Step 1:

Find a portrait with heavy shadows. This helps create the effect we will later be trying to achieve. Open this in photoshop.

Step 2:

Go to the taskbar and select Filters > Noise > Median. Drag the slider to find a suitable balance where extra details and noise is smoothed away, but the overall details are not lost. For my image, I

set the slider to 7, but you must judge the different levels depending on your image.

Step 3:

After you have smoothed your image, go back to your task bar and select: Image > Adjustments > Threshold. Again, adjust the slider to what looks best.

Step 4:

Final product. I set the threshold to 128, about halfway. Set the level so the broader details are still visible.