Video format conversionVideo format conversion
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Format conversions
size change frame rate conversion (de)interlacing
Size change
Normally treated as a problem of image resizing; each image is processed separately
Interlaced signal
Similar to a spatial quinqunx…
Interlaced signal
Similarly, the spectrum of a quinqunx is this:
Interlaced signal
Ideal deinterlacing:
Deinterlacing
In the areas without motion, the ideal process is temporal interpolation
Where there is motion, I can interpolate spatially Or, better (but more difficult), to use motion compensated
temporal interpolation (see later)
Deinterlacing
A video-temporal (VT) interpolation filter would theoretically solve the problem, if the signal were bandlimited prior to interlacing
Deinterlacing
Example of edge-dependent interpolation:
con
Deinterlacing
Example of VT median filter
Deinterlacing
Better: motion compensated temporal interpolation
Frame rate conversion
From film (24 fps) to TV (PAL/Secam)
- the film is accelerated (24 -> 25 fps) and each image is shown twice -> 50 fps
Not in the USA (60 field/s ,actually 29.97x2)-> telecine
- 12 field are added every 24 frame -> 60 fps:
2-3 pull-down:
- the film is slowed (24 -> 23.976)
- the third B is often omitted in DVDs
(its equal to the 1st): 480i24 format,
and the DVD adds it on-the-fly
- similarly, 3-2 pull-down:
AAABBCCCDD
Frame rate conversion... and if we need to return to progressive, 60fps: two ways Weaving takes two successive interlaced fields and reinterleaves
them to create a progressive frame - works well - if the original material was progressive, like a film that has
undergone the 2:3-pulldown process, and - provided the disc tells the player that it was.Bobbing, the normal process for generating a progressive signal
from interlaced video, takes a single field and creates a full progressive frame from it by line doubling or line interpolation
Frame rate conversion
If the original material was interlaced video, not 2:3-pulldown film, weaving can cause artifacts
More advanced progressive-scan conversion systems combine bobbing and weaving, depending on the content (motion…) of the image. If the monitor is 72 Hz: simply AAABBBCCCDDD…
Scan rate doubling
Field repetition: te*=to
to*=te
Gives loss of resolutionFrame repetition te*=te
to*=to
generates artifacts if motion is present
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