ComparativeGrain v2.0

Based on Bradley Friedman's workflow (http://www.fie.us/grain-management-101/) this gizmo samples grain by comparing the denoised plate to the original plate. A gamma correction is used to remove edge artifacts and then the captured grain can be applied either to teh whole comp or to a matted area.

Tested on Linux in Nuke 9 but should work on other platforms and earlier nuke versions as only basic nodes are used.

1.1 fixes a couple of issues with the Gizmo

2.0 Corrects the maths for Gamma and also allows 'LImit to Matte' to work in all modes.