In pure spatial processing vision chips only image enhancement, edge detection, or other stationary visual tasks are of concern. Spatio-temporal vision chips are concerned with the time dependent features of the image. Although spatial vision chips have shown a degree of robustness for operation under different lighting environments, there are still no claims about the robust operation of spatio-temporal vision chips. The complicated nature of motion detection for VLSI implementation is from the fact that in almost all models some form of delay or storage element is required.
Most algorithms also require inputs from several time frames.
Storage or delay elements, apart from being very area consuming, are difficult to implement. Another reason for the less robust operation of motion detectors is the required temporal contrast for reliable motion detection. The temporal contrast of objects in real scenes is relatively small, and can hardly trigger many analog motion detection chips. The unsatisfactory results from most motion detector chips is driving recent implementations towards intuitive but robust solutions with some structural deviations from the original models. Some early implementation were based on the optic-flow theory, which belongs to the computational category.