I can answer that question, but then it leads right back to something ELSE that's probably my fault. :-)
OK, so PNG is, by specification, "unassociated alpha" (what some people call "un-premultiplied"), and OIIO by convention always passes <ahem, CORRECT> "associated alpha", which means that when reading unassoc files it will automatically multiply RGB by A before giving the values to the app. Your file has alpha = 0, which is supposed to mean (for PNG) that the appearance is black everywhere. This auto-conversion of unassociated to associated that happens in OIIO's PNG reader can be disabled with a special configuration attribute, so the correct command line should have been this: oiiotool -iconfig oiio:UnassociatedAlpha 1 steveparker.png -ch R,G=R,B=R,A=R -o out.tif ... Except something is going wrong there as well. Ugh. I'm trying to understand why. Stand by. > On Feb 8, 2019, at 2:52 PM, Stephen Parker <[email protected]> wrote: > > Indeed. That was my first reaction too. But then why doesn't this work: > > oiiotool test.png --ch "R=R,B=R,G=R" -o out.png > > oiiotool test.png --ch "R=R,B=R,G=R,A=1.0" -o out.png > > I figured it was user error. > > > > > On Fri, Feb 8, 2019 at 2:39 PM Larry Gritz <[email protected] > <mailto:[email protected]>> wrote: > Doesn't the fact that everything interesting ends up in out-0.png tell us > that the alpha was black all along, and it was the red channel that you're > after? > > >> On Feb 8, 2019, at 2:03 PM, Stephen Parker <[email protected] >> <mailto:[email protected]>> wrote: >> >> ... actually, disregard the -swap as -separate is all that's needed. >> >> convert test.png -separate out.png >> >> On Fri, Feb 8, 2019 at 1:51 PM Stephen Parker <[email protected] >> <mailto:[email protected]>> wrote: >> Try: >> >> convert test.png -separate -swap 4,0 out.png >> >> You should get an image written out for each channel. "out-0.png" can be >> opened in Preview.app. >> >> -s >> >> >> On Fri, Feb 8, 2019 at 1:38 PM Larry Gritz <[email protected] >> <mailto:[email protected]>> wrote: >> On my mac, ImageMagick "convert test.png test.tif" also results in what >> appears to be a black image. >> >> And using ImageMagick's "identify -verbose", I see these stats: >> >> Alpha: >> min: 0 (0) >> max: 0 (0) >> mean: 0 (0) >> standard deviation: 0 (0) >> kurtosis: -3 >> skewness: 0 >> entropy: 0 >> >> Are you *sure* that the alpha channel isn't really 0 everywhere? >> >> >> >>> On Feb 8, 2019, at 11:55 AM, Larry Gritz <[email protected] >>> <mailto:[email protected]>> wrote: >>> >>> Hmmm... it's not just "--ch", that image looks "black" (all 0.0 values) in >>> all channels to all OIIO tools. (For example, `oiiotool -stats test.png`) >>> I'm suspecting something in the reader rather than an issue with channel >>> selection. >>> >>> Looking into it. >>> >>> -- lg >>> >>> >>>> On Feb 8, 2019, at 11:31 AM, Stephen Parker <[email protected] >>>> <mailto:[email protected]>> wrote: >>>> >>>> Hi Larry, >>>> >>>> I'm on the release branch. Here is the PNG in question (attached). >>>> >>>> thanks >>>> >>>> On Fri, Feb 8, 2019 at 11:12 AM Larry Gritz <[email protected] >>>> <mailto:[email protected]>> wrote: >>>> Which version of OIIO? >>>> And I don't suppose you can send me an example PNG that has the problem? >>>> Or is it weird for every png you try? >>>> >>>> >>>> >>>>> On Feb 8, 2019, at 10:59 AM, Stephen Parker <[email protected] >>>>> <mailto:[email protected]>> wrote: >>>>> >>>>> Hello, >>>>> >>>>> I'm having some trouble using oiiotool's copy channel operator. It might >>>>> be user error but I wanted to check and see if it's intended behavior. >>>>> I've only glanced at the code so far. >>>>> >>>>> My test image is a PNG (4-channel RGBA), but only has information in the >>>>> Alpha. When attempting to copy the Alpha into the other 3 channels and >>>>> write out an RGB image (no Alpha), I get black. Imagemagick's 'convert' >>>>> did what I expected. >>>>> >>>>> invoked as: >>>>> >>>>> oiiotool input.png --ch "R=A,G=A,B=A" -o output.png >>>>> >>>>> I also tried using the numeric channel labels to no avail. >>>>> >>>>> -sp >>>>> _______________________________________________ >>>>> Oiio-dev mailing list >>>>> [email protected] <mailto:[email protected]> >>>>> http://lists.openimageio.org/listinfo.cgi/oiio-dev-openimageio.org >>>>> <http://lists.openimageio.org/listinfo.cgi/oiio-dev-openimageio.org> >>>> >>>> -- >>>> Larry Gritz >>>> [email protected] <mailto:[email protected]> >>>> >>>> >>>> >>>> >>>> _______________________________________________ >>>> Oiio-dev mailing list >>>> [email protected] <mailto:[email protected]> >>>> http://lists.openimageio.org/listinfo.cgi/oiio-dev-openimageio.org >>>> <http://lists.openimageio.org/listinfo.cgi/oiio-dev-openimageio.org> >>>> <test.png>_______________________________________________ >>>> Oiio-dev mailing list >>>> [email protected] <mailto:[email protected]> >>>> http://lists.openimageio.org/listinfo.cgi/oiio-dev-openimageio.org >>>> <http://lists.openimageio.org/listinfo.cgi/oiio-dev-openimageio.org> >>> >>> -- >>> Larry Gritz >>> [email protected] <mailto:[email protected]> >>> >>> >>> >>> >>> _______________________________________________ >>> Oiio-dev mailing list >>> [email protected] <mailto:[email protected]> >>> http://lists.openimageio.org/listinfo.cgi/oiio-dev-openimageio.org >>> <http://lists.openimageio.org/listinfo.cgi/oiio-dev-openimageio.org> >> >> -- >> Larry Gritz >> [email protected] <mailto:[email protected]> >> >> >> >> >> _______________________________________________ >> Oiio-dev mailing list >> [email protected] <mailto:[email protected]> >> http://lists.openimageio.org/listinfo.cgi/oiio-dev-openimageio.org >> <http://lists.openimageio.org/listinfo.cgi/oiio-dev-openimageio.org> >> _______________________________________________ >> Oiio-dev mailing list >> [email protected] <mailto:[email protected]> >> http://lists.openimageio.org/listinfo.cgi/oiio-dev-openimageio.org >> <http://lists.openimageio.org/listinfo.cgi/oiio-dev-openimageio.org> > > -- > Larry Gritz > [email protected] <mailto:[email protected]> > > > > > _______________________________________________ > Oiio-dev mailing list > [email protected] <mailto:[email protected]> > http://lists.openimageio.org/listinfo.cgi/oiio-dev-openimageio.org > <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 -- Larry Gritz [email protected]
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