Filter shaders

A filter shader returns a spectrum as a function of shading parameters (UV coordinates, world-space position and normal, etc...). For instance, it may describe the spectral color of a diffuse material, and this color may vary across the object's surface.

Filter shader types

Constant

This filter shader returns a constant value, it does not depend on any parameter (wavelength or shading parameters)

Children nodes

none

Parameters

value

real

The constant filter shader value

Uniform

This filter shader returns spectrum and does not depend on shading parameters

Children nodes

spectrum

Spectrum : The uniform spectrum value

Parameters

none

Texture

This filter shader gets a RGB value from a texture at shading UV coordinates, and convert it to spectral values using the same algorithm as the RGB spectrum

An optional correction curve is applied to the raw RGB values, similar to a brightness/contrast/gamma adjustment:

• The value is first applied a gamma curve, controlled by the greypt parameter. The grey value (0.5) is mapped to greypt, hence setting greypt to 0.5 disables this correction
• Then, the value is scaled by the scale parameter
• And finally, offset is added to the value

In other words:

• Black(0) is mapped to the offset parameter
• White(1) is mapped to offset+scale
• Grey(0.5) is mapped to offset+scale*greypt

Children nodes

image

Image : The image to use as a texture

Parameters

greypt

real

The non-linear grey point adjustment, between 0.25 and 0.9

scale

rgb

RGB value scaling, or contrast adjustment

offset

rgb

RGB value offset, or brightness adjustment

uvscale

real

The UV coordinates scaling factor. Scales the texture spatially over the geometry

Environment ground matte

The envgroundmatte filter shader was applied with a lambertian material to a plane below the car, receiving cast shadows, and seamlessly integrating in the environment

This advanced filter shader computes the diffuse albedo of a horizontal lambertian surface, so that it has the same radiance as a ground point in the environment map. It assumes that envmap pixels below the horizon correspond to an horizontal, flat and diffuse ground.

This filter shader is very useful for rendering shadows cast over an envmap ground.

Children nodes

image

Image : The envmap image

Parameters

up

vec3

The direction where the top of the envmap (zenith) is oriented in space. Should be orthogonal to front

front

vec3

The direction where the center of the envmap is oriented in space. Should be orthogonal to up

center

vec3

The camera position for projecting the environment on the geometry.

rgbmax

vec3

Clamps the calculated RGB albedo values by this setting

See also

Node types