Inside this blend file there is a node group called perlinGain which implemented perlin gain using math node. The speed is however a little slow. So I wouldn't say it is ready for production use. I create this mainly for study use.

for more about perlin gain and what it does. You can check these pages:

[http://asserttrue.blogspot.tw/2010/01/fast-contrast-adjustment-using-perlins.html](http://asserttrue.blogspot.tw/2010/01/fast-contrast-adjustment-using-perlins.html)

[http://www.artofillusion.org/docs/texedtut/chapter4](http://www.artofillusion.org/docs/texedtut/chapter4)