I would suggest that the writer should automatically truncate channels that it doesn't know how to deal with. If this leaves fewer channels than it is expecting (e.g. an EXR with no RGBA, but beauty.r, beauty.g, beauty.b), then it should gracefully error (or maybe it could try to intelligently pick other channels to show? This sounds dangerous to me, unless there are only R, G, B channels but named differently, as in the example above).
The user would then also be able to specify channel shuffling if they want to use different channels, or if there is, as in the example above, no definitive channel group. Hugh Macdonald nvizible – VISUAL EFFECTS +44(0) 20 3167 3860 +44(0) 7773 764 708 www.nvizible.com On 3 Aug 2012, at 18:28, Larry Gritz wrote: > I hope you don't mind that I'm CCing oiio-dev with my reply. > > This is an interesting question. Currently, if you try to open a file for > output and request a number of channels that it can't support, the open() > call will fail. That said, it does seem an entirely reasonable operation to > want to convert, say, an RGBA file to a format that does not support alpha, > by copying the RGB only. > > I'm curious to hear people's opinions on how to address this problem. I can > think of several possible strategies: > > 1. (Logic in the plugins) Change the JPEG (and/or others) output to silently > and automatically truncate channels if asked to write more channels than the > format supports, much like how it will force uint8 data (because that's all > JPEG supports) even if you ask for something else. Or, we could keep the > default as it is (fail), but have JPEG support a request by the app to > truncate channels (via the "open with config" call) and have iconvert and > certain other apps make that request. > > 2. (Logic in the app) Leave the drivers alone, but make iconvert and oiiotool > check the failure messages and, if an open() fails and nchannels > 3, make an > intelligent guess by trying to open the file a second time with fewer > channels, and if that succeeds, output that way. > > 3. (Logic in the user's head) Add a --channels option to oiiotool that lets > you explicitly prune or shuffle channels, so you could > > oiiotool my5channelfile.exr --channels R,G,B -o besticando.jpg > > > Opinions? None are very hard, I can fix right away, but first I'd like to > get consensus on which level of the onion ought to have the control of this > behavior. > > > > On Aug 3, 2012, at 8:16 AM, Adam Wierzchowski wrote: > >> Hi, >> seems like iconvert cannot convert multichannel exr files to jpeg format: >> iconvert ERROR: Could not open "p:/1310.Adam-testy.Base/conv/outCh3.jpg" : >> jpeg does not support 5-channel images >> >> Is there a way to strip exr to rgb channels and convert it to jpeg anyway? >> >> regards >> Adam > > -- > Larry Gritz > [email protected] > > > _______________________________________________ > Oiio-dev mailing list > [email protected] > http://lists.openimageio.org/listinfo.cgi/oiio-dev-openimageio.org -- D I S C L A I M E R : This email and any files transmitted with it are intended solely for the intended addressee, and may contain confidential information or material protected by law, copyright or other legislation. If you have received this message in error, please return it to the sender or notify the sender by calling +44 (0)20 3167 3860, and immediately and permanently delete it. You should not copy it or use it for any purpose, nor disclose its contents to any other person. Only the intended recipient may place any reliance upon it. Nvizible Limited accepts no responsibility or liability for emails sent by its employees or personnel which are not sent in the course of its business or that of its clients. Nvizible Limited, 3 Richfield Avenue, Richfield Place, Reading, Berkshire, RG1 8EQ . Registered in England & Wales with Company Number: 6900121
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