Extract numeric value from image color

Hi there, I'm in need of some help here, I don't know how to proceed. 

The problem is the following: I have an image corresponding to a voronoi diagram done in grasshopper, I took it to photoshop and added a shade of grey to each cell (corresponding to external variables). I'd like to take the numeric value (rgb maybe?) of that grey which I guess I can insert in rhino as a picture frame? and make that affect future operations in its corresponding voronoi cell in grasshopper. I was thinking of maybe taking the center of each cell, use that point to evaluate somehow the color at that point of the picture frame I've inserted in rhino? and use that numeric value for future operations... I don't know if this is possible or if it is the correct way of doing it.

Any help, I'd be most appreciated! I'm attaching a rhino file and its grasshopper with the voronoi diagram which corresponds to the image I'm also attaching if it helps to understand what I'm trying to say.