Selective Sharpening

Here are two techniques for sharpening parts(s) of an image leaving other parts untouched.  In both cases, sharpening should be left until cropping, resizing and other adjustments have been completed.  It is convenient to sharpen on a composite layer.*

Using the History Brush
  1. Apply the Unsharp Mask filter to the composite image (Layer 1) as a whole, to produce the degree of sharpening required for those parts you wish to sharpen.
  2. Select the History Brush (NOT the Art History Brush) from the Tools Panel and click in the small box to the left of the Unsharp Mask entry in the History Panel (see Fig. 1)
  3. Revert to the previous History state by clicking on its description in the History Panel (see Fig.2).  The image will return to its original unsharpened state.
  4. With the History Brush still selected, adjust the brush size and hardness and paint over the areas you wish to sharpen.
Using a Layer Mask 
  1. Apply the Unsharp Mask filter to the composite image (Layer 1) as a whole, to produce the degree of sharpening required for those parts you wish to sharpen.
  2. Make sure that the Foreground / Background colours are black / white (see Fig.3)
  3. Hold down the [Alt] key and click the Add Layer Mask icon (second from left at bottom of Layers Panel).  This will give the composite layer a mask filled with black which renders this layer invisible. ( see Fig.4)  You will notice that it is the mask which is selected in the layers panel (has a double line around it) and that the foreground / background colours have now switched so that the foreground is white.
  4. You can now expose the parts of this layer that you want to show as sharpened by painting on the image with a brush, set to a suitable size and hardness.  Actually, you are creating a hole in the mask and this will appear as a white area in the mask representation in the Layers panel.  This technique has an advantage over the History Brush system in that if you make an error, you can switch the foreground colour to black (hit [X] on the keyboard) and paint over the error.  Hit [X] to switch back to white and continue revealing the layer.
  5. If you want to do any further work on this composite layer, don’t forget to select the image itself by clicking the picture icon on the layer to transfer selection from the mask.

* If you have done extensive work on an image and created several layers, then you can make a composite layer whilst still retaining the separate layers.  If you are unhappy with the work you subsequently do on the composite, it is easy to bin it and make a new one. Activate the top-most layer and click on the Create a New Layer icon (second from right at bottom of Layers panel)

Fill this new layer with a composite of all other visible layers by holding down the [Shift]  [Ctrl]  and [Alt] keys (a bit tricky!) and whilst doing so, hit [E].

Before sharpening, change the Layer Blend Mode to Luminosity.  This helps to avoid colour fringing.