In sports, researchers often use stroboscopic photography to analyze and guide athletes' movements. Stroboscopic photography is the rhythmic flashing of photographic light sources.

Stroboscopic photography means that when the photographic light source flashes rhythmically, the light emitted by the light source shines on the athletes and spreads, because the clothes worn by people are rough and uneven.

The light reflected by people becomes an inverted and restored real image through the camera. When gating, the background is required to be dark. If the background is bright, the image of people is not clear.

So the answer is: diffuse reflection, inversion, reduction, stereo, darkness.