Reflection (physics) in the context of "Inverse-square law"

Color (or colour in Commonwealth English) is the visual perception produced by the activation of the different types of cone cells in the eye caused by light. Though color is not an inherent property of matter, color perception is related to an object's light absorption, emission, reflection and transmission. For most humans, visible wavelengths of light are the ones perceived in the visible light spectrum, with three types of cone cells (trichromacy). Other animals may have a different number of cone cell types or have eyes sensitive to different wavelengths, such as bees that can distinguish ultraviolet, and thus have a different color sensitivity range. Animal perception of color originates from different light wavelength or spectral sensitivity in cone cell types, which is then processed by the brain.

Colors have perceived properties such as hue, colorfulness, and lightness. Colors can also be additively mixed (mixing light) or subtractively mixed (mixing pigments). If one color is mixed in the right proportions, because of metamerism, they may look the same as another stimulus with a different reflection or emission spectrum. For convenience, colors can be organized in a color space, which when being abstracted as a mathematical color model can assign each region of color with a corresponding set of numbers. As such, color spaces are an essential tool for color reproduction in print, photography, computer monitors, and television. Some of the most well-known color models and color spaces are RGB, CMYK, HSL/HSV, CIE Lab, and YCbCr/YUV.

An image sensor or imager is a device that detects and conveys information used to form an image. It does so by converting the variable attenuation of light waves (as they pass through or reflect off objects) into signals, small bursts of current that convey the information. The waves can be light or other electromagnetic radiation. Image sensors are used in electronic imaging devices of both analog and digital types, which include digital cameras, camera modules, camera phones, optical mouse devices, medical imaging equipment, night vision equipment such as thermal imaging devices, radar, sonar, and others. As technology changes, electronic and digital imaging tends to replace chemical and analog imaging.

The two main types of electronic image sensors are the charge-coupled device (CCD) and the active-pixel sensor (CMOS sensor). Both CCD and CMOS sensors are based on metal–oxide–semiconductor (MOS) technology, with CCDs based on MOS capacitors and CMOS sensors based on MOSFET (MOS field-effect transistor) amplifiers. Analog sensors for invisible radiation tend to involve vacuum tubes of various kinds, while digital sensors include flat-panel detectors.

A telescope is a device used to observe distant objects by their emission, absorption, or reflection of electromagnetic radiation. Originally, it was an optical instrument using lenses, curved mirrors, or a combination of both to observe distant objects – an optical telescope. Nowadays, the word "telescope" is defined as a wide range of instruments capable of detecting different regions of the electromagnetic spectrum, and in some cases other types of detectors.

The first known practical telescopes were refracting telescopes with glass lenses and were invented in the Netherlands at the beginning of the 17th century. They were used for both terrestrial applications and astronomy.

A biological pigment, also known simply as a pigment or biochrome, is a substance produced by living organisms that have a color resulting from selective color absorption. Biological pigments include plant pigments and flower pigments. Many biological structures, such as skin, eyes, feathers, fur and hair contain pigments such as melanin in specialized cells called chromatophores. In some species, pigments accrue over very long periods during an individual's lifespan.

Pigment color differs from structural color in that it is the same for all viewing angles, whereas structural color is the result of selective reflection or iridescence, usually because of multilayer structures. For example, butterfly wings typically contain structural color, although many butterflies have cells that contain pigment as well.

Infrared thermography (IRT), also known as thermal imaging, is a measurement and imaging technique in which a thermal camera detects infrared radiation originating from the surface of objects. This radiation has two main components: thermal emission from the object's surface, which depends on its temperature and emissivity, and reflected radiation from surrounding sources. When the object is not (fully) opaque, i.e. exhibits nonzero transmissivity at the cameras operating wavelengths, transmitted radiation also contributes to the observed signal. The result is a visible image called a thermogram. Thermal cameras most commonly operate in the long-wave infrared (LWIR) range (7–14 μm); less frequently, systems designed for the mid-wave infrared (MWIR) range (3–5 μm) are used.

Since infrared radiation is emitted by all objects with a temperature above absolute zero according to the black body radiation law, thermography makes it possible to see one's environment with or without visible illumination. The amount of radiation emitted by an object increases with temperature, and thermography allows one to see variations in temperature. When viewed through a thermal imaging camera, warm objects stand out well against cooler backgrounds. For example, humans and other warm-blooded animals become easily visible against their environment in day or night. As a result, thermography is particularly useful to the military and other users of surveillance cameras.

Digital imaging or digital image acquisition is the creation of a digital representation of the visual characteristics of an object, such as a physical scene or the interior structure of an object. The term is often assumed to imply or include the processing, compression, storage, printing and display of such images. A key advantage of a digital image, versus an analog image such as a film photograph, is the ability to digitally propagate copies of the original subject indefinitely without any loss of image quality.

Digital imaging can be classified by the type of electromagnetic radiation or other waves whose variable attenuation, as they pass through or reflect off objects, conveys the information that constitutes the image. In all classes of digital imaging, the information is converted by image sensors into digital signals that are processed by a computer and made output as a visible-light image. For example, the medium of visible light allows digital photography (including digital videography) with various kinds of digital cameras (including digital video cameras). X-rays allow digital X-ray imaging (digital radiography, fluoroscopy, and CT), and gamma rays allow digital gamma ray imaging (digital scintigraphy, SPECT, and PET). Sound allows ultrasonography (such as medical ultrasonography) and sonar, and radio waves allow radar. Digital imaging lends itself well to image analysis by software, as well as to image editing (including image manipulation).

An optical prism is a transparent optical element with flat, polished surfaces that are designed to refract light. At least one surface must be angled—elements with two parallel surfaces are not prisms. The most familiar type of optical prism is the triangular prism, which has a triangular base and rectangular sides. Not all optical prisms are geometric prisms, and not all geometric prisms would count as an optical prism. Prisms can be made from any material that is transparent to the wavelengths for which they are designed. Typical materials include glass, acrylic and fluorite.

A dispersive prism can be used to break white light up into its constituent spectral colors (the colors of the rainbow) to form a spectrum as described in the following section. Other types of prisms noted below can be used to reflect light, or to split light into components with different polarizations.

The visual appearance of objects is given by the way in which they reflect and transmit light. The color of objects is determined by the parts of the spectrum of (incident white) light that are reflected or transmitted without being absorbed. Additional appearance attributes are based on the directional distribution of reflected (BRDF) or transmitted light (BTDF) described by attributes like glossy, shiny versus dull, matte, clear, turbid, distinct, etc. Since "visual appearance" is a general concept that includes also various other visual phenomena, such as color, visual texture, visual perception of shape, size, etc., the specific aspects related to how humans see different spatial distributions of light (absorbed, transmitted and reflected, either regularly or diffusely) have been given the name cesia. It marks a difference (but also a relationship) with color, which could be defined as the sensation arising from different spectral compositions or distributions of light.