Underexposed

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An image is underexposed when detail is lost in the shadows, while the full range of highlights are not exploited. An image can be underexposed in two ways:

• The gamma is too dark, resulting in a clustering of the majority of values at the left of the histogram
• The highlights and shadows are set incorrectly, so that there are no values on the right of the histogram, whie values are stacked up on the extreme left.

A simple gamma correction using curves will solve the first issue. The second issue may be solved in curves or levels, but it may be that the image has been incorrectly captured and there is no information in the deep shadows to be recaptured.

Correction of a heavily underexposed image tends to create substantial noise.

Histogram of an underexposed issue, seen in Adobe Camera Raw. There are no values on the right of the histogram, and the values that there are are clustered at the left. This image can be easily corrected because importing from Raw allows the user to adjust the exposure up. In this case the exposure should be increased by 1 full stop (1 EV).

Histogram of the same image, once corrected.