TableSphere
The TableSphere recipe compares renderings from PBRT and Mitsuba for a scene of modest complexity and realism.
Above, PBRT rendered the scene.
Above, Mitsuba rendered the scene.
The parent scene contains a mesh approximation of a sphere, sitting on a rectangular table. The table stands on a floor, in a room with 3 walls and a ceiling. 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. A perspective camera views the sphere and table together, including the sphere's shadow.
The sphere is manipulated to use a Ward material sphere with beige-looking diffuse reflectance and uniform specular reflectance. The table is manipulated to use matte material and gray-looking reflectance. The floor is manipulated to use green-looking reflectance. The floor and walls are manipulated to use gray-looking reflectance.
The mappings file specifies the path tracing light transport integrator so that light may 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 executive script MakeTableSphere.m produced the images above. It is located at here:
(path-to-RenderToolbox3)/ExampleScenes/TableSphere/MakeTableSphere.m
The executive script MakeTableSphereFigure.m produces a figure with a summary of results from the 3 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. All the distributions are normalized by maximum value, so that illuminant and pixel spectra 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.