Alpha channel and Material ID

leonardoamadeo

Hi!
This is my question; I always render with vray my proyects and usually find the same problem at postproduction time, at SELECTION VEGETAL MATERIALS. I mean, leaves with alpha material, such png, sometimes let me select the follage content thanks to Material ID channel on VFB Channels. But sometimes NOT. Sometimes there's a color assigned on alpha channel, and this is a problem to select materials behind on photoshop, you know?

I want to use those components but they're a problem for me. I was trying to convert diffuse image to any kind as tiff with alpha or 16 bits image... but no success. Then... WHICH IS THE CORRECT WAY TO CREATE THIS KIND OF MATERIAL??

Thanks everybody for the help

PD- I link images from my test with 2 materials imported, the one right and the one wrong (the right is a TexBlend Material)