Image Map Tool

Images are scaled before display since the dynamic range of the data generally
does not match the number of pixel values available. The simplest way is to
map the minimum value of the data to the lowest pixel index and the maximum
value to the maximum index. This is almost what the browser does but it
first examines the histogram of the image and excludes a fraction of the
smallest and highest values in the data. When these fractions are small,
this approach excludes "unusual" pixels that can otherwise have a malodorous
effect on the display. These fractions are the hbot and htop parameters
which default to 0.001 and 0.999 thereby excluding 0.1% of the small and
large values. They can be adjusted to affect the min/max range. The
other parameter is a "gamma" which controls the shape of the mapping
between the limits. Gamma is the power of the transforming function. A gamma
of 1 is a straight line. A higher gamma shows higher contrast and emphasizes
bright structures. A gamma less than 1 emphasizes dark structures.

Note that changing these parameters only affects subsequent image displays
since it only affects the mapping of the image values to the pixel values
and not the colors/brightness associated with the pixel values.

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