The problem is that scaling procedure interpolates pixels position and size while scaling it. If you want to use sharp pixelart-images you must prepare all resources and never rely on scaling by setting
_imageView.contentMode = UIVIewContentModeCenter;
OR
set scaling filters to value kCAFilterNearest
[_imageView.layer setMagnificationFilter:kCAFilterNearest];
[_imageView.layer setMinificationFilter:kCAFilterNearest];
if you like the second way, i'd recommend to set all ImageView frames with EVEN (2,4,6,8 etc) sizes and origins to avoid pixel misalign