SimpleSphere
The SimpleSphere recipe compares outputs from 3 different renderers: PBRT, Mitsuba, and the Sphere Renderer Toolbox. The Sphere Renderer Toolbox tests some rendering principles with a simple implementation, so it is able to validate the outputs from relatively complex renderers.
Above, the Sphere Renderer Toolbox rendered the scene.
Above, PBRT rendered the scene.
Above, Mitsuba rendered the scene.
The parent scene contains a sphere illuminated by a point light. The camera views the sphere under orthographic projection. The camera is located "below" and to the "left" of the point light, so that the light, camera, and sphere are not collinear.
The sphere is manipulated to use the Ward material, with orange-looking diffuse reflectance and uniform specular reflectance. The point light is manipulated to use the CIE D65 "daylight" spectrum.
Each renderer renders the scene once. By visual inspection, the renderings are all similar.
The executive scripts MakeMatlabSimpleSphere.m and MakeSimpleSphere.m produced the images above. They are located at here:
(path-to-RenderToolbox3)/ExampleScenes/SimpleSphere/MakeMatlabSimpleSphere.m
(path-to-RenderToolbox3)/ExampleScenes/SimpleSphere/MakeSimpleSphere.m
The executive script MakeSimpleSphereFigure.m produces figure with a summary of results from the SimpleSphere renderings.
6 images at the top of the figure show sRGB representations of renderer outputs: one image for each renderer, and one difference image for each pair of renderers. The differences were computed before sRGB conversion. The 6 images are arranged so that each difference image neighbors both of its source images.
By visual inspection, the difference images show the most obvious difference at the location of the sphere's specular highlight. The 2 difference images that involve the Sphere Renderer Toolbox "reference" also show a "halo" around the top edge of the sphere. This may be the result of image reconstruction filtering performed by PBRT and Mitsuba. The Sphere Renderer Toolbox does not perform the same filtering.
The plot at the bottom of the figure shows power reflected towards the camera at one wavelength, across the height of each rendering, at the location of the dashed orange blue, or gray line. The spectral power follows the curvature of the sphere and illumination provided by the point light, with a sharp peak at the location of the sphere's specular highlight.
The reflected power for PBRT, Mitsuba, and the Sphere Renderer Toolbox "reference" generally agree. The most obvious difference occurs near the left end of the plot: the reference power rises sharply from zero to approximately half of its maximum value, but PBRT and Mitsuba each show an intermediate value at approximately one quarter of maximum. This corresponds with the "halo" seen in the difference images above, and may be the result of image reconstruction filtering.