Scientists who study solar weather try to find patterns in the violent, chaotic motion of magnetic field lines above the sun's surface. Though the lines aren't actually visible, their patterns are illuminated by the streams of hot plasma that travel along them. But, while the giant coronal loops that form during major solar storms are easy to pick out, the field lines are generally so tangled up that it's hard to pick any one of them out.
To help solve that problem, researchers can apply a gradient filter to the images. The filter increases contrast, bringing the solar weather patterns into focus ( via popsci.com ).