 Computer graphics is used to create all sorts of images, but at the end of the day they're just pixels that are being given a certain color value. Computer scientists who work in computer graphics work out how to take an object. Do some calculations and translate that to a computer screen. For example, we need to think about an object's rotation, its position in 3D space, and its size. This also involves specifying colors mathematically. And working out what objects should appear in front of... and how to add shadows and reflections. Even working out which pixels to use to draw a circle or a line isn't that simple. In this chapter we're going to look at some of the challenges and some of the calculations needed to get the right pixels in the right places on the screen.