Parallax

• Parallax

  • Overview

    • Parallax is the apparent shift in an object's position when it is seen from two different places. Near objects shift more than far ones, so the size of the shift tells how far away something is.
    • By extension, viewing one subject from several positions reveals a dimension that no single view shows.

  • Mechanism

    • Hold a finger at arm's length and close each eye in turn: the finger jumps against the background. Move the finger closer and the jump grows.
    • The brain merges the two slightly different views from the two eyes into a sense of depth, a process called stereopsis.

  • Examples

    • Astronomy. As the Earth travels around the Sun, a nearby star shifts against more distant stars. Measuring that shift from opposite sides of the orbit gives the star's distance. A parsec is the distance at which the shift is one arcsecond.
    • Web design. Parallax scrolling scrolls background layers more slowly than foreground layers, so a flat page appears to have depth. Website/Misato Town gets a related effect another way, by tying scroll position to an animation timeline.
    • Layered media. A recording published in several layers, from raw session to finished piece, lets a listener compare versions of the same moment, as with the layers planned for GitP/A in Week/Review/26/10/11 Sun. A Palimpsest and a Diagram/Cross-Section show their subject in layers in a similar way.