Measurement of point spread function for characterization of coregistration and resolution: Comparison of two commercial hyperspectral cameras

Abstract

For spectral cameras, the spatial resolution and coregistration of bands are important performance characteristics. The paper discusses how these can be quantified in a way that is relevant for the spectroscopic processing step which is at the beginning of most spectral image analysis methods. It is argued that the most appropriate measure of resolution may be the ensquared energy of the mean point spread function (PSF) within the specified pixel field of view. For spatial coregistration, it is argued that a previously proposed coregistration metric is well suited, by characterizing the full shape and position differences between PSFs of different bands. A relatively simple method for imaging the PSF is demonstrated, based on tomographic reconstruction from line spread functions measured in different directions. The method is used to characterize two presumably comparable commercial hyperspectral cameras, a SpecIm PFD dating from 2012 and a HySpex VNIR-1600 dating from 2016. The measurements reveal significant differences, but it is pointed out that the present measurements by themselves do not constitute a proper comparison of the camera types. The main point made in the paper is that full characterization of the PSF in all bands is possible with moderate experimental effort, and provides clarifying measurements of actual camera performance.