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For example, starting at a light source, we may trace a ray of light to a surface. At this point, one or more of three things might happen with this light ray: absorption, reflection, and refraction. If the surface has any transparent or translucent properties, it refracts a portion of the light beam into itself in a different direction while absorbing some (or all) of the spectrum (and possibly altering the color). It may also reflect all or part of the light ray, in one or more various ways. It can also absorb part of the light ray, resulting in a difference in color or intensity of the reflected and/or refracted light (Note: Between absorption, reflection, and refraction, all of the incoming light must be accounted for, and no more. A surface cannot, for instance, reflect 66% of an incoming light ray, and refract 50%, since the two add up to be 116%.) From here, the reflected and/or refracted rays may strike other surfaces, where their absorptive, refractive, and reflective properties are again calculated based on the incoming rays, and eventually contribute to the final rendered image.

Ray tracing's popularity stems from its realism over other rendering methods (such as scanline algorithms); effects such as reflections and shadows, which are difficult to simulate in other algorithms, follow naturally from the ray tracing algorithm. The popularity of the ray tracing method also benefits from the fact that it is relatively simple to implement and yet yields fairly impressive graphical results; it thus often represents a first entry into graphics programming for many individuals.

The main drawback of ray tracing is that it can be an extremely slow process, due mainly to the large numbers of light rays which need to be traced, and the larger number of potentially complicated intersection calculations between light rays and geometry (the result of which may lead to the creation of new rays). Since very few of the potential rays of light emitted from light sources might end up reaching the camera, a common optimization is to trace hypothetical rays of light in the opposite direction. That is, a ray of light is traced starting from the camera into the scene, and back through interactions with geometry, to see if it ends up back at a light source. This is usually referred to as backwards ray tracing.

Ray tracing for producing computer graphics was first used by scientists at Mathematical Applications Group, Inc., (MAGI) of Elmsford, New York, in the late 1960s under contract with the defense department. At that time, the "Rays" traced were gamma rays emited by hypothetical sources of radiation. MAGI's software calculated not only how the gammma rays bounced off of surfaces, but also how they penetrated and refracted within. These studies helped the government to determine certain military applications, such as how to construct military vehicles that would protect troops from radiation, but also how to design re-entry vehicles for space exploration. Under the direction of Dr. Philip Mittelman, the scientists developed a method of generating images using the same basic software, and started a commercial animation studio in 1972. This studio used ray tracing to generate 3-D computer animation for television commercials, educational films, and eventually feature films -- they created much of the animation in the film "Tron" -- using ray tracing exclusively. MAGI went out of business in 1985.

Since this time, much research has been done on acceleration schemes for it. Many of these schemes focus on speeding up the determination of whether a light ray has intersected an arbitrary piece of geometry in the scene, often by storing the geometric database in a spatially organised data structure. Ray tracing has also shown itself to be very versatile, and in the last decade ray tracing has been extended to global illumination rendering methods such as photon mapping and Metropolis light transport.

Ray tracing in computer graphics derives its name and principles from a much older technique used for lens design since the 1900sCenturies: 19th century 20th century 21st century Decades: 1850s 1860s 1870s 1880s 1890s 1900s 1910s 1920s 1930s 1940s 1950s Years: 1900 1901 1902 1903 1904 1905 1906 1907 1908 1909 Events and Trends Technology Orville and Wilbur Wright make the first doc. Geometric ray tracing is used to describe the propagation of light rays through a lens system or opticalSee also list of optical topics. Optics is a branch of physics that describes the behavior and properties of light and the interaction of light with matter. Optics explains and is illuminated by optical phenomena. The field of optics usually describes the instrument, allowing the properties of the system to be modelled. This is used to optimise the design of the instrument (e.g. to minimise effects such as chromatic aberrationChromatic aberration is caused by the dispersion of the lens material, the variation of its refractive index n with the wavelength of light. Since the focal length f of a lens is dependent on n it follows that different wavelengths of light will be focuse) before it is built.

The principles of ray tracing for computer graphics and optical design are similar, but the technique in optical design usually uses much more rigorous and physically correct models of how light behaves. In particular, optical effects such as dispersionIn optics, dispersion is a phenomenon that causes the separation of a wave into spectral components with different frequencies, due to a dependence of the wave's speed on its frequency. It is most often described in light waves, though it may happen to an, diffractionIn physics, diffraction is a wave phenomenon: the apparent bending and spreading of waves when they meet an obstruction. Diffraction occurs with electromagnetic waves, such as light and radio waves, and also in sound waves and water waves. Diffraction als and the behaviour of optical coatingAn optical coating is a thin layer of material placed on an optical component such as a lens or mirror which alters the way in which the optic reflects and transmits light. One type of optical coating is an antireflection coating which reduces unwanted res are important in lens design, but are less so in computer graphics.

Before the advent of the computertower of a personal computer. A computer is a device for making calculations or controlling operations that are expressible in numerical or logical terms. While factually accurate, this definition and those found in other dictionaries are so broad that th, ray tracing calculations were performed by hand, but now they are common features of optical design software such as Zemax . A simple version of ray tracing known as ray transfer matrix analysisRay transfer matrix analysis (also known as ABCD matrix analysis is a type of ray tracing technique used in the design of some optical systems, particularly lasers. It involves the construction of a ray transfer matrix which describes the optical system; is often used in the design of optical resonator s used in lasers.