Assigning material based on bitmap colour

Hello,

searching around I found only the “opposite” – rendering ID colours to create masks in the finished render.

I, however, need to assign a material to a part of a surface based on the colour of the underlying bitmap pixel. For example #FFFFFF → silver, #FFFFFE → gold, #FFFFFD → matte green plastic, etc.

In essence I have a complicated surface for which I create many many itterations of graphics in 2d software. Cutting the surface in rhino and assigning materials to each part is not an option.

If you know of something even remotely simmilar to this kind of workflow I´d be very grateful for a hint in the right direction. Although I realize it´s a very specific problem and the solution might not be around.

Thanks for any response

Depending on your renderer, it may have a type of material for stacking other materials, with masks (bitmaps) for each, so if you are able to generate the masks, you could get different materials rendering in different portions of uv space.