Sharpness (Focus)
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The purpose of this dialog is to improve sharpness and edges of the pictures, thus solving focus problems. Many blurred pictures can be dramatically improved by the algorithms provided.

Sharpness

This tab allows you to regulate the precision of details in a picture: you have both the option to increase or decrease sharpness, moving the slider to the right or to the left.

Enhance Edges

This correction increases the contrast of those pixels that are near the borders or edges inside a picture, thus making the borders more visible and precise.

Unsharp Mask

This is a progressive technique to increase the sharpness of a picture without increasing background noise, that is the grain of the picture itself. Many simple sharpness tools produce unwanted artefacts and thus ruin the image.

To distinguish between true edges and normal noise (grain), a copy of the picture is heavily blurred using a Gaussian algorithm with a given radius. The unsharp algorithm then uses this copy to decide where to apply a sharpen filter and where not.

The correction has 3 parameters: Amount, Radius and Threshold.

·Increase Amount to increase the sharpness effect  
·Increase Radius to reduce the noise. The bigger the picture, the bigger the radius should be, though rarely you will need to use values greater than 3.  
·The threshold represent the selectivity of the algorithm to edge detection: the greater the threshold, the less edges will be detected.  

Common values for these parameters are:

·Amount: between 0.5 and 2  
·Radius: between 0.6 and 2.5  
·Threshold: between 2 and 6  

Example of Unsharp Mask  
 
Note, that in this example the grain of the blurred background is sharpened only minimally, and the effect of distance is thus preserved. Use the Unsharp Mask for delicate sharpness adjustments to otherwise proffessional photographs.  

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icon_tipImportant
 
·If you only want to apply Sharpness or Blur to certain parts of an image, you can create Selections or use the Retouch Brushes.  
 
·When selecting parts of the image using the selection tools, all brushes and correction dialogs only apply to these selections. Selections can also have a feather, reducing the effect of the brush or correction close to the selection borders.  

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