Barely noticeable, not obvious, indistinct.
Tenuous; rarefied; of low density or thin consistency.
Cleverly contrived.
Cunning, skillful.
Insidious.
Hard to grasp; not obvious or easily understood.
dulled or intentionally blunt.
out of focus; blurry.
To sharpen (an image) by creating a blurred ("unsharp") negative as a mask, and then combining that mask with the original.