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Pseudocolor and Rendering

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. The Look-up Table Manipulation interactive Java tutorial illustrates a few popular color tables. Finding a color table that suits the needs of a particular image and situation is difficult at best.

Interactive Java Tutorial
Look-up Table Manipulation
Explore how to enhance feature visibility by using a variety of color look-up tables. 

Another less-used but very powerful way to enhance the visibility of image detail is to treat the brightness levels as elevations to generate a rendered surface representation. Human vision is highly adapted to interpreting surface geometry from the pattern of light that scatters in various directions. In a full implementation of this method, the specularity of the surface can be varied from mirror-like (polished metal) to diffuse (plaster of paris), and the light source can be positioned at an elevation and azimuth to reveal minor details without obscuring the rest of the structure. The Surface Rendering interactive Java tutorial shows several illustrations.

Interactive Java Tutorial
Surface Rendering
Discover how a rendered surface representation enhances feature visibility. 

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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