The Tri-Filter Effect, also known as the Harris Shutter, is where three photos are taken and merged together. Unlike TiltShift, the Tri-Filter takes the three images with different color filters: Cyan, Yellow, Magenta (some refer to as the Red/Green/Blue). Since the three photos are taken one after the next, any areas that move will show as a ghost on the final photo in a particular color. Imagine a person walking across the street, if you take three photos quickly, the background and road are still but you will have three of the people as they progressed between the time you snapped the shot.
Take that idea and apply it to anything that moves a bit like water or clouds. You can also move the camera to cause a color shadow on the objects in the photo. A few examples sites/pages: Tri-Filter Landscapes, Harris Shutter Flickr Discussion, “Apply Filter” looking at Tri-Filter photo options.
Since we have a iPhone in our hand and don’t want to haul around a bunch of filters to change out, there is an app to handle that magic for us. HarrisCamera will snap the three photos with digital color filters across 1, 2, 5, or 10 seconds. Then, save the image to your iPhone Album, email or share on Facebook, Twitter or Tumblr.