View Full Version : green/white/blue screen ?
we will start to shoot a short film. it will be located inside a room and there will be a window where we have to add in post some differents skies pre.rendered - that's the problem. the director want to put a white screen with a light in front of the windos which it'll going to illuminate the room and to make some nice shadow effects with the shape of the actor... but the actor will going to dance in front of that window.. the white screen its a problem to make a proper key and composite at the end, right? if we'll put the bluescreen (which is better to key) we'll going to loose the light effects of the white screen with the light...
i hope i've been clear... sorry for my english :)
don't answer me back 'rotoscoping' ... please ;)
6th June 2008, 23:07
If the shot/sequence is a short one you would could probably get away with the white screen and roto/luma key it out. Maybe a half-solution, a lighter blue screen which would not produce as much coloured spill. If it is a long sequence then going with procedural green/blue screen process would make more sense. Sometimes vfx requirements have to win out over aesthetics.
7th June 2008, 03:03
if the actor is wearing light colors, welcome to roto, if not, try multiple luma keys, MK and a little roto...OR ask the DOP to make a curved green screen and keep it Behind the light that he/she is gonna bounce through the window, check the video assist monitor to make sure its adjusted correctly..keep in mind that the 10k or whatever light the DOP will use will be on a slim stand, so its easy to fix the green screen behind it..the DOP maybe using the white screen to soften the light, with green behind it will help, but beware of the burnt centre where the light hits the white screen...OR roto it all. :) im assuming you are shooting on 35mm film ? cos if your shooting HD or "below" it might be best to simply roto everything
7th June 2008, 14:13
Try to convince the director to use bluescreen. With the white you'll end up spending a lot of time trying to remove white edges on your actor, especially in the hair. If the the bluescreen is far away from the window you'll be able to put some lights between the bluescreen and the window to achieve the same light effect.
ok. I see...
thanks so much at all!
7th August 2008, 17:00
Having just done a small job for a friend with white behind the window, as well as more blue and greenscreen keying than I care to think about, here's a few observations:
- white is OK, as long as you aren't too concerned with getting a good edge, and as long as the view you will be putting in behind is bright. And as long as the foreground isn't lit too bright itself. Be prepared for a lot of roto cleanup and a so-so result.
- blue or green is great, because it actually gives you the ability to do a proper key, with good transparency on defocussed, transparent and motion blurred edges. With white, you will be strugging to get any of those.
- If someone wants to get bright interactive light into the set, that is very good news. It shows that they are thinking about the lighting more than often happens with DOPs and blue/greenscreen interiors. Having decent backlight/rimlight on your foreground room and characters will go a long way to helping the final comp work. Often the reason a comp shot with a view through a window looks bad is because of insufficient backlighting of the foreground.
- Your blue/green screen tending to block this interactive/ambient light from outside is a common problem. Have a larger screen placed a lot further back from the window/set (always good practice, and the best way to minimise spill). The further back the better. This also means you will then get a better space in which to mount the fixtures for the backlight into the room.
- Light the blue/green screen with heavily blue or green gelled lights to pump up the saturation. It should be bluer than the bluest thing you ever saw in your life.
- run a test on the exposure on the blue/green screen. Better to be safe than sorry. Saturated blue or green freaks out light meters, and a DOP who isn't experienced in vfx will often misinterperate the reading.
- minimize spill by keeping the screen far back, if it is large enough, but remember that good keying software (eg Keylight in Shake) allows you to replace spill with the ambient colour of your choice.
- given the choice between blue and green, generally I would go for blue. It works better. Unless there is a lot of blue in the set/costumes, or the lighting on the foreground is very cool.
- Examine photos of a real interior with a window, and the inside/outside lighting ratio. Work out if you want a "realistic" look (outside is usually several stops over exposed - this looks fine if it's that you want) or a "studio" look, where the balance is closer.
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