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Color

Color
Color (American English) or colour (British English; see spelling differences) is the visual perceptual property corresponding in humans to the categories called red, blue, yellow, and others. Color derives from the spectrum of light (distribution of light power versus wavelength) interacting in the eye with the spectral sensitivities of the light receptors. Color categories and physical specifications of color are also associated with objects or materials based on their physical properties such as light absorption, reflection, or emission spectra. By defining a color space, colors can be identified numerically by their coordinates. Because perception of color stems from the varying spectral sensitivity of different types of cone cells in the retina to different parts of the spectrum, colors may be defined and quantified by the degree to which they stimulate these cells. The science of color is sometimes called chromatics, colorimetry, or simply color science. Physics of color Perception

Lightness Three hues in the Munsell color model. Each color differs in value from top to bottom in equal perception steps. The right column undergoes a dramatic change in perceived color. In colorimetry and color theory, lightness, also known as value or tone, is a representation of variation in the perception of a color or color space's brightness. It is one of the color appearance parameters of any color appearance model. Various color models have an explicit term for this property. In subtractive color (i.e. paints) value changes can be achieved by adding black or white to the color. Relationship between lightness, value, and luminance[edit] Observe that the lightness is 50% for a luminance of around 18% relative to the reference white. Priest et al. provide a basic estimate of the Munsell value (with Y running from 0 to 1 in this case):[4] Newhall, Nickerson, and Judd prepare a report for the Optical Society of America. Realizing this is quite close to the cube root, they simplify it to: where .

Tints and shades In common language, the term "shade" can be generalized to furthermore encompass any varieties of a particular color, whether technically they are shades, tints, tones, or slightly different hues;[2] while the term "tint" can be generalized to refer to the any lighter or darker variation of a color (e.g. Tinted windows).[3] When mixing colored light (additive color models), the achromatic mixture of spectrally balanced red, green and blue (RGB) is always white, not gray or black. It is common among some artistic painters to darken a paint color by adding black paint—producing colors called shades—or to lighten a color by adding white—producing colors called tints. An extension of the color wheel: the color sphere. References[edit] See also[edit]

Optics Optics is the branch of physics which involves the behaviour and properties of light, including its interactions with matter and the construction of instruments that use or detect it.[1] Optics usually describes the behaviour of visible, ultraviolet, and infrared light. Because light is an electromagnetic wave, other forms of electromagnetic radiation such as X-rays, microwaves, and radio waves exhibit similar properties.[1] Some phenomena depend on the fact that light has both wave-like and particle-like properties. Explanation of these effects requires quantum mechanics. When considering light's particle-like properties, the light is modelled as a collection of particles called "photons". Optical science is relevant to and studied in many related disciplines including astronomy, various engineering fields, photography, and medicine (particularly ophthalmology and optometry). History[edit] Optics began with the development of lenses by the ancient Egyptians and Mesopotamians. . where and

Light A triangular prism dispersing a beam of white light. The longer wavelengths (red) and the shorter wavelengths (blue) get separated Light is electromagnetic radiation within a certain portion of the electromagnetic spectrum. The word usually refers to visible light, which is visible to the human eye and is responsible for the sense of sight.[1] Visible light is usually defined as having a wavelength in the range of 400 nanometres (nm), or 400×10−9 m, to 700 nanometres – between the infrared (with longer wavelengths) and the ultraviolet (with shorter wavelengths).[2][3] Often, infrared and ultraviolet are also called light. The main source of light on Earth is the Sun. In physics, the term light sometimes refers to electromagnetic radiation of any wavelength, whether visible or not.[4][5] In this sense, gamma rays, X-rays, microwaves and radio waves are also light. Electromagnetic spectrum and visible light The behaviour of EMR depends on its wavelength. Speed of light Optics Refraction where

Óptica geométrica Formación de un arco iris por medio de la óptica geométrica. La óptica geométrica usa la noción de rayo luminoso; es una aproximación del comportamiento que corresponde a las ondas electromagnéticas (la luz) cuando los objetos involucrados son de tamaño mucho mayor que la longitud de onda usada; ello permite despreciar los efectos derivados de la difracción, comportamiento ligado a la naturaleza ondulatoria de la luz. Esta aproximación es llamada de la Eikonal y permite derivar la óptica geométrica a partir de algunas de las ecuaciones de Maxwell. Propagación de la luz[editar] Reflexión y refracción[editar] El fenómeno más sencillo de esta teoría es la de la reflexión, si pensamos unos minutos en los rayos luminosos que chocan mecánicamente contra una superficie que puede reflejarse. La segunda ley de la reflexión nos indica que el rayo incidente, el rayo reflejado y la normal con respecto a la superficie reflejada están en el mismo plano.[2] Ley de Snell[editar] Lentes[editar] Espejos[editar]

Luz Se llama luz (del latín lux, lucis) a la parte de la radiación electromagnética que puede ser percibida por el ojo humano. En física, el término luz se usa en un sentido más amplio e incluye todo el campo de la radiación conocido como espectro electromagnético, mientras que la expresión luz visible señala específicamente la radiación en el espectro visible. La óptica es la rama de la física que estudia el comportamiento de la luz, sus características y sus manifestaciones. El estudio de la luz revela una serie de características y efectos al interactuar con la materia, que permiten desarrollar algunas teorías sobre su naturaleza. En el 55 A.C., Lucrecio, un poeta romano atomista, escribió: "La luz y calor del sol; Estas están compuestas de átomos diminutos que, cuando se metieron, no pierden ningún tiempo en el tiroteo intermedio del aire en la dirección impartida por el empujón. –" De rerum natura Velocidad finita[editar] Refracción[editar] Ejemplo de la refracción. Interferencia[editar]

Cámara oscura La cámara oscura es un instrumento óptico que permite obtener una proyección plana de una imagen externa sobre la zona interior de su superficie. Constituyó uno de los dispositivos ancestrales que condujeron al desarrollo de la fotografía. Los aparatos fotográficos actuales heredaron la palabra cámara de las antiguas cámaras oscuras. Esquema de una cámara oscura del siglo XVIII. Originalmente, consistía en una sala cerrada cuya única fuente de luz era un pequeño orificio practicado en uno de los muros, por donde entraban los rayos luminosos reflejando los objetos del exterior en una de sus paredes. Etimología[editar] La frase cuarto oscuro (del latín camera obscura) fue acuñada por Johannes Kepler en su tratado Ad Vitellionem Paralipomena de 1604. A su vez, "cámara" procede de la lengua árabe que la introdujo por primera vez el físico y matemático musulmán Alhacén, إبن الهيثم. Historia[editar] Cámara oscura y alquimia[editar] Uso[editar] Véase también[editar] Referencias[editar]

Paper size A size chart illustrating the ISO A series and a comparison with American letter and legal formats. Comparison of some paper and photographic paper sizes close to the A4 size. Paper sizes affect writing paper, stationery, cards, and some printed documents. International paper sizes[edit] The following international paper sizes are included in Cascading Style Sheets (CSS): A3, A4, A5, B4, B5.[2] A series[edit] A size chart illustrating the ISO A series. The base A0 size of paper is defined as having an area of 1 m2 and a dimension ratio of 1 to √2, making the A0 paper size exactly m × m. Successive paper sizes in the series A1, A2, A3, and so forth, are defined by halving the preceding paper size across the larger dimension. The significant advantage of this system is its scaling: if a sheet with an aspect ratio of √2 is divided into two equal halves parallel to its shortest sides, then the halves will again have an aspect ratio of √2. The DIN 476 standard spread quickly to other countries.

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