Keying out windows?

Alexis Hanawalt · March 23, 2006

I'm shooting a low budget spec spot in HDV and I need to composite an artificial background outside the windows of an office location.

I don't really have lights to spare besides the practical office lighting. I intend to tape up cardboard painted chroma key green to the windows and just keep the actors a good distance away - but I'm curious if it might be good to leave about 1 inch all the way around each window with light still coming through to maintain the illusion of real daylight spilling in. I'm concerned that this might allow for a lot of spill. I'm using Keylight with After Effects, so I know I'll have a lot of control, but I just want to be sure I do this in the best possible way.

Any suggestions?

Austin Schmidt · March 23, 2006

The problem with covering the windows rather then placing the green outside is that you will prevent natural light coming through them and so you will need to create that same light inside plus light the green as well. In otherwords, a lot of lighting units is needed which it doesn't seem like you have. A post fx guy and I solved this problem by covering the windows with tracing paper and letting them go overexposed with a consistent white. He then used this "pure white" as a frame to cut out the window as a hard matte. If you need the shot to be moving it can be done easily if trackers are taped along the outside of the windows. Best thing to do is to just shoot a cheap test (even with a minidv camera) to see how the hard matting will look (If it passes on the minidv test then I'm sure it will be fine on HDV). Key is to blend it together so it doesn't look like you cut and paste (but thats why the post guys get paid the big bucks)

Adam Frisch FSF · March 24, 2006

If the camera isn't moving, all you need to do is to expose once for the action in the room and then record a plate exposed for the exterior. Then you combine the two in post via a Difference Matte - no need for green screen.

On my latest music video, all the day interiors in the hotel (except the one in dusk) were done this way. First a normal pass in telecine with the beauty grade, then a fully cranked down one for the exterior - a so called two pass in telecine. Film has the upper hand here though - it can hold information in the highlights that video can't. But you can always expose for the sky with video as a plate.

Have a look at it here:

http://www.adamfrisch.com/music/lauramiche...indexmovie.html

Alexis Hanawalt · March 25, 2006

I shoot today - I think I'll try both with a greenscreen taped to the window and the Difference Matte route... Thanks for the suggestions!

mark preston · June 25, 2006

I was wondering if the bus shots within that music video were also done the same way as I am planning on using a stationary train carriage and keying out all the windows? The bus interior shots looked liked they might have been done the same way.....but somehow I doubt it.