Rotoscoping on Interlaced Footage
 

Many moons ago I asked a question here about how to rotoscope lightsaber blades onto interlaced footage while still maintaining it as interlaced. In other words I wanted to keep the 60fps look of the video. The consensus was that I'd just have to deinterlace the footage and live with it.

But I seem to have found another way which I thought I'd share here. You deinterlace the footage using a blend fields option first. Create your filmstrips in adobe premier and edit them in photoshop as normal. However, at the same time you create your filmstrips, create "blank" as in black filmstrips for the corresponding snips. When you take your photoshop layers to paste onto the original filmstrip, paste onto the black on instead.

Then, in Premier, open up the original interlaced version of your footage and put your filmstrip onto a second video track and set its transparency mode to "Screen." Premier will take your rotoscoped effects and composite them onto the interlaced footage. Your effects themselves will still be 30fps, but the underlying footage will still be 60i with the smooth motion thereof.

You have to use blend frames to deinterlace the footage because you want each frame of your rotoscoping to account for the full two fields of the interlaced frame. For instance, when the lightsaber moves fast, it creates a blur across the frame. That blur will be wider when then fields are blended than if you only take alternating fields to make full frames.

I'll post a sample soon if anyone's interested to see the result.

Update:

So the interesting thing that I notice now is that the smoothness of the underlying footage makes the 30fps rotoscoping even more apparent, and sometimes distracting.

What I would love to know, and it's too late at this point but in the future, is if there's a way to rotoscope individual fields so you can actually do it at 60fps. It would involve, I guess, somehow creating 720 x 240 filmstrips and editing them that way. Possible?

i was under impression that commotion could rotoscope frames and you could take it to individual fields .. or was it combustion ?

I've used Vegas to convert 60i to 60p. Set the deinterlace method to "interpolate" and turn off resampling on the source clip. Render to 59.94 progressive and Vegas will turn each field into a full frame. Render to uncompressed AVI, not DV. Rotoscope that, then bring it back in and render to your interlaced format.
///d@

Cool, that would do it. Thanks. Of course it would take twice as long to rotoscope then! :)

What I decided on doing was cutting camera angles right before the rotoscoping begins and right after, to minimize the noticability of the transition. It seems to work ok.