Vision is one of our most prized senses, and a picture is the oldest form of recorded communication. Long before mankind learned to write, artists drew animals and hunters on their cave walls to chronicle their lives, or bring the depicted hunt luck. The first machine patented in the United States to show animated pictures or movies was a device called the "wheel of life" or "zoopraxiscope". Patented in 1867 by William Lincoln, a spinning circle of drawings or photographs was watched through a slit, creating an illusion of movement via the strobe effect. The first real movie projector was the Vitascope invented by Edison in 1896, and the world hasn’t been the same since.
There are many ways to generate an image with a projector, with the only constant being the need to generate a bright enough light, almost always processed in the primary colors of red, green, and blue (RGB). The only non-CRT solution to a lamp-based device is a laser projector, and that has been covered in excellent detail by erias in the Laser Projector node.

A projector can be placed in front of or behind the screen. Rear-projection systems are often used for mainstream wide-screen TV sets, as they are cabinet-based units that are easy to set up and operate. Front-projection units have the advantage of being able to create a larger image, as the distance between the projector and screen can be greater than that allowed by a rear-projection TV's cabinet. The disadvantage to a front-screen projector is the device's placement. This is being remedied to a great extent by newer lens designs with keystone correction that allow for off-axis placement of the projector.
  • Film projector – this type of projector works by shining a bright light through a piece of film that is then focused upon the screen through a lens. Sequential images recorded on individual frames of the film create the illusion of movement. A light-interrupting device blocks the light so that it only shines through the film when an individual frame is properly positioned.
  • CRT projector – this type uses cathode-ray tubes like the one in a TV set, one for red, one for green, and one for blue. These tubes project the portion of the image for their color through lenses onto the screen, where they mix to create a color-balanced image.
  • LCD projector – this type uses one or three LCD screens to create the image. Either there is one LCD and a color wheel rotating through the colors to build up an image on the screen, or there is light engine with dichroic mirrors or prisms splitting the lamp light into the three primary colors, routing each to a dedicated LCD. Single-LCD units are smaller and cheaper than the triple-LCD units, but have a lower image quality and produce 2/3rds less light.
  • DLP – a digital light processing projector uses micromirror technology. A silicon chip has a field of microscopic mirrors representing every pixel in the image. A light passes through a color wheel and the reflected image is created by all of the mirrors needed to reflect each active pixel in the picture. The key advantage here is that the light used can be much more intense, as it is reflecting off of the device instead of passing through it, as with an LCD. Also, non-polarized light can be used, increasing the projector’s efficiency, in contrast to an LCD, which needs polarized light to operate.
  • LCoS liquid crystal on silicon technology is reflective like DLP, so it has the advantage of being able to handle a higher intensity light as well. It still requires polarized light, however, so pound for pound, it isn’t as bright as a comparable DLP device. The advantage with this technology is that current technology enables them to have a higher pixel density than DLP, so LCoS chips can be made smaller with the same resolution. In addition, since LCoS devices are made by multiple manufacturers (DLP is the sole property of Texas Instruments), price competition should bring lower prices faster.

Pro*ject"or (?), n. [Cf. F. projeteur.]

One who projects a scheme or design; hence, one who forms fanciful or chimerical schemes. L'Estrange.

 

© Webster 1913


Pro*jec"tor, n.

An optical instrument for projecting a picture upon a screen, as by a magic lantern or by an instrument for projecting (by reflection instead of transmission of light) a picture of an opaque object, as photographs, picture post-cards, insects, etc., in the colors of the object itself. In this latter form the projection is accomplished by means of a combination of lenses with a prism and a mirror or reflector. Specific instruments have been called by different names, such as radiopticon, mirrorscope, balopticon, etc.

 

© Webster 1913

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