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Wednesday, June 10, 2009

••◊ It's not easy being green

Last night I attended a meeting of the San Diego Filmmakers. When I arrived I peeked in the cyc room and found a well furnished green screen studio (see photo below). Panasonic also let us demo the brand new HPX300 camera for the evening. Normally this room is painted a beige-ish white, so it was a unique experience to walk into a room surrounded by green screen matte paint (expensive stuff, not Home Depot goo in a can). We had to wear hospital over-the-shoe booties on the paint so as not to get it dirty. Poor Mike (stage manager) is probably still cleaning up after our filthy footwear.

Our guest speaker for the evening was Michael Brueggemeyer, a well experienced DP. His first advice was if you can avoid green screen, do it. I generally accept his advice, but after the demo I was convinced I should. Mike had previously shot a scene at the beach and the demo involved a young woman walking in front of the green screen and being composited into the beach background.

Mike first lit the backdrop mainly using overhead lights and an Arri 1K lamp mounted on a c-stand on the floor. The overhead lights were faced toward the wall and tilted slightly down with black foil to flag off light back-spilling onto the talent. The production video monitor in the picture below shows the even nature of the green screen brightness. His comment was to keep the brightness on the green wall even to within 0.5 stop at about 60 IRE for typical optimal results. Ideally the semi-horizontal line (in white) on the production monitor would be a thin perfectly horizontal line to indicate perfect brightness from edge to edge...however, close enough is close enough. As you can see on the monitor the brightness droops to the left a little, but still works.

Mike next lights the talent and assumes that some of the talent lighting will spill onto the green screen. This means iterative tweaking of the lights to re-optimize the green screen to even brightness again. The more even the green, the easier your job in post. Still, with a very well lit background it still may require a mask around the talent in post to perfectly optimize the matte pull. Mike had to do this during the demo because of some light fall off at the edges of the video frame. He mentioned this was typical of finalizing green screen work for video/film.

The final part of the demo showed how difficult it was to color match the person in the green screen video to the outdoor scene. This is probably a color correction specialty in itself and beyond my ordinary patience capability. Thank goodness for the talented people at ILM.



Finally the night ended with a few technical questions and the reminder that it's better to shoot the talent on location if you can. Questions came up, like green versus blue screen...? Well, if your subject has blond hair sometimes it's better to shoot blue screen because blond hair has less blue. Can you use green clothes with a green screen...? Maybe, as the demo showed. It depends on how saturated the color of the clothing is.

One interesting piece of information is that in the days of yester-year, they would light local TV weather forecasters with rimming magenta lights from the side. Why? Because Magenta is the opposite of green and would counter act the green reflection off the back wall (green+magenta=white) and allow the compositing computer to pull the matte better. Now it's done by the computer alone.

Green screen is a lot of cool technology at work, but I think I still prefer reality when available. Thanks for passing on your knowledge Mike.



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