One of the most important kinds is the Photoshop file format. You can read the entire specification, current as of 2013, updated on Adobe’s website. The more of it you read, the more you learn about the history of commercial software. Because Photoshop has to be backwards-compatible, and it has to deal with every kind of image imaginable, and it ultimately has to do that perfectly for millions of people.
You might think that a Photoshop file is just, like, a bunch of pixels. But not at all —- via Postlight