Merging the brightest and darkest parts is not too hard but the arbitrary gradient in the middle would be a bit more difficult unless you can apply a...
I don't really have any tutorials; I learned how to do the relief from a tutorial on the Guild though, its by Ascension, if you search for his Swiss...
Photoshop, Artrage, Watercolor & Various traditional tools.
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Jaxilon
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“When it’s over and you look in the mirror, did you do the best that you were capable of? If so, the score does not matter. But if you find that you did your best you were capable of, you will find it to your liking.” -John Wooden