Canyon or Ridge?

From NASA's Earth Observatory:

Canyon or Ridge?

On August 29, 2015, NASA astronaut Kjell Lindgren tweeted this photograph of a canyon from the International Space Station. "Flying over Arizona. Crazy how the shadows make this canyon look like a ridge!" he noted. Lindgren was noticing an optical illusion called relief inversion. The effect happens because most of us expect an image to be lit from the top left corner. When the sunlight comes from another angle (especially from the lower edge), the shadows fall in ways we don’t expect and our brains turn valleys into mountains to compensate. The problem is usually resolved by rotating the image so the light appears to come from the top of the image. In this case, does that work for you?

Read more about relief inversion at
http://go.nasa.gov/1LekxKa

Read a blog post about relief inversion at
http://go.nasa.gov/1LekApd

Read more about relief inversion from Shaded Relief at
http://go.nasa.gov/1Leky0u

See Lindgren's original tweet at
http://go.nasa.gov/1Leky0w