Friday, October 9, 2009

TFS-GreenScreen Part1

Boy am I glad I video taped a lot of stuff back in the spring when I was in production. Now, I can just upload videos, and still feel like I'm keeping my blog alive (when I don't have much time to actually write postings).

Anyway, about this video- green screening (or bluescreening) are pretty common practice in stop motion. You use it for all sorts of reasons. In this example, I am using green screen because the final shot would be too complex to shoot all in front of the camera at one time. The shot entails 4 characters, separately entering the frame, spinning down down down into a vortex of insanity... then, a flood of rabies cells grows from the centre of the vortex, and eventually swarm the whole frame. Try THAT all at once, in front of the camera. And have fun in HELL.

So instead I shot the vortex as a cycle of animation. It was just a card painted to look like a vortex, that I did about 20 frames of animation on, until I had a nice cycle. That would be the background element.

Working towards the camera from the background, the next layer of elements is 4 different puppets. I shot them all on their own, on a green background. I had them posed and animated imagining that later, they would be digitally brought into the frame in the extreme FG, and rotated and scaled down (as if falling away into a vortex).

The final element was a whole bunch of clay rabies cells, each animated this time on bluescreen. They would all be composited together and scaled accordingly, to create the swarm effect.

They were shot on BLUE instead of green, simply because the rabies cells were green themselves. If they were shot on a green background, it would be nearly impossible to crop them out from the background. So that is often why green is used, or blue is used- if the characters have a colour that's the same as the bg, trouble will ensue in post.

I guess an important thing to realize is- sometimes camera/lighting people lose themselves in setting up a green or blue screen. They get really picky, and overly insane about the light on the screen. There are some important things, covered in the video, but it can also be VERY simple and easy. Compositing software makes the cropping process very easy. In the past I've had very impressive results with just some iMovie plugins, a table lamp, and a piece of blue construction paper!

That being said- working smart at the production stage is what makes it "easy" in post. So hopefully this video will help in that sense.

I'll post a "Part 2" another time...


Noddegamra said...

I love these "behind the scenes" videos :-)

Carla Veldman said...

Speaking as a member of the post-team, I think it was a good thing in this case that the characters were not staying in one spot too much. The screen not being evenly lit meant that for some of the characters, removing the green in after-effects was a bit tricky because there would be an uneven removal (due to an uneven amount of green present and often pixelations of it clustered round the character). Getting rid of that meant increasing the threshold (of green removal or what-have-you) along the puppet's outer edges and then adding a slight gaussian blur to soften it up a bit, essentially eating into the edges of the puppets. If you watched the clips before they were rotated and swirling, you might notice the puppets' arms - or fingers especially - shrink a little if they moved from in front of the puppet to their sides or were outstretched. This wasn't too noticeable in the final shot due to the additional movement - but that said, lighting is key!

ChrisW said...

I had to leave SOMETHING for the post crew to do!


Lauren Thomas said...