FXAA Parameter Confusion

Question

I have a question about the popular FXAA shaders that are out there written using HLSL or GLSL, and they all mainly feature these three parameters:

#define FXAA_REDUCE_MIN (1.0 / 128.0)  //0.0078125
#define FXAA_REDUCE_MUL (1.0 / 8.0)  //0.125
#define FXAA_SPAN_MAX 8.0

I looked all over the Internet, but could not find a proper explanation about the function of each parameter. Can anyone help?

Answer 1

This is the same question in a shader forum that was answered after the posting of this question:

http://reshade.me/forum/shader-discussion/1641-fxaa-parameter-confusion