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Thanks for nothing. Flamers. I could have at least used a run down of how the unsharp mask algorithm works so I could adapt a similar method in my script.
Unsharp masking is part art, part science. There is no set way to use it which works for all images.
Generally speaking, however:
The Unsharp Mask filter works by exaggerating areas of high contrast–ie, edges. This gives the appearance of sharper edges, and increases the apparent overall sharpness of the image. While it can’t make a blurred or out-of-focus image sharp (nothing can do this), it can dramatically increase the perception of sharpness. And unsharp masking is a requirement to get good-looking images in print.
The Amount slider dictates how much edges are increased in contrast. If the value in this slider is too high, the image will appear to have "halos" around the edges.
The Radius slider determines how wide the area of enhanced contrast is around edges. In general, the amount you put in the Radius field depends on the resolution of the image; the higher the resolution in pixels per inch, the wider the Radius.
A good place to start is (image resolution/200). If the image is screen resolution–100 pixels per inch or less–try a Radius of 1. Increasing the Radius will also create undesireable halos around edges.
If you are sharpening an image which will be printed on a printing press, and your image is the recommended resolution (twice the frequency of the halftone you will be using to reproduce the image on press), use a Radius of (halftone screen/100). So, for example, if your image is being printed on press with a 150-line-per-inch halftone, use a Radius value of 1.5.
The Threshold command determines how far apart two neighboring pixels must be in tonal value in order to be sharpened. I usually start with a Threshold of 3. Lower Threshold values exaggerate noise along with edges; higher values don’t sharpen noise, but also produce more muted sharpening overall.
Note that if your image is intended for print, you should set the Amount value so that the image looks slightly over-sharpened on your screen! This is because the process of halftoning the image for print decreases the apparent sharpness of the image (which is why all images should have USM applied if they are going to be used for print).
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