Character recognition experiments, carried out with reflection matched filters, are described. The reflection filters are obtained by means of volume holograms, recorded in photographic emulsion and suitably processed. These filters allow a good discrimination among similar characters and exhibit large positioning tolerances. They turn out to be well comparable with transmission hologram filters. An advantage of reflection filters is that the filtering operation can be performed with one-lens processor, thus reducing by one-half the size and the cost of the processor.
G. C. Righini, V. Russo, and S. Sottini, "Reflection Holographic Filters for Compacting Optical Processors," Appl. Opt. 13, 1019-1022 (1974)