- Procedural texture
A procedural texture is a
computer generated image created using analgorithm intended to create a realistic representation of natural elements such aswood ,marble ,granite ,metal , stone, and others.Usually, the natural look of the rendered result is achieved by the usage of
fractal noise andturbulence functions. These functions are used as anumerical representation of the “randomness ” found in everything that surrounds us.In general, these noise and fractal functions are simply used to "“disturb”" the texture in a natural way such as the undulations 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 1988 */ /* 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 [http://www.photoshoproadmap.com The Photoshop Roadmap] with written authorization"
ee also
*
Texture synthesis
*Procedural generation
*Perlin noise
* [http://illusions.hu/index.php?task=100&lang=0&statpage=114 Procedural wallpapers]
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