Here's an easy method, but it doesn't leave a lot of room for variation:
Open the image. Press the 'D' key to set the foreground and background colors to their default white/black.
Create a new blank layer (Layer> New> Layer). Go to the paintbucket tool (g) and fill the new layer with white.
Click on the background (original) layer, and go to Select> Color Range. Choose 'shadows' from the drop-down menu, and click OK.
Open the paths pallette. Click on the 'Make work path from selection' icon at the bottom of the pallette. (see screenshot below)
Here's the beauty of the method: converting the selection to a path smooths it
automatically!
Now click on the 'load path as selection' icon (see screenshot) to convert your newly smoothed path into a selection again.
Go back to the Layers pallette, click on the blank layer to highlight it, and go to Edit> Fill... The background color should still be black, so choose 'background color' from the drop down menu.
You're done. Here's the result:
And a side-by-side before and after:
Hope this helps!
-Medley.
