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A Book on General Image Editing Concepts?
halftrack asks: "Someone I know wanted 'Photoshop for Dummies' for Christmas because she wanted to learn how to use it properly (who hasn't struggled trying to draw a simple line?) However, having a strong disliking for any sort of vendor lock-in I went searching for a book that would teach image editing without tying it too strongly to Photoshop (or Gimp for that matter). However, all my searches turned out blank. Thus I was wondering if there exists such a book, or is the field too diverse? The ideal would be a (thick) book that would cover the basic concepts (layers, paths, selections, channels etc.,) before presenting how these concepts are implemented in different applications. Such a book should provide the reader with a portable skill-set and give her/him the ability to objectively choose the right tool for the job, at the right cost. Does this book exist?"
The book that you are looking for is called Real World Photoshop. It's not going to teach you how to apply lens flares and things like that. What it does go over is how to get good scans, how to properly apply colour correction, how to adjust the exposure without making it looked washed out, etc. It also explains the hows and whys of the things you were asking about such as blurs and sharpening.
Slashdot: Failed Car Analogies. Amateur Lawyering. Anecdote Battles.
I wonder if knowing those things help?
Convolution Matrix: reads a 3x3 or 5x5 area of pixels, 'multiplies' that grid by the convolution matrix, performs a sum of the values, and replaces the central pixel in that 3x3 or 5x5 grid with the cumulative value.
Does not explain at all HOW this produces sharp filters, but that's a convolution matrix.
Unsharp mask: Creates a blurred representation of the image, compares it to the original, and any place that is similar in value remains unchanged. Any place that shows a difference indicates a boundary, and that area is brightened. The point is that you fool the human eye into thinking an image is 'sharper' because the edges are more in focus. This is akin to drawing black lines on a cartoon to make the edge more distinctive.
This doesn't explain of course why radius, amount, and threshold are used.
Gaussian blur: Uses the guassian function to average pixel values (like in the convolution matrix!). The gaussian function is the probability function of the normal distribution.
This doesn't explain how it works either.
What is probably most useful:
Convolution matrix: Create a grid of weights that is multiplied against a grid of pixels; the sum of these products is then used to replace the center of the grid, normally 3x3 or 5x5.
Unsharp mask: Increases the contrast around the edges in a picture; threshold limits how blurry an edge can be, radius tells the function how far away to look for an edge, and amount tells the function how much to increase the contrast.
Gaussian blur: Averages the values around a pixel using the Gaussian distribution, otherwise known as a bell curve. The Guassian function is used to populate the grid of a convolution matrix.
GPL Deconstructed
If you aspire to be a hardcore Photoshop user, this book is probably the one you want above all others. It's not a step-by-step tutorial, a mere reference book, or a book that leads you through the tools and various functions of the software. Instead it discusses the fundamental concepts you need to know to use Photoshop to its fullest. ... Most of the book is still applicable since Photoshop today still has channels, alpha channels, paths, layers, and calculations. This book hasn't been updated since it was written in 1998, but it really doesn't need to be. It's not about how to use particular tools and new features. It's about how to think with Photoshop. ...
Unfortunatelly it is out of print:-(
Amen. Photoshop for Dummies is the book you're looking for. I checked that book out from the library when I was donated a 1992 version of Adobe Photoshop for Mac (because I was the only Mac user known to that person). I haven't used that version since, but I have used Fireworks and GIMP (latest versions), and the editing philosophy is exactly the same. I know how to use those programs because of the Photoshop book.
There is no image editing program with layers, paths, filters, etc. that does not use an interface that imitates Photoshop. And there never will be, because those terms are the Photoshop interface.