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"Sharpen."

A slight softening of detail occurs when reducing an image's size. Some subtle resharpening can restore the "bite" to your image. There are many sharpening methods but a simple one that works well with resizing is "Unsharp Mask".

In Photoshop CS this is found under Filters > Sharpen > Unsharp Mask

The effect should be subtle. Do NOT overdo the sharpening! A good starting point is with "Amount" set to 20%, "Radius" to 1.0, and Threshold to 0. With "Preview" selected you can see the effect on your image and adjust the settings until you are satisfied with the result. By switching "Preview" off and on, the changes will be easier to spot.

People sometimes ask why a sharpening process uses the contradictory term "unsharp". Well, it goes back to the days of film processing when a slightly blurred "inverted negative" was made from the original negative. Placed together in an enlarger, the light passing through them both reduced some detail from the original. This masking effect accentuated contrast of edges to give the impression of sharpness. That's just a very brief description but I hope it is enough to explain where the apparent contradiction in the name arose.

The same principle is used in digital processing but of course it is possible to be much more flexible in its application, changing at will parts of the process that, in the days of film, would have been extremely laborious to do. How lucky we are!

Unsharp Mask
© David McHutchison (Deemacphotos)
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