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Multispectral and true-color images are often enhanced using
histogram-based methods, usually by adjustment of color components after
transformation to a selected secondary color system. Enhancement aimed
toward the preservation of certain important perceptual qualities generally
calls for the secondary coordinate system to be perceptually based.
However, independent modification of the secondary components seldom uses
the full extent of the RGB gamut unless some color values are clipped at
the RGB boundaries. Preserving perceptual attributes is sometimes less
important than obtaining the greatest possible color contrast improvement.
This is especially true for color composites derived from multispectral
images, which have no significant basis in human perception.
We developed
new, multivariate enhancement techniques, such as "histogram explosion,"
which are able to exploit nearly the full RGB extent without clipping.
While not
generally based upon a perceptual model, these methods can preserve original hue
values when parameters are chosen properly. Experimental results
demonstrated that dramatic improvement in the color contrast can
be achieved through these multivariate histogram modification techniques.
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