Well over half of the book is spent on introductory concepts and "background" material, such as data structures for raytracing, implementation of reflection models, and a section on writing PPM-format graphics. The first 200 pages could easily be replaced with the words "This book assumes a reasonable level of familiarity with the raytracing algorithm."The example code is somewhat useless as it deals only with very basic photon mapping. None of the useful techniques are even mentioned, such as using shadow photons, building caustic maps, final gathering, or irradiance caching.Readers will probably learn just as much from any one of the dozens of free web pages that can be found by searching the Internet for "photon mapping." I wish I could have my money back.