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Keystoning
The keystone effect is the apparent distortion of an image caused by projecting it onto an angled surface. It is the distortion of the image dimensions, such as making a square look like a trapezoid, the shape of an architectural keystone, hence the name of the feature. In the typical case of a projector sitting on a table, and looking upwards to the screen, the image is larger at the top than on the bottom. Some areas of the screen may not be focused correctly as the projector lens is focused at the average distance only. In photography, the term is used to describe the apparent leaning of buildings towards the vertical centerline of the photo when shooting upwards, a common effect in architectural photography. Likewise, when taking photos looking down, e.g., from a skyscraper, buildings appear to get broader towards the top. The effect is usually corrected by either using special lenses in tilt–shift photography or in post-processing using modern image editing software. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Trapezoid
In geometry, a trapezoid () in North American English, or trapezium () in British English, is a quadrilateral that has at least one pair of parallel sides. The parallel sides are called the ''bases'' of the trapezoid. The other two sides are called the ''legs'' or ''lateral sides''. (If the trapezoid is a parallelogram, then the choice of bases and legs is arbitrary.) A trapezoid is usually considered to be a convex quadrilateral in Euclidean geometry, but there are also crossed cases. If ''ABCD'' is a convex trapezoid, then ''ABDC'' is a crossed trapezoid. The metric formulas in this article apply in convex trapezoids. Definitions ''Trapezoid'' can be defined exclusively or inclusively. Under an exclusive definition a trapezoid is a quadrilateral having pair of parallel sides, with the other pair of opposite sides non-parallel. Parallelograms including rhombi, rectangles, and squares are then not considered to be trapezoids. Under an inclusive definition, a trapezoid is ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Keystone (architecture)
A keystone (or capstone) is the wedge-shaped stone at the apex (geometry), apex of a masonry arch or typically round-shaped one at the apex of a Vault (architecture), vault. In both cases it is the final piece placed during construction and locks all the stones into position, allowing the arch or vault to bear weight. In arches and vaults (such as quasi-domes) keystones are often enlarged beyond the structural requirements and decorated. A variant in domes and crowning vaults is a lantern (architecture), lantern. A portion of the arch surrounding the keystone is called a Crown (arch), crown. Keystones or their suggested form are sometimes placed for decorative effect in the centre of the flat top of doors, recesses and windows, so as to form an upward projection of a lintel, as a hallmark of strength or good architecture. Although a masonry arch or vault cannot be self-supporting until the keystone is placed, the keystone experiences the least stress of any of the voussoirs, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lens (optics)
A lens is a transmissive optical device that focuses or disperses a light beam by means of refraction. A simple lens consists of a single piece of transparent material, while a compound lens consists of several simple lenses (''elements''), usually arranged along a common axis. Lenses are made from materials such as glass or plastic and are ground, polished, or molded to the required shape. A lens can focus light to form an image, unlike a prism, which refracts light without focusing. Devices that similarly focus or disperse waves and radiation other than visible light are also called "lenses", such as microwave lenses, electron lenses, acoustic lenses, or explosive lenses. Lenses are used in various imaging devices such as telescopes, binoculars, and cameras. They are also used as visual aids in glasses to correct defects of vision such as myopia and hypermetropia. History The word ''lens'' comes from , the Latin name of the lentil (a seed of a lentil pla ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Architectural Photography
Architectural photography is the subgenre of the photography discipline where the primary emphasis is made to capturing photographs of buildings and similar architectural structures that are both aesthetically pleasing and accurate in terms of representations of their subjects. Architectural photographers are usually skilled in the use of specialized techniques and cameras for producing such specialized photography. History The first permanent photograph, '' View from the Window at Le Gras'' by Nicéphore Niépce, was also the first architectural photograph as it was a view of buildings. Similarly, photographs taken by early photographer William Henry Fox Talbot were of architecture, including his photograph of a Latticed window in Lacock Abbey taken in 1835. Throughout the history of photography, architectural structures including buildings have been highly valued photographic subjects, mirroring society's appreciation for architecture and its cultural significance. By the 18 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tilt–shift Photography
Tilt–shift photography is the use of camera movements that change the orientation or position of the lens with respect to the film or image sensor on cameras. Sometimes the term is used when a shallow depth of field is simulated with digital post-processing; the name may derive from a perspective control lens (or tilt–shift lens) normally required when the effect is produced optically. "Tilt–shift" encompasses two different types of movements: rotation of the lens plane relative to the image plane, called ''tilt'', and movement of the lens parallel to the image plane, called ''shift''. Tilt is used to control the orientation of the plane of focus (PoF), and hence the part of an image that appears sharp; it makes use of the Scheimpflug principle. Shift is used to adjust the position of the subject in the image area without moving the camera back; this is often helpful in avoiding the convergence of parallel lines, as when photographing tall buildings. History and use Mo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Stereoscopy
Stereoscopy, also called stereoscopics or stereo imaging, is a technique for creating or enhancing the depth perception, illusion of depth in an image by means of stereopsis for binocular vision. The word ''stereoscopy'' derives . Any stereoscopic image is called a stereogram. Originally, stereogram referred to a pair of stereo images which could be viewed using a stereoscope. Most stereoscopic methods present a pair of two-dimensional images to the viewer. The left image is presented to the left eye and the right image is presented to the right eye. When viewed, the human brain perceives the images as a single 3D view, giving the viewer the perception of Three-dimensional space, 3D depth. However, the 3D effect lacks proper focal depth, which gives rise to the Vergence-accommodation conflict. Stereoscopy is distinguished from other types of 3d display#3D displays, 3D displays that display an image in Three-dimensional space, three full dimensions, allowing the observer to ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Depth Of Focus
Depth of focus is a lens optics concept that measures the tolerance of placement of the image-capturing plane (the plane of an image sensor or a film in a camera) in relation to the lens. In a camera, depth of focus indicates the tolerance of the film's displacement within the camera and is therefore sometimes referred to as "lens-to-film tolerance". ''Depth of focus'' versus ''depth of field'' The phrase ''depth of focus'' is sometimes erroneously used to refer to ''depth of field'' (DOF), which is the object position range over which objects are acceptably focused on an image, whereas the ''depth of focus'' refers to the zone behind the lens wherein the film plane or image sensor is placed to produce an in-focus image. Depth of field depends on the focus distance, while depth of focus does not. ''Depth of focus'' can have two slightly different meanings. The first is the distance over which the image-capturing plane can be displaced while a single object plane remains on it wi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Video Projector
A video projector is an image projector that receives a video signal and projects the corresponding image onto a projection screen using a lens system. Video projectors use a very bright ultra-high-performance lamp (a special mercury arc lamp), Xenon arc lamp, metal halide lamp, LED or solid state blue, RB, RGB or fiber-optic lasers to provide the illumination required to project the image. Most modern projectors can correct any curves, blurriness and other inconsistencies through manual settings. Video projectors are used for many applications such as conference room presentations, classroom training, home cinema, movie theaters, and concerts, having mostly replaced overhead, slide and conventional film projectors. In schools and other educational settings, they are sometimes connected to an interactive whiteboard. In the late 20th century, they became commonplace in home cinema. Although large LCD television screens became quite popular, video projectors are ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Homography (computer Vision)
In projective geometry, a homography is an isomorphism of projective spaces, induced by an isomorphism of the vector spaces from which the projective spaces derive. It is a bijection that maps lines to lines, and thus a collineation. In general, some collineations are not homographies, but the fundamental theorem of projective geometry asserts that is not so in the case of real projective spaces of dimension at least two. Synonyms include projectivity, projective transformation, and projective collineation. Historically, homographies (and projective spaces) have been introduced to study perspective and projections in Euclidean geometry, and the term ''homography'', which, etymologically, roughly means "similar drawing", dates from this time. At the end of the 19th century, formal definitions of projective spaces were introduced, which extended Euclidean and affine spaces by the addition of new points called points at infinity. The term "projective transformation" originated in ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Perspective Control
Perspective control is a procedure for composing or editing photographs to better conform with the commonly accepted distortions in constructed perspective. The control would: * make all lines that are vertical in reality vertical in the image. This includes columns, vertical edges of walls and lampposts. This is a commonly accepted distortion in constructed perspective; perspective is based on the notion that more distant objects are represented as smaller on the page; however, even though the top of the cathedral tower is in reality further from the viewer than base of the tower (due to the vertical distance), constructed perspective considers only the horizontal distance and considers the top and bottom to be the same distance away; * make all parallel lines (such as four horizontal edges of a cubic room) cross in one point. Perspective distortion occurs in photographs when the film plane is not parallel to lines that are required to be parallel in the photo. A common case ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
