[FFmpeg-user] decomb versus deinterlace

pdr0 pdr0 at shaw.ca
Sun Apr 19 02:16:13 EEST 2020

Mark Filipak wrote
> Deinterlacing is conversion of the i30-telecast (or i25-telecast) to p30
> (or p25) and, optionally, 
> smoothing the resulting p30 (or p25) frames.

That is the description for single rate deinterlacing. But that is not what
a flat panel TV does with interlaced content or "telecast" - it double rate
deinterlaces to 50p (50Hz regions) or 59.94p (60Hz regions). The distinction
is important to mention; one method discards half the temporal information
and motion is not as smooth.

Deinterlacing does not necessarily have to be used in the context of
"telecast".  e.g. a consumer camcorder recording home video interlaced
content is technically not "telecast".  Telecast implies "broadcast on

The simplest operational definition is double rate deinterlacing separates
and resizes each field to a frame +/- other processing. Single rate
deinterlacing does the same as double, but discards either even or odd
frames (or fields if they are discarded before the resize)

> Combing is fields that are temporally offset by 1/24th second (or 1/25th
> second) resulting from 
> telecine up-conversion of p24 to p30 (or p25).

I know you meant telecine up conversion of 23.976p to 29.97i (not "p"). But
other framerates can be telecined eg. An 8mm 16fps telecine to 29.97i. 

"Combing" is just a generic, non-specific visual description. There can be
other causes for "combing". eg. A warped film scan that causes spatial field
misalignment can look like "combing". Interlaced content in motion , when
viewed on a progressive display without processing is also described as
"combing" - it's the same underlying mechanism of upper and lower field
taken at different points in time

> Decombing is smoothing combed frames. 

Yes, but this is an ambiguous term. "Decombing" can imply anything from
various methods of deinterlacing to inverse telecine / removing pulldown .

> It seems to me that some people call combing that results from telecine,
> interlace. Though they are 
> superficially similar, they're different.

Yes, it's more appropriately called "combing".

When writing your book , I suggest mentioning field matching and decimation
( inverse telecine, removing pulldown) in contrast to deinterlacing. 

I recommend describing the content. That's the key distinguishing factor
that determines what you have in terms of interlaced content vs. progressive
content that has been telecined

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