This very old book has nothing of value to say on hardware that you can't find in a computer museum, and even its programming environment is a dinosaur. However, the mathematical formulas for the special effects described, as well as the demonstration images make this text a timeless classic. It shows in plain language how to perform such Photoshop effects as solarization simulation, the twirl effect, the fisheye lens effect, the "pinch" effect, and the ever-popular oil painting effect. It shows how simple mathematical manipulation of pixels can yield very interesting results, such as the "Chesson Effect" which manipulates an image into looking like something from the late 1960's painted on glass, and the funhouse mirror effect by manipulating transcendental functions in combination with the image's original pixel values. Once you see how these effects are done, it will stimulate your imagination to create your own original visual effects. The book is considered such a cult classic that a webpage exists for it. Since Amazon throws out reviews with web addresses in them just type "Beyond Photography - The Digital Darkroom" into Google and it should be at the top of the list of links. The website includes - but is not limited to - updates by the author, a user's group, and a zipfile of the original source code. The list of transforms for which there is C-like pseudocode in the book is as follows:
Making a Negative, Logarithmic Correction, Simulated Solarization, Contrast Expansion and Normalization, Focus Restoration, Blurring, Enlarging by an Integer Factor, Shrinking by an Integer Factor, Mirroring, Turning the Picture Upside Down, Rotating by 90 degrees Clockwise, Rotating by 90 degrees Counterclockwise, Averaging Three Images, Weighted Average, Relief, Op-Art Effect, Warping one image with another, Fisheye Lens, Funhouse Mirror, Pinch Effect, Polar Transform Effect, Cartesian Transform Effect, Glass Effect, Spin Painting, Composites with Mattes, Arbitrary Composites, Plotting a Grid, Oil Painting, Picture Shear, Slicing, Tiling, Melting, Making a Matte

This book is only 116 pages long, but it has a wealth of information about digital image manipulation. Not really the interactive kind you might do in Photoshop, but the math behind some interesting transformations. This book presents a simple image manipulation language (popi) and the interpreter for it as well. I think that is this available on the net too. Overall this is a great book for anyone interested in getting into the programming/math side of image manipulation.

Oh, many of their sample images are of famous people from the Unix community at Bell Labs.