Special Effects - The Photoshop: Professional Retouching and Compositing Tips, Tricks, and Techniques - page 269

Figure 4.70
4. On the same layer, go to Image > Adjustments > Invert, which restores the picture
to how it originally appeared; however, the image has now been set up to enhance
details.
5. Convert the layer to a Smart Object by going to Filter > Convert for Smart Filters.
Add the details by going to Filter > Blur > Surface Blur.
6. In the Surface Blur properties, set the Radius and Threshold settings to the same
number. I find that settings not exceeding 30 produce the best results ( Figure
4.71 ) .