An FFT Method To Optimize The Removal Of Coherent Noise In Small And Large Images
J.-R. Kramm, H.Uwe Keller · Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE · 1989
Three parameters (amplitude, frequency, and phase) describe the behaviour of a coherent noise contribution to an image. Therefore, this noise can be removed yielding a significant improvement of the image quality. Usually FFT (Fast Fourier Transform) methods are used to determine these parameters. For small images the results can be disappointing. If the image size is not a multiple of the dominating noise wavelength then the energy of the noise will be distributed over additional Frequency locations. A technique is described that improves the accuracy of the noise reduction by successive adjustments of the size of the image array to integer multiples of the actual wavenumbers. Prefiltering routines are applied to the images in both the spatial and the frequency domains to optimize the conditions for a non-interactive coherent noise removal. The efficiency of this method is demonstrated on images of comet Halley taken by the Halley Multicolour Camera on board ESA's spacecraft GIOTTO.