Computer Graphics for Java Programmers by Leen Ammeraal is a damn good book and the most complete introduction to computer graphics that I've seen. A professor of mine once called it "the SICP of computer graphics." In that respect, it has clear explanations and great exercises. However, it is also dense and math-heavy, so it will take some discipline to work through the book.

If you just want to play around with graphics or don't like to program in Java, there are programming environments made especially for programming graphics like Processing [http://processing.org] and Nodebox [http://nodebox.net/]. Both are free and have tutorials readily available.