Direct Lighting cont.

January 9, 2014 - 9:19 pm by Joss Whittle C/C++ Graphics PhD

Continuing on with my work implementing direct lighting contributions to the renderer I thought I’d take a second to show off some shots I’m most happy with.

This first shot I am most pleased with, though it could possibly be subject bias due to my having stared at it for hours as I program; however, I am convinced this looks physically plausible. Or at least, it’s the most physically plausible thing I have rendered so far. This image was rendered using 1250 samples with a 1 unit thick coat of clear varnish on the diffuse red sphere.

I decided to try combining the sphere shader with texture mapping to see how good it would look as a glossy stone shader. Due to the high variance from the two balls this image was rendered at 2x resolution (1024 x 1024) and then downsized back to the normal resolution. The upscaled image was rendered with 100 samples.

The next image was rendered using 1000 samples. Despite the increased convergence speed of the red glass sphere compared to the ceramic one in the first image, the presence of mirror box adds variance back into the image due to it’s broad specular caustics.

I also experimented with testing different light positions to see how robust the direct lighting contribution was compared to Naive Path Tracing alone. A more complete comparison of light positions using 25 samples per image is shown further down this post. For the next image, the light is placed on the floor along the rear wall of the Cornell Box. The shot was rendered with 1000 samples and 1 unit varnish on the sphere.

Next the same shot is shown, this time rendered with only 250 samples and a clear glass sphere. Even after this relatively small number of samples, well defined caustics can be seen on the right wall and on the surface of the sphere, indirectly, through the mirror box.

Light connectivity comparison: (25 samples each)

Below, four renders are shown with varying light positions. The overhead light is a 1 x 1 unit square which emits light uniformly in a downward facing hemisphere, while the three backlit images are lit by unit spheres placed just above the ground.

As you can see, while convergence is still impressive for such a low sample count using a small surface area light source, variance still remains a major issue. Now that I know the direct lighting calculation works however, I think it can be implemented into the Bi-Directional Path Tracer which should help solve some of it’s shading issues.