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Color Look-up Tables
Substituting a palette of colors for the brightness values of a monochrome image produces a false-color or pseudo-color result that in some cases makes it easier to see small changes in brightness, or to compare the brightness of features. Because most people can see color, and can distinguish hundreds of colors, vs. only tens of gray scale brightness levels, this seems like an appealing idea and is very widely used.
If the color look-up table (CLUT) has colors that change gradually, for instance through a rainbow or heat scale, the overall impression of the image is retained but small changes are not easily detected. If, on the other hand, the colors oscillate wildly or randomly, small changes become visible but the gestalt of the image is lost. Finding a color table that suits the needs of a particular image and situation is difficult at best. This interactive tutorial illustrates the substitution of colors from a table for the grayscale brightness values of the original pixels.
The tutorial initializes with a randomly selected specimen appearing in the Specimen Image window. The Choose A Specimen pull-down menu provides a selection of specimen images, in addition to the initial randomly chosen one. The Choose A LUT pull-down menu provides a selection of several Look-up Tables (which are displayed) which produce the resulting Output Image shown on the right.
Contributing Authors
John C. Russ - Materials Science and Engineering Dept., North Carolina State University, Raleigh, North Carolina, 27695.
Matthew Parry-Hill, and Michael W. Davidson - National High Magnetic Field Laboratory, 1800 East Paul Dirac Dr., The Florida State University, Tallahassee, Florida, 32310.
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