True HDR images are created from a series of three or more individual exposures created from a camera mounted on a tripod, each with a different exposure value.
But you can create a psuedo-HDR image from a single exposure that has the same look.
The image above is an example of a pseudo-HDR image created from a single original image. Created with a program called Dynamic HDR (available from Mediachance.com), this image used a moderate amount of the HDR effect. Stronger use of the effect creates images that are obviously manipulated. This image is perhaps just over the line, and the trained eye can easily see that some kind of HDR effect was used.
This image uses a lesser amount of HDR manipulation. Most viewers probably wouldn’t think it was manipulated. But the HDR effect helped add detail in the shadow areas while retaining saturated colors.
The concept of HDR, High Dynamic Range, is to reduce contrast between the darkest and lightest areas of the image. In a normal outdoor image, particularly one taken on a bright, sunny day, because of the limitations of the photographic process — either film or digital capture hardware — you’ll see either highlights that are completely white or shadows that are completely black. That’s not always bad. But sometimes, you may want to retain detail in both highlight and shadow areas, and that’s where an HDR effect can deliver.
HDR works primarily by reducing contrast, but the resulting visual effect is increased detail in the image. Instead of seeing areas of complete black or complete white, the viewer sees detail and gradations of color everywhere in the image. Used in moderation, the HDR effect adds the feeling of increased sharpness and definition to an image.
Recent versions of Adobe Photoshop can produce an HDR effect. There are at least a dozen specialized software products on the market that generally do a better job. There are even some freeware products that produce the effect.