Line Pattern Optical Illusion

Is this illusion made up of anything but horizontal and verticle lines?

See Another Random Optical Illusion

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Only horizontal and verticle lines are in this image! The diamond shapes in the middle are formed by patterns of the other lines.

Explanation

Our mind tries to make sense of what we see. In this optical illusion, the straight up and down lines are interpreted as being grouped together into patterns to form shapes.