The main problem with this book is its title. It's not misleading exactly, but it doesn't tell you what it's all about.

The subtitle "Using Free Tools for Photographers" gives you a much better idea of what it is really about. Image Processing usually means algorithms for manipulating images in technical ways - edge finding, feature extraction and so on - and it is usually coupled with pattern recognition and artificial vision. This book is really about digital retouching of photographs - and as such it is fairly good but you need to know more accurately its subject matter. 

Rather than take the well-trodden path of explaining how to use PhotoShop or one of the other commercial pages this book focuses (pun?) on using free open source tools - mainly Gimp a general purpose image editor. As a long time user of PhotoShop (at work) and Corel (at home) I have often considered switching to Gimp but never managed to get into it. Reading this book has more or less persuaded me that Gimp is at least as good if no better than what I currently use.

The first two chapters of the book are well off topic in dealing with the fundamentals of photography and in particular digital photography. They deal with things like the effect of focal length on perspective and composition rules - the sort of thing you might find in any photographic book aimed at the technically minded. Chapter 2 explains the ideas behind vector and bitmap graphics and tries to sort out the details of colour and spatial resolution. You certainly need to know these basics, well perhaps not the rules of composition and some other purely photographic ideas, but they could just as reasonably be assumed. This said the ideas are well explained and there are some nice and simple illustrations of the ideas. It is at this point however you start to notice the poor quality of the black and white printing used for the examples. In some cases it doesn't help with making the point - especially when the point is about color balance say!

When we reach Chapter 3 the book still hasn't really got into its core topic. Now the subject is geometric manipulations - resizing, rotating and cropping. This is all very simple stuff and probably not worth more than a mention. There are lots of half empty pages with single photo illustrations of something fairly obvious. The only deep idea - that of interpolation is treated in a few paragraphs. The whole idea of information loss and redeployment as you resize an image would have been a better topic to concentrate on. This chapter is mostly a how to use Gimp and ImageMagick to resize, rotate and crop images.

Chapter 4 deals with color transformations - colour balance, contrast, brightness etc. Again this is basically a tutorial on using Gimp and its histogramming to correct images and create special effects. If you don't know about contrast and gamma then it's a good explanation. As already mentioned, the lack of color printing makes the color correct section harder to follow.

From this point the book begins to get into its core topics - the basics having been dealt with. Chapter 5 is about filters - again a tutorial on using the built-in filters in Gimp.  Chapter 6 is about photo retouching - red eye removal, object removal and so on. What the section on metadata is doing in this chapter I'm not at all sure.

The rest of the book is on special techniques. Chapter 7 is on HDR imaging using Qtpfsgui. It also has a good explanation of how HDR works.  Chapter 8 is about distortion correction - removing perspective, barrel, radial etc distortion. Then onto another "special technique" panoramas using image stitching provided by Hugin.

The final few chapters deal with video editing and using the Canon hack package. How interesting these topics are of course depends on your interest in video editing and whether you own a Canon.

This is a difficult book to sum up. It is mostly a set of tutorials on how to use open source free software to do fairly standard photo tasks. If you don't know the theory then it's a useful introduction. If you do know the theory then the tutorials simply point out how Gimp or some other program does the job. I enjoyed reading the book and the examples were mostly convincing. if low quality. What did strike me was the number of topics that were left out - what about unsharp mask filtering, noise removal, moire reduction, making your own filters, image compression, combining images and so on.

This is a book that would suit a technically-minded reader who might have missed out on some of the basics of photography. It might also suit a reader wanting to discover what open source image software can do. It's a well written book that is a mix of how it works with tutorials showing how to do it. A fun book for the right reader.