Adobe Photoshop LE Tutorial-16 
Adobe Photoshop LE Tutorial-16
Filters Noise/Dust-2
A Dialog Box will appear. It has two slider scales.
Threshold sets how different the pixel values must be before they are eliminated.
Drag the Threshold control to 0 so that you can observe an unaltered image.The Threshold control works best between 0 & 128.
Radius controls how far the filter
should search for these differences.The Radius control makes the image blurry
and it should be used judiciously!
Both of these control the degree to which the dust will be removed.
In the example above, the Threshold and Radius are set at 1. This is basically an unmodified setting.
The small blue box shows the dust speck in
the image. This is magnified in
the Preview screen inside the box. The Preview Screen is set
at 100%. This can be increased or decreased by the (+) & (-) buttons below the screen. This
setting depends on the degree to which you want to examine the image. 
In this example the Radius has been increased to 3 pixels. This almost removes the dust speck. However, it also reduces the sharpness of the image.
It is possible to select small areas of the image which have dirt and use this filter on these areas rather than the whole image.
The image can be sharpened with another filter which we will explore later.