We were asked to do CG snow for the opening sequence of the movie. It was filmed in different locations and most of them without the enough amount of snow that the director wanted.
As we were facing more than 40 shots of CG snow, we created a system that was fairly easy to set up from one scene to another. It basically works for every shot. Then if the shot required some extra turbulence particles like when the car drives next to the camera, we had to run a few extra simulations. The tricky part was to track and model any kind of objects where the snow could collide. Since the very beginning we were told that they wanted real snow, not a 2D layer, so there was no other way then do everything in 3D.
The complexity of the snow sequence was very wide from one shot to another. It could go from just adding one simple layer of falling snow to completely transform a sunny summer day to a cold winter shot. Since adding snow in all the shoots of the opening sequence was not contemplated in the beginning, we didn’t have any camera information and a lot of tracks where really hard to get: lots of motion blur, lens distortion, no tracking points, zooms, etc etc…
On the other hand, a shot that I enjoy a lot was the face replacement of Jane Moffat when she was at Helvetia cabin. At last moment, Andres Muschietti (Director), wanted a more deadly face then the one they recorded. I had to track the face (no tracking points or any second camera to help witch did the task way harder), then imported the geometry into 3D nuke workspace where I converted it to a 2D surface. I made all the texturing over the 2D surface and then projecting it back to the tracked geometry, add a few distortions to make it thinner and it was good to go.share