Progressive Frames Deinterlace

[TheLastOfThem]

Hi Everyone

I had a question. What happens if you deinterlace a progressive source? Handbrake claims it "lowers the vertical resolution" but I am wondering why this is ? Wouldn't a deinterlacer simply not work on progressive frames.

I read up on this and know there's many types of deinterlacer..and the one I use is a "discard" deinterlacer

[jagabo]

Depends on the deinterlacer. Discarding one field and resizing the remaining field is one of the worst forms of deinterlacing and will indeed reduce vertical resolution by half. That's a bad thing to do with interlaced video, and especially stupid with progressive video.

[TheLastOfThem]

Does deinterlace produce dupe frames when it discards or does it half the FPS if a source is true interlaced?

[jagabo]

It depends on the type of deinterlacer. A simple discard field and resize produces the same rate, 30i becomes 30p. A double frame rate deinterlacer doubles the frame rate, 30i becomes 60p, usually called a bob.

[LigH.de]

The main difference between deinterlacers is how much efforts it takes to reconstruct content in each discarded field. Some only calculate a spatial average. Others try to take adjacent fields into account. But they have to assume that there is a regular and continuous temporal progress from field to field. That's the point of interlacing: The camera recorded the video content as one field at a specific moment, the next field after a little delay, the next after twice the delay, and so on ... weaving two fields from different moments to a frame is "artifical", only required to fill the whole screen, but looking at a frame means looking at two different moments at the same time, which is not intended, you should rather look at them with the same delay as they were recorded (field after field).

[pandy]

Depends from deinterlacer - Bob may introduce vertical jitter as usually video lines are shifted by 0.5 line up and down - for real progressive content this may lead to jittering in vertical direction visible on screen (in fact this distortion is quite common on PC - dumb bob may be annoying, another example are cheap TV - they frequently introduce vertical jitter for progressive source sent as interlace).

[hello_hello]

Hi Everyone

I had a question. What happens if you deinterlace a progressive source? Handbrake claims it "lowers the vertical resolution" but I am wondering why this is ? Wouldn't a deinterlacer simply not work on progressive frames.

I read up on this and know there's many types of deinterlacer..and the one I use is a "discard" deinterlacer

If a media player is clever it'll only de-interlace frames with an interlaced flag (which properly encoded interlaced video should have) and leave progressive frames alone, but I don't know how clever VLC is. I assume when it's de-interlacing is set to "automatic" that's what happens, but I don't know for sure.

There's some screenshots here. They're not all supposed to be normal de-interlacing samples, but the first lot is progressive animation and the last screenshot is de-interlaced with Yadif. I don't know why your VLC guide says Yadif (2x) is heavy on a CPU. Maybe it was written ion 1998. I'd try Yadif (2x). Or use a player such as MPC-HC and the video card will probably do the de-interlacing.
The second screenshot labelled "After separating the fields, applying decimation and resizing as needed" shows what happens when you simply discard one of the fields.

[LigH.de]

Most DVD Video content was produced in interlaced encoding mode, no matter whether the content was field or frame based. Just to be safe. Because encoding progressive content in interlaced encoding mode doesn't hurt; but encoding interlaced content in progressive encoding mode would become very ugly. So the MPEG-2 encoders were simply fixed to interlaced mode.

[manono]

Most DVD Video content was produced in interlaced encoding mode...

Most PAL DVD Video content was produced in interlaced encoding mode. Which means, I believe, that most PAL DVD players will deinterlace those films on PAL DVD that were encoded as interlaced. Since most deinterlacers in players and televisions are fairly decent these days, the deinterlacing going on might not be noticeable, but the results are still slightly degraded compared to what would have happened had the films been encoded as progressive.

Just to be safe.

Something I never quite understood. The NTSC houses, also, in the early days of DVD often encoded everything as interlaced. It was just easier. And safer, as you say. But films on NTSC DVDs produced by reputable companies haven't done that for a long time now.

While there are plenty of NTSC DVDs of films with hard telecining and even field blending sometimes, any decent label encodes films at progressive 23.976fps with soft pulldown. Even the cheapest flag reading player with progressive scan will output whole untouched/undeinterlaced/undegraded frames to a progressive display such as a 1080p LCD television.

To answer the original question, " Wouldn't a deinterlacer simply not work on progressive frames.", the answer is 'no', not for the vast majority of DVD players out there, since what they do is based on a flag in the video - interlaced or progressive. That's for DVDs, of course, but if you tell any program to deinterlace, unless it has a mode where it deinterlaces only what it detects as interlaced, it will deinterlace everything. Handbrake does have its so-called 'Decomb' filter which claims to deinterlace only what it 'sees' as being interlaced, but I don't know whether or not TheLastOfThem was referring specifically to that deinterlacing filter.

[LigH.de]

"Legacy" DVD players (with analogue output only) won't deinterlace video content. Progressive content will have been shown on interlacing CRT TV sets coming from DVD players just like coming from TV broadcasters: Two matching fields after another, then the two matching fields of the next frame... LCD and similar flat screen TV sets today may deinterlace. Or just weave, depending on their firmware "smartness". But they will preferably be connected with digital interfaces, so that the TV can know if the video was encoded in interlaced or progressive mode.

Progressively encoded PAL DVD material was a rarity. I remember "Animatrix". It had an annoying GOP quantization pumping, BTW. But if you have NTSC-Film material to be encoded with soft telecine flag (so that "legacy" DVD players will telecine their analogue output for NTSC TV sets), I guess they may have been encoded in progressive mode sometimes because setting up the encoder was distinct enough from the required setup for true interlaced NTSC, anyway. No idea though, I don't have statistics here.

[hello_hello]

Most DVD Video content was produced in interlaced encoding mode, no matter whether the content was field or frame based. Just to be safe. Because encoding progressive content in interlaced encoding mode doesn't hurt; but encoding interlaced content in progressive encoding mode would become very ugly. So the MPEG-2 encoders were simply fixed to interlaced mode.

That's a fair point. I should have thought of that. Even if, as manono says, it mostly only applies to PAL these days.

I must have assumed the OP was referring to VLC for playback because he referred to a "discard' de-interlacer, but maybe that was a bad assumption.
For a software player, "automatic" is probably the best option (while selected the highest quality de-interlacing) unless you're happy to manually enable or disable the de-interlacing as required.
Mind you for VLC I've no idea if "automatic" de-interlacing means it checks for combing before de-interlacing, or if it just de-interlaces according to any interlaced flags. Probably the latter.

For re-encoding.... I think Handbrake's de-interlacing filter de-interlaces everything when it's enabled, whereas the decomb filter only de-interlaces if it detects combing.... which works, but it does tend to ignore frames with only small amounts of combing in places.

[TheLastOfThem]

Hi everyone,

Okay seems things went overly complicated because I wasn't specific enough (d'oh. Lesson learned)

What happens to progressive sources if you deinterlace them? How can one see JUST the frames from one field on AviSynth?

People say that most sources NTSC are made up of fields when they're interlaced - how does one see the image from Field 1 vs Field 2? And also how does deinterlacing a progressive source where Field 1 and Field 2 are from the same moment in the clip fares?

[manono]

How can one see JUST the frames from one field on AviSynth?

SeparateFields()

If you want to see those fields as full frames then put on a bobber instead, anything from Bob to Yadif(Mode=1) to QTGMC.

People say that most sources NTSC are made up of fields when they're interlaced

All sources - NTSC or PAL, progressive or interlaced - are made up of fields. One field from a frame consists of all the even numbered rows of pixels, the other of all the odd numbered ones. Interlaced or progressive has nothing to do with that.,

how does one see the image from Field 1 vs Field 2?

I already showed how - either separate the fields or put on a bobber.

And also how does deinterlacing a progressive source where Field 1 and Field 2 are from the same moment in the clip fares?

Add:

Bob().SelectEven()

to your progressive source and see what happens. Look for diagonal lines or thin lines like telephone wires. All deinterlacers will damage progressive frames, some more than others depending on the quality of the deinterlacer.

[TheLastOfThem]

Thank you again manono. Very much value your time and explanations!! <3