Experiments for character recognition using CGH (computer-generated hologram) matched filter are reported. In the first method, a matched filter for the letter 'P' is fabricated, and letter 'P' in the input plane is transformed by this filter as a bright autocorrelation spot in the output plane. In the second method, a matched filter for code translation (i.e., translation of letter 'P' into Code '+') is fabricated and the letter "P" in the input plane is transformed by this filter as a code '+' in the output plane.
If the input differs in scale or orientation from the object used to form the matched filter a severe loss in the signal-to-noise ratio (SNR) of the correlation peak occurs.
For rotation invariant correlation, the multiplexed hologram is fabricated and the rotated pattern is identified by the rotated correlation spot.
For scale invariant correlation, the Mellin transform for simple square patterns is performed with CGH filter mask.
In this case, the CGH filter is used for geometrical transformation which transforms the input coordinates to logarithmic coordinates.
