Camera manufacturers design cameras to capture an image so that 18% of the picture will be neutral gray.  This is not by accident.  Statistically, a large percentage of pictures will contain 18% neutral gray and everything will look just perfect.  However, when you photograph a scene that is not 18 percent neutral gray, the picture will either be over exposed or under exposed.  There are two classic examples.  Objects in a night scene will not be as dark as they are in the actual scene.   And when taking a picture where there is a lot of snow, the snow will not appear to be white.

This is an example of a 18% neutral gray image, a mix of light and dark areas

This is an example of an image with a predominance of dark areas

This is an example of an image with a predominance of light areas

To some extent this problem can be corrected post capture in software programs such as Lightroom or Photoshop, but it is always your best plan to capture an picture as correctly as possible in camera.

Depending on if you shot in manual mode or one of several automated capture modes, the ability to correct the problem in camera is fairly simple.  In manual mode, you either over expose by one stop when taking a picture of snow or under expose by one stop when taking a  picture of a night scene.  For all of the automated capture modes, you simply adjust the expose compensation setting to be under exposed by one stop for a night scene and over exposed by one stop for a snow scene.

The great thing about digital photography is that you can take multiple pictures if you’re not sure how much you should over or under expose a particular picture.  When in doubt, take more pictures and pick the correct one later.

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