What is HDR Mode?
Before I explain what HDR Mode is, I need to explain dynamic range. In a short, easy-to-understand explanation, dynamic range is the range of lights and darks in an image. Don't get this confused with contrast, which instead relates to the difference between lights and darks in a nearby area. Take a read here if you want a more in-depth and more technically accurate description of Dynamic Range.
Unfortunately, digital cameras can only record within a certain dynamic range at one time. The exact range differs from camera to camera. At multiple times in your photography career, you've likely taken photos and found them to have either overexposed whites or underexposed darks, or even both. For example, you may have tried taking a photo of a building, only to find the foliage surrounding it has become very dark. No matter how much you adjust your exposure, you cannot seem to get everything to be reproduced accurately - you can't get a nice building without dark plants, or nice plants without a bright building.
The problem here is that your scene has a higher dynamic range than your camera can record in one exposure - the range of lights (building) to darks (bushes) is too great. This is precisely where HDR Mode can step in to help you take a nicer photo. In fact, if you haven't noticed already, HDR stands for High Dynamic Range!
The camera cannot record a broad enough dynamic range in one exposure to maintain nice detail in the shadows without overexposing the tricycle.
HDR Mode works by taking a number of photos (usually three) at different exposures in quick succession, and combining the right parts of these photos to produce an image with a higher dynamic range. The greater the difference in exposure between the three images, the greater the intensity of the final HDR result. To recycle the previous example; your camera may take a photo which provides a good balance of exposure between the building and the plants (so that the building is slightly too bright and the plants are slightly too dark), then take one photo a bit darker to replace the parts of the building which are too bright, then take one photo a bit brighter to replace the parts of the plants which are too dark. The result is an image with a nicely exposed building and foliage!
At a fairly moderate HDR intensity, more detail can be seen in the shadows, and the tricycle itself is not overexposed.
When and Why should I use HDR Mode?
You should only use HDR Mode when the dynamic range of your scene is too great for your camera to record, such as in the buildings vs plants example above; so long as it makes sense to use it and you are unhappy with the look of the image otherwise. For example, if you are taking a portrait photo, it is possible that the sky may be slightly overexposed. It doesn't make sense to take an HDR photo just to get the sky properly exposed (unless it's important to your photo), and you may not necessarily be unhappy with the sky being that way.
Furthermore, sometimes it may simply not be easy or convenient to take an HDR photo. As you can guess, things need to be pretty still for a successful HDR photo to be taken - if anything moves during the three exposures, the combination of the three photos will cause things to get blurry.
- Use a tripod, if you can. It is, however, possible to take an HDR photo without one if you can hold the camera still enough.
- Raise your shutter speed if possible.
- Models will have to pose very still.
- Anything which has a candid nature to it, such as street photography, running children, sports events, weddings, and so forth, are probably not going to work with HDR Mode.
- Still and relatively unchanging scenes, such as landscapes and architecture, work better.
Whatever you do though, do not use HDR Mode as an "effect" or "filter". Not only is it simply unintended for this sort of usage, but you're also ruining your photo. Seriously, don't do it.
How do I use HDR Mode?
Activating HDR Mode differs from camera to camera, so do a quick Google search or get your manual out to find out how to activate it. Not all cameras have the mode available. You can also manually take three different photos at varying exposures, or set your camera to do it automatically (once again, Google or manual), and put the photos together later either also manually or through specialised software.
An important thing to consider is the difference in exposure between your three (or more) different photos, otherwise you'll ruin your photo. This is especially important to think about if you're manually producing an HDR image. Some cameras will offer different options towards this (or even automatically decide), whereas others may not.
What NOT to do with HDR Mode!
When used incorrectly, without care, or too intensely, HDR starts to ruin an image. Colours will begin to look strange and contrast and saturation will go all over the place. You'll start to get white halos around objects and weird dark looking areas, or vice-versa. It will become increasingly difficult to distinguish depth in your photo. Never use this as an "effect" or "filter", it's just not a good look.
The colours are starting to look too funky, there are weird halos everywhere, and depth is being lost. A crime against photography!!
At this point, it's better to either tone down the intensity of HDR Mode or turn it off altogether and expose for the most important area of your scene. It's better to get an photo with one or two areas slightly over- or (usually) under-exposed, instead of one which is entirely ruined.
Alternatives to HDR Mode
If you want to altogether avoid the downsides of HDR Mode, you may want to opt for other methods which can sometimes, in fact often, work better.
If underexposed areas, such as the bushes, are your problem, it's usually pretty easy to digitally brighten the dark area with very little quality compromise, especially if you are shooting in RAW. Any image editing program, such as Photoshop, GIMP, and Lightroom should be able to do the job. I personally don't know much in the way of RAW images (Lightroom), but if you're working with raster images (Photoshop, GIMP), tools such as Curves and Levels will be very helpful in brightening the darker areas of your image. Take a look at this tutorial by cypher-neo for more information on working with RAW images.
Dark areas have been digitally brightened using the Curves tool.
In-camera options for doing this also exist. Nikon has the Auto D-Lighting system and Canon has the Auto Lighting Optimizer system for dealing with high dynamic range, and other brands may have similar such options too.
Dark areas have been digitally brightened using in-camera settings (specifically, Nikon's D-Lighting setting).
Unfortunately, it's not as easy to retain quality when darkening light areas; which is why it's better to underexpose rather than overexpose, and then brighten a greater portion of your image.
By overexposing (in order to get the ground nicely exposed), detail was lost in the highlights of the photo. No amount of skillful editing will bring these details back, leaving ugly flat grey areas!
Happy shooting! I hope this article has helped.