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