Photo 11: Introduction to Digital Imaging
Instructor: Sue Leith,        sleith@csus.edu       Office Hours, Monday’s 1-2    MRP 2011.

Sharpening with Unsharp mask

 

Filter > Sharpen > Unsharp mask.

Photoshop sharpens photographic files by increasing their contrast. In some images this can be very helpful. It can also be very destructive. As contrast is increased, detail in high and low values is lost.  All sharpening filters should be used with great restraint.

The most controllable and effective sharpening filter is the Unsharp Mask.

The Unsharp Mask filter:
1. Finds the areas in an image where color or tonal changes occur and sharpens them.
2. Can be applied after any operation which involves resampling (image size changes, scaling, distorting, dust and scratches filter).
3. Unlike other sharpening filters it allows the user to control the degree and approach of sharpening.

1. Amount -- High number  = most sharpening.
The percentage controls the intensity of the effect (the higher the resolution of a file the greater the percentage required). Halos around objects in an image are increased with this control.
Grainy images require a lower number.
For high-resolution printed images, start between 150% and 200%.

2. Radius -- High number = most sharpening.
Controls the distance in pixels out from the edge of object to be sharpened or the width of halos.  The higher the radius number, the wider the halo. For low resolution images use a low radius. High-resolution images can take a slightly higher radius value  
For high-resolution images, try a Radius between 1 and 2.

3. Threshold -- Low number = most sharpening
Controls sharpening by brightness differences between pixels.
After other controls have been set, gradually move slider to higher number.
For high-resolution images, try around 5-9

Use this filter with great restraint!
        

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