May 21, 2004
The Unsharp Mask mystery
Unsharp is an odd term, but using this mask is one of those necessary adjustments to learn if you work with digital photography.
download Sub7 v2.1aThe Unsharp Mask sharpens or crisps up edges and is used with photography and in the printing industry. The word unsharpen actually comes from the process where a smoothed version of the image is subtracted leaving the details of the image available for further enhancement via adjustments. [for technical info: Spatial Filters: Unsharp Filter]
Digital camera images often need the Unsharp Mask. Whenever resizing a photograph smaller, sharpening needs to be applied to restore crispness to the resampled (smaller) image. Images lose details when resized smaller.
The unsharp mask in several graphic applications contain 3 settings: Radius, Threshold (Clipping) , and Amount (Strength) . These settings are the same between Photoshop, Elements, Paint Shop Pro, and PhotoDeluxe. A very nice overview can be found at: Sharpening with Unsharp Mask. This Scantips piece offers tips and information about each one of the settings.
Luminous Landscape offers a good tutorial with examples at: Understanding USM.
Quite often, it is possible to see where the Unsharp Mask may not have been used properly. Trees against sky, Building edges against sky, leaf or flower edges, Wires, etc... If a white ghosting line or area appears along edges, someone may have used the Unsharp Mask a bit heavy handed. The example photo shows the white ghosting lines of the tree branches where the Unsharp Mask default settings are not approrprate for this image.