In this chapter we have analyzed the basic characteristics of incoherent optical processing, considering three major classes of systems: (1) systems that rely on diffraction; (2) systems that rely on plane-to-plane imaging in the geometrical optics sense; and (3) systems that rely on diffractionless geometrical optics “shadow casting” for their operation. Incoherent systems are often characterized by a redundancy and immunity to noise not associated with coherent optical systems. However, the non-negative real nature of the information-bearing irradiance distributions precludes direct implementation of incoherent systems in many signal processing applications, and various tricks must be employed. Dynamic range limitations with incoherent systems are an area of active study, and the relative advantages of incoherent systems over coherent systems are not known conclusively.

Incoherent Optical Processing

The angular selectivity of volume diffraction gratings is exploited to form a spatial-frequency filter. The filter is recorded in a thick recording medium as a superposition of several simple gratings or as a single grating with a modulation that varies in depth. Such a device can have controlled angular selectivity so as to alter the relative amplitude and phase of selected spatial-frequency components. A coupled-wave formalism is used to analyze the angular selectivity of this device and experimental results demonstrate its usefulness in improving motion-blurred images.

Volume holograms for image restoration

Defocused pictures are restored by the convolution operation with a special scanning aperture. The scanning aperture has a circular shape with an extent smaller than twice that of the defocused point-spread function, and is divided into ten concentric rings with equal separation. The restoration experiment is executed using a digital computer image-processing system, and some experimental results evaluating the effectiveness of the aperture are described.

Restoration of Defocused Pictures by Image-scanning Method

The potentialities of photographic transaxial tomographic methods are discussed. It is shown that unfiltered, transaxial tomographic summation images can yield high-quality tomograms of high-contrast objects. A direct and efficient photographic method for recording transaxial tomograms (grazing incidence tomography) is demonstrated, and various means for analog filtering are discussed. Grazing incidence tomography allows for high geometrical resolution for high- or medium-contrast objects. The present contrast performance is an order of magnitude different to that of computerised tomography, but an improvement of the method seems possible.

Grazing incidence tomography

Image deblurring by convolution with an impulse response operator

An approach to image processing is made by means of image scanning with an aperture array. The restoration of one-dimensional linear blur is taken as an example, and methods of designing the aperture array and evaluating its performance are discussed. The quality criterion of restored images with regard to resolution and detection is introduced and applied to the practical system.

S. Ishiguro

Papers

Image Processing by Multiple Aperture Scanning