Abstract
Image enhancement techniques (such as edge and contrast enhancement) are essential for many imaging applications. In incoherent holography techniques such as Fresnel incoherent correlation holography (FINCH), the light from an object is split into two, each of which is modulated differently from one another by two different quadratic phase functions and coherently interfered to generate the hologram. The hologram can be reconstructed via a numerical backpropagation. The edge enhancement procedure in FINCH requires the modulation of one of the beams by a spiral phase element and, upon reconstruction, edge-enhanced images are obtained. An optical technique for edge enhancement in coded aperture imaging (CAI) techniques that does not involve two-beam interference has not been established yet. In this study, we propose and demonstrate an iterative algorithm that can yield from the experimentally recorded point spread function (PSF), a synthetic PSF that can generate edge-enhanced reconstructions when processed with the object hologram. The edge-enhanced reconstructions are subtracted from the original reconstructions to obtain contrast enhancement. The technique has been demonstrated on FINCH and CAI methods with different spectral conditions.
Highlights
Image enhancement methods have played a crucial role in identifying the key features of an image and for increasing the contrast in X-ray imaging [1], ultrasound imaging [2], synthetic aperture radar (SAR) imaging [3], and many other imaging applications
We propose a computational optical technique for engineering the point spread function (PSF) for edge enhancement in interferenceless imaging techniques and in Fresnel incoherent correlation holography (FINCH) with reconstruction by cross-correlation
The apCAI) with different spectral configurations
Summary
Image enhancement methods have played a crucial role in identifying the key features of an image and for increasing the contrast in X-ray imaging [1], ultrasound imaging [2], synthetic aperture radar (SAR) imaging [3], and many other imaging applications. While edge enhancement is preferred in many applications, in some cases (such as SAR), edge enhancement is critically essential, as SAR data are highly heterogenous, unlike regular image data, and without edge enhancement, the detection rates cannot reach acceptable values [3]. One well-established method is using Fourier optics, where only the higher spatial frequencies responsible for the edge information are allowed and the lower spatial frequencies are blocked [4]. Another widely used method is the use of vortex filters to enhance the edge information [5,6,7,8]. The above approach has been successfully implemented in incoherent three-dimensional (3D) imagers
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