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ADOBE PHOTOSHOP CS2
User Guide
High Dynamic Range images
About High Dynamic Range images
The dynamic range (ratio between dark and bright regions) in the visible world far exceeds the range of human vision
and of images that are printed or displayed on a monitor. But whereas human eyes can adapt to very different
brightness levels, most cameras and computer monitors can capture and reproduce only a fixed dynamic range.
Photographers, motion picture artists, and others working with digital images must be selective about what’s
important in a scene because they are working with a limited dynamic range.
High Dynamic Range (HDR) images open up a world of possibilities because they can represent the entire dynamic
range of the visible world. Because all the luminance values in a real-world scene are represented proportionately and
stored in an HDR image, adjusting the exposure of an HDR image is like adjusting the exposure when photographing
a scene in the real world. This capability lets you create blurs and other real-world lighting effects that look realistic.
Currently, HDR images are used mostly in motion pictures, special effects, 3D work, and some high-end photog
raphy.
A
B
C
Merging images of different exposures to create an HDR image
A.
Image with shadow detail but highlights clipped
B.
Image with highlight detail but shadows clipped
C.
HDR image containing the dy
namic range of the scene
In Photoshop, the luminance values of an HDR image are stored using a floating-point numeric representation that’s
32 bits long (32-bits-per-channel). The luminance values in an HDR image are directly related to the amount of light
in a scene. This is not so with (non-floating point) 16-bits-per-channel and 8-bits-per-channel image files, which can
store luminance values only from black to paper white; this represents an extremely small segment of the dynamic
range in the real world.