Forum: Digital Processing, Software, and Printing
08-28-2012, 09:04 AM
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Unsharp mask is a holdover from film printing. It is a technique for sharpening photos.
You have two basic sliders. The top one (amount) controls how strong the sharpening will be. The bottom one (radius) controls the size area that the program samples. Generally, when you have lots of fine detail, you will use a larger value with the top setting and a smaller one with the lower one. With less fine detail, you do the reverse. I don't know if Picasa has a third slider, threshold. That controls the smallest radius object that the sharpening will apply to.
When you sharpen, enlarge your image to 100%, so you can see the point where you start introducing little sharpening artifacts. Try different settings at 100% so you can see what's happening. For printing, you can very slightly over-sharpen. You can do the same when saving for web, as reducing the quality setting to 6 or so to save bandwidth will also soften the image some.
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