Optical Spatial Frequency Filtering of Radiographs

Paper presented at a Conference on “New Trends in Radiography” organized by the Science Committee of the Royal Photographic Society. 8-9 December 1970 in London.

Abstract

The frequency content of a photographic image can be considerably modified by using a suitable optical system. The Fraunhofer diffraction pattern (the Fourier transform) of a transparency is produced by using parallel light from a laser. This spatial frequency spectrum can be differentially filtered to produce a reconstructed image of arbitrary frequency content. The radiographic image is a convolution of the X-ray source with the object under examination. The filtering operation lessens the degrading effect of penumbra by means of a deconvolution with a filter that is representative of the Fourier transform of the X-ray source.

Manufacture of the spatial filter is described and results showing enhancement of detail in radiographs by reduction of penumbra are presented.

Notes

Paper presented at a Conference on “New Trends in Radiography” organized by the Science Committee of the Royal Photographic Society. 8-9 December 1970 in London.