Relief Inversion

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Is this a ridge or a canyon? Relief inversion plays tricks on the brain with this image of the Colorado River in Arizona. Photo: NASA

Is this a ridge or a canyon? Relief inversion plays tricks on the brain with this image of the Colorado River in Arizona. Photo: NASA

When looking at aerial and satellite imagery, telling the difference between a canyon and a mountain can sometimes be tricky due to an optical illusion known as relief inversion.  Most people have a subconscious interpretation of images based on the assumption that objects are illuminated from above.  We expect the light source to come from the upper left corner of an image and when it doesn’t our brains flip mountains into canyons  and vice versa to compensate.

In a great example of relief inversion, NASA astronaut Kjell Lindgren tweeted a photograph taken from the International Space Station while flying over the Colorado River in Arizona in which he noted how the shadows make the canyon look like a ridge:

Oftentimes with relief inversion, the proper visual interpretation can be achieved by rotating the image so the perceived light originates from the upper left corner.

Flipping the image helps the brain correctly interpreted this image of Grand Staircase-Escalante National Monument as canyons. Image: NASA.

Flipping the image helps the brain correctly interpreted this image of Grand Staircase-Escalante National Monument as canyons. Image: NASA.

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