Get Emission Color/Weight#
Get Emission Color and Get Emission Weight are 2 texture operators designed to improve the quality of emission importance sampling texture when enabling Emission Importance Sampling or working with Geometry Lights. For more information information please refer to Emission Importance Sampling and Geometry Light.
These 2 texture operators are meant to simplify the extraction of the chromaticity and emission weight from any input texture operators:
- Get Emission Color extracts the chromaticity (color without its intensity component).
- Get Emission Weight extracts the emission weight of the color.
These two nodes work with any kind of textures that can either be an HDR/SDR texture map or the multiplied result of the emission color and weight textures when emission is defined by 2 textures.
The idea is to plug an input texture to both a Get Emission Color and Get Emission Weight. Then plug the output of Get Emission Color to Emission Color of a material or the Color attribute of a geometry light and Get Emission Weight to Emission Weight attribute of the material or the geometry light.
When having this setup, the color will no longer affect the emission weight. Emission Texture Importance Sampling can be set to Weight and you are free to do any operations to the color that doesn't introduce luminance information such as Hue. For example, it is possible to use a randomization to shift the hue of the color for example:
Using the Get Emission Color to extract the chromaticity and Get Emission Weight to extract the intensity of the color. The output of Get Emission Color can then be randomly shifted in hue without affecting the quality of the sampling.
You can also use an input HDR texture and Get Emission Color and Get Emission Weight to output the proper color and weight.
The path tracer fails to correctly importance sample the texture when Emission Texture Importance Sampling is set to Weight while texturing the emission color of a Polysphere surrounding the scene with a HDR.
Using Get Emission Color and Get Emission Weight to split the proper color chromaticity from the emission weight, the texture is properly sampled.