Image represents any RGBA image. Internally, it stores each channel as an independent
allocation which enables such things as constant-time channel swapping along with making the
data cheaper to copy to a GPU which expects CHW ordering vs the packed format HWC.
Iter enables the simultaneous traversal of 4 separate channels of image data. It works
with any type that can be converted to a &[Numeric]. Image data is returned pixel-by-pixel
in a [N; 4] format with (R, G, B, A) ordering.