Sub-pixel non-parametric PSF estimation for image enhancement

Applying standard resolution enhancement and sub-pixel measurement techniques to an imaging system is problematic when the system characteristics are not known. The importance of precise system characterisation is often underestimated in resolution enhancement and sub-pixel measurement. The methods presented allow accurate sub-pixel measurements of system characteristics to be made with minimal assumptions. The non-parametric technique developed accurately characterises the properties of an imaging system. This is demonstrated by measuring the point spread function (PSF), along with static and dynamic distortions, for a high precision thermal imaging system to sub-pixel accuracy. The PSF is estimated to +/-0.1 of a pixel and imaging system errors to the order of +/-0.1 of a pixel are identified. The improved precision of PSF estimation is shown to benefit resolution enhancement. A novel feature of the method used to estimate the PSF (and to enhance the image) is that the estimation of the spatially invariant subpixel PSF and of geometric distortion are performed independently.