The HIST_EQUAL function returns a histogram-equalized byte array. The HISTOGRAM function is used to obtain the density distribution of the input array. The histogram is integrated to obtain the cumulative density-probability function and finally the lookup function is used to transform to the output image.
The resulting array is always of byte type and is scaled from 0 to the value set by the TOP keyword.
Note: Floating-point arrays should not have small ranges, (e.g., less than around 255) unless a binsize is specified.
This routine is written in the IDL language. Its source code can be found in the file
subdirectory of the IDL distribution.
Create a histogram-equalized version of the byte array,
, and display the new version. Use a minimum input value of 10, a maximum input value of 200, and limit the top value of the output array to 220. Enter: