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 sub-pixel PSF and of geometric distortion are performed independently.