Using Blend If to Apply Noise Reduction Only to Shadows

 
I’ve been using Blend If in the Layer Style window for quite some time as an easy way to combine/composite images with white/dark backgrounds, but I never thought to use it to selectively apply noise reduction to shadow areas.
 
Also, Blake’s use of the Color Fill Layer (via Clipping Mask) to visualize where the noise reduction is taking place is simple yet ingenious. [Sean]