DAVE JOHNSON, TECHHIVE:
"In the days before digital photography, seemingly every corner store had rack upon rack of film on display. Each roll of film was marked with a speed—measured in ISO—such as 100, 200, or 400. Higher-speed film was handy for low-light photography, but it had a serious disadvantage: grain.
"Film grain was every photographer’s nemesis. Instead of smooth, natural textures, grain put ugly blotches all over a photo. And though the days of grainy photos are far behind us, digital photos have a similar problem: digital noise.
"You’ve undoubtedly seen noise in your own photos. On the plus side, noise tends to be very small; and when you view a many-megapixel photo on a computer screen, pixel-size noise is so small that it usually disappears into the background. You might look at a very noisy photo and not even know it. Noise becomes apparent, though, when you zoom in—if you crop it down to a small detail, for example, or if you attempt to make a large print. Let’s learn how to control noise."
Learn more, here.