Tag Archives: ettr

Expose To The Right (ETTR) Is Obsolete

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(Lake Moogerah — underexposed by two stops to save the highlights and exposure adjusted in Lightroom)

Expose to the right (ETTR) is a technique that became popular when digital photography started to pick up. I will not discuss the details of this technique but I’ll try to cover the basics. Before you continue make sure that you understand the concept of exposure. If you are a bit rusty on this topic then consider reading my previous article on understanding exposure.

The goal of ETTR is to maximise your sensor’s capacity to capture data. We know that every stop of exposure is equivalent to doubling the amount of captured light. So imagine if you have a glass that is half full of water, increasing the amount of water by a “stop” would mean filling the glass up to the brim. If we translate this into photography, say, using the zone system, this means that zone IX is practically half of the entire capacity of your sensel, zone VIII is a quarter, zone VII is an 1/8th and so on. That’s basically how camera sensors work. You would want to maximise the capacity of your sensels by forcing them to fill up with photons. It means that you would always want to have a zone IX otherwise you are wasting half of your data.

So why am I saying that this technique is obsolete? After all, digital capture is still digital capture. Sensels still respond linearly to incoming photons. What has changed?

Digital photography has advanced so much in the past five to eight years. In the early days, shooting beyond ISO 400 was a nightmare. I remember shooting with my Canon G10 and I would never dare shoot at ISO 400 unless I really had to. All my images at ISO 400 were just too noisy and were almost unusable. At present, point and shoot cameras can easily shoot at ISO 6400 with very acceptable results.

What does this mean? Recall that ISO has got nothing to do with exposure. Bumping up the ISO does not increase the amount of captured photons. In fact, bumping up the ISO forces your camera to underexpose. For example, if your camera has a base ISO of 100 and you are shooting in broad daylight, your exposure would go something like ISO 100, f/16, 1/125s (basic sunny 16 rule). If you increase your ISO to 200 then the exposure would go f/16 at 1/250s. At ISO 400 you have f/16 at 1/500s. Every time you bump your ISO you are forcing underexposure. That means your sensels would receive half the number of photons for every stop of increment in ISO. What I’m trying to say is that the fact that you can shoot at ISO 6400 is testament to the amazing ability of modern sensors to handle extreme underexposure. If any of these do not make any sense then please go back to that link I provided in the first paragraph. Read and understand the basic concepts of photographic exposure.

Again, every time you increase your ISO beyond the base ISO, you are forcing your camera to underexpose. Bumping up the ISO is the exact opposite of ETTR. It follows that ETTR only ever makes sense when shooting at base ISO. Performing ETTR at higher ISOs is stupid.

Let me explain that previous paragraph with examples and (stupid) counterexamples. Let’s consider shooting during an overcast day. A typical exposure at base ISO of 100 might go f/5.6 at 1/125s. Performing a stop of ETTR would mean shooting at f/5.6 at 1/60s or you can choose to maintain your shutter speed at 1/125s but shoot at f/4 instead. Look what happens when you bump the ISO to 200: the exposure would now read f/5.6 at 1/250s. If you perform a stop of ETTR at ISO 200 you get f/5.6 at 1/125s which is basically the original aperture and shutter speed combo at ISO 100. Your image might be brighter because of the increase in ISO but the truth is that you have NOT performed ETTR at all! It’s the same exposure of f/5.6 at 1/125s. If you want real ETTR at ISO 200 then you would have to shoot at f/5.6 at 1/60s (same as ISO 100 ETTR) but because of your ISO bump your final image loses dynamic range in the highlights! ETTR plus ISO bump is like taking a step forward and two steps backward. It’s stupid.

Again, with cameras capable of shooting natively at ISO 6400 and some of them even going as high as ISO 746123550123656128561249571243865 (looking at you Sony A7S) we know that modern sensors are now very very good at handling FORCED underexposure. But then the other side of the story is that modern sensors are still VERY BAD at handling OVERexposure. Once you clip your highlights there is no way you can recover that data. FACT!

Losing data is not the only problem of overexposure. When you overexpose by force, it is very difficult to judge the tones and colours just by looking at your LCD. When you ETTR, your blue skies will look bright grey, you lose the sunset colours, your shadows become dull. Of course you might be able to “fix it later in the computer” but you have practically deprived yourself the capability to properly judge how your image might look like and make decisions (i.e. adjust exposure) while you still can.

Again, let’s consider the facts:

  1. Cameras can shoot natively at high ISOs which means they can handle extreme underexposure.
  2. Cameras are very bad at handling overexposure.

Is ETTR really worth it? Shouldn’t you give your camera the best fighting chance by utilising its strengths instead of gambling with its weaknesses?

The ETTR ship has sailed. Move on.

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Choosing the Dark Side

Canon vs Nikon. They never end. Lucky Sony, Olympus, Pentax and other underdogs for not having to deal with the stupid arguments. But this post isn’t about brand wars.

Expose to the right (ETTR) is a common advice in digital photography. It simply means, try to make sure that you expose your shot with bias towards the right end of the histogram. Make it as bright as practically possible without blowing out the highlights. If you understand how digital photos are stored, this makes sense. You want to maximize every bit of those 12-14 bits.

There is danger in blindly following this advice since the linear profile of digital camera sensors is not very forgiving. Once you clip past a certain limit, no data is stored in the photograph. This is characterized by blown highlights. Unfortunately, it is a lot easier to blow the highlights than lose the shadows.
There is something I discovered just a few months ago that I would like to share with you: It is better to underexpose than expose to the right. Not just underexpose but severely underexpose especially if the dynamic range of the scene is too wide.
Have a look at this photo because I quite pushed the camera beyond its limits when I took the shot:


Very dark isn’t it? The exposure was ISO 400, f8, 30 seconds after +2.5 stops of exposure compensation from the metered reading. That’s pushing the sensor a bit too much. I could have opened up to f5.6 but my cheap lens is very soft at that aperture. Going ISO 800, on the other hand, will only introduce more noise.
Now have a look at the same photo after post processing:


That’s a world of difference! I just pushed the exposure by +1.35 stops and then pulled some of the shadows with fill light. I have managed to extract details in the shadows while preserving the highlights. There’s more: peep all you want but there is barely a trace of luminance or chroma noise even after brightening the shadows. Amazing!!!

The photo was captured with a Pentax K5. It’s really amazing how modern sensors have improved. I would expect the same performance in the Nikon D7000 and Sony A55 because all of them use the same Sony sensor (surprise?!!!).

This is not the only instance where I managed to salvage a seemingly hopeless exposure. I do a lot of HDR work when the scene is too contrasty and I normally bracket at -2,0,+2. Many times, I was able to scrap the HDR because I was able to extract enough information from the -2 frame. Single exposure shots are still way cleaner than HDR so I always try to pull the shadows if I can.

Experiment with your own camera and see how much you can extract from a severely underexposed image. Make sure you shoot RAW.

So who’s coming with me to the dark side?

Edit:
My new iPad blogging software ruined the original post. Lesson for me: sticking to one buggy software is sometimes better than switching software.