As a follow up to my recent presentation on HDR imaging, I thought I’d write a series of blog posts summing up my procedure for shooting and processing HDR images.

HDR, or High Dynamic Range photography expands the range between the darkest dark and brightest white in your images. Since your camera can’t see as great a dynamic range as you eye, a little photo trickery is needed to create something that represents what your eyes can see in a high contrast situation.

When is HDR helpful?

HDR’s greatest usefulness is in high contrast scenes, particularly with back lit subjects. Some common situations where you might shoot HDR are:

• At sunset when you want to retain the colours of the sky while not allowing the foreground to become a silhouette
• When shooting towards the sun in a scenic or landscape shot
• When shooting on an overcast day, to retain cloud texture
• When shooting indoors where bright windows would otherwise turn completely blow out
• Any other time where your camera’s histogram can’t contain all the pixels without them piling up on the ends. (see the histograms in the graphic above)

Shooting Procedure

The first step to creating great HDRs is to get it right in the field. We’ll need a bracket of photos, often three but sometimes more, that between them capture detail in the brightest highlight and the darkest shadow.

The easiest way to shoot the files is by using your camera’s Aperture Priority Mode (That’s A on a Nikon SLR and Av on a Canon). You can also do it in manual mode, but if you do, you’ll want to adjust your shutter speed, rather than your aperture to capture the different exposures. Our goal in capturing HDRs is to get a bracket of images that are as identical as possible, except for the over all brightness. Since changing the aperture will affect the amount of depth of field in the image, we want to lock down the aperture and use shutter speed as the variable for our images.

In most moderately high contrast scenes, shooting a bracket of three exposures should be sufficient for HDR. A “correct” exposure, one that is 2 stops underexposed (¼ the shutter speed of the normal shot) and one that is 2 stops overexposed (4 times the length of the normal shutter speed). Many Nikon cameras only allow you to vary the exposure of a bracket by 1 stop, but they will often allow you to take a bracket with 5, 7 or 9 shots. A 5 shot bracket at 1 stop increments will give you the same range, with some intermediate shots between the extreme values. These can sometimes increase the quality of your HDR, but 5-shot brackets will very quickly fill your hard drive, so you might want to delta the intermediate exposures in post processing.

In very high contrast scenes, like dark interiors with bright windows or when shooting toward the sun,  you may need greater range. What I typically do in these situations is to set my auto bracketing to 1 stop increments.  If it’s very important to preserve highlight detail, I’ll centre the first bracket on -2 (resulting in -3, -2, -1) and then shoot a second bracket centred on +1 (0, +1, +2). If the shadow detail is more important, I’ll centre the two brackets on -1 and +2. Otherwise, I can point my camera’s metre at the brightest part of the scene and take a photo. Then start shooting a series of images with brighter exposures in one to two stop increments until I get one with good detail in the darkest shadows (or at least the darkest ones I’d like to see into).

If you want to keep track of your HDR brackets, you can shoot a visual cue before and after the bracketing, like one finger before the bracket and two fingers afterward. This will help you see where the brackets start and end if you use a visual browsing program like Lightroom, Bridge, Aperture, Elements Organizer or Picasa. Just remember that the finger shots will eat up additional hard drive space and that you need to shoot them before/after you turn the bracketing on or off, so the shots aren’t part of the bracket.

 Additional Considerations

If you can shoot raw with your camera, doing so will give your HDR editing software more information to work with. If you have no choice but to shoot JPEG, if your camera gives you picture styles, try to set it so the contrast is low and the sharpening is turned off.

While the software can do a pretty good job of aligning images, a tripod is a handy thing to have when shooting HDR.  Just remember if you’re just shooting a standard bracket, the brightest shot will take 4 times longer than a standard exposure, so you’ll very easily venture into camera-shake territory without a tripod. A cable release is also helpful, but if you don’t have one, use your camera’s self-timer instead. If you have the 2 second self-timer, you’ll be much happier than if you only have the 10 second self-timer.

In the next instalment in the series, we’ll look at how to prepare camera raw files for the HDR process