Oblique Illumination And Matched High Spatial Frequency Cut-Off For Edge Enhancement

F. Quercioli; G. Molesini

doi:10.1117/12.935414

26 October 1983 Oblique Illumination And Matched High Spatial Frequency Cut-Off For Edge Enhancement

F. Quercioli, G. Molesini

Proceedings Volume 0399, Optical System Design, Analysis, and Production; (1983) https://doi.org/10.1117/12.935414
Event: 1983 International Technical Conference/Europe, 1983, Geneva, Switzerland

Abstract

Referring to edge enhancement effect obtained with detuned interference filters already reported, a model is discussed where the source is made of a narrow annular aperture in the front focal plane of a lens, producing a narrow spatial frequency band illumination with circular symmetry in the back focal plane. Such a plane is made to coincide with the object plane of a 4-f optical processor. In the Fourier plane of the processor a circular aperture is placed, to perform low-pass spatial frequency filtering whose cut-off matches the spatial frequency of the illuminating configuration. In reasonable operating conditions the overall processing turns out to be described by a directional Hilbert transform of the object transparency along radial lines of the Fourier plane. Computation and experimental evidence are presented for the case of a simple object as a slit, showing up edge enhancement and background attenuation according to the image intensity distribution which consists of two equally energetic terms, the one associated to the geometrical image and the other to the sharp edge effect.

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F. Quercioli and G. Molesini "Oblique Illumination And Matched High Spatial Frequency Cut-Off For Edge Enhancement", Proc. SPIE 0399, Optical System Design, Analysis, and Production, (26 October 1983); https://doi.org/10.1117/12.935414

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KEYWORDS

Spatial frequencies

Interference filters

Optical filters

Transmittance

Image enhancement

Image filtering

Molybdenum

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