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Projection

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Projection, projector, or projective may refer to:

Optical projection

Projection display devices

Main article: Projector (disambiguation)

A projector displays a predefined image or pattern onto a projection screen or other surface.

Optical projection through a point

A three-dimensional object or scene scatters and/or emits light. Some of the light passes through a point of projection and reaches a surface, producing a two-dimensional image that is a geometric projection of the scene. This is how most cameras, telescopes, and eyes work.

The aperture cannot strictly be a point; in order to pass more than zero light, it must have an area larger than zero. A larger aperture increases the brightness of the image, but it reduces sharpness (increases blurring).

  • A convex lens generally performs better than an aperture. The lens reduces the penalty for a large aperture by reconverging (focusing) the rays from given points in the scene to single points in the image, but only for a specific distance from the lens. A simple lens defines a point of projection at its center. Some lens designs and lens systems can place the point of projection physically outside the lens, even at infinity.
  • An array of collimators also defines a point of projection. Parallel collimators define a point of projection at infinity. A "focused" collimator array defines a point of projection at a specified distance. Collimator arrays are used in some gamma cameras.

Non-compound eyes detect light that has been projected through an aperture (pit organ), a lens, or a collimator array (lobster eyes).

Not all lenses or other devices define a single point of projection for all rays in the image. If the image is recognizable as showing the original scene, it is a projection.

Optical projection from a point

A very small source of light (X-ray source or gamma-ray source) acts as a physical point of projection. The emitted photons travel in all directions, in straight lines (rays). The photons that pass around or straight through the object reach a surface, producing an image that is a geometric projection of the object.

  • If no light passes straight through the object, the projection is a shadow or silhouette.
  • If some radiation passes straight through the object, the projection is a radiograph.

Ideally, photons pass around the object, pass straight through the object, or are absorbed by the object. Photons that are scattered, reflected, refracted, diffracted, or converted by material in the scene (including the air) and ultimately reach the image area of the surface reduce the contrast of the image.

The source or focal spot cannot strictly be a point; in order to emit more than zero light, it must have an area larger than zero. A larger source increases the brightness of the image, but it reduces sharpness (increases blurring).

Graphical projection

Main article: Graphical projection

In technical drawing and computer graphics, graphical projection produces a two-dimensional drawing or image of a three-dimensional drawing, object, or scene. The projections used can correspond to possible optical projections, or they can be mathematically defined transformations that are difficult or impossible to produce with real optics. Projecting computer models to computer images is known as rendering.

Cartography

Map projection produces flat maps from geographic data about a curved surface. Many projections have been devised.

Chemistry

Several systems have been devised for drawing 2-D representations of 3-D molecules:

Mathematics

Other

See also

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