Image histogram is a type of histogram that acts as a graphical representation of the tonal distribution in a digital image. Image histograms are present on many modern digital cameras. Photographers can use them as an aid to show the distribution of tones captured, and whether image detail has been lost to blown-out highlights or blacked-out shadows. So a histogram with lots of dark pixels will be skewed to the left and one with lots of lighter tones will be skewed to the right.
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| As light tones increases right hand side shows a sudden rise |
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| Shot 1 |
The photograph has a predominantly lighter tones. As a result on the right hand side of the histogram you can see a sudden rise. The extreme values on the right hand side indicate an over exposed shot. Second shot has a lot of dark tones. The shot is underexposed and the resulting histogram has the values skewed to the left hand side.
Different subjects and photographic styles will produce different histograms. A silhouette produces a histogram with peaks at both ends of the spectrum and nothing much in the middle of the graph. Taking a shot of someone at the snow, extreme sunlight or against a white background will produce a histogram with peaks on the right hand side.
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| Shot 2 |
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| As shades becomes darken in shot2 histogram shifts |
Histograms with dramatic spikes to the extreme ends of either side of the spectrum may indicate that a lot of pixels are either pure black or pure white. Image could be either over or under exposed. The histogram is just a tool to give you more information about an image and to help you get the effect that you want. Camera shows histograms during the view process to assist you explain how your images are exposed. Learning to read them will help to work out whether you’re exposing a shot as you had hoped. Understanding histograms also helps to understand level correction while post production.
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