NationMaster - Encyclopedia: Procedural textures

A procedural texture is a computer generated image created using an algorithm intended to create a realistic representation of natural elements such as wood, marble, granite, metal, stone, and others. The seawater creature in The Abyss marked CGIs acceptance in the visual effects industry. ... Flowcharts are often used to represent algorithms. ... A news/talk radio station on the frequency of 1300 AM in Grand Rapids, Michigan. ... Marble This page is about the metamorphic rock. ... Granite is a common and widely-occurring group of intrusive felsic igneous rocks that form at great depths and pressures under continents. ... Hot metal work from a blacksmith In chemistry, a metal (Greek: Metallon) is an element that readily forms ions (cations) and has metallic bonds, and metals are sometimes described as a lattice of positive ions (cations) in a cloud of electrons. ... Stone can refer to any of the following: Stone may be used as a building material, as in this dry stone wall and a wall made of stone tht has dog piss up it lol ha ha A rock. ...

Usually, the natural look of the rendered result is achieved by the usage of fractal noise and turbulence functions. These functions are used as a numerical representation of the “randomness” found in everything that surrounds us. The Mandelbrot set, named after its discoverer, is a famous example of a fractal. ... In general usage, noise can be considered data without meaning; that is, data that is not being used to transmit a signal, but is simply produced as an unwanted by-product of other activities. ... Turbulent flow around an obstacle; the flow further away is laminar Laminar and turbulent water flow over the hull of a submarine Turbulence in the tip vortex from an airplane wing In fluid dynamics, turbulence or turbulent flow is a flow regime characterized by low momentum diffusion, high momentum convection... In general, a function is part of an answer to a question about why some object or process occurred in a system that evolved or was designed with some goal. ... This article discusses the use of the word Number in Mathematics. ...

In general, these noise and fractal functions are simply used to “disturb” the texture in a natural way such as the movement of the veins of the wood. In other cases, like marbles textures, they are based on the graphical representation of fractal noise.

Example of a procedural marble texture:

(Taken from The Renderman Companion Book, by Steve Upstill)

 /* Copyrighted Pixar 1989 */ /* From the RenderMan Companion p.355 */ /* Listing 16.19 Blue marble surface shader*/ /* * blue_marble(): a marble stone texture in shades of blue * surface */ blue_marble( float Ks = .4, Kd = .6, Ka = .1, roughness = .1, txtscale = 1; color specularcolor = 1) { point PP; /* scaled point in shader space */ float csp; /* color spline parameter */ point Nf; /* forward-facing normal */ point V; /* for specular() */ float pixelsize, twice, scale, weight, turbulence; /* Obtain a forward-facing normal for lighting calculations. */ Nf = faceforward( normalize(N), I); V = normalize(-I); /* * Compute "turbulence" a la [PERLIN85]. Turbulence is a sum of * "noise" components with a "fractal" 1/f power spectrum. It gives the * visual impression of turbulent fluid flow (for example, as in the * formation of blue_marble from molten color splines!). Use the * surface element area in texture space to control the number of * noise components so that the frequency content is appropriate * to the scale. This prevents aliasing of the texture. */ PP = transform("shader", P) * txtscale; pixelsize = sqrt(area(PP)); twice = 2 * pixelsize; turbulence = 0; for (scale = 1; scale > twice; scale /= 2) turbulence += scale * noise(PP/scale); /* Gradual fade out of highest-frequency component near limit */ if (scale > pixelsize) { weight = (scale / pixelsize) - 1; weight = clamp(weight, 0, 1); turbulence += weight * scale * noise(PP/scale); } /* * Magnify the upper part of the turbulence range 0.75:1 * to fill the range 0:1 and use it as the parameter of * a color spline through various shades of blue. */ csp = clamp(4 * turbulence - 3, 0, 1); Ci = color spline(csp, color (0.25, 0.25, 0.35), /* pale blue */ color (0.25, 0.25, 0.35), /* pale blue */ color (0.20, 0.20, 0.30), /* medium blue */ color (0.20, 0.20, 0.30), /* medium blue */ color (0.20, 0.20, 0.30), /* medium blue */ color (0.25, 0.25, 0.35), /* pale blue */ color (0.25, 0.25, 0.35), /* pale blue */ color (0.15, 0.15, 0.26), /* medium dark blue */ color (0.15, 0.15, 0.26), /* medium dark blue */ color (0.10, 0.10, 0.20), /* dark blue */ color (0.10, 0.10, 0.20), /* dark blue */ color (0.25, 0.25, 0.35), /* pale blue */ color (0.10, 0.10, 0.20) /* dark blue */ ); /* Multiply this color by the diffusely reflected light. */ Ci *= Ka*ambient() + Kd*diffuse(Nf); /* Adjust for opacity. */ Oi = Os; Ci = Ci * Oi; /* Add in specular highlights. */ Ci += specularcolor * Ks * specular(Nf,V,roughness); }

This article was taken from The Photoshop Roadmap with written authorization

See also