  Field distortion is widespread in imaging systems. If it cannot be measured
and corrected well, it will affect the accuracy of photogrammetry. To this end,
we proposed a general field distortion model based on Fredholm integration,
which uses a reconstructed high-resolution reference point spread function
(PSF) and two sets of 4-variable polynomials to describe an imaging system. The
model includes the point-to-point positional distortion from the object space
to the image space and the deformation of the PSF so that we can measure an
actual field distortion with arbitrary accuracy. We also derived the formula
required for correcting the sampling effect of the image sensor. Through
numerical simulation, we verify the effectiveness of the model and
reconstruction algorithm. This model will have potential application in
high-precision image calibration, photogrammetry and astrometry.
