A nice way to darken colours

While experimenting with creating my own "Pencil Sketch" effect, I happened to discover this effect -- it's a nice way to darken colours and increase their contrast and saturation without getting the "candy colour" effect that the Hue/Saturation filter can cause.

My apologies if this technique is well-known.  You veterans can post this on your refrigerator for times when you need a good laugh!

Here's the original:

If a Hue/Saturation layer is used to boost the colours, even with modifying it by using an additional Brightness/Contrast layer:

the colours can look a little too "sweet":

Here's what I found:

1. Duplicate the Background layer.
2. On that Background Copy layer, use Filter...Other...HighPass with these settings:
   
3. Change the blend mode of the highpass layer to "Color Burn" and reduce its opacity to about 45%:
   

The result is kind of nice:

Enjoy!

Ken