introduce 2d gaussian blur, i still have to shift the kernel correctly using fftshift
try to implement dipimage style arrays (xx, yy). doesn't work so far, not sure if it would even make sense in lisp
found some bugs in the array functions
the hologram reconstruction works rather nicely in real space.
the lowpass filter is a kernel with sigma=8 pixels. probably it would
be faster, not to use fourier transforms for this.
implement multiplication with checkerboard pattern using only dipimage style functions