interlace

Simple interlacing filter from progressive contents. This interleaves upper (or lower) lines from odd frames with lower (or upper) lines from even frames, halving the frame rate and preserving image height.

   Original        Original             New Frame
   Frame 'j'      Frame 'j+1'             (tff)
  ==========      ===========       ==================
    Line 0  -------------------->    Frame 'j' Line 0
    Line 1          Line 1  ---->   Frame 'j+1' Line 1
    Line 2 --------------------->    Frame 'j' Line 2
    Line 3          Line 3  ---->   Frame 'j+1' Line 3
     ...             ...                   ...
New Frame + 1 will be generated by Frame 'j+2' and Frame 'j+3' and so on

It accepts the following optional parameters:

'scan'

This determines whether the interlaced frame is taken from the even (tff - default) or odd (bff) lines of the progressive frame.

'lowpass'

Vertical lowpass filter to avoid twitter interlacing and reduce moire patterns.

'0, off'

Disable vertical lowpass filter

'1, linear'

Enable linear filter (default)

'2, complex'

Enable complex filter. This will slightly less reduce twitter and moire but better retain detail and subjective sharpness impression.