apparent movement of pixels over time
- can be caused by lighting changes w/o actual motion
- GOAL: recover image motion at each pixel from optical flow
- function of spatio-temporal image brightness variations
Formally
- given two frames, estimate apparent motion field between them - u (horizontal motion) and v (vertical motion)
assumptions when estimating optical flow
- small motions - points do not move far
- spatial coherence - points move like their neighbors bc they belong to same rigid object
- brightness constancy - brightness of a pixel is constant btw consecutive frames
- aperture problem
- next: lucas-kanade