Masksize is the size of the mask (an integer, defaults to 7).
Ratio is the ratio between the standard deviations of the inhibitory and excitatory Gaussians and defaults to 1.4. (when ratio = 1.0, the middle ring is flat. when ratio > 1.0, the middle ring is a valley. otherwise, middle is a slope from center top to side edge).
If no input file is redirected, the program outputs an impulse response in a 7 x 7 x 7 frame.
3dog -A .6 53 1.6 -s7 bird | scale_gray | histoeq | slice -v 30 | xhips
After filtering, slice along x axis turned clockwise 30 degree about the
center.