Under Exposure


Chinook sky over Canada Olympic Park, Calgary
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Despite cameras giving you the correct exposure when they are run in Automatic mode, there is a place for “incorrect exposure”. In this web page I will discuss “Under Exposure”.

Automatic Exposure systems converts the light hitting your camera sensor into shades of grey. The camera averages the incoming light to a neutral grey value (18% grey) and then adjusts the aperture, ISO and shutter speed to create, what it considers, the proper exposure.

Consider the many places where Automatic Exposure gives you an incorrect result. A dimly lit room with a single window throwing light in a certain direction, leaving most of the room relatively dark. An interesting scene on the ground of a dense rain forest dimly lit due to the thick tree cover. A night scene with a few bright street lights and some well lit shop windows.

Looking at a scene with your own eyes, versus looking at a properly exposed picture are two entirely different things. The human brain, most of the time, interprets a scene different than the camera’s automatic exposure system. Images most often, need to be “adjusted” with software to match the “mood” or “feeling” of a scene.

This becomes very clear when taking photos at night.  Dawn or dusk are a bit more ambiguous. In this “dusk”scene above, human perception focuses on the beautiful orange yellow colors reflected by the clouds. The rest of the picture is secondary. However, in the real environment, when you cast your eyes down your pupil will adjust rapidly and the darker ground cover suddenly becomes brighter. A lot more detail is revealed. The camera however is not capable of this adjustment, it averages the whole scene. (In-Camera HDR is an exception, which will be discussed in a later article). In this example the sky is under exposed to bring out the rich color. The escarpment at Canada Olympic Park is so poorly exposed that there is virtually no detail, just a hint of snow.  In this case Under Exposure is  intended for aesthetics, a form of artistic expression. It is understood that the image is “inaccurate” for aesthetic reasons.

Exercise: Photographing high contrast (dark) interiors.

High contrast dark interiors are more difficult to photograph. I found this interior a great example for this course. We stayed at the historic 1920’s Selkirk Hotel in the Fort Edmonton Park. There is detail and interest in the 1920’s style sheers covering the windows, however when taking properly exposed pictures this detail is lost. And, if you adjust the camera to expose for the details in the sheers the interior becomes too dark and loses detail.

Consider this very “Under Exposed” image. The histogram is heavily weighted to the left, showing the mostly dark color intensities of this picture. This is technically and aesthetically under exposed. However the window sheers are properly exposed, and the immediately adjacent tables have enough aesthetic interest. Look at the rich brown colors of the seat backs in the row of seats next to the windows. (Click the image to enlarge, use browser back button to return here)

Compare that with this properly exposed picture. The histogram shows a nicely distributed set of color intensities, with only a spike in the very right hand side of the graph. This is the blown out part, or over exposed part of the picture and consists of the ultra bright portions of the windows. Technically this is the better picture, but the loss of detail in the window coverings makes this a poor picture.


Here is a merged happy medium, achieved by combining both images in Photoshop HDR Pro, and choosing photorealistic representation. Still technically under exposed somewhat, as per the histogram, but far more pleasing, and with enough detail in the bright windows. (See full image below)