Enhancement. A gimg provides functions to select a statistically significant range of image values for display. The option -func has four values: NONE, LINEAR, HISTS and HISTEQ. A value of NONE defines no function to automatically select optimal data ranges for display. Instead, data ranges are manually specified by the options -low0, -high0, -low1, -high1, -low2 and -high2 for the tthree respective data channels. A value of LINEAR defines a linear function based on both standard deviations and means of the image data. A value of HISTS defines a stretch function based on the image histogram. A value of HISTEQ defines a stretch function based on an accumulated image histogram. In addition, the option -range defines a way to calculate a range of image data for enhancement. The option -range has two values: MEAN and DETAIL (default). MEAN defines a range calculation in which it is centered at the mean value, plus and minus the number of standard deviation, which is defined by the option -std, for the low and high boundaries. DETAIL defines a range calculation in which the same amount of tails of the original range are cut off at both the low and high ends to make new boundaries. The total amount of tails (in percentage) to be cut off are also defined by the option -std. 

Once a value of the option -func is configured, data range boundaries associated with the options -low0, -high0, -low1, -high1, -low2 and -highh2 are updated with new calculated values. An exception is NONE of the option -func, which keeps these boundary values as they were. 

The following examples show a raw Space Shuttle image of the city of New Orleans, Louisiana (upper left) and three enhanced images with different options. The raw image was cropped from the original Space Shuttle image archive, sts030-046-071, taken on May, 1989.
 

-func NONE	-func LINEAR -range MEAN
-func HISTEQ -range MEAN	-func HISTS -range MEAN