Lecture 25 Computer Science Dvision EECS at UC Berkeley讲座25 计算机科学部是由加州大学伯克利.pptVIP

Design Realization lecture 25 John Canny 11/20/03 Last time Improvisation: application to circuits and real-time programming. Optics: physics of light. This time Reflection, Scattering Refraction, TIR Retro-reflection Lenses Wavefronts and Rays EM waves propagate normal to the wavefront surface, and vice-versa. The ray description is most useful for describing the geometry of images. Reflection Most metals are excellent conductors. They reduce the E field to zero at the surface, causing reflection. If I, R, N unit vectors: I?N = R?N I?(N ? R) = 0 Ray-tracing By tracing rays back from the viewer, we can estimate what a reflected object would look like. Follow at least two rays at extremes of the object. Lambertian scattering For most non-metallic objects, the apparent brightness depends on surface orientation relative to the light source but not the viewer. i.e. brightness isproportional to I?N Refraction – wave representation In transparent materials (plastic, glass), light propagates slower than in air. At the boundary, wavefronts bend: Refractive index Refractive index measures how fast light propagates through a medium. Such media must be poor conductors and are usually called dielectric media. The refractive index of a dielectric medium iswhere c is the speed of light in vacuum, and v is the speed in the medium. Note that ? 1. Refraction – Snell’s law Incident and refracted rays satisfy: Refraction – ray representation In terms of rays, light bends toward the normal in the slower material. Refraction in triangular prisms For most media, refractive index varies with wavelength. This gives the familiar rainbow spectrum with white light in glass or water. Refractive index Refractive index as a function of wavelength for  glass and water Refractive index High-quality optical glass is engineered to have a constant refractive index across the visible spectrum. Deviations are still poss