Understanding digiital histograms can make you a better, more creative photographer. Histograms aren’t all that complicated to understand and being conversant with them will assure you better exposed pictures. Sadly, most camera manual barely mentioned them. There’s a wealth of information available on the web concerning histograms as they apply to digital cameras as well as digital editing software and this article will barely scratch the surface. I hope that after reading this article you will see their value and explore the subject more fully on your own.
Light range for proper exposure
Those of you who started out shooting with film you’ll recall that the exposure range was limited to a few f-stops. Transparency film was limited to 3 or 4 “stops” of light while negative films extended the “stops” of light out to 5 or 6. Most digital camera sensors are a little more sensitive than transparency film and a little less sensitivity than negative film but this is quickly changing with the introduction of extended range sensors on some high-end professional cameras. Unfortunately, many of the high contrast subjects that we shoot contains over 12-stops of light values which is more than any digital or film camera can capture today.
The histogram is a graph that displays the range of light stops that a camera’s sensor can capture. The stops are displayed in 256 steps from 0 for absolute “Black” to 256 for “Absolute White.” The range from just above 0 to just below 255 contains all the picture details. The mid-range of the histogram, around 125, is where you find the grays and other mid colors like, light browns, and greens. A real world histogram looks like a mountain peak or a series of mountain peaks on your camera’s LCD screen.
With a properly exposed picture, the entire histogram will appear within the histogram window without being jammed against either side of the window. Most histograms will consist of a series of peaks because its own peak will represent each prominent color. The thing that you need to remember at this point is that if you have a histogram that is partially clipped off on the left hand side the picture is too dark, it’s badly under-exposed. On the other hand, if the histogram is partially clipped off on the right hand side, the picture is over-exposed. In either case, you need to adjust your camera setting accordingly.
How the eye reacts to light
Since the human eye tends to know that the shadows are supposed to be black, it’s better to set our camera to properly expose the highlights. The eye is not use to seeing scenes so bright that the details in the highlights disappear so it’s best to adjust the settings on our camera so that the right side of the histogram barely touches the right side of the histogram frame. When shooting it’s best to expose for the highlights. When we do that we will lose some details in the shadows but we will pull them out doing post processing using the histogram for levels in your editing program. The levels histogram in editing programs like Adobe PhotoShop and in Adobe PhotoShop Element have sliders that allow you to adjust all three areas independently.
If you are shooting in a situation, where the quality of the light changes rapidly set you camera up to shoot bracket exposures +3-3. Most digital cameras have a menu for programming the camera to automatically bracket each shot by plus and minus a number of f/stops. Unlike when shooting with film, it doesn’t cost you anything to bracket your shots and by bracketing them you have several shots to choose from during post-processing.
Now that I’ve showed how understanding histograms can make you a better shutterbug, go to the Nikonian Site and peruse their informative tutorial on this subject.
