A suggestion: avoid images completely, and use https://github.com/galaxas0/Core-Graphics-Additions to draw the conical gradients required for the slider. Would this increase overhead?
Hmm. Not sure, will take a look.
The reason why I used images is because that happens to be how the Music player handles it. If you use 0xced's UIKit-Artwork-Extractor, you can see that whoever built the original anisotropic slider used the UIImages method.
Oh, that makes sense. It's just that Core Graphics perfectly scales and you can do all sorts of fun stuff with it.