In today’s lesson we’re going to take a detailed look at the benefits of exposing to the right.
Why isn’t exposure easier?
Let’s start by looking at why exposure can be so problematic. There’s no doubt that arriving at the optimum exposure is not always easy. That’s why your camera comes with several exposure modes, so you can select the one that is most appropriate to the subject you’re photographing and the way you work.
Exposure and digital photography
Your approach to exposure depends on whether you are using the JPEG or Raw format. If you’re shooting JPEGs, you need to get the exposure as accurately as possible at the time you shoot. You can adjust exposure in post-processing, but thanks to the limited bit-depth of JPEG files it’s best to think of that as fine-tuning rather than as a way to compensate for over or under-exposed images.
If you’re shooting Raw however, the aim is slightly different. You want to create the best possible Raw file for post-processing, and that means one that contains as much information as possible that can be used by your Raw processing software. An important point about exposing to the right is that, for these reasons, it only works with Raw files.
Exposing to the right
So, where does exposing to the right (often abbreviated to ETTR) fit in? Exposing to the right is a technique for minimizing noise in your images. To understand what exposing to the right is intended to do, we need to understand where noise comes from.
Signal to noise ratio
All digital camera sensors have a certain level of background noise. The amount of noise you see in the end photo depends on several factors, including the signal to noise ratio. Signal, in this case, is light.
Lets say that you’re shooting in bright light, and this gives you an exposure of 1/125 second at f8 at ISO 100. Now imagine that you are shooting the same scene but in much dimmer light. To use the settings of 1/125 second and f8 you need to raise the ISO to 1600.
At this setting, the quantity of light hitting the sensor during the exposure is 1/16th of that in the initial photo taken at ISO 100. There is less signal, and the result is more noise in the final image. That’s the basic reason why there is more noise at high ISO settings than low ones.
The histogram and exposing to the right
Take a look at the histogram below. You can see that the histogram is bunched up in the middle, indicating that I’ve just taken a photo of a low contrast subject.
Exposing to the right simply means increasing exposure so that the histogram is closer to the right hand side of the graph. The increase in exposure means that more light, or signal, hits the camera’s sensor during the exposure, reducing the noise levels in the image.
Ideally you want to get the histogram as close to the right as possible, but without clipping any highlights. If the image is too bright you can darken it when you process the Raw file.
Now take a look at this histogram.
It’s the same subject as the previous one, but I’ve increased the exposure by a stop and that’s pushed the histogram to the right. Twice as much light has hit the sensor during the exposure resulting in, according to the expose to the right theory, a processed image with less noise.
Does exposing to the right work?
How well does exposing to the right work? Now it’s time to look at the photos to find out. But before we look at the results, there are a couple of points to bear in mind.
First, is that noise levels vary between cameras. Generally speaking, newer cameras are less noisy than older ones, and full frame cameras are less noisy than cameras with smaller sensors. If you have a Nikon D750, for example, you’re probably not too worried about noise, especially if you only shoot at the lower ISO settings.
Noise can also be treated in other ways in post-processing. I use Lightroom and the default noise reduction settings produce good results. There are also other applications that reduce noise. Exposing to the right is not the only treatment for high noise levels.
This is a comparison of the two images that belong to the histograms above.
You’re looking at a 100% magnification, and we can clearly see a big improvement in image quality in the photo that has been exposed to the right. Both images were processed with Lightroom at the default noise reduction settings. The right hand image has been darkened using the exposure slider until it matched the brightness of the first one.
Sharp-eyed readers will already have spotted that I took these photos at ISO 25,600. I used this ISO setting as I knew the difference would be quite marked. But exposing to the right makes a visible difference to image quality at all ISOs. It’s most notable when using the Shadows slider in Lightroom to lighten the darkest areas. The more you expose to the right, the less noise there is in the shadows when you brighten them.
Another factor to consider is that in order to expose to the right, you have to increase the exposure, usually by at least a stop. Assuming you keep the ISO the same, this means that you have to open the aperture or use a slower shutter speed, and this may not always be practical, especially if you are shooting in low light.
But, in my experience, you can raise the ISO without increasing noise. You’ll see less noise by using, say, ISO 6400 and exposing to the right than you will by using ISO 3200 and giving the image a stop less exposure.
Test your camera
I recommend that you take some time to test your camera and see if exposing to the right makes a difference to the type of images you take at high ISO settings on your camera. This is the best way to see if the technique will benefit you.
Bear in mind that exposing to the right works when the brightness range of the subject is smaller than your camera’s sensor is capable of capturing. This is most likely to happen when you’re shooting in soft light (like shade) or at the end of the day after the sun has set.
It’s not a technique you can use when the brightness range of the scene is greater than your camera’s sensor can record.
This is the sixth in a series of lessons about exposure. You can catch up with the other lessons using the links below.
Mastering Exposure ebook
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