Human depth perception comes from a variety of clues: objects overlapping each other, aerial haze where distant objects are bluer and less distinct, or relative motion between close and far objects as you move. However, stereo vision, or stereopsis, creates the appearance of depth because the images in each eye are slightly displaced, giving a 3-D view. But stereopsis is only effective at certain distances—if an object is too far away, like in the view from an airplane, then the effect cannot be seen because the distance between your eyes is too small. However, by taking two images at slightly different times, where the plane has been allowed to travel to create a greater difference between each view, a stereo pair can be made. Another artifact of a stereo pair is that the combined images have greater quality then each individual frame by themselves.