Simple rotating circle – lens distorton correction?

[David Bogie]

I cannot see what you’re seeing but the only possible explanation is that the pixels aren’t really square.
“Absolute” is exactly absolute so you do not really have square pixels, regardless of what your display is telling you.
The difference between setting up a comp for square pixels and having your display set properly to correct pixel aspect ratio for preview purposes only can get confusing.
Try to find a perfect circle built in Illustrator or Photoshop and import it into your comp.

bogiesan

[Owain Street]

Thank you for the response! I have imported an eps of a circle from Illustrator – canvas of 100 x 100 pixels. Made a comp from it and again rotated it in the Y axis. Again the circle appears to travel from side to side (just a little) as it rotates – rather than staying absolutely dead centre. Maybe this is just the way AFX does this, but it seems a little suspect!

[Kevin Camp]

i’m not able to reproduce your problem either… i created a 100×100 square pixel comp, added a 100×100 square pixel solid, double clicked the circular mask too (to add a 100 px diameter circle), key framed a 360 rotation loop and did a ram preview… the circle doesn’t move or distort at all…

double check both the comp settings and the solid’s settings and make sure they are both using square pixels…

Kevin Camp
Senior Designer
KCPQ, KMYQ & KRCW

[David Bogie]

[Owain Street] “Maybe this is just the way AFX does this, but it seems a little suspect!”

Negative. After Effects does not introduce pixel aspect errors.
I can’t help you figure this out other than to refer you to the documentation and help system. but i can assure you that when you fix it, you’re going to know it was a simple user error, not the software.

bopgiesan

[Kevin Camp]

i think i do see what talking about (i didn’t read carefully enough)… it’s not wobbling, it’s rotating in 3d, so you’re seeing the foreshortening of the layer as the perspective changes. so the ‘half’ that is closer to the camera appears larger that the ‘half’ that is further from the camera. that’s just how things are in a 3d world…

if you don’t want that, you could use the old ‘fake’ 3d rotation on the y-axis trick by animating the x-scale from 100 to -100 (that’s ‘negative’ 100). that should behave a bit more like you are wanting…

Kevin Camp
Senior Designer
KCPQ, KMYQ & KRCW

[David Bogie]

Okay, Kevin, you win the prize for reading between the lines to decipher hidden meaning among the implicit meanings. I assumed a typo in this statement:

> As I rotate this ‘circle’ in the Y axis the edges bow out toward me (especially around the 90 / 270 degree mark).< ... which sounds like a standard circle to me. How you made the leap to 3D rotation is a small miracle. Way to go. bogiesan

[Owain Street]

Thanks guys for taking the time to respond to my initial query! You were right that I was rotating the circle in 3D, and you are right again that I could simply animate a 2D circle (in the X from 100 to -100) in order to get the effect without the 3D foreshortening etc. Also, by creating and adjusting a camera, I could create less (or more) foreshortening. Thanks again!

Owain Street