Not all digital noise is bad; here are a few examples of the different types of noise.
Image noise can come for luminance. This is known as “grayscale noise.” It can put that film grain look in your digital image. It may show up in continuous tone spaces.
Chroma noise appears in an image’s colored artifacts. These can be unattractive flecks of color that primarily appear in the shadow areas of your photos.
Both become more prominent during the sharpening process.
Adapted from Stoppees’Guide to Photography & Light by Brian & Janet Stoppee Focal Press, 2008; $35)