Rotoscoping is tracing something, usually manually, for the purpose of compositing something into the shot.  I guess one could say he rotoscoped the outline of the door, though rotoscoping tends to imply a more frame-by-frame process.

Some of my films have little set extensions like this as well, though generally not as subtle.  It's a cool effect, NXT!

Smeagol, that's probably one of my favourite effects in Unrenewable.

ANP, you could do a couple things. You could try to use 3D programs to build the city, then create a matte painting with it. Another technique you could use would be to build smaller scale buildings one at a time, then composite them together and make a matte painting from that.

You say onion skin, yet the technique you mention is blue screening.

Instead of painting parts of it blue, try using .png files. When you make your backgrounds (in Photoshop) and export as a png, any pixels that aren't occupied will be transparent, which means you can just plop it onto your footage and not have any white spots.

So basically, you're just drawing black over that part of the set? @JP I'm not sure, but I think this is what you're talking about.

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I also painted a door, but yes, it was pretty simple. However, as seen by Smeagol's work with it, it can prove to be incredibly useful.

This matte painting is scarcely as impressive as the previous two

When filming Coffee With The General I was taking still exterior shots and since it was cramped I couldn't frame the the shots properly to fit the rather wide aspect ratio I was using. So I had to shrink the photo but that would leave gaps at the side but since I had used plants in the foreground it allowed me to expand the plants to fit the aspect ratio (most of what I added turned out to be black in the end so it would be similar to leaving the gaps there anyway)

Similar to what NX did, I also had small gaps between the bricks where you could see the blue background leaking in so I patched those up too. The last frame is the colour corrected shot that appears in the film.

If I thought about this in advance what I would have done is taken the photo without the plants then subsequently took photo of the plants on their own and cut them out and then I would have done the digital zoom in on the two different layers at different speeds and this would have added a 3D feel to the shot.

I've wondered the same exact thing.

He uses Photoshop.

I use Final Cut for video editing. I'm not sure what you use, but it should be able to handle .png transparencies.

Nice work, RP!