Three D

• Remember, that your eye only gets a 2D picture.
• There are lots of mechanisms that the human visual system uses to get 3D vision.
• Many of these are done in computer vision.
• The standard answer is stereopsis. You have two eyes, and when the two pictures are combined, you get depth information.
• If you've only got one eye (or camera) you can move the camera, and compare the two pictures. It's like stereopsis, but has the problem that movement is difficult, and the scene may also be changing.
• Occlusions, if something occludes something else, it's in front of it.
• Motion Parallax: things that are far away don't change much when you move, but things that are nearby do.
• That's why it looks like the moon is following you when you drive down a road. It's not changing position because it's so far away.
• Texture Changes: similarly textures of things that are far away don't change much when you move, while the texture of things nearby do.