This is a really great idea from Keith Lang, co-founder of Skitch. It’s actually quite an old post now, but I thought it was worth bringing up again because the new generation of small-screened, ultra-portable notebooks will need this kind of behaviour more and more.
Via UI&us
0 Preferences —> Memory Usage
Adjustments —> Brightness/Contrast
Filters
Blur (note the rendering of the thumb arrow)
Layer Blending
Layer Style
Threshold
Color Balance 
Things to keep in mind:


[Source] via Daring Fireball
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