...

The images above show a box illuminated by a small light source inside a wall sconce. Because the sconce blocks much of the direct light, most of the illumination in this scene is indirect. Equal-time renders: The image on the left is rendered with only forward path tracing (mergePaths=0, connectPaths=0) with 2048 samples per pixel. The image on the right is rendered with bidirectional path tracing (connectPaths=1, mergePaths=0) with 600 samples per pixel.

...

The left skull image was rendered using only forward path tracing (connectPaths=0, mergePaths=0) with 512 samples per pixel. Caustics are very noisy, and many fireflies are present due to the difficult to integrate lighting caused by the highly specular metallic skull. The right images was rendered using the full vertex connecting and merging algorithm (connectPaths=1, mergePaths=1) with 512 samples per pixel. Fireflies are almost nonexistent, and caustics are much better resolved.

The two images above show PxrVCM images of some interesting caustics. The left image shows a glass lens bisected by a matte plane, and a perpendicular matte plane on the right. The light from the small light source is refracted by the lens, creating an elongated caustic on the matte surfaces. In the right image the lens is replaced by a glass sphere.

...