Here's a quick Photoshop Tutorial, after quite some time. Today I'll show you how to suppress shadow Noise. It is often the case that noise generated by digital sensors is visible only in shadows. Try it yourself, if you'd like: take a photo of a bright, well-lit wall at ISO 6400, then do the same for a dimmer environment (e.g. turn some lights off). Although your exposure values are the same, you will notice that the noise levels are more visible in the second case.