Incoherent Optical Correlator Research Articles

Optical median filtering using threshold decomposition

A hybrid optical/electronic system performs median filtering and related ranked-order operations using threshold decomposition to encode the image. Threshold decomposition transforms the nonlinear neighborhood ranking operation into a linear space-invariant filtering step followed by a point-to-point threshold comparison step. Spatial multiplexing allows parallel processing of all the threshold components as well as recombination by a second linear space-invariant filtering step. An incoherent optical correlation system performs the linear filtering, using a magnetooptic spatial light modulator as the input device and a computergenerated hologram in the filter plane. Thresholding is done electronically. By adjusting the value of the threshold, the same architecture is used to perform median, minimum, and maximum filtering of images.

An Incoherent Optical Correlator for Real-time Pattern Recognition

A new incoherent optical image correlator is presented which does not require a hologram to store the reference image information. Theoretical analysis is given to describe the system operation. Experimental results have confirmed that this correlator is capable of performing real-time pattern recognition. A one-dimensional edge-enhancement technique can be used to sharpen the correlation peak. Scale-invariant operation has been realized by adopting an adaptive frequency modulated acousto-optic device.

Pattern recognition using incoherent OTF synthesis and edge enhancement

This paper describes a system for pattern recognition using an incoherent-optical correlator. The system uses optical transfer function synthesis to perform correlations with an edge-enhanced image of the object or pattern being sought. The resulting correlations are free of bias and show good discrimination between objects. In addition, the difficult or time-consuming computations are performed before the operation of the system; this reduces the amount of postprocessing by computer and should allow real-time operation at video rates.

Registration fiducials for automated alignment with optical processing

Since automated assembly, as well as automated inspection and sorting, usually require prealigned work-pieces, the availability of rapid and simple automatic alignment is a prerequisite to widespread acceptance of such systems. Coherent optical correlators potentially offer the necessary speed, but they have required mechanically coupled image rotation prisms and spatial light modulators and are, therefore, quite complicated and cumbersome. We describe here an alternative approach in which circularly symmetric fiducials are incorporated into the object itself and detected with an incoherent optical correlator. With incoherent correlators there is no need for spatial light modulators; also, the fiducials are so chosen that the correlation is not rotation sensitive. Since several (typically three) identical fiducials are used, their location can provide sufficient information on the object orientation. The approach was tested in the laboratory, and some experimental examples are included.

Incoherent Optical Matrix Multiplication

An incoherent optical method for the multiplication of two matrices is described. The input matrices are represented as arrays of apertures of transmittance values proportional to the matrix elements. Alternatively, one of the input matrices can be given as an array of incoherent light sources of luminous intensities proportional to the matrix elements. The product matrix is obtained in what is best described as a multichannel incoherent optical correlator based on image casting. The elements of the product matrix, represented by brightness values, are formed simultaneously and displayed in the usual matrix arrangement.

Associative reproduction of pictures by means of optical correlation

Holography is interpreted as a convolution of a key picture with the correlation between a pair of associated pictures. With an incoherent optical correlator an associated picture was reproduced from the correlation using a key picture, either the original or similar ones. A so-called ghost image reconstruction was also attained.

Information process using homograms as delineating elements in incoherent optic correlators

Optical systems are of great importance for the realization of systems for processing large amounts of information. An example of optical information processing will be shown for an incoherent-optical correlator. The conventional method, which is based on the geometrical optics, will be compared with a new method which yields a considerable gain of power of resolution in the correlation plane. For correlating two optical patterns on of the two is replaced by its hologram. The correlation is carried out with incoherent light. The resolution is only limited by the aperture of the hologram and by the wavelength of the used light.