To make “impossible” pictures possible. To capture a scene that is simultaneously too dark and too bright.

To the human eye light & dark are relative terms. How dark is black, how bright is white? How black is ink? How white is paper? How dark is your TV or computer monitor when turned off? How bright is your slide projector bulb? How bright is the sun? In the everyday world we can see with our eyes the darkness of a cave and the brightness of a the sun but we cannot capture with our eyes or with most devices, both extremes of intensity at the same time.

All means of recording light are limited to a certain range of brightness or light intensity. This is true quite clearly with typical photography. For example you've probably taken a photograph of people in the shade of a tree but later found out that the beautiful sunlit scenery beyond the tree is greatly overexposed..

The goal of photography is to capture what we see. But what our eyes and mind see is not what the camera sees. The camera sees an instantaneous sampling of the physics in play in the scene, our eyes & mind, however, see many small areas of the scene at different "exposures" and calculates a translation and interpretation of what exists using the best information it saw. Similarly HDR imaging is a technique to record the nearly full dynamic range of light of a scene, pick out the best sampling of information and . display it in a manner that attempts to recreate the feeling and ambience and human interpretation of the original scene.

Think of the intensity of light in terms of musical octaves, each higher light octave being twice as bright as the previous. A typical outdoor scene (without looking directly at the sun) covers about 13 octaves or zones of brightness from the dark shadows deep in the bushes, to the glare from the water or sun reflections from windows. We can see this wide dynamic range of light because our eyes are dynamic instruments, the pupil is continually changing to create the correct “exposure” for where we are looking. The brain is a marvel of computation that uses continual comparison and localization and interpretation of many small areas of the scene to build up a mental picture of the entire environment without seeing it all at once. From the black snake in the grass under the bush to the white clouds in the bright sky. No normal photograph can capture this range of light dynamics. Normal film negative and typical digital cameras can record about 9 zones of brightness. Typical computer monitors can display about 8 zones, and ink on paper can only display about 7 zones.

Another major use for full range HDR images is to archive a scene in full detail and to provide accurate light intensity and light direction information to 3D graphics programs. This technique is used to provide near-real lighting information for artificial scenes created by 3D graphics.
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Computer programs to create an HDR image use a similar process but execute it in much finer detail and with more sophistication. Often 3 or 5 or 7 or more images are combined depending of the accuracy and range of light dynamics needed. By artfully condensing the 13 zones of an outdoor scene into the 7 zones displayable on paper we can come close to representing the mental impression of the original scene.
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A more common use of HDR images is to use the full light range captured in an HDR image to produce an image that is not over or under exposed when displayed on paper or on a computer screen. This technique is what is displayed in this website in our gallery and in these discussions of HDR Imaging. This technique essentially compresses (or maps) the extreme light and dark values of the HDR image into the 8-bit range of color channel values that can be represented on the computer screen or on paper. This process is often called "Tone-mapping" and the result is more properly called a "Tone-mapped HDR Image". This distinction though is often omitted when discussing HDR because it is usually obvious how the image is being used.

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