This technique takes advantage of parallax in revealing parts of a scene that are hidden from one viewpoint.  If the subject of interest is partly obscured by something in front of it (for instance, a sign or a lamp-post), take a second picture after stepping to one side.  The amount you need to move to reveal the originally hidden part depends on the distance between subject and obstruction as well as between you and the subject.  Then combine the two images in layers, align them, and erase the unwanted parts.

• Duplicate the layer you wish to apply the filter to.

• On the higher layer, with a soft-edged brush, erase those areas to which you would like to apply the filter. (It is a good idea to turn off the visibility of the background while doing this.)

• Apply the noise reduction filter to the lower layer. The effect will only be visible through those areas you erased from the layer above.