Q&A: Do Digital Photos Have Grain?
I am well into digital photography after spending 40 years in film. I am confused on one issue, though. What is the digital equivalent of film "grain," if there is one?
--Jim Sell, Lapeer, Michigan
Well, Jim, the grain is gone--but in its place, we've got pixels and digital noise.
In film photography, grain is a result of the film itself. Each frame of film is covered with a few million tiny "grains" of a metal called silver halide. They are sensitive to light and are directly responsible for creating the picture. Your picture appears grainy when you enlarge it too much, which brings the film's grains into better view. You also see grain when you shoot with film that's extra-sensitive to light, since those grains tend to stand out more. Photographers, as you may know, often go to great lengths to minimize grain in their pictures by shooting with low-ISO film, avoiding overexposure, using certain aperture settings, and more.
In the digital world, there's no film, so there's no grain. But a digital camera's light sensor is packed with pixels, and these pixels translate directly to the resolution of the pictures you take. Enlarge a picture too much, and you'll see pixels.
You also get noise--random dots of color--that looks a lot like grain from the film world. Noise happens when you shoot in low-light situations or crank up the camera's ISO beyond the lowest value. And remember that all digital pictures include some noise; like film photographers of old, it's our job to try to keep that "digital grain" to a minimum. You can do that by not overexposing your pictures, by shooting in situations where there's enough natural light, and by using the lowest ISO possible.