cart2tripolar

The code starts with a Cartesian image of square pixel size dx*dy=1, and outputs a polar image of polar pixels that has a similar amount of information in polar coordinates dr*dtheta~=1. The signal in each polar pixel is determined via its fractional overlap with the four surrounding Cartesian pixels. The result is a triangular polar representation,
as the number of polar pixels per radius per angle increase with radius, i.e. the larger the radius the higher the angular resolution. The code was originally used in the context of analyzing images with symmetry around a quadrant so that functionality was kept. The code support NaN valued pixels for masking