Nonlinearity effects in the pure phase correlation method in multiobject scenes.

The nonlinearity used in the pure phase correlation method can improve pattern recognition, but it causes high-order harmonics in the correlation plane in the case of multiobject scenes. High-order harmonics and the presence of aliasing may cause false alarms. We show that these effects are strongly diminished when the periodicity in the scene is broken (by different objects, random distribution, etc.).

Processing measurements of the directional content of Fourier spectra.

Directional analysis and filtering make use of the most straightforward properties of optical Fourier transforms. A quantitative study of the detectability of angular maximums in Fourier spectra and its relationships with the shape and distribution of elements in the object is proposed. The problem is modeled by using a simple object which consists of the superimposition of two random distributions of rectangular grains, one being rotated with respect to the other. Computing the Fourier spectrum of this object allows the expression of the amount of light integrated through a wedge which scans the spectrum. An index of angular separability of the two distributions is made up from such measurements. It is shown to depend on the rotation angle as well as the grain shape. Using an additional spatial filter can improve this index. The influence of its radius is studied. Experimental results obtained either in real time with optical fibers or on photographic records with a microdensitometer are compared with the theoretical ones. They show the necessity of the implementation of optimal estimation schemes to reduce the influence of the noise. Two linear least squares filters are used: an angular Wiener filter and an autoregressive one. In the case of a high signal-to-noise ratio, the Wiener filter reduces to a Laplacian filter which does not depend on the shape of the grains.

Reconstruction of a Fraunhofer hologram recorded near the focal plane of a transforming lens: experiment and results.

The holographic system for an optical memory is examined. A Fraunhofer hologram of an array object is recorded near the focal plane of a thick transforming lens. This hologram is read out with a spherical wave, and the intensity distribution in an image plane is theoretically calculated and experimentally measured. The concept of a traveling subaperture connected to a local recording of information in the hologram is verified.

Reconstruction of a Fraunhofer hologram recorded near the focal plane of a transforming lens.

A Fraunhofer hologram of M x N array of binary coded data is recorded in a plane located near the focal plane of a transforming lens, and the amplitude transmittance of that hologram is calculated. In the reconstruction process a plane wave as well as a spherical wave with a Gaussian amplitude distribution is applied, and the field distribution in the image plane is theoretically found. All calculations are performed for a linearly recorded hologram of a finite aperture. Intermodulation noise is neglected.