This is similar to the auto-levels feature in Photoshop: the red, green, and blue channels are re-mapped from their original values to a min of 0 and a max of 255. This provides better contrast (and often, saturation), and generally removes major color casts. It is not a substitute for proper color editing, but is useful where images are unlikely to be color corrected before being uploaded.
•Add an up-to-date JQuery library to the HTML head (ie, src="http://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js")
•Add the colorLevels script to the HTML head (ie, src="js/colorLevels.js")
Note: this script will replace all img tags with canvas tags, so edit your CSS accordingly. For compatibility with browsers that have JS disabled, leave in CSS for img (the images will simply remain unedited). Setting the width on the original img tag will determine the number of pixels the script runs through, so fixing a smaller img width will speed up the script.