The acronym HDR stands for High Dynamic Range (32 bit editing). In Adobe's implementation within Photoshop CS2, this is accomplished by using a series of photographs which one takes in the same manner as with previous blending techniques, and then, using floating point 32-bit (per channel) math, merging these files automatically into one huge high dynamic range image. Reading Michael Riechmann's tutorial "Merge to HDR in Photoshop CS2" intrigued me, so I began investigating further. Industrial Light and Magic developed the OpenEXR format in response to the demand for higher color fidelity in the visual effects industry. Roger Clark has done some thorough investigation comparing the dynamic range of digital, transparency, and print films, and Norman Koren has also done some exhaustive testing with RAW format conversion and tonality. It's all very fascinating—if only we had printers that were capable of better than 8-bit printing!
Posted by DAVID EMERICK