Joseph L. Horner

Phase-only matched filtering

From image processing work, we know that the phase information is significantly more important than amplitude information in preserving the features of a visual scene. Is the same true in the case of a matched filter? From previous work [ J. L. Horner , Appl. Opt.21, 4511( 1982)], we know that a pure phase correlation filter can have an optical efficiency of 100% in an optical correlation system. We examine this relationship between phase and amplitude in the case of alphanumeric characters, with and without noise, using a computer simulation. We compare the phase-only and amplitude-only filters to the classical matched filter using the criteria of discrimination, correlation peak, and optical efficiency. Three-dimensional plots of the autocorrelation and cross-correlation functions are presented and discussed.

Optical pattern recognition for validation and security verification

We propose an idea for security verification of credit cards, passports, and other forms of identification so that they cannot easily be reproduced. A new scheme of complex phase/amplitude patterns that cannot be seen and cannot be copied by an intensity-sensitive detector such as a CCD camera is used. The basic idea is to permanently and irretrievably bond a phase mask to a primary identification amplitude pattern such as a fingerprint, a picture of a face, or a signature. Computer simulation results and tests of the proposed system are provided to verify that both the phase mask and the primary pattern are separately readable and identifiable in an optical processor or correlator.

Metrics for assessing pattern-recognition performance.

Various metrics used to measure correlation filter performance are discussed. Their similarities and deficiencies are noted, and modifications are suggested. A computer simulation is included to highlight these differences.

Light utilization in optical correlators

An analysis is made of the overall light efficiency in a coherent optical correlator. The results are applied to a matched filter and an inverse filter. Kogelniks coupled wave theory is applied to analyze the diffraction efficiency of a filter recorded on a high-efficiency phase medium such as dichromated gelatin. Experimental results are presented for a matched filter and out-of-focus spatial filter, and the former is compared to the theory with good agreement.

Single spatial light modulator joint transform correlator

We describe a joint Fourier transform image correlator that employs thresholding at both the input plane and the Fourier plane. This suggests using a single binary spatial light modulator (SLM) to read in sequentially the binarized input signal and the binarized Fourier transform interference intensity. The performance of the single SLM joint Fourier transform correlator (JTC) is compared with that of the classical JTC in the areas of correlation peak intensity, peak-to-sidelobe ratio, signal-to-noise ratio (SNR), and correlation width. We show that the single SLM JTC outperforms the classical JTC in all such areas. Using a single binary SLM results in significant reduction in cost, size and complexity of the system.

1-f binary joint transform correlator

A one lens focal length binary joint transform correlator is described. This correlator uses a magneto-optic spatial light modulator, lens, and standard 8-bit resolution CCD camera. Computer simulations and experimental results of the effects of changes in scale, in-plane rotation, out-of-plane rotation, target/reference separation, and multiple targets are discussed. The performance using actual sensor imagery containing clutter is presented.

Applying the phase-only filter concept to the synthetic discriminant function correlation filter

A modified form of a composite or multiplexed matched filter has been computer simulated and tested. The modification consists of using only the phase function and setting the amplitude function equal to unity - a so-called phase-only filter (POF). The original filter was D. Casasents synthetic discriminant function (SDF) filter. The filter and test images were made from actual IR imagery. The results are compared in terms of efficiency, correlation peak height and width, and signal/noise ratio. A binary phase version of the SDF/POF was also tested. Its performance is between the SDF and the SDF/POF.

Optical fingerprint identification by binary joint transform correlation

We describe an optical fingerprint identification system that optically reads a latent fingerprint for correlation using a binary joint transform correlator. The fingerprint is read using the total internal reflection property of a prism. The system was built, tested, and the experimental results are presented.

Additional properties of the phase-only correlation filter

Computer simulations of the scaling and rotation sensitivity of a phase-only filter were performed, showing that it is much more sensitive to such input variations than is a classical matched filter. Values of the peak correlation spot power versus both rotation angle and scale factor are presented for both filter types. Several theorems are derived for calculating the optical efficiency of any filter in both input space and frequency space.

Amplitude encoded phase-only filters

The phase-only filter (POF) and binary phase-only filter (BPOF) have been shown to have high optical efficiency, good target discrimination, and virtually no sidelobes. We present a simple method of amplitude encoding the signal phase information. These new filters have most of the same advantages of a POF or BPOF so that amplitude modulating spatial light modulators or photographic film can be used.