Basic parallax animation not smooth in Safari (Mac), IE (Windows), and Chrome (but only sometimes)

[eculeus]

Hiya

I'm a newbie scrollmagic user, and was hoping to use it to implement some basic parallax scrolling. Not sure if its overkill for that application :) I've written a "vertical parallax scrolling" function that can be used to effect parallax sections ... but alas, it appears jumpy in some instances (firefox seems to perform fine, chrome seems to perform fine in the jsfiddle but not in my actual site (which is confounding since I'm using the same functions), and safari/ie seem to be very jumpy).

My guess after reading up on these forums is that the problem is either a lack of hardware acceleration or possibly that the image is somehow rendering twice, perhaps the first time without the css property. Or maybe the images are just too big and too memory intensive, and this is not a valid use of scrollmagic?

Here's the jsfiddle link to my code: http://jsfiddle.net/z9htepy7/8/

Any insight would be appreciated :) Thanks!

[eculeus]

Nevermind ... I think I got it to stop being jumpy using fixed elements :) Sorry for the newbie question :)