Well, that's pretty unfriendly on Nuke's part. PNG is pretty clear what is and isn't supposed to be in the file. --jono
On Thu, Jul 24, 2014 at 3:46 PM, Rangi Sutton <[email protected]> wrote: > 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 >> >> > > _______________________________________________ > Oiio-dev mailing list > [email protected] > http://lists.openimageio.org/listinfo.cgi/oiio-dev-openimageio.org > >
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