[MPlayer-users] How-to on constructing customtex file for gamma correction?

[galenz at zinkconsulting.com]

 From the man page:

customtex=<filename>
Load a custom "gamma ramp" texture from <filename>. This can be used  
in combination with yuv=4 or with the customprog option.

I want to use a custom gamma ramp. What format do I need to input? Any  
data would be appreciated, particularly a how-to!

-Galen