A Photo Illusion

Photoshop is perhaps the best gift that I was ever given. While taking pictures is my main artistic release, messing around on Photoshop comes in at a close second. And it doesn't even take long to drastically alter the mood of a picture, either. Take this picture of Chicago shown below. The first one is bright, vibrant and full of energy. The second one is darker, more dismal and slightly ominous, but there's nothing to really indicate why you feel that way, making it slightly unnerving.
Come to think of it, that's kind of scary that I make images like that in my spare time.