An unsharp mask is a type of spatial filter. A mask is created by low-pass filtering (smoothing) an image. The mask is scaled and then subtracted from the original image, producing a sharpening effect. Unsharp mask is a commonly used technique because the user has a substantial amount of control over the effect. A strongly-blurred mask can remove large-scale brightness variations, while a slightly-blurred mask will strongly emphasize fine detail. The strength of the filter can be controlled by adjusting the scaling factor.