Top-left lighting is an artistic convention in which illustrations are produced so that the light appears to come from the top left of the picture.
The vertical element of the convention comes from the human intuition that sunlight comes from above. Most people prefer lighting from the left when resolving a convex-concave ambiguity, and this preference may be stronger for right-handed people. This is reflected in Roman mosaics and in Renaissance, baroque and impressionist art.
In cartography, the predominant custom of placing the shadow on the right-hand side of hill profiles was established during the 15th century.Computer interfaces tend to use top left lighting as well (cf. Windows 9x and macOS screenshot), although this trend has gradually shifted more towards light coming straight from the top (cf. Android key light.)
There are notable exceptions to this convention, such as Sandro Botticelli's The Birth of Venus due to the point of view which may represent geographical perspective and location.
Viewing images that do not conform to this convention may show a form of convex/concave ambiguity.
A Cartesian coordinate system is a coordinate system that specifies each point uniquely in a plane by a set of numerical coordinates, which are the signed distances to the point from two fixed perpendicular oriented lines, measured in the same unit of length. Each reference line is called a coordinate axis or just axis of the system, and the point where they meet is its origin, at ordered pair (0, 0). The coordinates can also be defined as the positions of the perpendicular projections of the point onto the two axes, expressed as signed distances from the origin.
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 and polished or molded to a desired 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.
A mirror is a smooth or polished surface that returns an image by reflection. Technically, a mirror or reflector is an object such that each narrow beam of light that incides on its surface bounces in a single direction. This property, called specular reflection, distinguishes a mirror from objects that scatter light in many directions, let it pass through them, or absorb it.
North is one of the four compass points or cardinal directions. It is the opposite of south and is perpendicular to east and west. North is a noun, adjective, or adverb indicating direction or geography.
The focal length of an optical system is a measure of how strongly the system converges or diverges light; it is the inverse of the system's optical power. A positive focal length indicates that a system converges light, while a negative focal length indicates that the system diverges light. A system with a shorter focal length bends the rays more sharply, bringing them to a focus in a shorter distance or diverging them more quickly. For the special case of a thin lens in air, a positive focal length is the distance over which initially collimated (parallel) rays are brought to a focus, or alternatively a negative focal length indicates how far in front of the lens a point source must be located to form a collimated beam. For more general optical systems, the focal length has no intuitive meaning; it is simply the inverse of the system's optical power.
The trapezoid bone is a carpal bone in tetrapods, including humans. It is the smallest bone in the distal row of carpal bones that give structure to the palm of the hand. It may be known by its wedge-shaped form, the broad end of the wedge constituting the dorsal, the narrow end the palmar surface; and by its having four articular facets touching each other, and separated by sharp edges. It is homologous with the "second distal carpal" of reptiles and amphibians.
The trapezium bone is a carpal bone in the hand. It forms the radial border of the carpal tunnel.
In vertebrates, thoracic vertebrae compose the middle segment of the vertebral column, between the cervical vertebrae and the lumbar vertebrae. In humans, there are twelve thoracic vertebrae and they are intermediate in size between the cervical and lumbar vertebrae; they increase in size going towards the lumbar vertebrae, with the lower ones being a lot larger than the upper. They are distinguished by the presence of facets on the sides of the bodies for articulation with the heads of the ribs, as well as facets on the transverse processes of all, except the eleventh and twelfth, for articulation with the tubercles of the ribs. By convention, the human thoracic vertebrae are numbered T1–T12, with the first one (T1) located closest to the skull and the others going down the spine toward the lumbar region.
Multistable perception is a perceptual phenomenon in which an observer experiences an unpredictable sequence of spontaneous subjective changes. While usually associated with visual perception, multistable perception can also be experienced with auditory and olfactory percepts.
Moulding, also known as coving(United Kingdom, Australia), is a strip of material with various profiles used to cover transitions between surfaces or for decoration. It is traditionally made from solid milled wood or plaster, but may be of plastic or reformed wood. In classical architecture and sculpture, the molding is often carved in marble or other stones.
A tava(h), tawa(h), tapa, saj, or saj tava is a flat or concave disc-shaped frying pan or griddle, usually made of cast iron, aluminum, or carbon steel. It may be enameled or given a non-stick surface. It is used in the cuisines of Central, West, and South Asia, and of the Caucasus, the Caribbean, and the Balkans. The large concave styles of tava, sometimes called a saj or sac tava, may be turned upside down for cooking a variety of flatbreads on the convex side. The concave side is used like a wok or frying pan.
The Hollow-Face illusion is an optical illusion in which the perception of a concave mask of a face appears as a normal convex face.
An optical flat is an optical-grade piece of glass lapped and polished to be extremely flat on one or both sides, usually within a few tens of nanometres. They are used with a monochromatic light to determine the flatness of other surfaces, whether optical, metallic, ceramic, or otherwise, by interference. When an optical flat is placed on another surface and illuminated, the light waves reflect off both the bottom surface of the flat and the surface it is resting on. This causes a phenomenon similar to thin-film interference. The reflected waves interfere, creating a pattern of interference fringes visible as light and dark bands. The spacing between the fringes is smaller where the gap is changing more rapidly, indicating a departure from flatness in one of the two surfaces. This is comparable to the contour lines one would find on a map. A flat surface is indicated by a pattern of straight, parallel fringes with equal spacing, while other patterns indicate uneven surfaces. Two adjacent fringes indicate a difference in elevation of one-half wavelength of the light used, so by counting the fringes, differences in elevation of the surface can be measured to better than one micrometre.
Portrait photography or portraiture in photography is a photograph of a person or group of people that captures the personality of the subject by using effective lighting, backdrops, and poses. A portrait picture might be artistic, or it might be clinical, as part of a medical study. Frequently, portraits are commissioned for special occasions, such as weddings or school events. Portraits can serve many purposes, from usage on a personal Web site to display in the lobby of a business.
A curved mirror is a mirror with a curved reflecting surface. The surface may be either convex or concave. Most curved mirrors have surfaces that are shaped like part of a sphere, but other shapes are sometimes used in optical devices. The most common non-spherical type are parabolic reflectors, found in optical devices such as reflecting telescopes that need to image distant objects, since spherical mirror systems, like spherical lenses, suffer from spherical aberration. Distorting mirrors are used for entertainment. They have convex and concave regions that produce deliberately distorted images. They also provide highly magnified or highly diminished (smaller) images when the object is placed at certain distances.
Terrain cartography or relief mapping is the depiction of the shape of the surface of the Earth on a map, using one or more of several techniques that have been developed. Terrain or relief is an essential aspect of physical geography, and as such its portrayal presents a central problem in cartographic design, and more recently geographic information systems and geovisualization.
A rectilinear polygon is a polygon all of whose edge intersections are at right angles. Thus the interior angle at each vertex is either 90° or 270°. Rectilinear polygons are a special case of isothetic polygons.
Cube with Magic Ribbons is a lithograph print by the Dutch artist M. C. Escher first printed in 1957. It depicts two interlocking bands wrapped around the frame of a Necker cube. The bands have what Escher called small "nodules" or "buttonlike protuberances" that make use of the dome/crater illusion, an optical illusion characterized by shifting perception of depth from concave to convex depending on direction of light and shadow. Escher's interest in reversible perspectives, as seen in Cube with Magic Ribbons, can also be noted in an earlier work, Convex and Concave, first printed in 1955.
Two-dimensional rotation can occur in two possible directions. Clockwise motion proceeds in the same direction as a clock's hands: from the top to the right, then down and then to the left, and back up to the top. The opposite sense of rotation or revolution is anticlockwise (ACW) or counterclockwise (CCW).
Robert Irwin is associated with the Modern Art movement and is best known for his Installation art. Philosophers influence Irwin’s work, such as Maurice Merleau-Ponty’s ideas of engagement and interaction between the physical world and people. Irwin reflects these ideas through his disc installations. From 1967-1969 he worked on this installation, which consists of convex discs made of metal and plastic. The discs hang on a wall and are illuminated by floodlights to create the illusion of no edges. It is a play on light, dark, shadows, and the space in which the discs lie in.
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