ptfilter [-filter photonmap|ssdiffusion|mergeicf] [-nphotons n] [-material apple|chicken1|chicken2|ketchup|marble|potato|skimmilk|wholemilk|cream|skin1|skin2|spectralon] [-unitlength length] [-scattering r g b] [-absorption r g b] [-albedo r g b] [-diffusemeanfreepath r g b] [-ior ior] [-maxsolidangle m] [-progress p] inputfiles outputfile
ptfilter reads one or more files in Pixar's point cloud file format and generates a new point cloud file with different data. The type of the new data is determined from the filter mode: photonmap, ssdiffusion, or mergeicf.
In photonmap mode, the input point cloud must be a photon map in which each point contains a power and incident direction. The irradiance at each point is estimated from the power and density of the nearest n points (photons). -nphotons can be used to specify how many points should be used for the irradiance estimates; the default value is 50. The output is a point cloud where each point contains an irradiance value computed as the sum of the power of the nearest photons divided by the area they cover.
In ssdiffusion mode, the input point cloud must contain irradiance values (either direct or global illumination). The data values of the output point cloud are computed with a subsurface scattering diffusion approximation. The scattering properties of the material can be specified in three equivalent ways:
1: The simplest is to just specify a -material and -unitlength. The built-in materials are apple, chicken1, chicken2, ketchup, marble, potato, skimmilk, wholemilk, cream, skin1, skin2, and spectralon; the data values are from [Jensen01]. The default material is marble. The data values assume that the scene units are mm; if this is not the case, a unitlength parameter can be passed to ptfilter. For example, if the scene units are cm, use -unitlength 10.
2: Specify -scattering (the reduced scattering coefficients, sigma's), -absorption (the absorption coefficients, sigmaa), and -ior (index of refraction) of the material.
3: Specify -albedo (BRDF albedo), -diffusemeanfreepath, and -ior (index of refraction) of the material. If varying albedo and/or diffusemeanfreepath values are to be read from the input point cloud, use -albedo fromfile and/or -diffusemeanfreepath fromfile.
The -maxsolidangle determines which octree nodes can be used for subsurface diffusion calculations; it is a time-quality knob with default value of 1. If the -progress parameter is set to 1, a few progress lines will be written out during subsurface diffusion simulation. If set to 2, more verbose information is written. The default is 0 (no progress lines written).The mergeicf mode is for backwards compatibility with earlier releases of PRMan where txmake could be used to merge icf (and ocf) files. In this mode, a number of icf (or ocf) files are read and merged into a new icf (or ocf) file.
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Pixar Animation Studios
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