The generic Flat Black Paint BSDF is a parametric scatter model that has only one user input; the Total Integrated Scatter (TIS) at normal incidence. FRED takes the TIS value and scales the BSDF accordingly. The BSDF used in this model is a complex 3 dimensional polynomial fit to the scatter distribution from a flat surface treated with a generic flat black paint. It is nearly Lambertian at normal incidence but at large angles of incidence there is significant scatter in the (forward) specular direction, which is a characteristic of all flat black paints.
WARNING:The TIS entry is for normal incidence. If this entry is greater than 0.25, the scattered power at high angles of incidence can exceed the incident power, which violates conservation of energy. Use with caution.
The following picture shows a normalized log space plot of the reflected hemispherical scatter intensity distribution in direction cosine space. The Flat Black Paint scatter parameters are TIS = 0.02. The specular angle is 30 degrees.
This feature can be accessed by selecting Flat Black Paint as the Scatter Type in the Create a new scatter model dialog box.
The TIS entry is measured at normal incidence. FRED uses this entry as an offset to shift the magnitude of the BSDF up and down, but the functional form of the distribution is unchanged.
The TIS scatter model is wavelength invariant.
Scatter in transmission and reflection All scatter models describe the BSDF as measured over a maximum of 2p steradians. Both transmitted and reflected scatter can be modeled by specifying the two scatter directions simultaneously with the appropriate direction controls found under the Scatter tab in the Surface Dialog.
Multiple scatter models can be attached to the same surface. The scatter direction controls are then imposed on every attached model.
Scripting with Flat Black Paint Subroutines •AddBlackPaint YourScatter •SetBlackPaint IndexInScatterList, YourScatter •GetBlackPaint IndexInScatterList, YourScatter
Data structure T_BLACKPAINT •Name – (string) holds the name of the mode. Default is an empty string. •Description – (string) holds the description of the model. Default is an empty string. •Refl – (double) The value of the Normal Incidence Reflectivity coefficient. Default is 0. •Vd – (double) holds the ABBE number at the ‘d’ wavelength. Default is 0. •ApplyRefl – (Boolean) Applies the scatter model on reflection. Default is False. •ApplyTrans – (Boolean) Applies the scatter model on transmission. Default is False. •HaltIncident – (Boolean) Halts the incident ray. Default is False.
This example adds a Black Paint Scatter model to the FRED file associated with this script.
Dim s As T_BLACKPAINT
This example sets the fourth Scatter model’s name to “Black Paint Example 2”, as long as that scatter model is a Black Paint model. It fails if it is any other scatter type.
Dim s As T_BLACKPAINT
This example gets the fourth Scatter model and prints its name, as long as that scatter model is a Black Paint model. It fails if it is any other scatter type.
Dim s As T_BLACKPAINT
ABg – for polished surface scatter Binomial - plane symmetric case of general Polynomial Extended Harvey-Shack - shift variant form of the Harvey-Shack model Extended Scripted - User-defined scattering function that allows manipulation of the scattered rays' polarization state Harvey-Shack – for polished surface scatter K-Correlation – analytic PSD Lambertian – for diffuse scatter Phong – cosn from specular Polynomial - General polynomial with diffuse and Lorentzian component Scripted - User-defined scattering function Surface Particle (Mie) – for particulate contamination Tabulated BSDF – measured BSDF data Tabulated PSD – measured PSD data
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