Deinterlacing in Premiere

[Nikolaj Marquez von Hage]

Anyone knows how advanced is the de-interlacing at export in Premiere?

I use it all the time and find it good, but it just hit me: what if Premiere just does something basic, like blending two adjacent lines.

I know there are advanced filters for VirtualDub, that do motion detection and stuff, so I'm wondering: how much do I lose by being lazy and just check-marking "De-interlace" at export?

Thankful for any advice or thoughts.

Nikolaj

[Tripp Woelfel]

I'd be very interested in this as well. Best I can figure is that PP deinterlaces with blue smoke and black magic. Actually, I think it just throws away one field like Photoshop does. Someone might know a better way.

[Graham Hickling]

The Premiere deinterlace is not a "smart" deinterlace of the kind that the Vdub and Avisynth plugins can achieve. If you want to actually quantify how big a difference there is with the various methods, then I would recommend filming a resolution chart in interlaced mode, then examine frames captured from the footage after it has been deinterlaced by the methods you are considering - its really quite a quick test to do.

There are various resolution charts online ... easily found via Google Images.

[Nikolaj Marquez von Hage]

Thank you both. Tripp, I don't think Premiere throws one field away. I base this on some observations I did comparing the image sent to external monitor (which is one field only in my setup) with the one deinterlaced/exported. Field blending is my guess. But I will conduct some experiments and return with my observations.

I have used de-interlacers in VirtualDub that are said to be the best free ones out there.
But they require tweaking and sometimes they give strange results.

[Tripp Woelfel]

Originally Posted by Nikolaj Marquez von Hage

I don't think Premiere throws one field away.

I don't think it can use both fields in deinterlacing because of the temporal displacement between the two. I would think that using both fields would create artifacts commonly called jaggies or mice teeth. But I could be talking through my hat.

I'm also curious about "smart deinterlacing" versus the alternative. "Not smart"?

[Graham Hickling]

A better term is perhaps "motion compensated" deinterlacing, with motion vectors being calculated from more than just the immediate two fields. There's a short paragraph about it in the "Deinterlacing" entry on Wikipedia.

[Nikolaj Marquez von Hage]

Quote:
"I don't think it can use both fields in deinterlacing because of the temporal displacement between the two. I would think that using both fields would create artifacts commonly called jaggies or mice teeth. But I could be talking through my hat."

I'm obviously no authority on deinterlacing, an activity I hope to abandon altogether in a year when stepping up to Panasonics P2 camera... but anyway: Blending two fields will replace the jaggies with a more homogeneous looking "motion blur" area, which is more representative of what one would expect if filming progressively with double the exposure time compared with filming in interlaced mode.

Did I express that well? Hmmm...

[Tripp Woelfel]

Originally Posted by Nikolaj Marquez von Hage

Blending two fields will replace the jaggies with a more homogeneous looking "motion blur" area, which is more representative of what one would expect if filming progressively with double the exposure time compared with filming in interlaced mode.

I understand what you're saying. But if a motion blur is applied to a jaggy don't you just get a fuzzy jaggy? On fast motion, it might mitigate the jaggy problem but they'll still be visible.

I'm probably poking about in the dark with a barge pole.

[Mike McCarthy]

An easier way to figure out what Premiere is doing, would be to make an image in photoshop, and paint in horizantal lines, maybe black and white in one area, red green in another, and maybe a small checkerboard with 1x1 and 2x2 pixel patterns. Don't fill the whole image, just enough to have a consistent pattern, like 10 lines. Then import that still into PPro and interpret as interlaced. Export and analyse the result in Photoshop. This has picqued my curiousity and I may test it myself, if I have some time tomorrow.

[Robert Martens]

Originally Posted by Tripp Woelfel

I understand what you're saying. But if a motion blur is applied to a jaggy don't you just get a fuzzy jaggy?

Yes, and if I'm not mistaken that's simply called a "blend". Looks better than field doubling, but still nothing to write home about.

There are far more complex techniques, for example Xin Li's New Edge-Directed Interpolation, a technique that I don't believe is offered in the base package of any video editing or compositing application (Premiere, Vegas, After Effects, Combustion, Shake, etcetera) unless you start buying plugins.

If you explore the realm of open source software you can find freely available examples of the algorithms in question, one of which I've in fact just offered up to Nikolaj himself in this thread, over on the PC editing board. The thread focuses on ultimately upscaling SD footage, but part of the process involves a version of NEDI as part of the deinterlacing process, implemented as an Avisynth filter. Motion compensation, while not always used in conjunction with deinterlacing, is also part of the steps I've outlined there, and has been ably explained (or so I assume; I can barely handle algebra) in The Engineer's Guide to Motion Compensation by John Watkinson of Snell & Wilcox. More whitepapers and guides can be found in the company's Knowledge Center.

As for figuring out Premiere's method, until Adobe starts publishing technical details this intricate, Mike's suggestion sounds like the way to go.

[Nikolaj Marquez von Hage]

Tripp and Robert, I have to point out, just for the record, that field blending DOES make the jaggies disappear. It's not motion blur applied on jaggies.

Field blending is just blending two fields together and then using the result as a replacement for both fields. You get half the vertical resolution, but use info from both fields, not just one of them as in field doubling.

Correct me if I'm wrong.

Hey Robert... Still have to apply all the steps, it's quite complicated with my source footage being spread out on several disks...

[Nikolaj Marquez von Hage]

By the way: field blend is the most stable de-interlacing method from my experience.
Even though in theory it sounds good to do various motion-detection stuff, in practice, if you're not prepared to tweak parameters in VDubs "Smart" filter (to take an example) for hours... field blending never gives unexpected artefacts and doesn't require tweaking...

Mikes suggestion is acually great. I might try it tonight.

[Robert Martens]

No need to correct you, I just wasn't thinking; you're right, I think that is actually how field blending works, my mistake.

As for most stable, I think you're in for a pleasant surprise. The motion compensated NEDI used in the TGMC script is extremely stable, even with only the default settings, despite being a bobber. It has problems with shallow diagonal lines, like most deinterlacing does, but does an excellent job of avoiding the jumpiness that other bob software usually produces. Donald Graft's "Smart Deinterlacer" for VirtualDub is good, but I've never gotten results out of that as easily as I have TGMC, or that were as good looking. A blend is much faster, of course, so it's give and take between all these methods.

[Nikolaj Marquez von Hage]

Well that's very interesting; I'll definitely try the NEDI.

[Mike McCarthy]

Where are the deinterlace options in CS4? I usually use CS3 at work, but only have CS4 on my system at home. Unless I find those options on CS4, I will put off the test until I have a CS3 system available next week.