Know of a good sky replacement tutorial?
 

I'm seeking good thorough tutorials on sky replacement using After Effects or Combustion that deal with common problems like matting leafy tree branches etc.

Funny, Robert, I had a lengthy discussion about just this subject last night with a friend who has done effects work on a bunch of movies. We were talking about the really suspect sky replacement during the Griffith Park Observatory scene in "Charlie's Angels 2", the one where the Angels fight with Demi Moore. Apparently McG insisted on changing the sky to a very specific blue even though the photography had been done with overcast skies. My friend was telling me that in general, sky replacement is extremely difficult to pull off, and in this case it was never going to look realistic no matter how much color correction or contrast work they did--the overcast white sky tends to wrap around objects as a reflection, especially branches as you have discovered. He had to do the same sort of thing on the Times Square sequence on Spiderman.

I guess this doesn't answer your question but it might be worthwhile to know that it is one of the harder things to do, even for folks working on those big shows with all of their resources.

I can't do "sky replacement" like masking and stuff, but in Vegas, if I have a blown out sky, I use my 2 layer method and on the bottom layer put a bump map where the darker side is to the blown out sky, and then i make it a little blue, so it give the sky some blue, so it doesn't look like full blown out white, it does make it look better though, and it's pretty simple, no masking needed or anything.

I'll see if I can post a example later if I can find a picture with a blown out sky.


EDIT -- Here, I found a couple pictures to do it to, the first one is from my camera, 2nd is from dvspot.com, which doesn't look as good because of all the lines and trees which caused some of the orangish to bleed.

http://img.villagephotos.com/p/2003-8/274445/sky.jpg

http://img.villagephotos.com/p/2003-8/274445/sky2.jpg

Send me your video and i'll use my magic and make it look like film, for a small fee. :D

;)

Charles, yes, sky replacements are a dime a dozen but good ones are worth their weight in 1999 Enron stock certificates. To do them right in shots that contain reflective surfaces requires tracking and comping over such surfaces with CG doubles of themselves. This process is far from effortless and usually not affordable for directors unless your name happens to be George Lucas. BTW the Spider-Man work was quite passable--kudos to your friend. What company does he work for?

I'm still interested in seeing if there are any tutorials out there, particularly if they offer tips that aren't immediately obvious...

Heh, I don't think I could take on something like that. When I do this music video for this band, I plan changing the sky to a time lapse of a sky, but I'll avoid trees, and just get the house in the shot, hopefully, heh.

Maybe if you send me or post one of the frames, I could see what I can do. I've tried stuff like that in even photoshop before, without much luck, it always turns out crappy.