The general steps include:
1. duplicate the image layer
2. apply a Gaussian blur to the duplicated layer
3. change blending mode to darken at 30% opacity
4. duplicate the new layer
5. change blending mode to lighten at 50% opacity
6. Group the two new layers
7. Add a layer mask to the grouped layers
8. paint with black on the white layer mask to reveal areas of desired sharpness from the original image layer.
