wrote:
> > On 04.07.2010 12:24, clipka wrote:
> >> Some other image file formats, such as OpenEXR and TIFF, officially use
> >> associated - or premultiplied - alpha, which means that the data is
> >> stored in the file already pre-composed against a black background, so
> >> simply ignoring alpha would indeed give what you'd expect.
> >
> >
> > To clarify and to prevent a new bug within POV-Ray:
> >
> > I do not know where you did get the information/impression that TIFF
> > "officially use associated - or premultiplied - alpha". This is not true
> > as TIFF allows *everything*.
> > You might have misread the TIFF 6.0 specs section 18: Associated Alpha
> > Handling. This section applies only *IF* the "ExtraSamples" tag is
> > present and the value of the tag reads 1. In most cases (in all if the
> > TIFF was written by any Adobe software) the value of the ExtraSample tag
> > will be 0 - i.e. unassociated, non-pre-multiplied, straight.
> >
> > -Ive
> >
>
> Umm, and to correct myself an "ExtraSample" value of 0 actually means
> undefined but was always used by Adobe to indicate unassociated alpha,
> (but could actually mean something else e.g. no "alpha" data at all).
> The correct value to identify unassociated, non-pre-multiplied alpha
> would be 2.
>
> -Ive

I'm happy that there has indeed been some improvement. I hope you don't mean
that it's impossible to get the desired behaviour? For now I just have
deactivate either anti aliasing or background alpha in the blender exporter. And
sorry to get to blender again in the discussion, I am prepared for someone to
answer that it simply is buggy or wrong, but it behaves without any of its
million count userbase complaining. It doesn't seem to premultiply the
background as there is no trace of it when we use the show alpha button in the
image window. I made a little screenshot with the process to render and see what
I mean if you have a version of blender around:
http://dl.free.fr/ucR4swaMX

Maybe the source code can be an inspiration?... just for this very point of
course, no matter how bad it may be for anything else :-P ?

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