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Author
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Topic: Entering the StarGate (Masking/compositing)
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TrAcKa
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posted 12-19-2000 07:21 AM
I've been for a while trying to work out exactly what method exactly is used to mask the Sg1 crew through as they walk through the Stargate. I know that when they walk through the Rings there is a green screen behind the Gate, and then they put the event horizion in (liquid plasma water stuff)and they appear to walk through it, i figure they do a bit of masking to make it appear they walk through, and vice versa when they walk out of it.
How exactly would they do the masking to make it look like it does? Like what exactly would you do in a program like after effects, detail? step by step?
Please some one help, i've been trying to achieve this effect for some time now, so sorry if it seems like i've aked this question before. |
potmonkey
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posted 12-20-2000 05:02 AM
I guess if you had someone walking towards a green screen, you would want to identify the farthest away parts of the body from the camera - and paint these out green. It would take a lot of work though.
What might be cool! Have a large pool full of really thick green liquid -- I mean really thick -- have your actor lie on the surface and slowly sink in! That way they would be absorbed! --ok, maybe that's a little ott. |
drnw04a
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posted 12-20-2000 11:24 AM
I think once you have your basic mask set up, you could warp the edges to create the liquid effect. You could probably set up a few keyframes and just tweak rather than having to hand-mask frame by frame. |
cdolsen
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posted 12-20-2000 01:31 PM
Create a screen of green colored strips of cloth, torn into stips not cut. Have several layers back to back with the strips overlapping. Have the actor step through. Use strong lights reflecting on the actor, bounced off mylar that is beign rippled or shaken.compost the effect.
layer 1 - liquid effect
layer 2 - bg
layer 3 - the actor
the liquid replaces the 'gate', and this compost replaces the green strips the actor steps through. use strong lights replecting on the actor bounced off mylarhtat is beign rippled or shaken.
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EricM
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posted 12-20-2000 02:14 PM
I'm pretty sure the transition through the gate was done with rotoscoping. The green screen creates a matte that alows the men to apear infront of the gate, but when they step through the matte is hand animated.
A common tool for this is sometimes called rotosplines. A spline is a curve defined by three or more points. The artist places the points and the computer draws a nice curving line through the points. These points can be animated and keyframed.
So for Stargate, an artist would draw a rotospline around the actor and animate it so that it crreates a matte that wipes the actor out of the picture in a way that looks like he's passing through the gate.
I don't know if they did this for Stargate, but a cool way to assist with the proper placement of the matte would be to have a laser line hit the actors at the point where the gate is supposed to be. As the actor walks through the laser, the compositor would erase the part of him that is on one side of the line.
How can you do this in After Effects? I don't know 'cause I don't use it. I'm not sure it can even do hand animated mattes like rotosplines. |
drnw04a
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posted 12-20-2000 02:53 PM
I don't know the step-by-step since I'm not in front of AE, but if you treat your mask as a separate track, and keyframe the changes to the shape, you should be able to pull it off. Maybe even in Premiere, although it would probably look crappy.There might be more going on with the CG gate itself, maybe some transparency mapping. |
Imhotep
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posted 12-21-2000 07:53 AM
I know of a different strategy that I think has been explained on this board before, although I haven't tested it just might work!1. Get a laser liner(or pen) and point it at rotating mirrors (get a hobby dc motor and build the mirror shaft) to create a vertical beam of light. 2. Film your actors as they move through this vertical light beam. If viewed from the right angle it should produce a clear "cut-line" on your actors. 3. Import footage into photoshop(as filmstrip if animation) and create a mask using the laser line. (A lot of work has to be done here, although not tricky) 4. Use this mask in AE (or ...) to produce the CG effects desiered. Understandable? |
