High Dynamic Range
photography, or HDR as it’s more commonly known, is a popular and often
misunderstood method of photography. Here, we’ll look at what HDR is, how to
use it to good effect and throw in some inspiration to boot.
Maximum Dynamic Range
Dynamic range is a measure of your camera's signal-to-noise ratio.
In any given photograph, there are a variety of tones: some parts of the
scene that are bright, then a range of colours and greys, and then parts
that are shrouded in shadow. Sometimes the difference between light and dark can be extreme; we call this "high contrast."
Your camera is optimised to work with a limited dynamic range. Above and below that range, detail will be "blown out" to bright white or "crushed" with noise in the blacks. Just how much difference between white and black the camera is able to record determines a whole bunch of photographic decisions you have to make to successfully take a picture.
It’s difficult to
expose everything perfectly every time: some scenes have black levels and white levels that exceed the abilities of your camera. In these high-contrast scenes, often the right thing to do is make a compromise and choose an exposure that will "protect" the shadows
or the highlights, depending on what matters most to you.
In some situations, however, it's possible to use clever post-processing techniques to produce images that exceed the innate abilities of your cameras: enter HDR.
Poor, Misunderstood, Maligned HDR
When compensating and trying to achieve a high dynamic range, you can end up with an unnatural, over-saturated look to your images and, unfortunately, that’s where most of the bad press surrounding HDR comes from. Typically, this ‘over-use’ of the method has been applied to architecture and particularly, urbex photography; where it’s become somewhat of a running joke and the subject of many a meme.
Tone Mapping
I’ve heard tone mapping and HDR used interchangeably but they’re not really the same. You can apply tone mapping to an HDR image for starters.
Tone mapping bumps up the contrast whilst (in theory) preserving details and colour. This can be done in two ways, either globally, where every pixel is mapped the same way, or locally, where the algorithm is adjusted for each pixel depending on the surrounding ones and what’s going on in the image.
Used subtly and sparingly, tone mapping can add extra punch to your image. Used incorrectly and you’ll highlight problems such as noise and sensor spots, cause contrast rings and haloing. It’s a delicate balance.
What You Need
HDR is achievable with any hardware as it’s all about the processing afterwards. Ideally, you’ll have a camera that will allow you to shoot in RAW, so that you can get the most out of your images.
Exposure Bracketing
AEB is a useful feature to have on your camera too. It stands for Auto Exposure Bracketing and allows you to set the camera to take a picture at a predetermined number of stops apart. For example, you might set it to EV: -2, 0, +2 which would take an image at your settings, two stops lighter and two stops darker.
The idea behind this is that it gives you the best possible chance of having one image that exposes for the shadows, one for the midtones and one for the highlights. When they’re blended together, in theory you’d have a perfectly exposed photograph with a high dynamic range.
You can achieve this without an AEB function, but you’d have to set it manually and it increases the chances of you moving the camera or something in your shot changing or moving.
A Tripod
Again, this isn’t essential but it is very useful. It means you can keep your shot lined up and completely still while the camera takes its multiple exposures. Even the steadiest of us would find it tricky to keep the camera in the exact same position for several shots.
HDR Post-Processing Software
Software that can properly blend HDR images varies greatly in price. The popular Photomatix has a two-tiered pricing package starting at £39. If you already have Photoshop or Lightroom then both are capable of this, so you can use them to blend your images. If you don’t have any of these and prefer a free option, then there’s open source software, Luminance HDR which has several blending options and is a great place to start or the highly popular (and recently made free) Nik Collection which includes an option to blend multiple exposures or tone map from a single exposure but the latter isn’t true HDR and you can probably bring in as much detail by making your adjustments in RAW.
Inspiration
Downtown Chicago
I wouldn’t say this was a natural-looking HDR, exactly, but nor is it cartoony and oversaturated. I really like the
limited colour palette and the warmth of the buildings. To me, this almost feels like a graphic
designer’s interpretation of a city and definitely benefits from the lack of
people in the shot.
Red Rocks at Sunset
You can bet that the original image(s) had some very dark shadows in the tree and cliff lines and some very bright highlights in the sky. This balances them well and the detail brought back to the sky is beautiful. To my eye, the green and red could be a touch more subtle—less saturated and slightly darker—but other than that it’s a great blend.
Irish Cliffs
Although ‘avoid movement’ is great advice when it comes to HDR, I think the grass blowing actually works here. It looks slightly soft, giving the illusion that it’s still swaying in the wind—I bet you can nearly feel the bracing wind on that cliff top!
Lights at Dusk
Including lights in a composition is absolutely my favourite thing when it comes to bringing out the best in the dynamic range. The warm glow on the water here is lovely and the town is just sharp enough to stand out and draw your eye without looking overdone.
Sunset in St. Louis
Sunsets and sunrises are lovely times to bring out the various colours and tones. Using many exposures will give you a great range, particularly as the light is changing all the while.
A Compromise
As well as blending or tone mapping, some presets or actions claim to give an HDR effect to your images. Below is one of my images. The unprocessed RAW file is quite flat:
I used Sodasong’s Dramatic Landscape Action pack for Photoshop, which includes an HDR effect. Now obviously this can’t be true HDR as there’s no blending or tone mapping involved, but it claims to replicate the HDR look.
When I ran the action, it created a mask to cover the dynamic range and then broke down into layers like sharpening, brightness, contrast and colour. These are all non-destructive, so you can compare to your original image at any time. It also means you can adjust each layer until you get the desired result.
I decided to leave the settings as they were so you could see the result from literally just pressing play on the action:
You can see that there’s a strong colour, contrast and sharpness increase and the shadows and highlights haven’t been crushed or blown out.
Here’s the image with before to the left, and after to the right:
For
a one click solution, it’s not bad at all. The difference is subtle, but subtle is best when it comes to HDR. You know you've hit HDR success when the results just feel normal, integrated, and natural.
If you’re pushed for time and you
just want to give your images a boost, then the action is a great solution: it
doesn’t take long to run, it's subtle, and doesn't go overboard. This is exactly what you want in an action, to leave you free to make your own adjustments.
Technique
Make Your Exposures
At the very least you need to shoot two images, but ideally it will be at least three: one of normal exposure, one exposed for the shadows, and one exposed for the highlights. Setting the bracketing mode (AEB) on your camera and using the burst mode will allow you to capture three shots in quick succession
Remember not to make changes to your settings between taking the images. This means that ideally, you should be shooting manually so that the camera doesn’t change the ISO or aperture between shots.
Watch out for things like movement which will add ghosting to your images when they’re merged. Even the wind in the trees will cause you problems so be aware of your subject and what’s going on within the frame.
If you’re going to be attempting the same or similar images, one after another, I find it useful to break them up with a photograph of something blank, so that it’s easy to distinguish which shots should be grouped together. I usually take a picture of my hand so that I can spot the breaks easily from thumbnail images.
Keep Your Exposures Close
When you use AEB,
don’t use really extreme differences unless you’re taking lots of
exposures.
For most things, three photos is enough to make a great HDR image. Avoid
extreme combinations like [-5, 0, +5]; instead keep to one, two or
three stops apart. If you’re taking more shots, five instead of three,
for
example, then it’s okay to push it further.
Again, bracketing one or two stops above and below your base exposure is usually enough though, especially with RAW. For pictures of people, you’ll probably want to try taking your images a stop or less apart. For high drama images such as cityscapes and landscapes, you can increase the range to two or three.
Blending Your Photos
Each piece of software capable of processing HDR photographs, like the ones I mentioned earlier, will have different features and options but mostly approach it in a similar way.
The software will get you to manually put in the exposure value for each image if it can’t automatically recognise it. It will usually also have options such as Correct Chromatic Abberation, Reduce Noise and Reduce Ghosting. These can all be very useful as they’re common problems with HDR, so don’t be afraid to play about with the sliders to see what improves your image.
Once you’ve got things how you want them, your software will blend the exposures into one 32-bit image and will probably look pretty darn awful. That’s normal, so don’t worry, it’s where tone mapping comes in. Here you’ll make adjustments to fine tune your image—choosing whether to enhance the details, further compress tones, and where to reduce or increase saturation.
Potential Problems
Movement
As you’ll be taking at least three images to get an HDR image, it makes sense to avoid movement. If something is moving, even a tree in the breeze, then it makes sense it won’t be in the same position for all photos and so will look blurred or odd in the final blend.
Over-Saturation
If a scene is full of colour or high contrast, using HDR will intensify that, often to the picture’s detriment. It might be necessary to desaturate your image after you’ve processed it, to take the edge off. Likewise, in areas of low contrast or colour, you may end up with a flat, milky look to your images,
Computer Issues
If you’re processing many, large RAW images your computer may well struggle. Make sure any updates that are scheduled don’t start during processing and that you have the available memory to be able to cope with what you’re doing. Computers today are great at dealing with high volumes of large images but you still might find your editing software grinds to a halt if you ask too much of it.
Top Tips to Getting HDR Shots
- Use a tripod to keep your camera still.
- Set your camera to AEB to capture your images.
- Keep your exposures close together, no more than two or three stops apart.
- Take more images to get a wider dynamic range.
- Make use of the tools in your HDR blending software and work conservatively to avoid that ‘cartoon’ look often associated with HDR.
Further Resources
- What is HDR Video? 3 Ways to Create High Dynamic Range Video: High Dynamic Range photography is one of the most popular forms of computational photography, but did you know you can make HDR video, too?
- How to Make a Long Exposure High Dynamic Range Photo: Long exposure HDR is the same as regular HDR photography, except that longer exposure times are used. Long exposure HDR creates a very particular look. Some subjects, such as water or clouds, benefit from a lengthened exposure time that blurs their movement, while others, like the night sky, require long shutter speeds to be correctly exposed.
- Creating an HDR Time Lapse with SNS-HDR Pro: How to shoot and post-process a high dynamic range time-lapse video
Final Thoughts
HDR is often misjudged and photographers can be a little snobby about it. Don’t let that put you off though, using HDR blending in the right way can produce some really amazing images. The best ones aren't instantly recognisable as an HDR blend.
The key to a great looking HDR is to first do the best possible job you can when taking shots. That means avoiding movement so that you don’t get ghosting and taking more pictures with the exposures closer together in order to take advantage of the greatest dynamic range you can.
When you’re
blending, don’t just go for the standard settings. They’re a great start, but
only a start: you should play with the sliders until you feel comfortable
about what they do and the effects they achieve. Remember that less is more, and
although you’re trying to bring the best out of the tonal ranges you should
keep the saturation, structure and sharpening effects to a minimum in order to
maintain a realistic look.
