gamma correction vs photoshop levels

IM's gamma correction differ compared to Photoshop's
"levels".

Which is more correct?

Original image.
http://213.11
5.175.18/test_original.png
Output with "Photoshop levels=3.0"
http://213.115.175.
18/test_ps.png
Output with "Imagemagick convert -gamma 3.0"
http://213.115.175.
18/test_im.png
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