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*If no light passes straight through the object, the projection is a [[shadow]] or [[silhouette]]. |
*If no light passes straight through the object, the projection is a [[shadow]] or [[silhouette]]. |
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*If some radiation passes straight through the object, the projection is a [[projectional radiography|radiograph]]. |
*If some [[radiation]] passes straight through the object, the projection is a [[projectional radiography|radiograph]]. |
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Ideally, photons pass around the object, [[transmittance|pass straight through the object]], or are [[absorption (electromagnetic radiation)|absorbed]] by the object. Photons that are [[scattering|scattered]], [[reflection (physics)|reflected]], [[refraction|refracted]], [[diffraction|diffracted]], or [[fluorescence|converted]] by material in the scene (including the air) and ultimately reach the image area of the surface reduce the contrast of the image. |
Ideally, photons pass around the object, [[transmittance|pass straight through the object]], or are [[absorption (electromagnetic radiation)|absorbed]] by the object. Photons that are [[scattering|scattered]], [[reflection (physics)|reflected]], [[refraction|refracted]], [[diffraction|diffracted]], or [[fluorescence|converted]] by material in the scene (including the air) and ultimately reach the image area of the surface reduce the contrast of the image. |
Revision as of 22:17, 11 November 2017
Projection, projector, or projective may refer to:
Optical projection
Projection display devices
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.
- A small aperture is a physical point of projection. It is used in pinhole cameras and the original camera obscura.
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.
- Like a lens, a concave curved mirror also defines a point of projection. Concave mirrors are used in telescopes and some modular camera lenses.
- 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
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.
- Parallel projection
- Orthographic projection, including:
- Multiview projection
- Plan, or floor plan view
- Elevation, usually a side view of an exterior
- Section, a view of the interior at a particular cutting plane
- Axonometric projection, including:
- Multiview projection
- Oblique projection, including:
- Orthographic projection, including:
- Perspective (graphical) projection
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
- Projection (mathematics), any of several different types of functions, mappings, operations, or transformations
- Projection (linear algebra)
- Projection (relational algebra)
- Projection method (fluid dynamics)
- Projection (set theory)
- Projective geometry is a non-Euclidean geometry that involves projective spaces. In another direction, projective modules and projective objects generalize free modules
- 3D projection
- Vector projection
Other
- Projection (alchemy), process in Alchemy
- Projection areas, areas of the brain where sensory processing occurs
- Military power projection, the capacity of a state to implement policy by means of force, or the threat thereof, in an area distant from its own territory
- Psychological projection, or "Freudian projection," a defense mechanism in which one attributes to others one's own unacceptable or unwanted attributes, thoughts, or emotions
- Projection fibers, in neuroscience, white matter fibers that connect the cortex to the lower parts of the brain or the spinal cord.
- "Projections" (Voyager episode), an episode of the television series Star Trek: Voyager
- Projections (album), 1966 album by The Blues Project
- Projections (John Handy album), 1968 album
- Projections (film), 2013 Croatian film
- Forecasting of future developments based on current statistics and trends
See also
- All pages with titles beginning with Projection
- All pages with titles containing Projection
- Project (disambiguation)
- Projection effect (disambiguation)
- Projector (disambiguation)
- Philosophy of perception