So what is Unsharp Mask?
It's probably the best technique to use to sharpen most pictures!
This is the technique the professionals use, i.e. preparing images for
reproduction - litho printing - as it works by hiding or 'masking' the
parts of an image that are not sharp (i.e. unsharp). It does this by
controlling the amount of sharpening (i.e. the strength), the radius
of pixels it acts upon (working on clusters of pixels and sharpening
the pixels within that cluster) so the bigger the radius the more
pronounced the effect, and finally the threshold (or clipping)
or range of pixels that will be affected. It's a bit like a contrast
control, a low threshold applying the effect to pixels of similar
brightness, a high threshold allowing a greater range of pixels,
therefore a more enhanced effect. Already you can see that this range
of controls is more sophisticated than a plain old sharpen filter!
Open the image 'camping girl' (sharpening.jpg) from the sample images page.
First, use FILE > SAVE AS to save the image with a new name to preserve the original.
In the Unsharp Mask dialogue box (shown left) set the following: Radius: 2 or 3 pixels, Strength: 100, Clipping: 3 or 4. To help you see the filter effect, use the preview screens, by zooming in using the small magnifying symbol below the left hand picture (original), also put your mouse over the left hand image and 'drag' it until you can see the sunglasses in the frame.
To apply the mask click OK.
You might want to use FILE > SAVE AS at this point to save a copy of the image with a new name.
Then go back and try the filter again with a higher Radius and/or Clipping setting (look at a Clipping setting of 15 or 20).
Open the original image again and compare it side by side with your masked image(s).