High Dynamic Range Imagery
HDRI = High Dynamic Range Imagery. Take multiple photos of a wide contrast scene, varying the exposure up and down to capture the full range of data available. Using special software, you combine the images, and use tone-mapping to convert the scene-wide contrast into "micro-contrast". This compresses the tonal range a bit, and enables details that would have been lost to come through.
Here's some images I made a couple years back to explain it...
http://www.vaughnsphotoart.com/misc
http://www.vaughnsphotoart.com/misc
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Labels: Canon 5d Mark II, HDR, HRDI, photography