The Myth of “Exposing to The Left”

You are probably familiar with the Exposing to the Right (ETTR) technique, where an image is intentionally captured as bright as possible in order to maximize the potential of a digital camera sensor. I recently came across some forum posts and articles on other resources that talk about Exposing to The Left (ETTL) and its benefits. In this article, I want to point out why ETTR is the only proper way to get good exposure from a digital camera and why terms like ETTL do not make any sense.

My purpose is not to create a provocative article, but rather to educate our readers on this important topic. Please keep in mind that this article is fairly technical and it is not for everyone.

What is Proper Exposure?

A properly exposed digital image contains plenty of information to be able to recover both highlight and shadow detail. This means that the image should be neither grossly overexposed to the point of losing highlight detail, nor underexposed to the point of losing shadow detail. The “feel and look” of an image in terms of its brightness is a whole different matter – a properly exposed image can be developed to intentionally look brighter or darker, depending on what the photographer is trying to achieve.

Ideally, an image should have the least amount of noise in both highlights and shadows once post-processed, with enough dynamic range to cover the whole range of darks and whites.

In order to maximize signal-to-noise ratio and get the least amount of noise in images, you should overexpose your image as much as possible, without blowing out any highlights. Simply put, the more of the image is distributed to the right of the histogram, the better. This is especially important for the shadows, because that’s where you are likely to see the most amount of noise in your images when you recover them through post-processing software.

All this means that on a modern digital camera sensor, the ideal exposure should be shot at the base ISO of the camera, and the scene should be exposed as brightly as possible, which is what the ETTR technique is all about.

However, some scenes, particularly high contrast ones, might have such a wide range of highlights and shadows, that they might not fit the dynamic range capabilities of an image sensor. In such cases, as we will see below, there is simply no such thing as “proper exposure” using a single image. The only proper way to correctly capture both highlights and shadows, will be to split it into two or more images.

There are also cases where “proper exposure” is all about capturing the details of a particular subject, while ignoring the rest of the scene (as is often the case with portraiture).

ETTR Histogram Examples

Unfortunately, ETTR is misunderstood by many photographers, because they think that ETTR images always show a curve to the right of the histogram. That’s certainly not the case! ETTR is all about getting proper exposure for a digital sensor, which means retaining data, not losing any of it. Hence, if most of the image is to the right of the histogram, but some parts of the image are getting blown out, that’s not ETTR – that’s overexposure.

Let’s take a look at a few images and their corresponding histograms to understand how wide the range of ETTR histograms can be:

Those who do not understand how ETTR works would only qualify the rightmost image to be ETTR, purely because of the way the histogram appears. However, both left and middle images are also shot using the ETTR technique.

Although the leftmost image appears very dark in the shadows and there seems to be some clipping of the darks, it was exposed to be as bright as possible while keeping highlights from blowing out. The middle image contains a range of tones, and although it shows a pretty big spread in the middle of the histogram, the rightmost side of it shows that the highlights were fully preserved.

All three images have something in common – they are exposed to take advantage of a modern digital sensor. However, there is certainly a problem with the left image – its darks are very underexposed and there might be some clipping taking place there, which is not ideal. In such cases, the dynamic range is too wide for the camera to be able to effectively capture both sides of the histogram. The solution is to capture multiple images and blend them together via HDR / Exposure Blending techniques, which I will discuss below.

Exposing to the Left: Film vs Digital

Film photographers sometimes “Expose to The Left”, because there is more leverage in the highlights than in the shadows when using negative film (such as silver-based black-and-white). With such film, you can recover a few stops in the shadows, but the real recovery potential is in the highlights, where even 8+ stops of overexposure is workable. Because of this, it makes sense to ensure that shadows are not very underexposed, since that’s one area that is tough to pull during development.

Digital, on the other hand, has great tolerance to underexposure, with its ability to recover 6+ stops in the shadows, while the highlights are typically clipped at just a couple of stops of overexposure.

To summarize, with film, you expose for the shadows and develop for the highlights. Whereas with digital, you expose for the highlights and recover the shadows.

The above chart is a very rough approximation of film vs digital response to under- and over-exposure. As you can see, film has more legroom in the highlights, while digital has more legroom in the shadows.

Let’s take a look at a couple of images below:

The “before” image above was the result of intentional underexposure to show off the dynamic range capabilities of a digital camera. The “after” image is what it looked like after 5+ stops of exposure recovery. The histogram, at the time of capture, looked very far to the left, appearing quite clipped, and yet it retained so much information.

All this essentially means that we should be worrying more about the highlights vs the shadows when shooting with digital cameras. By pushing our exposure as much to the right of the histogram as possible without blowing anything out (ETTR), we make sure that maximum information is retained at each pixel. This might result in a histogram that appears quite left-heavy, but that’s OK, because we have plenty of leverage in the shadows.

Speaking of which, the histogram is not particularly useful for assessing the recovery potential of the shadows in digital cameras. Even though the histogram for the “before” image above appears completely to the left, indicating severe underexposure, there is quite a bit of data residing in those shadows, as evidenced from the “after” image and its histogram:

Very little data is actually clipped here, which is remarkable. The good news is, most modern digital sensors have superb dynamic range and are capable of such recovery.

The Problem with “ETTL”

So where does this leave Exposing to the Left? Not in a good place for sure! Trying to expose for the shadows has no benefits on digital camera sensors. By pushing the histogram to the left, you are simply underexposing the image, which is going to end up hurting the overall image quality of the photograph once it is post-processed.

Take a look at the below images:

Here, the “before” image was captured with the ETTL technique, which was roughly two stops underexposed compared to ETTR. Once both images were post-processed and matched in brightness, it is clear that the “before” image contains a lot more noise compared to the properly exposed “after” image.

This proves that underexposing images is not a good idea in digital cameras. In almost every case, your goal should be to make the image as bright as possible, not the other way around!

The interesting thing is that many photographers are so confused about ETTL, that they often refer to ETTR as ETTL, just because of what they see in their histograms.

There is No Such Thing as “ETTL”

Some photographers argue that ETTL can be useful for portraiture, because ETTR often results in subject underexposure, which leads to too much noise on the subject’s face after the shadows are recovered.

Photographing people is obviously different from photographing landscapes. While landscape photographers do their best to make sure that all highlight and shadow details are preserved, that’s not a typical priority for portrait photographers. When doing portraiture, photographers focus on the subjects, making sure that they are properly exposed, as they are the “highlight” of the photograph. As a result, these photographers are probably going to expose for the subject and ignore potential overexposure issues, which could be seen in the foreground or the background, or both.

So, would such cases be referred to as “Exposing to The Left”? After all, the shadows are much brighter and the histogram appears heavy to the left? No, this is still ETTR!

If you are purposefully making your image brighter to expose for what’s important (your subject), while completely ignoring some parts of the image that might be blowing out, you are still using the ETTR technique. Because your end goal is to reduce image noise, which is the essence of ETTR.

For the above headshot, I exposed for the subject. If my goal was to preserve all the highlights in that small part of the sky on the top of the image, my subject would have turned out very dark and I would have ended up with an unnecessary amount of noise in the shadows. This would have been especially bad at ISO 1000, which is noisy “as-is”.

By letting the small part of the sky blow out (which is out of focus anyway), I might not be following ETTR strictly, but that’s because I made that choice. Losing a little bit of highlight detail is not a problem, since it does not change the essence of my photograph and that part of the sky is not particularly distracting to me. What’s important, is that I am making my subject look their best with the help of ETTR.

So, for those photographers who intentionally overexpose their images to get better shadow detail – you are using ETTR, not ETTL.

In fact, I would argue that there is no such thing as “ETTL”. ETTR is a technique to get the best out of your image sensor. ETTL is simply “underexposure”, with zero benefits. That’s all there is to it. And no, there is no such thing as ETTM (Exposing to the Middle) either. Stop looking at the histogram and making up terms please :)

High Dynamic Range Scenes

If the dynamic range of the scene is so wide that ETTR results in a severely dark image, some of the shadow detail might be getting lost / clipped. In other cases, recovering that shadow detail is going to add too much noise to the image. In such circumstances, a single ETTR exposure is simply insufficient and two or more exposures must be taken in order to recover shadow detail. That’s what specific camera and post-processing techniques are for.

Landscape and architecture photographers will often bracket their cameras in order to get three or more images that cover both highlight and shadow areas of the scene. These images are then brought into post-processing software in order to be merged together into a single HDR image. Other times, two or more images can be blended together using Luminosity Masks. In cases of extreme exposure recovery, or when high ISO is used (with noise and other artifacts showing up in the shadows), other techniques such as “image averaging” can be used to reduce noise and improve the overall quality of the image.

In short, not everything can be captured via a single shot ETTR technique, which is something you always have to keep in mind.

Hope you found this article useful. If you have any questions or concerns, please let me know in the comments section below!