Sample SizeBy default the Magic Wand tool samples colors using a point (1 by 1 pixel) sample. You can actually change this by adjusting the Eye Dropper tool settings.

Select the Eye Dropper tool and in the option bar change the sampling size to 3 by 3 or 5 by average.
Depending on the image that you want to extract, this new sampling size can improve the quality of the extraction.