Realistic material reflectance

Owned by Mihai Iliuta (Unlicensed)
Last updated: 23 Nov, 2013
2 min read

Avoid setting the Reflectance 0° color too bright. Setting it to 255 for example means this material will reflect back all the light it receives, which does not happen in the real world.

Maxwell Render still keeps the amount of light reflected/absorbed within physical limits but the result with such high Reflectance values means the light will keep bouncing around in your scene with very little loss in energy, which will produce noisier renders and a washed-out look with very little contrast.

A reasonable setting even for very bright materials would be around 225-230. For example, the Reflectance value of a white piece of paper, when converted to RGB, is around 225. Please note that this only matters for the Reflectance 0° color. The Reflectance 90° color can be left at fully white (RGB 255).

Left: unnaturally high Reflectance 0° at 255 results in loss of contrast, unrealistic shading and slightly more noise. Right: correct Reflectance 0° set at 225

 

Layers in Additive mode

In the Maxwell material system, you can stack Layers on top of each other in either Normal or Additive blending mode. Special care needs to be taken when using the Additive blending mode, as there is not a typical normalization of material reflectance as in Normal blending mode. Please keep the following points in mind when building a material with Layers set to Additive blending:

  • do not use many layers in Additive mode, especially if all of them are set to 100% and the base Layer color is very bright (meaning the bottom Layer in the material stack is set to a very white material for example)
  • in most cases, for example making a plastic, it will be more efficient in rendering if you use a one Layer approach which contains two BSDFs (one for the diffuse base color set to a high roughness, another with a lower roughness for the sharp highlights and set to about 15-25% weight).

Example of what NOT to do. This material, even though the reflectance 0 is set to a medium grey, will reflect back too much light because of the multiple layers set to Additive mode and produce noisy renders and loss of contrast.