Efficient techniques to implement correlation filters on fast SLMs

We propose a brief overview of different techniques to implement complex-valued filters on binary spatial light modulators (SLMs), including encoding techniques at both pixel- and cell- (i.e. group of pixels) levels. We show that group-oriented methods offer extended coding domains, at the expense of a reduced space bandwidth product and spurious noise in the correlation plane. We propose the concept of a time multiplexing technique that combines at the pixel level the pseudo-random encoding method with the minimum Euclidean distance approach. This pixel-oriented method offers the advantage to keep the full space bandwidth of SLMs, and the possibility to very efficiently encode ternary filters (-1, 0, +1) on binary phase (-1, +1) SLMs. Tested on a sequence of images acquired with an IR sensor in a tracking scenario (1 target), encoded ternary filters have offered superior performance in terms of peak-to-clutter ratio than classical BPOF (+45% in the simulation, +35% in the first optical experiments).