Learning to expose to the right can be one of the most valuable photography tips you learn as a photographer. ‘Exposing to the right’ is a technique for getting the maximum amount of image data in an image which is then adjusted to make its brightness correct.
When you expose to the right what you are doing is relying on using the camera’s histogram view and/or highlight alert to guide the exposure and avoid burning out important details or capturing a dark noisy image.
This is an especially useful technique for shooting landscape photography who want to preserver detail in bright clouds and avoid enhancing noise in dark shadows. The best results are achieved by shooting raw format files as these have the maximum amount of data for adjustment.
Why not just underexpose?
When the highlights in a scene are overexposed and burned out they are gone forever, they can’t be brought back by any amount of Photoshop adjustment.
To avoid having these featureless blobs of highlights in their images many photographers underexpose their images to some degree and then brighten them post-capture.
The problem with this approach is that image shadows tend to have more noise than brighter areas and brightening shadows brings out the noise.
This means if you capture a dark shot that needs brightening you are recording a noisy image and then make the noise more obvious.
Lighter parts of the image have a stronger signal and less noise, so provided that you don’t burn out anything important, it’s better to record a bright image and make it darker.
If you photograph a scene with a light source such as a candle or a light bulb in it you wouldn’t expect, nor want, to be able to see the detail of the candle flame or the bulb’s element.
You would expect these areas to be burned out. Similarly, if you are photographing a sparkling sea you expect the specular highlights to be burned out.
It would be a problem, however, if all the detail in the ‘white horses’ of the waves in the sea are a featureless mass of overexposed white.
These areas are the important highlights or critical highlights and the exposure needs to be set to protect them.
Using your histogram to expose to the right
Most DSLRs, compact system cameras and high-end compact cameras can display an exposure histogram for an image.
It is similar to the Levels histogram that can be seen (and adjusted) image editing software packages such as Photoshop CS6 and Elements 11.
This is a graph that shows the brightness distribution of an image with the peaks indicating the number of pixels (or size of the area) within the image that have a particular brightness. The dark pixels are shown on the left while the bright ones are on the right.
A ‘normal’ histogram for an ‘average’ scene will look something like this:
The majority of the pixels are grouped around the centre of the graph indicating that their brightness is towards the middle of the range, but there are a few darker and brighter pixels.
Underexposing the same scene would produce a histogram like this:
The main body of the peak has shifted over towards the left and the trace doesn’t reach the far right of the scale, indicating that there are no white objects in the image at this exposure.
If the scene is overexposed the histogram looks like this:
The peaks all move over towards the right of the graph indicating that many pixels are brighter than a mid tone.
A large peak at the very highest value indicates that there are lots of completely white pixels, suggesting that some areas are burned out, having no detail or tonal gradation.
How to expose to the right
The aim with this technique is to capture the maximum amount detail and minimise the level of noise while avoiding burning out any important highlights.
This means that the exposure should be set so that the histogram is towards the right without having a large peak at the furthest point.
This can be done by taking a shot and inspecting the histogram before adjusting the exposure and taking another shot until the histogram looks correct.
You want the histogram trace to just reach the right side of the scale and not have a large peak of white pixels. If possible look at the histogram for teh colour channels to ensure none of them burn out.
Alternatively, the camera’s highlight alert can be activated to indicate when highlights are burned out, or in some cases close to being burned out.
Then instead of looking at the histogram view you can just look for the flashing that indicates that important highlights are being lost.
The trick is to find the exposure level just before this happens. In many cases reducing the exposure by 1/3EV below the value at which the critical highlights are just starting to be lost is enough.
Most compact system cameras and high-end compact cameras, as well as some DSLRs in live view mode, are capable of showing a ‘live’ histogram that displays the brightness of the scene at the selected exposure before it is shot.
Using this avoids the need for trial and error shots. You will see the peak in the histogram move as you adjust the exposure settings.
The last step
Once you have your correctly overexposed images they may need to be adjusted to get them looking as you want.
You can use your preferred editor or raw file converter to darken the image, but keep an eye on the histogram as you do it so you understand how the adjustments change the graph.
Most scenes have at least some black areas, so the histogram trace should reach both the far right and left points of the graph, but its more important that the image looks correct rather than the histogram adheres to this guide.