What is HDR photography? How to shoot and process high dynamic range images

October 15, 2015Jeff Meyer

So what is HDR photography all about? In short, HDR techniques allow you to take pictures of high-contrast scenes and preserve all that important shadow and highlight detail. But it comes with a lot of jargon. Here we answer all the common questions about HDR photography.

What does HDR stand for?
HDR stands for high dynamic range; and the abbreviation is often used in a longer form, HDRI – high dynamic range imaging. HDR is a form of photography that enables you to create a picture with a greater dynamic range than is usually possible.

To understand what it is and to appreciate its use, you first need to have a grasp of what dynamic range is all about.

So explain dynamic range to me
Dynamic range is a measure of the range of different light levels – from the darkest black to the brightest white – that can be recorded or displayed by a device. It defines the amount of contrast you can capture or show without losing detail at the extremes.

The dynamic range that can be captured with your SLR is greater than can be displayed on your monitor.

Why is this important?
Some scenes contain too much contrast for us to capture successfully with our cameras. We avoid taking pictures in the midday sunshine as our cameras can’t cope with the full range of light levels. Low-light scenes are another common problem area – we can expose successfully for the shadows, but not for the brightly-lit areas or vice versa.

SEE MORE: 20 tips for faster photo editing

Exposure for midtones

Are there ways around this?
Digital imaging has made it easier to resolve because we can see the result immediately and take remedial action. We can also use flash to help reduce contrast on a sunny day and use a graduated ND filter to balance the brightness difference between the sky and landscape.

What’s more, there are processing tricks we can use in Photoshop, particularly if we shoot in raw, that enable us to get information from the darkest and lightest parts of our pictures.

So where does HDR come in?
HDR enables us to shoehorn a greater range of brightness into an image in a way that a straightforward picture can’t achieve. A true HDR image is created from several shots of the same scene taken with slightly different exposures.

Each exposure captures part of the full tonal range. They are then combined into a single image with software. The trouble is that these true HDR images are hard to see…

What do you mean?
A true HDR image contains a far greater range of tones – too many, in fact, to be displayed on a normal computer monitor, or printed out on paper.

They are typically stored as 32-bit files – allowing 4.3 billion shades in each colour channel. By comparison, a standard JPEG image allows 256 (8-bit) shades per channel, and a raw file 4,000 (12-bit) to 16,000 (16-bit) shades per channel.

So what do you do with these very large files?
The next stage in most HDR images is tone mapping. Here the program uses the 32-bit HDR image to create an image with a contrast range that can be shown in print or on a monitor.

Each tonal value is remapped onto a scale that creates an image in which you can see detail in the brightest highlights and the darkest shadows, and without any clipping in these extreme areas of brightness. It’s this tonal mapping that creates the controversy with HDR.

Why the controversy?
Tonal mapping brightens shadows and darkens highlights, which slightly flattens the contrast of an image and increases edge definition.

But many HDR enthusiasts use the software to go further, creating an image in which all the detail can be seen clearly, but which no longer looks realistic. The effect is similar to that used in ‘hyper-real’ styles of painting. Some people like it, some don’t.

SEE MORE: Recover clipped highlight detail: how to rescue your over-exposed photos

Exposure for shadows

What sort of software do I need?
There are lots of HDR programs available – including some free ones. The best known is Photomatix Pro, but the latest version of Photoshop (CS5) has a built-in HDR facility.

HDR programs usually have a range of sliders to help you control the tone-mapping effect to your own taste.

How do I take pictures in preparation for HDR effects?
Essentially, the process is the same as that used for bracketing. The number of shots you need is largely dependent on the actual tonal range of the scene you’re shooting. The more contrast, the more shots you need.

Three is the usual starting point, but you may need to take as many as nine, each with a one-to-two stop difference. Some SLRs have an AEB (automatic exposure bracketing) function, which will enable you to do this without too much fuss.

SEE MORE: Truthful Tone-mapping: a quick guide to realistic HDR in Photomatix Pro

Exposure for highlights

What other settings should I use?
Your sequence of exposures should be as similar in content to each other as possible (although obviously, the brightness will vary). Any changes caused by movement can create a ghosting effect that the software will struggle with.

Set the focus manually, use a tripod, and set the exposure to aperture priority (so the depth of field remains constant). Set the camera to the fastest continuous drive setting available.

Is there an easier way?
Creating HDR images involves some effort at the time of shooting and processing but it’s relatively straightforward. However, there are easier ways.

A number of programs offer false HDR effects that can create realistic-looking HDR images from just a single picture. Similarly, a number of DSLRs and compacts now have built-in automatic HDR facilities that will take the sequence of pictures for you and compile them into your tone-mapped image in the camera itself.

SEE MORE: How to blend two photos for perfect exposure

How to shoot and edit your first high dynamic range image

One of the limitations of digital camera sensors is that they simply cannot record detail in both the shadows and highlights in high-contrast conditions. You’ll frequently encounter this sort of situation shooting outdoors on bright days, or when you’re photographing interiors or night photography scenes.

Landscape photographers typically resolve this by using graduated filters to balance the exposure between the land and the sky. However, there are limitations with this.

Not only are the filters expensive, they are fiddly to use, and the technique relies on a straight horizon for the best results as there’s no way to mask out a lone tree or standing stone that breaks through the horizon.

However, there is another solution. You can take several pictures at different exposures and combine them in the digital darkroom to create an image with an expanded range of tones. This is known as a High Dynamic Range image – better known as HDR photography.

Shooting HDR photography is not as complicated as it sounds. All you need to do is take a sequence of images by bracketing at different exposures, from underexposed to overexposed. How many images you need and what the difference in exposure between shots should be largely depends on what you’re photographing.

Here’s how to make a high dynamic range image.

SEE MORE: 77 photography techniques, tips and tricks for taking pictures of anything

HDR photography step by step

01 Keep it steady
As you’ll be combining multiple shots to make your final image, the composition needs to be exactly the same in each photo. This means a sturdy tripod is vital. You’ll also need to take steps to avoid any camera movement between shots, so use a cable release so you don’t have to touch the camera at all during the process.

02 Camera settings
Your aperture has to remain constant throughout the sequence, otherwise the depth of field will change between shots and this will make aligning them more of a challenge. So, switch to your digital camera’s A, or aperture-priority mode. Now the camera will vary the exposure by changing only the shutter speed. We used an aperture of f/11.

SEE MORE: The best camera settings for landscape photography

03 How many shots?
In most cases, three to five images with a one- or two-stop difference between one shot and the next is enough for constructing an HDR image, but if the scene has a very wide brightness range you may need to shoot five or seven frames. Most HDR software can process NEF files, so set image quality to raw format for the best results.

04 Auto Bracket
Activate your camera’s auto bracket feature. This will calculate and adjust the exposures in your sequence. There are two settings. One is the number of shots – three is the normal number, but some cameras let you shoot five. The second setting is the interval between the shots. This can be 1EV, 2EV or, on some cameras, 3EV.

SEE MORE: How to combine photos to achieve perfectly balanced exposures

05 Continuous mode
Now set your camera to the continuous shooting mode. If you have a choice of speeds, pick the fastest available. This will minimise any cloud and tree movement between each shot which can cause nasty ‘ghosting’. You’ll now be able to take all the shots you need for the HDR sequence without touching the camera.

06 Test shots
Take some test shots before starting. The longest exposure should show detail in the darkest areas, such as the shadows, while the shortest exposure should show detail in the brightest ones, such as the sky. Use the histogram to assess exposure. Our scene had a medium to high brightness range, so we took three shots at intervals of 2EV.

SEE MORE: The 10 Commandments of Landscape Photography (and how to break them)

07 Get HDR software
Download the free 15-day trial version of HDR Efex Pro 2 from Nik Software. We’ve installed it as a plug-in to Photoshop CS5. Browse to your images in Adobe Bridge and select the five raw files. Go to Tools>Nik Software>Merge to HDR Efex Pro. Your images should open in the HDR Efex Pro window. This can take several minutes.

08 Blend your shots
You’ll notice presets on the left panel of the HDR Efex Pro window. These are especially handy if you’re new to this technique. We used the Realistic Strong preset. These settings can be further refined using the sliders in the panel on the right side. We applied these settings: Stricture 48%, Blacks -44%, HDR Method Clean and Method Strength 35%.

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