Hey, I think it's a good thing Nuke doesn't try and second guess you and make "intelligent" decisions about what you're trying to achieve. For this case, if the nuke script contains pre-mulitplied alpha, then un-premultiply it (divide by alpha) before writing out your png files.
Unless I'm missing something! Cheers, r. Rangi Sutton VFX Supervisor Cutting Edge On 25 July 2014 04:32, Mikael Sundell <[email protected]> wrote: > Aaaargggh :-) > > Skickat från min iPhone > > 24 Jul 2014 kl. 19:49 skrev Larry Gritz <[email protected]>: > > The fun with PNG never seems to end. And by "fun", I mean a hot poker in > the eye. > > > On Jul 24, 2014, at 1:20 PM, Mikael Sundell <[email protected]> > wrote: > > I seems as if Nuke writes data with associated alpha in PNG files, > according to the spec it's not valid: > > http://www.libpng.org/pub/png/spec/1.2/PNG-DataRep.html > > "The color values stored for a pixel are not affected by the alpha value > assigned to the pixel. This rule is sometimes called "unassociated" or > "non-premultiplied" alpha. (Another common technique is to store sample > values premultiplied by the alpha fraction; in effect, such an image is > already composited against a black background. PNG does not use > premultiplied alpha.)" > > This causes the PNGReader to associateAlpha(…) on already alpha multiplied > data. Did anyone else experience this problem? > > Mikael > > > -- > Larry Gritz > [email protected] > > > > _______________________________________________ > Oiio-dev mailing list > [email protected] > http://lists.openimageio.org/listinfo.cgi/oiio-dev-openimageio.org > > > _______________________________________________ > Oiio-dev mailing list > [email protected] > http://lists.openimageio.org/listinfo.cgi/oiio-dev-openimageio.org > >
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