Personally I would be happy with selecting the first 3 or 4 channels (or the number supported by the output format) under that given circumstance, but if we want to go the extra mile and do some checking, maybe that would be a plus?
Maybe this is a dumb question, but what do you think the average image viewer does when displaying images with arbitrary channels? Do they look for R,G,B labeled channels, or maybe load the first N channels? On Sun Feb 08 2015 at 2:36:26 PM Larry Gritz <[email protected]> wrote: > OK, so how about this proposed heuristic for oiiotool: > > If the output format doesn't support as many channels as the input image, > then it will perform the equivalent of "--ch R,G,B" (or "R,G,B,A", if the > format does support an alpha channel) before saving. If the input doesn't > contain (somewhere in it) channels named R, G, and B, then it's an error. > > Or should we just ignore the issue of specific channel names and write the > first 3 (or 4) channels and call it a day? > > -- lg > > > PS. WTF, Jono, don't you have someplace more important to be tonight? > > > On Feb 7, 2015, at 5:20 PM, Justin Israel <[email protected]> wrote: > > Well in my case, one specific example of an input image is a non-subimage > style stereo, with [RGB] and right.[RGB] labels. But oiiotool obviously > should not have any knowledge of special labels, and the goal was to not > have to pre-inspect the source images before converting to jpeg. > > Thanks Larry for breaking down the categories of when oiio wants to make > best default choices, vs erroring out. It does sound like a really similar > situation to the fact that it does automatically throw away the alpha > channel. If I have a source image with extra channels, and no channels have > specifically been selected, it would seem that choosing RGB by default > would be what the user most likely wants. If I knew I wanted specialized > channels, I would definitely select them. Otherwise, it should probably > complain about the alpha channel just as it does complain about 6 channels > passing through. > > > On Sun Feb 08 2015 at 2:11:06 PM Jono Gibbs <[email protected]> wrote: > >> If the input file format had 3 obvious r g b channels and then 3 which >> were not related to color (z, alpha, obj-id) then it seems like keeping the >> r g b channels when going to JPEG is in the spirit of "do the obvious >> thing". >> >> If it's a 6-channel color thing then it's unlikely any 3 channels make >> sense. >> >> Does the input format have no information like channel names? >> >> --jono --mobile-- >> >> > On Feb 7, 2015, at 4:35 PM, Larry Gritz <[email protected]> wrote: >> > >> > On one hand, we don't want to do operations that are not supported in >> the output format, thereby resulting in significant loss of data. On the >> other hand, we can't be too trigger-happy with the errors, or it would be >> impossible to get anything done. So when we encounter a request to do >> something not possible with a given format, we try to ask "is there a >> particular thing that the human almost certainly meant when they made this >> impossible request?" >> > >> > For example OpenEXR's least accurate pixel data type ('half') has more >> precision and range than JPEG's most accurate type, so there will be data >> loss, but we don't want to make every operation that starts with exr and >> ends with jpg to be an error. So we just convert any input pixel data type >> to UINT8 when outputting a JPEG. For most ordinary images, the data is LDR >> and our eyes are mostly satisfied with 8 bits in an sRGB-mapped intensity >> response, so this conversion will probably be fine. ("If you wanted to >> preserve the HDR data, you should not have output to JPEG, dummy.") >> > >> > But what if we are asked to save more channels than a file format can >> accommodate? If you just drop the channels, you're not just reducing >> precision, you are losing whole sections of the original data. So at >> present, we make it a hard error. >> > >> > As a special case (and maybe precedent?), we do just silently drop an >> alpha channel when saving JPEG. JPEG cannot accommodate alpha, but it's so >> common for an input to have alpha, it was painful for it to be an error >> when saving to JPEG. It seemed that the obvious human interpretation was >> "I'm using JPEG because this is final output for the web or for my mom to >> view, the alpha that was valuable for intermediate computations won't be >> needed for those purposes, so drop it." >> > >> > I think that at the low level of ImageInput, open() should fail if you >> ask for more channels than can be supported in any obvious way. But for >> oiiotool in particular, I think we can make more "best guess" heuristics. >> > >> > I'm certainly open to this being debated! >> > >> > When oiiotool is outputting to a format that doesn't support as many >> channels as the image appears to have, do you think we should just silently >> output the first 3 channels and drop the rest? Should this be the one and >> only behavior? Or should there be a "strict/lax" option that determines >> whether this (and potentially other conversions) are an error or silently >> do whatever is necessary to complete the action somehow? If so, should the >> default be strict or lax? >> > >> > -- lg >> > >> > >> > (Note for the pedants in the crowd: most of the places I wrote "JPEG", >> I'm not really talking about the JPEG compression, but rather the JFIF file >> format.) >> > >> > >> >> On Feb 5, 2015, at 3:56 PM, Justin Israel <[email protected]> >> wrote: >> >> >> >> I was curious about some behavior in oiiotool v1.4.14, when dealing >> with a source image that has 6 channels, and converting it to a jpeg. >> >> >> >> oiiotool source.exr -o out.jpg >> >> # oiiotool ERROR: jpeg does not support 6-channel images >> >> >> >> I presume this bubbles up from libjpeg. Fair enough. But I know that >> the mantra of OpenImageIO has usually been to try and do the right default >> action, and attempt to avoid failures if possible. That being said, do you >> think it would be more in line with that philosophy if the jpeg plugin >> ensured it would only use 1, 3, or 4 of the first available channels, if >> not using an explicit list already? That way you would still get a jpg >> output, even if you passed it a 6 channel image, but could still explicitly >> give is a channel list if you knew them up front. >> >> >> >> Currently I have to inspect the source image first before calling >> oiiotool, and ensure that I pass it a reduced channel list if needed. >> >> >> >> Justin >> > >> > -- >> > 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 > > > -- > 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
