Incoherent Spatial Filtering Research Articles

Real-time tunable incoherent spatial filtering: a two-pupil processing technique

A two-pupil heterodyne scanning system has been used previously to perform bipolar incoherent spatial filtering. In this paper, we exploit the system's potential in tunability. It is shown and verified experimentally that with two offset pupil functions, both having Gaussian shape, we can achieve tunable bandpass filtering operations. Potential applications in space-variant filtering on incoherent objects are discussed.

Pupil function design algorithm for bipolar incoherent spatial filtering

A two-step iterative algorithm is described for designing pupil functions for synthesis of bipolar point spread functions in a two-channel incoherent spatial filtering system. The first step uses the method of projections onto convex sets to determine an appropriate bias for the system pupil functions. This bias determines the complementary point spread functions and therefore the magnitude of the corresponding coherent spread functions. The phase of the coherent spread functions is obtained in the second step via iterative application of a magnitude constraint and a finite support constraint. With both magnitude and phase of the coherent spread functions established, the corresponding pupil functions are realized via Fourier transformation. Results are presented for a 2-D bandpass filter and compared with analytically obtained results. The comparison suggests that the iterative algorithm yields bias functions having less energy than bias functions determined by previously proposed analytic methods.

Incoherent spatial filtering with a scanning heterodyne system: amendment

Incoherent spatial filtering with a scanning heterodyne system: amendment

Incoherent spatial filtering with a scanning heterodyne system

Imaging systems with two pupils in the receiving optics have been used to synthesize bipolar point spread functions in incoherent image processing. We describe a two-pupil system using a scanning illumination technique and compare its attributes with more conventional techniques. Experimental examples using two-pupil interaction and an acoustooptic frequency offset for the direct 2-D bandpass filtering of diffusely reflecting objects are presented.

Hybrid incoherent optical pattern recognition system

A pattern recognition system that uses incoherent spatial filtering to recognize images directly from a narrowband phosphor television monitor is described. Images of real objects are captured with a television camera. These images are then edge-enhanced electronically and displayed on the TV monitor. The monitor output is used directly as the input to a holographic correlator. An optical multichannel analyzer at the correlation plane is used to analyze the shape of the correlation function and to determine the position of its peak. Experimental results agree well with theory. Concepts for handling rotation, aspect angle, and scale variations of the input are discussed.

Laser speckle reduction: equivalence of the moving aperture method and incoherent spatial filtering

The moving aperture and the moving random mask are two methods suggested for speckle reduction in recording images of diffuse objects with coherent light. An analysis is given that shows that these methods are equivalent to a two-step recording process: (1) recording the image with the full pupil in coherent light and (2) reimaging and recording this speckled image in incoherent light with the aperture or random mask in a fixed position. The two-step process makes it easy to understand the filtering effect and can be physically implemented to offer short exposure time in the coherent step and a wider choice of filtering functions in the speckle reduction step. Experimental results to support the analysis are presented.

Character Recognition by Incoherent Spatial Filtering

The character recognition method described here is based on the principle of incoherent spatial matched filtering. The input to this matched filter is not the unknown character itself, but its Fraunhofer diffraction pattern. The intensity distribution in this diffraction pattern is insensitive against shifting of the unknown character, avoiding the need for character registration. The incoherent matched filter is easier to implement than the coherent matched filter, since only binary rather than continuous-tone masks are required. The theory and some experiments will be discussed and compared with other optical character recognition methods.