USAGE: exposure -a amount infile outfile
USAGE: exposure [-h or -help]

-a amount ..... amount of exposure change in percent; -100<=amount<=100;
............... positive will be brighter and negative will be darker;
............... default=0 (no change)

PURPOSE: To change the exposure level of an image.

DESCRIPTION: EXPOSURE changes the exposure level of an image to make it either brighter or darker. It uses -level 0x(100-amount)% to make it brighter and +level 0x(100+amount)% to make it darker.

ARGUMENTS:

-a amount ... AMOUNT of exposure change in percent. Values are floats between -100 and 100. Positive values increase exposure (make it brighter) and negative values decrease exposure (make it darker darker). The default is zero or no change.

NOTE: This script requires IM 6.4.2-0 or higher due to the use of +level, if making the image darker.

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.