Does deinterlacing reduce video quality ?

[Blue_MiSfit]

YADIF is quick and decent quality

TGMC is slow and superb quality!

The only time you should NOT deinterlace IMO is if you plan on displaying on an interlaced CRT. Otherwise, AviSynth deinterlacing usually outperforms playback deinterlacing.

~MiSfit

[FredThompson]

Originally Posted by Blue_MiSfit

The only time you should NOT deinterlace IMO is if you plan on displaying on an interlaced CRT...

...and you don't expect any tech changes or need to ever access the source material.

Once you've changed the data, it's changed, irrevocably.

[wonkey_monkey]

The only time you should NOT deinterlace IMO is if you plan on displaying on an interlaced CRT. Otherwise, AviSynth deinterlacing usually outperforms playback deinterlacing.

That depends what's doing the interlacing. I haven't done any actual tests (which would only be subjective) but I always advocate Samsung TVs as brilliant deinterlacers.

David

[Blue_MiSfit]

Of course. Hence IMO

I've never been anything but disappointed by the deinterlacing / IVTC capabilities of TVs.

~MiSfit

[IanB]

The goal of deinterlacing on modern LCD and Plasma televisions is to present interlaced program material without the visual artefacts that are present when you use a simple progressive display device. i.e. so it looks as good as a quality interlaced CRT.

Proper deinterlacing and IVTC done in Avisynth can be subject to people examining individual frames in isolation and is held to a much higher standard. With a TV you have 1/50th or 1/60th of a second to see an artefact in a single frame. Most visible artefacts are visible because they keep repeating on subsequent frames and the flicker element associated draws your attention.

When dealing with interlaced material, you really need to evaluate it while watching it at normal display speed. Part of the interlaced compromise is spatial resolution is traded for temporal resolution. When interlacing was invented freeze frame and slow motion were not a consideration.
________________________________

Done correctly double rate deinterlacing (bobbing), especially if the original input lines are preserved should not reduce the inherent quality of the video being saved (because you can still retrieve the original data). However the double rate deinterlaced result may not look that great.

[2Bdecided]

Originally Posted by FredThompson

IMNSHO, storage costs are so low that it's best to save the source because tech improves over time. I DO compress NTSC DV to 4:2:2 at 8000 CBR with TMPGEnc to preserve temporal information and reduce size.

I always keep the source.

However, for watching it on a PC, or processing it into some other format, I want to use the highest quality software deinterlacers available. These cannot run in real time, and hence are not built into media players.

Cheers,
David.

[2Bdecided]

Originally Posted by Blue_MiSfit

YADIF is quick and decent quality

It depends on what your benchmark is. My benchmark is watching interlaced content on a native interlaced display. That will flicker (50Hz CRT) and twitter (fine interlaced detail). Other than these artefacts, the image will be sharp and artefact-free (as long as the source is! ).

You can't say that of any deinterlacer. They all go "wrong" on something.

Also, all the dumb-bob based ones (and most resort to dumb-bob as a last resort - some as a second resort!) soften the source horribly.

Cheers,
David.

[Manao]

Just a quick correction :

Originally Posted by 2Bdecided

On the more general point: if nothing moves, interlacing doesn't lose any information, and neither does deinterlacing! The same is true for horizontal-only movement.

No. Interlacing loses information, because it does a vertical low pass on the video. Interlacing a 50p video isn't equivalent to separatefields.selectevery(4,0,3).weave, but closer to resize(width, height / x).resize(width, height).separatefields.selectevery(4,0,3).weave, with x around 1.5.

[2Bdecided]

Originally Posted by Manao

Interlacing loses information, because it does a vertical low pass on the video.

It doesn't have to. It typically should (to avoid twitter on interlaced displays), but plenty of cameras and standards converters don't apply a specific vertical low pass filter.

Cheers,
David.

[Manao]

I think we already argued that subject here. I guess the only way to resolve that disagreement will be to get our hand on a 2160p50 video, and test what happens when you downsize it to 1080p50, then interlace it without downpassing. I still think I'm right, because last time I did that with 720p50 -> 576p50 -> 576i50 without downpassing on the last step, the content was unwatchable on both CRT SD TVs, and flat HD ones.

Regards,

Mathieu

[swiego]

Right now you have to compromise with modern equipment.

If you deinterlace and encode to some modern format, then you have lost some quality. However, you have gained convenience of playback on any device, and no longer have to worry about the capability of its deinterlacer.

If you try to send the original interlaced material to a display or processor with deinterlacing capabilities, and your source material is not a DVD from Blockbuster, then you take advantage of modern deinterlacers if and only if you can figure out how to get that video stream to the deinterlacer in a way that it can understand what to do with it. I have a player with a ABT2010 and a receiver with a Reon HQV and it's one heck of a challenge trying to get either to recognize a proper interlaced signal over HDMI... heck, it's a challenge just generating that signal.

As a result, I keep my source material and I also keep a highly compressed deinterlaced mp4 or x264 version as well.

[2Bdecided]

@Manao,

You should low pass. Much modern equipment doesn't. Where's the confusion?

I certainly find my own HD>SD encodings twitter horribly if I don't low pass filter.

Cheers,
David.

[hydra3333]

Heck. downpass, low pass... any links to a glossary ?

[Guest]

Originally Posted by hydra3333

Heck. downpass, low pass... any links to a glossary ?

Google.com

[wonkey_monkey]

Originally Posted by hydra3333

Heck. downpass, low pass... any links to a glossary ?

"blurs it a little bit"

David

[knutinh]

Originally Posted by Manao

Just a quick correction :

No. Interlacing loses information, because it does a vertical low pass on the video. Interlacing a 50p video isn't equivalent to separatefields.selectevery(4,0,3).weave, but closer to resize(width, height / x).resize(width, height).separatefields.selectevery(4,0,3).weave, with x around 1.5.

Just a quick correction:
No. As I have told you before (?) non-filtered interlacing is common enough that professional cameras even have a name for that mode.

This does not mean that all interlaced video is non-filtered, just like you are wrong in stating that it is. The truth seems to be that both possibilities happen.

-k

[Manao]

No. As I have told you before (?) non-filtered interlacing is common enough that professional cameras even have a name for that mode.

I must admit I had overlooked your link the first time. I just read it, then searched a bit about frame integration. And I have two remarks :
- I never found one link speaking about frame integration in a real use case. All the links I found were talking about frame integration for particle tracking in research experiment, for night vision shoots, or for video security.
- A lot of the links I found referred to old cameras shooting in SD. Now, I have tested SD without any lowpassing, and the video is unwatchable that way (take any bluray and make the experience yourself by downsizing it and interlacing it without lowpassing, you'll see).

So, the only case we're disagreeing is HD content. As I said, we will need a 2160p video to make the test, and that isn't that easy to come by. If I'm able to find one, I'll keep you informed.

[knutinh]

Originally Posted by FredThompson

Think about it. Interlaced video has twice the frame rate of progressive video. Deinterlacing throws out half the temporal information by replacing alternating interleaved fields with calculated guesses of what would be in those fields.

Go to a store which has 60 Hz and 120 Hz displays next to each other. If deinterlacing was "perfect" there would not be a need for 120 Hz, would there?

FWIW, 120 Hz displays also use "educated" guesses to create the "missing" fields but they keep far more of the temporal information.

I think that this post is confusing the reader rather than enlighting.

Progressive is a method for representing/capturing/reproducing video information in which all pixel sites are available at a number of times per second (framerate)

Interlacing is a method for representing/capturing/reproducing video information in which only half the pixel sites are available at a number of times per second (fieldrate)

Assuming no further data compression:

One motivation for interlacing seems to be simple lossy video compression, ala h264 and MPEG2 (although much cruder). Compared to 50p, 50i gives a 50% bandwidth-reduction at a moderate visual loss.

The table below gives examples.

method       field/framerate normalized bandwidth
progressive  25               1
progressive  50               2
interlaced   50               1

If one assumes further data compression, I think that interlacing is, for most cases in 2010 useless.

Interlacing has nothing at all to do with 60Hz and 120Hz displays. That technology is there to mask problems that lcd-technology has with reproducing believable motion (constant illumination).

To the thread-starter:
I would always try to keep the source or the original for backup purposes. If I was to do any processing of the video (recompression, scaling,...) I would deinterlace it as early as possible.

People tend to forget that the whole point of MPEG2, h264 and friends is to produce the best possible (the best that the codec developers were able to at that time) video for a given bitrate. Most codecs works best with progressive video. True interlaced displays are a dying breed, and hopefully interlaced cameras will go with them. My moral then when encountering interlaced material is to convert interlaced material to "double-rate" progressive (keeping all spatial and temporal information in the source, using a deinterlacer that introduce as few artifacts as possible), compress at whatever bitrate you can afford, using the best encoder that you have the time for.

Panasonic has recently released a nice hand-held "AVCHD"-type consumer video camera that records in 1080p60 using AVC/h264/MPEG4 codec at 28mbps. Bluray standards are going "3D" and with that may come the possibility of 1080p60 for regular video (if not, 720p60 is an excellent, if often overlooked option. Scaling spatially is a lot easier than scaling spatio-temporally).

-k