Special Effects - The Photoshop: Professional Retouching and Compositing Tips, Tricks, and Techniques - page 219

Figure 4.12
Tip
If you place your cursor within the preview inside the Reduce Noise filter, and
then click and release, you will see the before and after views.
5. Most times I apply this effect twice, but the second time I use a slightly lower
strength. Go to Filter > Noise > Reduce Noise, and this time set Strength to 5 and
click OK.
Applying this effect tends to reduce the sharpness in areas like the eyes, hair, and
so on. To bring some of this sharpness back but maintain the painterly effect, we
can use the High Pass filter.