I think your friends at Wikipedia differ on your definition, as do I on the 32-bit reference. Maybe Photomatix is 32-bits? Otherwise, it is a high dynamic range image made from several others that are blended together, in its simplistic form.
From
High dynamic range imaging - Wikipedia, the free encyclopedia
In
computer graphics and
photography,
high dynamic range imaging (HDRI) is a set of techniques that allows a greater
dynamic range of exposures (the range of values between light and dark areas) than normal digital imaging techniques.
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HDR images require a higher number of bits per color channel than traditional images, both because of the linear encoding and because they need to represent values from 10−4 to 108 (the range of visible luminance values) or more. 16-bit ("
half precision") or 32-bit
floating point numbers are often used to represent HDR pixels. However, when the appropriate
transfer function is used, HDR pixels for some applications can be represented with as few as 10–12 bits for luminance and 8 bits for
chrominance without introducing any visible quantization artifacts.