I did not completely understand your last post (RGB a,b,c ?), but wanted to point you into the direction of the new “Split into Multiple” option of psd-manager 3.1. While it has special behaviour for Multimatte render elements, you can also use it to split your ExtraTex render element into 3 PSD channels/layers. So you would get a selection from the red channel, one from the Green and on from the Blue channel of your ExtraTex render element. Here is a link to the screenshot from the psd-manager website that shows the option used with a MultiMatte render element.
http://www.cebasusa.com/psdmedia/Multimatte-Splitting-Large.png
So in the psd-manager render element output options just set your VRayExtraTex render element to:
- Create: Channel and enable Split into Multiple
- or if you prefer a layer for use as a selection, choose Create: Layer and enable Split into Multiple and enable Save Alpha as Transparency
Best Regards,
Daniel Schmidt