Website Background

This is an awesomely designed background for a website.

As you scroll down the page the image changes to something different. It is a very simple design but it has a huge effect I thought. At first you don't really notice it as you read the page and scroll down slowly, but once I realized that the sides were different it made me wonder how they had changed. I sped up the scrolling and figured out how they did it. I'm guessing both images are always there in the background and then they use the color gray that fades to black in the foreground to filter out which image is being shown at the certain spot in the page. That is a really cool idea. I feel that same idea could be used in other types of advertising or billboards. Simple yet effective design.