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Sky replacement if actor wearing same color as sky?

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Catherine SeguinSky replacement if actor wearing same color as sky?
by on Aug 17, 2016 at 9:15:20 pm

Help! I need to find out if this is possible or would be too difficult.
I have a whole shoot that I am shooting during the day, then turning into a sunset. I know how to do it fairly easily if the actor wasn't wearing the same color as the sky, but unfortunately, he is wearing white and I don't know if I can wait for a perfect blue sky.
How difficult would this be? The 2 techniques I know at the moment are luma key and keylight. I don't have any experience with masking, but could that be a possibility or would I have to therefore mask frame by frame and it wouldn't be feasible for a 5 minute short?
Thank you for your help!
Catherine


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Dave LaRondeRe: Sky replacement if actor wearing same color as sky?
by on Aug 17, 2016 at 10:12:28 pm

Can you clarify? I get the impression you're trying to do a time-lapse of the sky turning from daylight to sunset, with the white-clad actor in the foreground.

Dave LaRonde
Promotion Producer
KGAN (CBS) & KFXA (Fox) Cedar Rapids, IA


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Catherine SeguinRe: Sky replacement if actor wearing same color as sky?
by on Aug 17, 2016 at 10:57:43 pm

I have multiple angles. It's a short scene with a sunset in the background. I'm adding the background myself since Im shooting in the day time. No time-lapse.
The actors are indeed in the foreground.


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Chris WrightRe: Sky replacement if actor wearing same color as sky?
by on Aug 18, 2016 at 12:14:51 am

try to key out the sky, then use that as an alpha matte for sky replacement

this ae cs5.5 template might help. it can key out difficult white skies by procedurally keying saturation, color, and brightness.

https://f1.creativecow.net/7029/ae-cs55-sky


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Catherine SeguinRe: Sky replacement if actor wearing same color as sky?
by on Aug 18, 2016 at 2:25:51 am

I'm not sure how to use the template... will it function in cs6?


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Chris WrightRe: Sky replacement if actor wearing same color as sky?
by on Aug 18, 2016 at 3:53:31 am

yes, just find the effects window.


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Daniel WaldronRe: Sky replacement if actor wearing same color as sky?
by on Aug 18, 2016 at 1:56:26 pm

If possible, blow out the sky while keeping the actor (and his shirt) properly exposed. Then use the Extract effect to key out the highlights. Of course you may need a pretty big setup to achieve this using silks and/or flags. Not sure what the budget is for your shoot and how feasible that would be be for you.

You could rotoscope the actor using masks or the rotobrush, but if the actor's shirt is blending with the sky, that would be incredibly tedious.


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Josh BrineRe: Sky replacement if actor wearing same color as sky?
by on Aug 18, 2016 at 3:16:10 pm

Some options to consider

A) Sky Replacement: on a bright day, blow out the sky as suggested by Daniel, keeping your actor AND their white tshirt exposed correctly, then you will have a very easy post production sky replacement.

B) Secondary Colour Correction: Use a brightly coloured/distinguishable tshirt/colour that you can separate easily from the sky & everything else (if you are in a green field, dont use a green Tshirt) in post change its colour to white, for example, a bright red tshirt on an overcast day, using keylight you could key the red, get nice edges, invert the alpha channel, then use this as a track matte for an adjustment layer that will effect only that Tshirt, and use hue/saturation or levels etc etc to turn the tshirt white.

c) Have never used one but if the shot is locked and there is not alot of movement in the scene could perhaps a different matte help? (i honestly dont know)


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Catherine SeguinRe: Sky replacement if actor wearing same color as sky?
by on Aug 18, 2016 at 8:36:53 pm

Thanks for all the great suggestions guys! I'll try these techniques on past footage of other shorts I worked on and see what I like best for the short film! You guys are awesome!


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Spencer TweedRe: Sky replacement if actor wearing same color as sky?
by on Aug 21, 2016 at 4:49:51 am

I think Josh's solution is going to be the best you've got, but don't use a "bright" red shirt because that will probably clip out the red channel. Also red is too close to skin tones. Probably a soft green would be the best because it isn't blue (sky) or red (skin) and you can always run a spill suppressor on your footage to clean up any spill. You can also key it with keylight to create the matte for your color correction.

And for the record a difference matte isn't going to work for you, particularly in AE. I've gotten them to work in Nuke but only under extremely controlled conditions (like shooting a miniature in a studio with a camera control rig).

- Spencer


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