High Dynamic Range Imaging

This article from Wikkipedia gives insight to photographic techniques using HDRI.

In image processing, computer graphics, and photography, high dynamic range imaging (HDRI or just HDR) is a set of techniques that allows a greater dynamic range between the lightest and darkest areas of an image than current standard digital imaging techniques or photographic methods. This wide dynamic range allows HDR images to more accurately represent the range of intensity levels found in real scenes, ranging from direct sunlight to faint starlight, and is often captured by way of a plurality of differently exposed pictures of the same subject matter.^[1][2][3]

In simpler terms, HDR is an image processing technique that attempts to make pictures look more natural. Non-HDR cameras take pictures at a single exposure level. This results in the loss of detail in bright or dark areas of a picture, depending on whether the camera had a low or high exposure setting. HDR compensates for this loss of detail by taking multiple pictures at different exposure levels and intelligently stitching them together so that we get a picture that is clear in both dark and bright areas.

The two main sources of HDR imagery are computer renderings and merging of multiple low-dynamic-range (LDR) ^[4] or standard-dynamic-range (SDR)^[5] photographs. Tone-mapping techniques, which reduce overall contrast to facilitate display of HDR images on devices with lower dynamic range, can be applied to produce images with preserved or exaggerated local contrast for artistic effect.

High-dynamic-range photographs are generally achieved by capturing multiple standard photographs, often using exposure bracketing, and then merging them into an HDR image. Digital photographs are often encoded in a camera’s raw image format, because 8 bit JPEG encoding doesn’t offer enough values to allow fine transitions (and also introduces undesirable effects due to the lossy compression).

Any camera that allows manual over- or under-exposure of a photo can be used to create HDR images. This includes film cameras, though the images must necessarily be digitized for processing.

Some cameras have an auto exposure bracketing (AEB) feature with a far greater dynamic range than others, from the 3 EV of the Canon EOS 40D, to the 18 EV of the Canon EOS-1D Mark II.^[8] As the popularity of this imaging technique grows, several camera manufactures are now offering built in HDR features. For example, the Pentax K-7 DSLR has an HDR mode which captures an HDR image and then outputs (only) a tone-mapped JPEG file.^[9] The Canon PowerShot G12, Canon PowerShot S95 and Canon PowerShot S100 offer similar features in a smaller format.^[10] Even some smartphones now include HDR modes^[11].

These techniques are used often in photography and can be used extensively during photo tours.