If Nuke is just inherently writing incorrect PNG files in this situation, it might also be better to export as OpenEXR, TIFF, or something else that doesn't have a strict requirement for unpremultiplied alpha, and then as a second step do "oiiotool nuke_export.exr -o properly_conforming.png".
On Jul 25, 2014, at 10:32 AM, Mikael Sundell <[email protected]> wrote: > Hi! > > Dare I even ask why people are writing PNG files from Nuke? It's not exactly > a VFX-friendly file format. > > In this case we use Nuke to prepare production assets for webreviews and > distribution. > > You can force some kind of conversion with oiiotool. If you have a file that > saves as PNG but that somehow you know is already premultiplied, you could > try "oiiotool --no-autopremult in.png -o outputfile.ext" to suppress the > premultiplication that would ordinarily happen when reading PNG files, then > write to a new file. > > Sounds like a plan! >> But you are right, if you assume that Nuke doesn't know if alpha is >> associated or not, and some nodes assumes it's not and some assume that it >> is, then the situation can't really be improved other than perhaps a option >> on the file writer to make it more obvious. > > That's what I had in mind too, just a checkbox in the Nuke PNG reader/writer > to highlight the potential problem. It's not just the oiio reader that > premultiplies, Photoshop and other Adobe products does it too. They force > premultiply based on how data should be present according to the PNG > specification. > > Thanks all! > > Mikael > > _______________________________________________ > Oiio-dev mailing list > [email protected] > http://lists.openimageio.org/listinfo.cgi/oiio-dev-openimageio.org -- Larry Gritz [email protected]
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