How are we able to see 3d objects, like in the muffin pan illusion, even from light coming from a flat piece of paper?

We are able to view 3D images because each eye captures different parts of that image and "mixes" these parts into a single image, giving the impression of depth.

Explanation:

3D images deceive our brain and this deception is only possible because we have two eyes that capture different parts of the didimensional image and merge those parts in some points. With that we ended up seeing the parts seen by just the right eye, the parts seen only by the left eye and the "merged" part by both eyes. This allows us to feel that we are seeing an image in 3 dimensions and with depth.

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