Step 1
Open up your image you want to turn into a sketch, I"m using an image of jessica alba. First thing we need to do is desaturate it do this by press "shift + ctrl +u" or goto "image > adjustments > desaturate".
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Step 2
Now goto "filter > stylize > find edges".
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Step 3
Now press "ctrl + L" to open up the levels palette these are the settings I'm using, but play around with them, also adjust the output settings change the lightness of the image.
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and here's mine.
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