The Engineer's Guide to Standards Conversion - Snell

Input film frames at 24Hz
Optic flow of
film (no judder)
Judder due to
double and triple
image repeats
Fig 6a Origin of
judder for
60Hz 3:2
pulldown
telecine
2 3 60Hz output fields 2
Input film frames at 25Hz
Optic flow of
film (no judder)
Judder due to
image repeats
Fig 6b Origin of
judder for
50Hz
telecine
2 2 50Hz output fields 2
Fig 4.3.1
There is, however a worst case effect which is obtained when 60Hz telecine
material is standards converted to 50Hz video. The 3:2 pulldown judder inherent in
the 60Hz video is compounded by the judder resulting from 60/50 conversion and
the result is highly unsatisfactory. Some standards converter are adaptive, and select
different filter responses according to motion in the input. Such an adaptation
system is unable to cope with the 3:2 pulldown where there are two identical fields,
then a change followed by three identical fields. The solution is to design a
standards converter specially to deal with conversion of 60Hz video from telecine.
The converter has an input buffer which can hold several input fields and circuitry
which compares successive fields.
53