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Old 2nd July 2008, 11:05   #24  |  Link
2Bdecided
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Join Date: Dec 2002
Location: UK
Posts: 1,673
Quote:
Originally Posted by Alex_ander View Post
To have an illustration to what could happen sometimes, imagine a radical case of image type: all even lines in a still HD frame are black and all odd ones are white. NNEDI would simply alternate black and white frames, while Kernel bobber would still work somehow since it uses data from both fields.
Your point is well made - NNEDI "needs" to be used with something that can weave both fields as-is when necesary.

However your extreme example is too extreme. In an interlaced system, that image is ambiguous - the original image (before interlacing) could equally well be one frame black, then one frame white - or it could be two identical frames with alternate black/white lines. There is no way of knowing which, other than assuming.

All "smart" deinterlacing is based on assumptions - basically that the content changes little field by field - the camera is still pointing at roughly the same scene. If every field was completely independent, then a dumb bob would be the best you could do.

There are interesting graphs on pages 23 and 24 of this...
http://www.snellwilcox.com/community...des/edecod.pdf
...and I don't claim to fully understand them(!) but the stars represent typical content - mostly low detail and low movement (the centre of the stars) but a little fine detail and significant movement (the "arms" of the stars). If you had lots of fine detail and significant movement - almost random content, the frequency response wouldn't look like a star, but more like a square (up to the Nyquist limits for each dimension).

If you turn the stars into squares in the progressive plot, they don't overlap. If you turn the stars into in the interlaced plot, they do overlap. That's the ambiguous region. Your example is right in the middle of the overlap.

Cheers,
David.
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