TableSphere
The TableSphere scene compares renderings from each renderer for a scene of modest complexity and realism.
Above, PBRT rendered the scene.
Above, Mitsuba rendered the scene.
The scene contains a Ward material sphere with beige diffuse reflectance and uniform gray specular reflectance. The sphere sits on a rectangular table of matte material and gray reflectance. The table stands on a floor of matte material and green reflectance. The floor is part of a room with 3 walls and a ceiling of matte material and gray reflectance.
A single point light illuminates the scene, from above and in front of the sphere, so that the sphere casts a shadow on the table.
The camera views the sphere and table together, including the sphere's shadow and the region of interreflection between the sphere and table.
The scene was rendered with a path tracing integrator so that light could reflect realistically among the scene objects, especially between the table and the sphere in the region of the sphere's shadow.
The scene has 3 conditions that vary the emission spectrum of the point light:
- In the "reddish" condition, the point light emits high intensity at long wavelengths and ramps down to low intensity at short wavelengths. The ratio of high to low intensity is approximately 10:1.
- In the "daylight" condition, the point light emits with the CIE D65 "daylight" spectrum.
- In the "blueish" condition, the point light emits low intensity at long wavelengths and ramps up to high intensity at short wavelengths. The ratio of low to high intensity is approximately 1:10.
In all conditions, the sphere has a prominent specular highlight. The sphere casts a shadow on the table, and a curved reflection of the table is visible in the sphere.
By visual inspection the renderings from PBRT and Mitsuba are similar.
The script MakeTableSphere.m produced the images above. It is located at here:
(path-to-RenderToolbox3)/ExampleScenes/TableSphere/MakeTableSphere.m
The script MakeTableSphereFigure.m produces a summary of results from the TableSphere conditions.
Renderings and data from each condition are shown in separate columns.
The top row shows renderings from PBRT. The middle row shows renderings from Mitsuba.
The bottom row shows plots of spectral power distributions for the illuminant and for an output pixel of interest. The illuminant distributions were known and specified before rendering. The output pixel distributions were read from renderer outputs, at the location of the orange square or blue cross in the renderings above. Spectral power distributions are normalized by maximum value, so that illuminants and pixels appear comparable.
For all 3 conditions, the illuminant spectrum exerts a strong influence of the output pixel spectrum. The pixel spectrum is biased towards long wavelengths "reddish" condition, and towards short wavelengths in the "blueish" condition.
The pixel of interest was chosen in a region where light might reflect many times between the table and sphere before reaching the camera. The complexity of interreflection might have caused the renderers to diverge in their renderings. But in fact, the PBRT and Mitsuba spectra for the pixel of interest generally coincide.