This tutorial is for enhance an bad image to a more nice one. I use that image, not well exposed, not sharpen, not focused !
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First step is to clear dust from image with Spot Healing Brush Tool, after that duplicate background (CTRL+J). Now go to Filter-Sharpen-Unsharp Mask and use following values:

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Using ideal values for your images requires understanding its three settings: "Amount," "Radius," and "Threshold."

* Amount is usually listed as a percentage, and controls the magnitude of each overshoot. This can also be thought of as how much contrast is added at the edges.

* Radius controls the amount to blur the original for creating the mask. This affects the size of the edges you wish to enhance, so a smaller radius enhances smaller-scale detail.

* Threshold sets the minimum brightness change that will be sharpened. This is equivalent to clipping off the darkest non-black pixel levels in the unsharp mask. The threshold setting can be used to sharpen more pronounced edges, while leaving more subtle edges untouched. This is especially useful to avoid amplifying noise, or to sharpen an eye lash without also roughening the texture of skin.

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