USAGE: autolevel [-c colormode] [-m midrange] infile outfile
USAGE: autolevel [-h or -help]

-c .... colormode ..... colorspace/channel to use to compute
....................... min, max, gamma statistics; choices are:
....................... gray, intensity, luminance, lightness, brightness,
....................... average, magnitude, rgb; default=luminance
-m .... midrange ...... midrange value for autogamma part of script;
0<float<1; default=0.5

PURPOSE: To modify an image to automatically stretch the dynamic range between full black and white and automatically apply a gamma correction.

DESCRIPTION: AUTOLEVEL modifies an image to automatically stretch the dynamic range between full black and white and automatically apply a gamma correction. The minimum, maximum and gamma values may be computed from various graylevel representations of the image or individually channel-by-channel. The script then passes these values to the IM function -level.

ARGUMENTS:

-c colormode ... COLORMODE is the colorspace/channel to use to compute the minimum, maximum and gamma values. The choices are: gray, intensity, luminance, lightness, brightness, average, magnitude and rgb. Values of gray and intensity are equivalent. The default is luminance.

Gray or Intensity uses statistics from -colorspace Gray.
Luminance uses statistics from -colorspace Rec709Luma.
Lightness uses statistics from the lightness channel of -colorspace HSL.
Brightness uses statistics from the brightness channel of -colorspace HSB.
Average uses statistics from the first channel of -colorspace OHTA.
Magnitude uses aggregate statistics from all the channels.
RGB uses statistics independently from each channel of -colorspace RGB.
See definitions at: http://www.imagemagick.org/script/command-line-options.php#colorspace

-m midrange ... MIDRANGE is the midrange value for the autogamma technique, which uses the formula: Gamma = log(mean)/log(mid-dynamic-range). Values are in the range 0

CAVEAT: No guarantee that this script will work on all platforms, nor that trapping of inconsistent parameters is complete and foolproof. Use At Your Own Risk.