Coherent Path Tracing

Packet tracing is a popular and efficient method for accelerating ray tracing. However, packet traversal techniques become inefficient when they are applied to path tracing since the secondary rays are incoherent. In this paper, we present a simple technique for improving the coherency of secondary rays. This technique uses the same sequence of random numbers for generating secondary rays for all the pixels in each sample. This improves the efficiency of the packet tracing algorithm, but creates structured noise patterns in the image. We propose an interleaved sampling scheme that reduces the correlation in the noise and makes it virtually imperceptible in the final image. Coherent path tracing is unbiased, simple to implement and outperforms standard path tracing with packet tracing, while producing images with similar RMS error values.