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June 24, 2007
lsgl: another compositing strategy
by sven at 10:22 pm
Yesterday I ran into a tricky compositing issue... Which led to an interesting solution.
When combining footage of actors with a CG environment, it's critical that the camera angle from the real world and the camera angle in the CG world match.
One way to find that magic angle is to set up CG stand-in explorers. This works best when the actors are only moving from left to right (or right to left) across the screen.
Shots where there's depth -- where the actors are walking toward or away from the camera -- are harder. For those, you can create a sort of CG ruler. You make the ruler the same height as your actor, and the same depth as one stride. That allows you to match up the ball of the foot and the top of the head for the actor at point A and point B.
...But in the shot above? Neither of these strategies work. There's depth involved -- but I can't see the actor's feet. And, to make things even worse, the actors are crouching -- so I can't easily gauge their height.
After a lot of frustration, it occurred to me that I could maybe get the angle from footage I took with the same camera set up, but which isn't actually going into the film. I found a shot where you can see me taking a full step that seemed like it might work... (I include the actual clip here so you can laugh at my "directing" style.)
Before I got too far into that approach, though, I realized that I was staring at an even better ruler: the living room wall!
I got out my tape measure... That wall is 9' tall, 13'9" wide. Being just a flat panel, it was the easiest thing in the world to model.
Over in LightWave, I fussed and fiddled with the virtual camera until I got the CG wall to match up with the real one.
Then, I removed the CG wall, set up some stand-in Elder Things, and rendered out a test clip with the explorers reacting to them. Did it look right this time...?
YES!
posted by sven | June 24, 2007 10:22 PM | comments (4) | categories: let sleeping gods lie
Comments
(I include the actual clip here so you can laugh at my "directing" style.)
---- And the shorts! Dig those shorts man!
Hey Sven, I haven't posted much lately, but I really admire the way you're pushing ahead on this project, and everything is looking excellent! Well, maybe except for the shorts.....
;)
Posted by: Darkstrider at June 25, 2007 12:48 AM
.... You know what? Actually the shorts aren't that bad. I think it's the socks with the dark shoes! ;
(Sorry dude.... just messin wit ya!)
Posted by: Darkstrider at June 25, 2007 12:52 AM
ILM .....here Sven comes!!
nice work dood. jriggityPosted by: justin rasch at June 25, 2007 2:54 AM
No way! GENIUS! That wall idea rocks the casbah! And I thought the director clip was adorable. I think a reality show of your daily workings is even more interesting than any art could be. I guess that's why we all love the blogs! Nice to see a moving record tho.
but but... where's the resultant perspective working clip?
Posted by: shelley Noble at June 26, 2007 6:53 AM