What the Hell is Exposure Bracketing and Exposure Blending?
I still clearly remember when I first heard about exposure bracketing. I was shooting sunset in a classic spot in Vernazza (Cinque Terre) and the American guy next to me broke the ice by saying: “Boy!!! This is a classic exposure bracketing situation”. I just heard the word “exposure bracketing” for the first time in my life, but I confidently nodded and replied with a casual: “For sure. Easy-peasy, man” and then pushed some random buttons on my camera. Needless to say, I felt pretty dumb for the rest of that shooting session. When that guy left with all the other photographers, I was finally able to google: “What the hell is exposure bracketing?” If you want to avoid this kind of situation, here’s everything you need to know about exposure bracketing and exposure blending and why it is helpful for landscape photography.
What’s exposure bracketing and why is it useful?
If you have read my previous posts about the histogram and GNDs, you might recall that I mentioned that sometimes you might find a situation where the light disparities (or dynamic range) of your scene is far bigger than your sensor’s capabilities. You either end up clipping the highlights or the shadows and that’s when exposure bracketing comes in very handy. Exposure bracketing refers to the action of taking several shots of the same scene with different exposure values (EV). The pictures below show you a classic exposure bracketing series which consists in taking 3 consecutive shots: a basic exposure in the middle (EV 0), a darker exposure on the left (EV -) and a brighter exposure on the right (EV +). Taking the same shot with different EVs is helpful to expand your dynamic range beyond your sensor’s capabilities in order to capture all the information for both your highlights and shadows in the scene. The darker exposure is usually taken to preserve all the information in the highlights area (also referred as exposing for the highlights), while the brighter exposure preserves the details in the shadows (also called exposing for the shadows). Depending on the light of your scene and your camera, you can either bracket 3 shots (1 basic, 1 dark and 1 bright), 5 shots (1 basic, 1 darker, 1 dark, 1 bright and 1 brighter), 7 or 9 shots (though I have never taken a 7 or a 9 shots bracketing series).
Once you have shot your bracketing series, you can blend the images together in Lightroom or Photoshop to gather all those information in one single frame, which I like to call super-frame, while Lightroom ambiguously calls it HDR. This super-frame contains expanded information of both highlights and shadows and it’s a much more versatile RAW file for post-processing. Beware that exposure bracketing MUST be done on a tripod in order to have perfectly aligned images for the software to create the super-frame.
How to set up exposure bracketing on your camera
Setting up exposure bracketing on your camera is very simple. On your camera, there should be a button with the letters BKT (for Nikon shooters), AEB (for Canon shooters) and Sony shooters you’ll have to go into your menu or customise your buttons for bracketing (sorry!!!). You all know I shoot Nikon, so I’ll show you how to set up exposure bracketing on a Nikon camera, but I am pretty sure this is very similar with other cameras too. If you hold that BKT button down this screen pictured below should appear on your top screen. The number on the left is the number of shots of the series and, as I said before, it can be 0F, 3F, 5F, 7F and 9F, where F stands for frames (I guess). The number on the right, instead, is the stop between each frame or increment and it can be 0.3, 0.7, 1.0, 2.0 and etc. Mine is currently set on 1 stop and that means that my shots will have a full-stop difference between each other.
To change the number of shots in a Nikon camera, all you need to do is to move the rear dial, while to change the increment you need to move the front dial instead. Once you selected your number of shots and your stop gap, release the BKT button. You’ll see the BKT sign appear on your top and rear screen. This means that your automatic exposure bracketing is on and the camera will automatically shoot a bracketing series. If you are using a delayed shutter release, the camera will automatically capture 3, 5, 7 or 9 images and then stop, while if you are using a cable release, you’ll need to press down the button for each frame of the series. I suggest you to lock your release button on the remote as the camera will fire the bracketing series automatically and stop when done. This bracketing setting will stay on unless you hold the BKT button again and select 0F on the number of shots.
If you have been playing with your camera for a while, you’ll notice that the number of shots in an automatic bracketing series doesn’t stop just to 3F, 5F, 7F or 9F, but it goes to -2F, +2F, -3F and +3F. These options allow you to set up a slightly different but useful bracketing series as they will shoot only under-exposed or over-exposed series. The -2F option for example captures 1 basic frame and 1 dark frame and -3 captures 1 basic, 1 darker and 1 dark, while the +2F option captures 1 basic and 1 bright and the +3F 1 basic, 1 bright and 1 brighter. If you are a little bit confused, here’s another top secret NASA graph, which recaps all the different type of the bracketing set ups. In the graph on the left, you can see how changing the increment affect your bracketing series. A full stop of increment is a good place to start and honestly my favourite, but you can also change it to 2.0, where your shots will be incredibly dark or incredibly bright, or reduce the increment to 0.3, where your shots won't change that much. The graph on the right instead shows the different bracketing series with a full stop of increment when you change the number of shots. Goes without saying that bracketing can also be achieved manually by changing either shutter speed, aperture and ISO; though this can be fiddly and slow at times.
When should you use exposure bracketing?
I have actually said it already, but for the sake of this post I’ll say it again. Bracketing is useful to gather a large amount of information for your shadows and highlights and, therefore, it is useful in those light disparity situations with an extremely high dynamic range. Take this picture from Namibia as an example. I was shooting in the same direction of the setting sun and, even with a GND on, I kept blowing either my highlights and my shadows as the sky was much brighter than my foreground. This is the perfect scenario to activate that BKT button. Since I wasn’t clipping my highlights and shadows that bad (because of the GND), I selected a classic 3F frames bracketing with a full stop increment (1.0) and I let the camera fire away. As you can see by the series below, the basic exposure in the middle (EV 0) has some highlights and shadows clipped. The clipped highlights were recovered by the dark frame on the left (EV -1), while the clipped shadows were recovered by the bright frame on the right (EV +1). Once I had assessed that my bracketing series was good enough for that light situation, I kept shooting with the automatic bracketing on. How did I know that? I have checked the histograms on every frame of the series. Ideally, your under-exposed frame should have clipped shadows, but well-exposed highlights, while the over-exposed frame should have clipped highlights and well-exposed shadows (as you can see from the histograms). And that's it. Your bracketing series is ready to be processed.
Introduction to Exposure Blending
DISCLAIMER: I am not a computer-head-kind-of-guy, I barely know how to turn on the computer and many times I felt the need to just rip the freaking screen apart on my laptop when Photoshop crashes for no reasons. So, excuse my “tech vocabulary”, computer-induced rage and ignorance.
Just to recap, you now know everything about exposure bracketing, you confidently set it up without even looking at the camera screen anymore and you nailed it in Namibia (way to go!!!!). Now what?! Well, now it’s exposure blending time. Exposure blending is an extremely broad topic and it probably deserves more than one blog post alone, but this exposure bracketing post wouldn’t make any sense without a brief introduction on how to achieve that super-frame I mentioned at the beginning. There are many ways to blend your bracketing series together and here I will only show you how to do it automatically in Lightroom to keep this post short (yeah right!). Lightroom is made by Adobe and the automatic blending (or Photo merge) feature is similar to the one found in Adobe Photoshop; hence, the process I am about to show you can be applied in Photoshop with the same results. Like bracketing, Photo merge can also be done manually. While automatic Photo merge is convenient, reliable and time-saving, sometimes you’ll find out that it is worth spending some extra time blending the images manually to achieve a better and targeted result. But I am getting ahead of myself…
The first thing to do is to import your bracketing series into Lightroom. Let’s take as an example the previous images from Namibia. The first image is your basic exposure, the second is the under-exposed image and the last one is the over-exposed shot. Before doing anything to the images, select all of them, go to Photo, Photo Merge and select HDR. Lightroom will then show you a pop-up window, where it’s going to load a super-frame preview (or HDR preview as Lightroom calls it). In the HDR Option panel on the top right, make sure that the Auto Align box is ticked and the Auto Settings option is NOT ticked as per the image on the left. While the first option is helpful as it might help to ease the blending process, the Auto Settings will automatically “correct” the tones of your shot. It’ll basically process the shot for you, which is something I personally don’t want as I like to have complete control of my post-processing actions. Here’s a before and after the Auto Settings option (not good enough Lightroom. Not. Good. Enough).
The other important thing to set is the Deghost Amount, which corrects the parts of the scene that moved during the bracketing series. If you shoot your bracketing series on a tripod as I told you, you shouldn’t have any problems as your shots will be aligned. I was a good boy in Namibia and shot this series on a tripod with a fast bracketing; hence, the aligning should be spot on and I can just select None as Deghost Amount. In my scene though, there’s plenty of branches and leaves that could have moved during my series due to the wind and whatnot and just to be sure everything is ok, I can just select the Deghost option Low for a moment and, thanks to the Show Deghost Overlay box, see if there are any corrected parts. This "trick" can be useful to check images more sensitive to merging mistakes such as the one with trees or objects sticking out the horizon and frames with a large amount of high-contrast edges. The Photo merge feature marks the corrected areas in red, if there are any, and you can see from the screenshot on the right that no parts were corrected in my picture. In most cases, if you shoot on a tripod, I would recommend you to just choose the None option as you could trick the software in correcting non-existing problems. This was just an example to understand the Deghost Amount option. Having said that, I re-select None and then click Merge.
Here's another example from Riomaggiore. In this case, selecting a Low Deghost Amount actually corrected some parts that moved during the bracketing series, like clouds, boats and waves. If you see these red areas in your HDR preview, then select Low as Deghost Amount and click Merge. Don't try Medium or High as the software will "hunt" for corrections correcting almost all the edges in your picture. Once the HDR software has finished carefully check those areas at 100% to make sure Lightroom did not screw everything up. I don't usually recommend an automatic exposure blending for seascapes as the water movement between the bracketing series can confuse the Photo merge software. I prefer to blend seascapes like this manually, if I have to.
Once you click Merge on the Photo merge pop-up window, Lightroom creates an HDR-DNG file, which is a fancy term for RAW file, with all your shadows and highlights information of your 3 shots…a super-frame. Although this file looks similar to your basic exposure, it actually holds much more detailed information and it is indeed more versatile and prone for post-processing. For example, you can see how the Exposure slider of our super-frame from Namibia can go to + or -10, while the basic exposure can only go to + or -5. This means that our blended image has definitely more details and a higher dynamic range than a single shot and that you have more room to process your image to achieve the desired effect. The picture below on the left is the basic exposure with the Exposure slider down to -5 and it's clear that we can still see those highlights areas that were clipped to begin with; hence, a limited dynamic range. On the right, our super-frame is completely black due to the expanded dynamic range as the Exposure slider can be dragged to -10 as this file contains the exposure, highlights, mid-tones and shadows information of 3 shots. Believe me when I say that the post-processing flexibility of these super-frame (or HDR files) is extraordinary.
Let’s say I want to recover those highlights in the sky from my Namibia shot. If I close the highlights to -60 in my basic exposure, I still have some undefined white spots as this shot did not register any information in those areas. If I close the same amount in my super-frame (or HDR shot), I recover much more details in the sky than the basic exposure. This is because the super-frame has information of 3 different shots and those areas were registered by my under-exposed frame. Basically, exposure blending allows you to have the information of a determined amount of shots in just one image. This opens up a number of possibilities in your workflow and helps you recovering all the details you need for your final image. Don't be greedy though as the more shots you select for the Photo merge the more the software is likely to screw up the blending. An exposure blending of 3 shots is a fair amount of information packed in one RAW file and usually Lightroom won't make any mistakes if these shots have a reasonable increment like 1.0. Once your super-frame is created, always spend some time zooming in and checking if the software made some mistakes as this is always a possibilities. Whenever I do Photo merge in Lightroom, I always double check that Lightroom got the job done properly (I don't trust computers).
Bracketing-Like-Hell (aka BLH Syndrome)
Every year thousands and thousands of photographers are diagnosed with BLH syndrome, which is a disease only curable with new and bigger SD cards. Jokes apart, it’s easy to fall into the bracketing-like-hell syndrome once you realise the power of exposure bracketing and blending and what you can achieve with them. I know as I was one of the photographers affected. There was a period where I was just firing mindless brackets like there was no tomorrow, without even thinking about if I really needed a bracketing series; I was just doing it. Believe me when I say that this is not the way to shoot as your SD card will fill up very quickly and your Lightroom catalogue will become endless. My philosophy on bracketing is this: try to nail the exposure in one single frame, if you can’t push that damn BKT button then. I think this should be your first goal whenever you approach a composition: trying to capture the whole dynamic range in one shot. Bracketing can be used whenever you feel you might need 1 or 2 additional frames to recover some details in the highlights or shadows. Take this frame from Saxony for example, I composed my shot and then fired a test shot. The histogram told me that the highlights in the sky were a bit clipped, but shadows were fine. After trying to fit the whole dynamic range in one shot by changing the shutter speed, I realised I couldn’t do it as my shadows were closing too much. So, I decided to bracket. Instead of bracketing a thousand shots, I only shot a basic exposure and one darker frame for the sky as I did not need any additional frames for my shadows. By doing this, I reduced the number of shots in the field and eased up the blending process for Lightroom/Photoshop. I also had a happier and lighter SD card. I mean, sometimes you’ll definitely have to bracket 3 or even 5 shots as the light conditions might dictate that; just don’t run around like headless chickens bracketing the hell out of every single frame. That’s all I am saying, be a responsible bracketer.