The Cornell Box #
Introduction #
Here is a test rendering of the Cornell Box using Okapi Renderer with a naive diffuse path tracing integrator (hence the noise even though the image was rendered with 8192 spp):
The Cornell Box data can be found at the The Cornell Box website provided by the Cornell University. There is also a file sharing service provided by the Cornell University which is also called Cornell Box. I am not sure if this is deliberate and if the file service does know about its legacy.
The Cornell Box Data provided in the data section consists of a cubic box that has one open side. Inside the box, there is a tall and a short block. The tall block is left. The short block is right. All surfaces are assumed to be Lambertian. Note that there are also a lot of other variants of the Cornell Box and a few of them are mentioned in the History section. The Data section provides for the material and light information measured wavelength data. No RGB color data is provided. From the spectral measured data RGB values can be derived. Anyway, different variants are using different RGB color values. The following table gives an impression of which RGB values can be found in the wild.
| Renderer | Floor | Light | Ceiling | Back wall | Right wall | Left wall | Short block | Tall block | |
|---|---|---|---|---|---|---|---|---|---|
| Tungsten | R | 0.725 | 17 | 0.725 | 0.725 | 0.14 | 0.63 | 0.725 | 0.725 |
| G | 0.71 | 12 | 0.71 | 0.71 | 0.45 | 0.065 | 0.71 | 0.71 | |
| B | 0.68 | 4 | 0.68 | 0.68 | 0.091 | 0.05 | 0.68 | 0.68 | |
| Mitsuba | R | 0.885809 | 18.387 | 0.885809 | 0.885809 | 0.105421 | 0.570068 | 0.45 | 0.45 |
| G | 0.698859 | 10.9873 | 0.698859 | 0.698859 | 0.37798 | 0.0430135 | 0.30 | 0.30 | |
| B | 0.666422 | 2.75357 | 0.666422 | 0.666422 | 0.076425 | 0.0443706 | 0.90 | 0.90 | |
| Nori | R | 0.725 | 40 | 0.725 | 0.725 | 0.161 | 0.630 | 0.725 | 0.725 |
| G | 0.71 | 40 | 0.71 | 0.71 | 0.133 | 0.065 | 0.71 | 0.71 | |
| B | 0.68 | 40 | 0.68 | 0.68 | 0.427 | 0.05 | 0.68 | 0.68 |
For the rendering from above the RGB colors from Tungsten have been used.
Spectral rendering vs. RGB rendering #
The following images compares a spectral rendering of the Cornell Box with a RGB rendering. For rendering Mitsuba 3 has been used:
When only diffuse surfaces are involved there is no big difference between spectral an RGB rendering.