Optical correlation filters to locate destination address blocks in OCR

A wide variety of optical distortion-invariant correlation filters for possible use in United States Postal Service (USPS) destination address block location and reading are summarized. These filters allow the entire envelope to be processed in parallel and are selected in a hierarchy using symbolic encoding to locate (and read) key words on an envelope. With contextual data they can locate the address block the lines and key words in each and read these words at high rates with excellent P (percentage correct recognition) and Pe (percentage error).