Unsharp mask is another powerful tool that is misunderstood and misused. This tool should be used everytime, and the final tool used. I spoke of setting up the file for use as a CMYK file for printing or a RGB jpeg for the web. And most importantly a RGB tiff file for the master copy. Now I want to talk about.... why we don't sharpen until we sent the file off (final copy).
The Term Unsharp Mask comes from a the dark room technique. Back in the day. When a photographer had a photo that was soft (unsharp) They could save it in the dark room using a masking technique that would sharpen the edges. Thus Unsharp mask.
To understand unsharp mask, lets understand what the tool is doing. Basically it is adding a white and black dot pattern around every color dot in the image. That is why its so important to do this step at the end and only once.
Scott