Tuesday, February 23, 2010

Rear projection

Last night, Nance and I were watching a bit of Hitchcock's To Catch a Thief and we got into a discussion of rear projection.  For those that are not familiar, this was a technique that was used before blue (and subsequently green) screen chroma keying techniques for replacing elements in a shot or providing backgrounds.  Basically, a large translucent screen was placed behind the talent and a projector whose shutter was synchronized to the camera projected footage onto the screen.  This was used a great deal for car interior shots where everything was shot on a soundstage, the car set was mounted on springs, and grips would rock the car to simulate the car driving down the road.

Nance pointed out how obvious this technique was in the films.  We made a game out of guessing what scenes were using this technique and to be fair, there were some scenes where it was pulled off very well.  Others, not so much.  Today, audiences are MUCH more sophisticated and demand a much higher quality of compositing in films.  To give you an idea of just how much this technique is employed in popular content, check out the demo reel for Stargate Studios here:

Also note that not ALL of this is green screen. There is also a lot of matte shot replacement techniques in use here as well.


Rob:-] said...

So no rear projection? What's the difference between "matte shot replacement" and green screen? Do you mean it was hand rotoscoped? (Green screen/chroma-key is just an automated way of pulling a matte, right?)

I thought it was interesting that, toward the end of the video they didn't even bother to show us the green screen. I guess that's because it should have been obvious by then.

(The two I noticed were the "Saving Grace" shot where Holly Hunter is teetering on the edge of a pillar in the Grand Canyon and the shot in "Heroes" of Masi Oka blinking into existence in Time Square. Funny ... both characters just materialized in both of those shots.)

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B-Scene Films said...

Hi Rob. Generally, you will green screen in a situation where you need to have your talent in front of some action. If you look at the shot at 2:04 of the couple walking down the street and the guy ducking into the newsstand, you can see a good example of both techniques. The action behind the talent is green screen and a matching matte fills in the rest of the shot where the talent is not in need of background coverage.

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John Weir said...

This technology are sometimes also called as the micro display technology. It is quite different from the CRT technology, which is the most traditional one.
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