Day for Night effect with Canvas image filters
A simple method for adjusting the saturation, hue and levels of an image to make a photo shot during the day seem more like it was shot in the evening.
This effect is referred to in cinema as "Day for night" (see http://en.wikipedia.org/wiki/Dayfornight).
The filter code is based on "Image Filters with Canvas" by Ilmari Heikkinen (http://www.html5rocks.com/en/tutorials/canvas/imagefilters/)