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Demon face effect problems
Hello,
I’ve been using the demon effect tutorial on Andrew Kramer’s Videocopilot.net and recently I’ve had problems with motion tracking.
When I had to stablise the footate I clicked on rotation, position AND scale. The tutorial doesn’t ask you to click on scale but i had to do it in this case because the actor was moving towards the camera and therefore got bigger.
I did all the pick whip business fine and managed to stabilise the rotation and position but when it came to scale I didn’t know what to pick whip the scale with. I decided to pickwhip the scale in the original comp with the scale in the precomp. Now that didn’t work!
I tracked both eyes on the subject and the tracking worked fine because when I applied the distort effect , it stayed on the subject and resized to fit him as he moved towards the camera.
I’m not quite sure whether I picked a good point for scale because AE only gave me 2 tracking points (I did check the scale box, though, as well as rotation and position.
The only problem I have is that the composition keeps resizing, just as the composition will rotate and move before you do all that pickwhipping business. I think I have to pickwhip the scale to something but I’m not sure what! Any ideas anyone?
Cheers!
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1 Reply
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Forgive me if I don’t explain this effectively but I remember taking ages working this out when I was doing the tutorial, and it’ll be more useful to try explain it properly then just give the answer.
First of all a quick look at what you’ve done (at least how I remember it). Because the image warp effect layer can’t be moved you have to stabilize the face so it stays in place, before cancelling out that stabilisation in the next comp so it looks the same as it did before. All that ‘pickwhipping business’ was so that the motion of the stabilization was cancelled out, by subtracting the same amount it put on. (By reversing the value with * -1)
With scale added you essentially want to do the same thing – cancel out the footage’s scale by scaleing the comp.
To do this you’d want to scale down the comp when the footage scales up and scale up the comp when the footage scales down. If you try doing it manually (Scale the comp so you see all the footage) you should be able to start working out what expression you need. When the footage is scaled to 80% you need to scale the comp to 120% to make it fit. Likewise when the footage is 130% you need to scale the comp to 70%. In other words both values must equally 200. So to reverse the scale stabilization we use “200 – ‘footages current scale value'” which will give us the value we need to cancel it out, thus reversing it to normal.(Note however, because scale has two values (X and y) you actually need to write “[200,200] – ‘pickwhip footage scale value here'” else only one value will be reversed which won’t work at all.)
I hope that all made sense, I’m trying to keep it brief but expressions are a lot less confusing when you know what they’re trying to do and how they’re doing what they are. Have fun.
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Only in after effects do children get to pick and whip their parents.
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