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Preface

The title of this book, Grokking the GIMP, is drawn from Robert A. Heinlein's classic science fiction novel Stranger in a Strange Land. His story is about Valentine Michael Smith, the only survivor of the first human expedition to Mars and raised from infancy by Martians. The rescue mission arrives twenty years later to bring a young man knowing nothing of his own kind back to earth. The story recounts his repatriation and his adventures as he comes to grok the human race and his place in it. Grok, a word he often uses, is the Martian word meaning ``to drink,'' but which also serves as a quasi-religious metaphor in the Martian culture for having a profound appreciation and understanding for something.

Heinlein's book, published in 1961, drew immediate acclaim in the science-fiction world, and the story became a part of the iconoclastic cultural sentiment of the 60s in the United States. Today, the word grok is a part of the U.S. computer hacker vocabulary, and its definition can be found in The New Hacker's Dictionary (see [1]).

So, do you want to grok the GIMP? When I first came across it in 1996, I did. I was writing an article and had some photographs of poor quality I wanted to touch up and enhance before including them. I had heard about the GIMP so I downloaded it from the Internet and compiled it. When I ran the program, it popped up a small toolbox. Without too much trouble, I discovered how to open image files and access the image menu containing all the GIMP functions and filters. Wow! It looked very cool...and powerful! But, I didn't have a clue how to use it to solve my photo problems.

I didn't know which functions to use and I didn't even really know what was wrong with my photos. I just knew they looked flat and washed out. I wanted them to look better, and that's what got me interested in the GIMP. I felt compelled to learn about it!

I started to look for help. I searched the Web, checked out books from the library, and little by little discovered useful things about the digital touchup and enhancement of photos. It was a slow and frustrating process, and it seemed like there was no unified, conceptual treatment of what I wanted to learn.

The most annoying thing was that almost every book I picked up was full of tips and tricks. Tips and tricks? I felt like I was getting advice on betting the ponies. I didn't want tricks; I wanted the ideas. What is photo touchup and enhancement? Where's the beef? How could I work on my photos if I didn't understand the basic concepts? Moreover, I wanted to learn the practical techniques used by the master artisans of digital image manipulation. Out of the hundreds of functions and filters in the GIMP, which were the right ones to use, and why?

After a lot of detective work and filling in the blanks myself I finally felt I was beginning to grok what the touchup and enhancement of digital images was about. What's more, I was getting to know the GIMP tools more intimately. To share what I had learned, I wrote a tutorial called Photo Touchup and Enhancement with the GIMP and put it out on the Internet (see `http://www.geocities.com/SiliconValley/Haven/5179`).

That's the story of this book's beginnings and that explains the rationale for its underlying approach and philosophy. Working with digital images requires some understanding of what needs to be done. It's not a ``choose the right tool, one click, and you're done'' subject. Most books on digital image manipulation would have you believe the contrary...and perhaps they're right. However, that is not what this book is about. It is not about tips and tricks, and it's not a collection of recipes for solving someone's favorite image manipulation problems. It is first about understanding image manipulation concepts, second about knowing which GIMP tools are most effective, and third about the savvy use of these tools.

Many factors have contributed to the style and content of the material presented in this book. My educational training in signal processing, my professional work in various areas of imaging and image processing, the research I've done on colorspaces and image manipulation, and lots of experimentation with the GIMP. The result is a book that covers many areas of working with digital images, including touchup and enhancement, compositing, 3D rendering, and the presentation of graphics on the World Wide Web. This book also gives a unified and in-depth introduction to layers, selections, masks, colorspaces, and the use of blending modes.

This book is released under an Open Publication license. Please read the license agreement carefully. In a nutshell the license permits the book to be redistributed freely in all electronic forms including CD and for commercial profit. It may not, however, be commercially printed and distributed in paper form without permission from the author and publisher. It can be printed for personal use and for non-commercial distribution. Modified versions of the book must also adhere to the licensing agreement. Now, let's learn the GIMP, and, as Valentine Michael Smith might have said, ``May you grok it in fullness!''

> Carey Bunks
> Senior Scientist
> BBN Technologies
> Cambridge, Massachusetts
> October 26, 1999

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