Optical computation is usually performed on signals from the electronic domain, but it is especially powerful when applied to signals already in the optical domain. An example is shown here. Spatial filters representing the positive and negative parts of computer-designed linear discriminants operating in the spectral domain can be used to recognize and classify colors, species, and events. A demonstration in which colors are automatically sorted is given.
H. J. Caulfield,
P. F. Mueller,
"Direct Optical Computation Of Linear Discriminants For Color Recognition," Optical Engineering 23(1), 230116 (1 February 1984). https://doi.org/10.1117/12.7973245