Using histograms: 6 ways to react to common exposure problems
Seen a histogram graph on your DSLR or PC screen but not sure how to use one to fix exposure? Read on: it’s easier than you think. In this post we’ll show you how to spot and react to 6 of the most common contrast and exposure problems when using histograms in the field…
A histogram is a type of graph. In photography, it is a way of plotting the exposure of a digital image. By looking at the graph, you can see whether a shot is too bright or too dark.
The histogram used by your camera is essentially the same as used by Photoshop – or whichever form of photo editing software you use. The brightness of each pixel in the image is given a value along a 256-step scale – where zero is the darkest, blackest value possible, and 255 is the brightest, whitest value. The 256 steps correspond to all the brightness values possible in a typical JPEG image, which uses an eight-bit scale, where the brightness of each of the three primary colours is given a binary value from 00000000 through to 11111111.
Using histograms is a much more accurate way of judging whether a picture needs a bit more, or less, exposure. It’s not just used for judging exposure: the shape and position of the graph can also tell you about the contrast of the lighting in the scene.
Below we’ve rounded up 6 ways to respond to common exposure problems when using histograms.
The histogram is pushed to the left and fails to register any very bright areas on the graph. Retake the shot, dialling in a positive value of exposure compensation. Try a setting of +1, then check the new histogram.
The histogram is stacking up at the extreme right-hand side, producing clipped highlights and burnt-out clouds. Retake the shot, dialling in a negative value of exposure compensation. Try a setting of -1.
03 High key
Sometimes the picture is meant to bright, with a histogram that peaks on the right of the graph – as in this shot. However, it’s important that highlights aren’t clipped, because they shouldn’t all be pure white.
04 Low key
The graph here stacks up hard on the left, but isn’t under-exposed because the peak on the left corresponds with the black background. Shoot so the image is as bright as possible, without clipped highlights.
05 High contrast
Shooting a white building in bright light creates a very-high contrast scene with a histogram that squeezes up at both ends. Detail is going to be lost whatever settings you use. Try a different angle or time of day.
06 Low contrast
Some scenes don’t contain strong shadows or strong highlights and create a histogram that sits neatly in the middle.
To maximise picture detail, shoot so the histogram sits as far to the right as possible.
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on Thursday, December 27th, 2012 at 2:00 pm under Photography Tips.
Tags: camera tips, histogram