I could try and work on these changes myself once I had enough time, unless someone were inclined to do them sooner. The thread didn't start out with an idea for a patch, and it sort of evolved into one ☺
Do you think the default quality value should be reduced? 90? 75? I would hate for someone to get mad that they automatically get reduced quality jpegs as a result of this patch. But then again, if the default subsampling is 4:2:0 anyways, then it probably isn't inline with needing a 98 quality, right? I'm not exactly sure what the impact is, in changing it, but maybe 75 is more realistic. If someone is concerned with quality, then I would assume they would be specifying their settings explicitly anyways. On 18/10/2014 6:32 AM, "Larry Gritz" <[email protected]> wrote: > That's another possibility I would entertain -- automatically upgrading > the subsampling when a sufficiently high quality is requested. > > So, just to be explicit, are you proposing making these changes yourself > and submitting a patch? I'm basically on board with this general design > idea. > > I set the default quality for jpeg output (if no "quality" attribute is > found) quite high, 98. I'm also happy to revisit whether that's too much. I > can't say it was a principled reason for that particular value. > > > > On Oct 16, 2014, at 6:39 PM, Justin Israel <[email protected]> wrote: > > Awesome. > I would say it would seem natural to stick with the existing behaviour for > the default, which follows your philosophy of the reasonable defaults. And > for those in my situation where they need to control the sampling, they can > specifically apply the setting. FWIW, it appears the stated Imagemagick > behaviour is to use 4:4:4 automatically if the quality value is >= 90, and > disregard any sampling settings that were passed (or the default). > > On Fri, Oct 17, 2014 at 1:17 PM, Larry Gritz <[email protected]> wrote: > >> Yes, sounds reasonable. Let's set/accept an attribute called >> "jpeg:subsampling" set to one of those values for explicit control. >> >> We want to detect and set it in the reader as well, so that "copy"-like >> operations from jpeg to jpeg preserve the sampling of the original unless >> overridden. >> >> Now we just need to haggle over the proper default. >> >> http://en.wikipedia.org/wiki/Chroma_subsampling >> This states fairly clearly that 4:2:0 (what we do now) is the usual for >> JPEG/JFIF, MJPEG, DVD, BluRay, H.264, and many others. That's probably why >> the jpeg library uses this default. Maybe Nuke and ImageMagick go out of >> their way to request a somewhat higher quality? I'm tempted to argue for >> keeping the default as it is, and with the extra control, those who care >> could request 4:2:2 or 4:4:4. But I'm willing to be swayed if consensus is >> that the default should be higher quality. >> >> >> >> On Oct 16, 2014, at 2:59 PM, Justin Israel <[email protected]> >> wrote: >> >> So maybe the solution is to offer some constants like: >> >> - "4:4:4" - Calls jpeg_set_colorspace() with JCS_RGB >> - "4:2:2" - does this >> <https://github.com/LuaDist/libjpeg/blob/master/jcparam.c#L454>, but >> uses SET_COMP(0, 1, 2,1, 0, 0,0); for the first component instead >> - "4:2:0" - Does exactly what it does now >> - "4:1:1" - uses 4,1 1,1 1,1 for the 3 components >> >> Does that sound reasonable? Then you get as much control as >> Nuke/imagemagick would offer >> >> >> -- >> 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 > > > -- > Larry Gritz > [email protected] > > > > > _______________________________________________ > Oiio-dev mailing list > [email protected] > http://lists.openimageio.org/listinfo.cgi/oiio-dev-openimageio.org > >
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