I believe that the parameters for width and height are switched around in makedist.c in the repository for OpenGL Insights? The calls to computegradient and edtaa3 should have the parameters switched. Since you recently updated the repository maybe you would like to fix it since it took me a couple of hours of head scratching :) Great work btw!
Oups. Sorry about that. Another case of confusion from my many years of using Matlab, which uses Fortran-style memory layout for 2D arrays. I probably tested this code only with square images, or tested it without taking enough care to use the parameters according to their names.
I have this code posted to many different places, some of which are beyond my control or even unknown to me, but I will update it in where I can. Thanks for the bug report!