An image sensor is a device that converts a visual image to an electric signal. It is used chiefly in digital cameras and other imaging devices. It is usually an array of charge-coupled devices (CCD) or CMOS sensors such as active pixel sensors.
There are several main types of color image sensors, differing by the means of the color separation mechanism:
Bayer sensor, low-cost and most common, using a Bayer filter that passes red, green, or blue light to selected pixels, forming interlaced grids sensitive to red, green, and blue. The image is then interpolated using a demosaicing algorithm.
Foveon X3 sensor, using an array of layered sensors where every pixel contains three stacked sensors sensitive to the individual colors.
3CCD, using three discrete image sensors, with the color separation done by a dichroic prism. Considered the best quality, and generally more expensive than single-CCD sensors.
Wednesday, March 28, 2007
Film
Film is a term that encompasses individual motion pictures, the field of film as an art form, and the motion picture industry. Films are produced by recording actual people and objects with cameras, or by creating images using animation techniques or special effects.
Films are cultural artifacts created by specific cultures, which reflect those cultures, and, in turn, affect them. Film is considered to be an important art form, a source of popular entertainment, and a powerful method for educating-or indoctrinating citizens. The visual elements of cinema give motion pictures a universal power of communication; some movies have become popular worldwide attractions, by using dubbing or subtitles that translate the dialogue.
Films are made up of a series of individual images called frames. When these images are shown rapidly in succession, a viewer has the illusion that motion is occurring. The viewer cannot see the flickering between frames due to an effect known as persistence of vision — whereby the eye retains a visual image for a fraction of a second after the source has been removed. Viewers perceive motion due to a psychological effect called beta movement.
The origin of the name "film" comes from the fact that photographic film (also called film stock) has historically been the primary medium for recording and displaying motion pictures. Many other terms exist for an individual motion picture, including picture, picture show, photoplay, flick, and most commonly, movie. Additional terms for the field in general include the big screen, the silver screen, the cinema, and the movies.
Films are cultural artifacts created by specific cultures, which reflect those cultures, and, in turn, affect them. Film is considered to be an important art form, a source of popular entertainment, and a powerful method for educating-or indoctrinating citizens. The visual elements of cinema give motion pictures a universal power of communication; some movies have become popular worldwide attractions, by using dubbing or subtitles that translate the dialogue.
Films are made up of a series of individual images called frames. When these images are shown rapidly in succession, a viewer has the illusion that motion is occurring. The viewer cannot see the flickering between frames due to an effect known as persistence of vision — whereby the eye retains a visual image for a fraction of a second after the source has been removed. Viewers perceive motion due to a psychological effect called beta movement.
The origin of the name "film" comes from the fact that photographic film (also called film stock) has historically been the primary medium for recording and displaying motion pictures. Many other terms exist for an individual motion picture, including picture, picture show, photoplay, flick, and most commonly, movie. Additional terms for the field in general include the big screen, the silver screen, the cinema, and the movies.
Lens
A photographic lens (also known as objective lens or photographic objective) is an optical lens or assembly of lenses used in conjunction with a camera body and mechanism to make images of objects either on photographic film or on other media capable of storing an image chemically or electronically.
While in principle a simple convex lens will suffice, in practice a compound lens made up of a number of optical lens elements is required to correct the many optical aberrations that arise.
There is no difference in principle between a lens used for a camera, a telescope, a microscope, or other apparatus, but the detailed design and construction are different.
A lens may be permanently fixed to a camera, or it may be interchangeable with lenses of different focal lengths and other properties.
While in principle a simple convex lens will suffice, in practice a compound lens made up of a number of optical lens elements is required to correct the many optical aberrations that arise.
There is no difference in principle between a lens used for a camera, a telescope, a microscope, or other apparatus, but the detailed design and construction are different.
A lens may be permanently fixed to a camera, or it may be interchangeable with lenses of different focal lengths and other properties.
A practical camera lens will often incorporate an aperture adjustment mechanism, often an iris diaphragm, to regulate the amount of light that may pass. A shutter, to regulate the time during which light may pass, may be incorporated within the lens assembly, or may be within the camera, or even, rarely, in front of the lens.
The lens may usually be focused by adjusting the distance from the lens assembly to the image-forming surface, or by moving elements within the lens assembly.
The lens elements are made of transparent materials. Glass is the most widely used material due to its good optical properties and resistance to scratching. Various plastics, such as acrylic, the material of Plexiglas, can also be used. Plastics allow the manufacture of strongly aspherical lens elements which are difficult or impossible to manufacture in glass, and which simplify or improve lens manufacture and performance. Plastics are not used for the outermost elements of all but the cheapest lenses as they scratch easily. Moulded plastic lenses have been used for the cheapest disposable cameras for many years, and have acquired a bad reputation: manufacturers of quality optics tend to use euphemisms such as "optical resin".
The 1951 USAF Resolution Test Chart is one way to measure the resolving power of a lens in a standardized manner. The quality of the lens material, of the coatings and of the internal manufacture all influence the "resolution" of the lens, even at the same F-number and focal length. Today, most lenses are multi-coated in order to minimize lens flare and other unwanted effects. Premium lenses have a UV coating to keep out the ultraviolet light that could expose photosensitive materials and result in inaccurate colors.
The lens may usually be focused by adjusting the distance from the lens assembly to the image-forming surface, or by moving elements within the lens assembly.
The lens elements are made of transparent materials. Glass is the most widely used material due to its good optical properties and resistance to scratching. Various plastics, such as acrylic, the material of Plexiglas, can also be used. Plastics allow the manufacture of strongly aspherical lens elements which are difficult or impossible to manufacture in glass, and which simplify or improve lens manufacture and performance. Plastics are not used for the outermost elements of all but the cheapest lenses as they scratch easily. Moulded plastic lenses have been used for the cheapest disposable cameras for many years, and have acquired a bad reputation: manufacturers of quality optics tend to use euphemisms such as "optical resin".
The 1951 USAF Resolution Test Chart is one way to measure the resolving power of a lens in a standardized manner. The quality of the lens material, of the coatings and of the internal manufacture all influence the "resolution" of the lens, even at the same F-number and focal length. Today, most lenses are multi-coated in order to minimize lens flare and other unwanted effects. Premium lenses have a UV coating to keep out the ultraviolet light that could expose photosensitive materials and result in inaccurate colors.
CMOS
Complementary metal–oxide–semiconductor (CMOS) ("see-moss", IPA: ['si.mɜs]), is a major class of integrated circuits. CMOS technology is used in chips such as microprocessors, microcontrollers, static RAM, and other digital logic circuits. CMOS technology is also used for a wide variety of analog circuits such as image sensors, data converters, and highly integrated transceivers for many types of communication.
CMOS is also sometimes explained as complementary-symmetry metal–oxide–semiconductor. The words "complementary-symmetry" refer to the fact that the typical digital design style with CMOS uses complementary and symmetrical pairs of p-type and n-type MOSFETs for logic functions.
Two important characteristics of CMOS devices are high noise immunity and low static power supply drain. Significant power is only drawn when its transistors are switching between on and off states; consequently, CMOS devices do not produce as much heat as other forms of logic such as TTL. CMOS also allows a high density of logic functions on a chip.
The triple compound "metal–oxide–semiconductor" is a reference to the nature of the physical structure of early (and interestingly now, the very latest) field-effect transistors, having a metal gate electrode placed on top of an oxide insulator, which in turn is on top of a semiconductor material. Instead of metal, current gate electrodes (including those up to the 65 nanometer technology node) are almost always made from a different material, polysilicon, but the terms MOS and CMOS nevertheless continue to be used for the modern descendants of the original process. (See also MOSFET.) Metal gates have made a comeback with the advent of high-k dielectric materials in the CMOS transistor as announced by IBM and Intel for the 45 nanometer node and beyond [1].
The combination of MEMS sensors with digital signal processors on one single CMOS chip is sometimes known an CMOSens.
CMOS is also sometimes explained as complementary-symmetry metal–oxide–semiconductor. The words "complementary-symmetry" refer to the fact that the typical digital design style with CMOS uses complementary and symmetrical pairs of p-type and n-type MOSFETs for logic functions.
Two important characteristics of CMOS devices are high noise immunity and low static power supply drain. Significant power is only drawn when its transistors are switching between on and off states; consequently, CMOS devices do not produce as much heat as other forms of logic such as TTL. CMOS also allows a high density of logic functions on a chip.
The triple compound "metal–oxide–semiconductor" is a reference to the nature of the physical structure of early (and interestingly now, the very latest) field-effect transistors, having a metal gate electrode placed on top of an oxide insulator, which in turn is on top of a semiconductor material. Instead of metal, current gate electrodes (including those up to the 65 nanometer technology node) are almost always made from a different material, polysilicon, but the terms MOS and CMOS nevertheless continue to be used for the modern descendants of the original process. (See also MOSFET.) Metal gates have made a comeback with the advent of high-k dielectric materials in the CMOS transistor as announced by IBM and Intel for the 45 nanometer node and beyond [1].
The combination of MEMS sensors with digital signal processors on one single CMOS chip is sometimes known an CMOSens.
Charge-Coupled Device (CCD)
A charge-coupled device (CCD) is an image sensor, consisting of an integrated circuit containing an array of linked, or coupled, light-sensitive capacitors. This device is also known as a Color-Capture Device.
The capacitor perspective is reflective of the history of the development of the CCD and also is indicative of its general mode of operation, with respect to readout, but attempts aimed at optimization of present CCD designs and structures tend towards consideration of the photodiode as the fundamental collecting unit of the CCD. Under the control of an external circuit, each capacitor can transfer its electric charge to one or other of its neighbours. CCDs are used in digital photography and astronomy (particularly in photometry, sensors, medical fluoroscopy, optical and UV spectroscopy and high speed techniques such as lucky imaging).
The capacitor perspective is reflective of the history of the development of the CCD and also is indicative of its general mode of operation, with respect to readout, but attempts aimed at optimization of present CCD designs and structures tend towards consideration of the photodiode as the fundamental collecting unit of the CCD. Under the control of an external circuit, each capacitor can transfer its electric charge to one or other of its neighbours. CCDs are used in digital photography and astronomy (particularly in photometry, sensors, medical fluoroscopy, optical and UV spectroscopy and high speed techniques such as lucky imaging).
Image
In common usage, an image (from Latin imago) or picture is an artifact that reproduces the likeness of some subject—usually a physical object or a person.
Images may be two dimensional, such as a photograph, or three dimensional such as in a statue. They are typically produced by optical devices—such as a cameras, mirrors, lenses, telescopes, microscopes, etc. and natural objects and phenomena, such as the human eye or water surfaces.
The word image is also used in the broader sense of any two-dimensional figure such as a map, a graph, a pie chart, or an abstract painting. In this wider sense, images can also be produced manually, such as by drawing, painting, carving, by computer graphics technology, or a combination of the two, especially in a pseudo-photograph.
A volatile image is one that exists only for a short period of time. This may be a reflection of an object by a mirror, a projection of a camera obscura, or a scene displayed on a cathode ray tube. A fixed image, also called a hardcopy, is one that has been recorded on a material object, such as paper or textile.
A mental image exists in someone's mind: something one remembers or imagines. The subject of an image need not be real; it may be an abstract concept, such as a graph, function, or "imaginary" entity. For example, Sigmund Freud claimed to have dreamt purely in aural-images of dialogues. The development of synthetic acoustic technologies and the creation of sound art have led to a consideration of the possibilities of a sound-image comprised of irreducible phonic substance beyond linguistic or musicological analysis.
Images may be two dimensional, such as a photograph, or three dimensional such as in a statue. They are typically produced by optical devices—such as a cameras, mirrors, lenses, telescopes, microscopes, etc. and natural objects and phenomena, such as the human eye or water surfaces.
The word image is also used in the broader sense of any two-dimensional figure such as a map, a graph, a pie chart, or an abstract painting. In this wider sense, images can also be produced manually, such as by drawing, painting, carving, by computer graphics technology, or a combination of the two, especially in a pseudo-photograph.
A volatile image is one that exists only for a short period of time. This may be a reflection of an object by a mirror, a projection of a camera obscura, or a scene displayed on a cathode ray tube. A fixed image, also called a hardcopy, is one that has been recorded on a material object, such as paper or textile.
A mental image exists in someone's mind: something one remembers or imagines. The subject of an image need not be real; it may be an abstract concept, such as a graph, function, or "imaginary" entity. For example, Sigmund Freud claimed to have dreamt purely in aural-images of dialogues. The development of synthetic acoustic technologies and the creation of sound art have led to a consideration of the possibilities of a sound-image comprised of irreducible phonic substance beyond linguistic or musicological analysis.
Camera
A camera is a device used to capture images, as still photographs or as sequences of moving images (movies or videos). The term as well as the modern-day camera evolved from the camera obscura, Latin for "dark chamber", an early mechanism for projecting images, in which an entire room functioned much as a real-time imaging system. English scientists Robert Boyle (1627-1691) and Robert Hooke (1635-1703) invented the portable camera obscura in 1665/1666.[1]
Cameras may work with the light of the visible spectrum or with other portions of the electromagnetic spectrum. A camera consists of some kind of enclosed hollow, with an opening or aperture at one end for light to enter, and a recording or viewing surface for capturing the light at the other end. Most cameras have a lens positioned in front of the camera's opening to gather the incoming light and to focus the image, or part of the image, on the recording surface. The diameter of the aperture is often controlled by a diaphragm mechanism, but some cameras have a fixed-size aperture.
Cameras may work with the light of the visible spectrum or with other portions of the electromagnetic spectrum. A camera consists of some kind of enclosed hollow, with an opening or aperture at one end for light to enter, and a recording or viewing surface for capturing the light at the other end. Most cameras have a lens positioned in front of the camera's opening to gather the incoming light and to focus the image, or part of the image, on the recording surface. The diameter of the aperture is often controlled by a diaphragm mechanism, but some cameras have a fixed-size aperture.
Photography
Photography is the process of making pictures by means of capturing light on a light-sensitive medium, such as a sensor or film. Light patterns reflected or emitted from objects are recorded onto a sensitive medium or storage chip through a timed exposure. The most common process is done through mechanical, chemical or digital devices known as cameras.
Lens and mounting of a large-format camera
Wikibooks has more about this subject:
Photography
The word comes from the Greek words φως phos ("light"), and γραφίς graphis ("stylus", "paintbrush") or γραφή graphê, together meaning "drawing with light" or "representation by means of lines" or "drawing." Traditionally the product of photography has been called a photograph. The term photo is an abbreviation; many people also call them pictures. In digital photography, the term image has begun to replace photograph. (The term image is traditional in geometric optics.)
Lens and mounting of a large-format camera
Wikibooks has more about this subject:
Photography
The word comes from the Greek words φως phos ("light"), and γραφίς graphis ("stylus", "paintbrush") or γραφή graphê, together meaning "drawing with light" or "representation by means of lines" or "drawing." Traditionally the product of photography has been called a photograph. The term photo is an abbreviation; many people also call them pictures. In digital photography, the term image has begun to replace photograph. (The term image is traditional in geometric optics.)
Photograph
A photograph (often shortened to photo) is an image created using a record of light falling on a light-sensitive surface, usually photographic film or an electronic imager such as a CCD or a CMOS chip. Most photographs are created using a camera, which uses a lens to focus the scene's visible wavelengths of light into a faithful reproduction of what the human eye would see. The process of creating photographs is called photography.
Motion pictures, such as film or video, are not generally considered to be sequences of photographs.
Motion pictures, such as film or video, are not generally considered to be sequences of photographs.
Today, most traditional photographs are produced with a two-step chemical process. In the two-step process the film holds a negative image (colours and lights/darks are inverted), which is then transferred onto photographic paper as a positive image. Another widely used film is the positive film used for producing transparencies, usually mounted in cardboard or plastic frames called slides. Slides are widely used by professionals mostly due to their sharpness and accuracy of colour rendition. Most photographs published in magazines are taken on colour transparency film.
Originally all photographs were monochromatic, or hand-painted in color. Although methods for developing color photos were available as early as 1861, they did not become widely available until the 1940s or 50s, and even so, until the 1960s most photographs were taken in black and white. Since then, color photography has dominated popular photography, although the black and white format remains popular for amateur photographers and artists. Black and white film is considerably easier to develop than colour.
Panoramic format Images can be taken with special cameras like the Hasselblad Xpan on standard film. Since the 1990s, panoramic photos have been available on the Advanced Photo System film. APS was developed by several of the major film manufacturers to provide a "smart" film with different formats and computerized options available, though APS panoramas were created using a mask in panorama-capable cameras, far less desirable than a true panoramic camera which achieves its effect through wider film format. APS has become less popular and will be discontinued in the near future.
Digital photos are stored on computers in various file formats, of which JPEG is the most popular. Many other graphic formats are used, including TIFF and RAW.
An archival digital print is a digital photographic process that results in an image display life of 100+ years, if displayed indoors under glass. Special acid free archival inks or pigments are printed directly on acid free archival art papers. Ultrachrome, Ilfochrome, and Archival Pigments are examples of commercial inks available for the production of archival digital prints. Velvet Fine Art Paper, 100% Rag, Canvas, Enahnced Matte, Watercolor Paper, Premium Ultra Glossy and other papers are examples of printable media used in archival digital printing. These prints are sometimes given the coined name "Giclée" if they are images from another medium such as a Watercolor, Acrylic or Oil (a Digital Reproduction).
The process requires inkjet printers, IRIS printers, carbon pigment printing, or other similar processes. Recently, Epson, Canon, Hewlett-Packard, and other manufacturers have developed recreational
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