De-interlacing

[akkers]

I am just curious about the process of deinterlacing. Some software will just push up a 25i footage to 50p doubling the frame rate. Is that proper de-interlacing or is it more involved?
Is there a correct way to de-interlace? Using which software?

[poisondeathray]

I am just curious about the process of deinterlacing. Some software will just push up a 25i footage to 50p doubling the frame rate. Is that proper de-interlacing or is it more involved?

If the "25i" was interlaced content (e.g. sports, news), then 50p is correct. 25i interlaced content means 50 fields per second. 50 moments in time recorded per second . Deinterlacing essentially means each field is interpolated to a frame. If you deinterlace to 25p, then you would be discarding half the information and losing half the motion samples

If the "25i" was progressive content (e.g. some UK dramas), then 25p would be correct, and the fields should be "weaved" , not deinteraced. For many types of deinterlacers - if you deinterlace 25p content to 25p instead of weaving - you lose 1/2 the spatial data. Lines become jaggy and aliased with noticable quality loss

Is there a correct way to de-interlace? Using which software?

It depends on the source, and there is no "perfect" way to deinterlace, and the quality varies between different algorithms.

(Unless the "25i" content was actually progressive - which you would weave, not deinterlace)

[lollo]

Some software will just push up a 25i footage to 50p doubling the frame rate. Is that proper de-interlacing or is it more involved?

In addition to what master poisondeathray properly said, the best deinterlacers do not just double the frame rate (bobbing operation). They "modify" the fields (and the derived frames) to improve the final quality of the outcomes, based on many different strategies. As example, QTGMC in AviSynth.

[akkers]

Actually the footage I have is from PAL VHS and DV camcorders (25i). I have captured through firewire/capture card straight to 25i avi files.
So what I am doing is converting these to 50p MP4 files for playing on TVs.

[lollo]

Not all sources are interlaced, i.e. PAL VHS originated from films (movies and TV series). Poisondeathray already explained that to you.
When needed, use AviSynth and QTGMC to deinterlace at double frame rate.

[akkers]

Thanks for that. All my footage is my own from camcorders.

[salini]

Thanks for the help, Since my footage is from camcorders, I’ll give AviSynth with QTGMC a try for deinterlacing to 50p. It sounds like a better way than just doubling the frame rate. I’m excited to see how it turns out

[Alwyn]

I’m excited to see how it turns out

It's like night and day.

[poisondeathray]

Some camcorders (incl. DV camcorders) have a "25p" mode. It's "25p in 25i"

If you double rate deinterlace, and during a scene with motion, you see motion in every frame at 50p, then double rate deinterlacing is the correct way to handle it. If you see duplicates, then don't deinterlace because the content was not interlaced

[salini]

Thankyou for this helpful information.