One of the most difficult scenes to photograph accurately is snow. Actually anything that has white on white is difficult: a white dog lying next to a white wall, a person dressed in white walking on white sand, and so on. That's because camera meters look at the gray values in a scene in order to determine the ideal exposure. This works well when there are contracting elements in a scene. The exposure meter aims average the gray values. But when a scene consists of mostly or all white elements, creating an exposure that aims toward an average gray value makes the scene gray, not white. To get an accurate exposure, one must override the exposure meter by over exposing the scene, making it brighter so that the averaging done my the meter ends up being white.
These two images are the same scene, but the first is overexposed to get the correct white. The second looks gray, but the camera's light meter claims it is correctly exposed. You will notice a few cosmetic differences that have nothing to do with exposure. For example, you'll see a soft crease in the background of gray image. I "ironed" that out in post processing. I also cropped the whiter image just a bit.
