Use IRasterShader in add-in button?

Hello,

I want to create an add-in button that programmatically applies contrast, brightness, and gamma to a raster layer. I found the IRasterShader interface in the documentation, but no examples of how to use it. My efforts to use it have not been successful thus far.

Right now I'm doing something like:

IRasterLayer rLayer = map.get_Layer(index);
IRasterShader rShader = rLayer as IRasterShader;
rShader.Brightness = brightValue;

But rShader is null. Does anyone have any insight?

Thanks.