![]() Rayleigh Scattering Equation: A Comprehensive Overview Renderers, and is the specular equation for VRML.Explore the Rayleigh scattering equation, its applications in optics, atmospheric sciences, and a sample calculation for scattered light intensity. The halfway vector approach avoidsĮxplicit computation of R, and is simple to implement. When it deviates from N, the angle of deviation is easilyįor simplicity, we replace W( q ) with a single constant k s. Now this vector is exactly equal to N if the vector V is parallel to Instead of measuring angles between N, L, V and R, we define a vector H as Specular Reflection - Halfway VectorĪ slight variation on the Phong model is the so-called halfway See the textbook for graphs of typical W( q ) values. While W( q ) is roughly constant over a large range of q values, it deviates at large q, especially as q approaches 90 o. Replaces the constant k d in the diffuse formulae. Small value will lead to a dull-looking surface. A large value (>10) will lead to quite a shiny surface. The quantity ns is called the Phong exponent and is used to control the The viewing direction, then the specular reflection due to a light source q is given by:įrom V to R. It is the vector pointing away from the surface such that R+L is parallel to N. L is, where L is the direction to the light source. Perfect reflector reflects light along a direction R which is at the same angle to N that Many surfaces exhibit a specular (shiny) reflection or highlight. The light source q, then the diffuse intensity due to the source is If N is a unit normal to the surface, and L is a unit direction to The more normal the source is to the surface, the (power/area) of the light hitting a surface from a source depends on the angle between the Mean their reflected light is independent of the source direction however. Most surfaces scatter light uniformly in all directions, no matter Directional Diffuse Reflection - Lambertian Surfaces Normally 3 values used for k d to take this into account. Note: Although the value k d is a scalar,Īll the lighting equations can be repeated once each for R, G and B channels. The amount of ambient light that reflects off a surface isĭetermined by the surfaces ambient-diffuse reflection coefficient, k d. We measure the intensity of ambient light with The simplest lighting model is a uniform field of light in allĭirections, which is called ambient light. Specular surfaces, which model shiny materials like metals, plastics.Diffuse reflecting surfaces, which model matte surfaces like paper or.Light-emitting surfaces, which emit light without needing another.In simple rendering systems like VRML and OpenGL, surfaces come in 3 Turns into an integral in this case, but the method still works. You can model an area or distributed source as a sum of point sources. The number of lights need not be finite to apply superposition. Point in the environment is the sum of the intensities measured with just one of the That when there are two or more light sources, the total light intensity measured at any Light and shading is the principle of superposition. The most important principle to keep in mind when thinking about Intensity of light emitted may or may not depend on the direction in which it travels. A fluorescent light is well-modeled as a distributed light You may also hear about distributed light sources, Instead of emanating from a single point, the light emanates from many points in an area.Ī good example of an area source is a spot light, or a TV screen. The intensity is power/area so as theĪnother kind of light source is an area source. That's because the area that a given flux of rays Note that real light intensity from a point source decreases withĭistance at a rate of 1/r 2. It as power per unit solid angle, so that it does not decrease with distance. But sometimes its more convenient to measure Normally, it wouldīe measured as radiated power per unit area. But we wont be specific about how this power is measured. This is a measure of how much power (energy per unit time) is coming from It emits light in rays that emanate from a single point. The simplest kind of light source is a point source. CS184 Lecture 28 summary CS184 Lecture 28 summary Light Sources
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