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Old 30th August 2012, 07:53   #1  |  Link
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Join Date: Sep 2009
Posts: 378
YCC variants from consumer cameras

With reference to this:


Considered opinion as to which variant this is with reference to chroma range, 16-240 or 255 -127 +128 about 0?


Source includes full range flag set on VUI Option to force scaling to limited range would suggest 0-255 for chroma too?

Implications to handling this type of file? re levels, chroma placement, conversion to RGB, transcoding emphasis on retaining decent output. Avisynth doesn't appear to differentiate. Does Coloryuv support JPEG chroma range? I'm using ffmpegsource2 to decompress.

The underlying problem I'm having is with Adobe After Effects CS6 appearing to screw up linearizing the source in a 32bit float linear RGB workflow.

AE detects source as sRGB rather than rec709 so applies a inverse sRGB calc result is a combed histogram, assume this is as the source was encoded with a Rec BT 709 curve.

Making AE reinterpret the source as rec709, AE appears to ignore the full range and once again appears to screw up the linearizing.

Remuxing with patched MP4Box to remove the full range flag, AE accepts the mp4 and appears to do the YCC -> RGB conversion assuming 16-235 levels, so I get clipped RGB channels and overbrights.

If the source is really JPEG levels ie full range chroma then there is no headroom or footroom the whole range is used so lost the relationship between full luma + chroma in JPEG by doing 16 - 235 to RGB + overbrights as it's 32bit float.

But at least this route I keep the overbrights and can slide them to 1.0 by adjusting exposure, where they should be if indeed its JPEG JFIF to start with.

Last edited by Yellow_; 30th August 2012 at 18:00.
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