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, 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]
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