This book is very old for an IT book; it's from 2005, and it has not aged very well. Furthermore, it was probably not a very good book when it came out in 2005 in the first place.
First of all, this is a rather superfluous introduction to ImageMagick, and the author has desperately tried to fill 300 pages; lots of pages are really wasted on very irrelevant content, like the extensive part on the drawing operators (really?) and the relatively large part on APIs that have not aged very well (Perl? PHP? C? And no Java?). Since I think it is a rather superfluous introduction, I think the title 'Definitive Guide' is somewhat misleading...
Most content is a verbatim description of the filters with accompanying images. There is little background information on the actual filters; for example, on the -equalize filter, the author writes
ImageMagick can also apply histogram equalization to an image.
but the author does not specify on what histograms (R,G and B? H.S. and V?) This is not something I would expect from a book that describes itself as a 'Definitive Guide'.
I gave 2 stars because I learned a few new filters that I did not know before, but in general I would not recommend this book....