polkujäljitys

Polkujäljitys (path tracing) is a rendering technique used in computer graphics to simulate realistic light transport by tracing paths of light as they bounce through a scene. It solves the rendering equation through Monte Carlo integration, producing global illumination that includes direct and indirect lighting, soft shadows, color bleeding, and caustics. In a typical setup, rays are cast from the camera into the scene; when a ray intersects a surface, the algorithm computes the emitted light and the reflected radiance according to the surface’s BRDF and recursively spawns new rays to continue the light path.

As an unbiased estimator, path tracing converges to the correct solution as the number of samples per pixel increases. In practice, results with a small number of samples are noisy, so many rendering tasks rely on progressive rendering, temporal accumulation, or denoising techniques to reduce visible noise. The method often uses termination strategies such as Russian roulette to limit recursion depth while maintaining unbiasedness. Variants and enhancements include bidirectional path tracing, which connects light and camera paths; metropolis light transport, which focuses sampling on important light paths; and stochastic denoising or denoising-friendly sampling schemes.

Path tracing is widely used in offline rendering for film, visual effects, and architectural visualization due to its ability to reproduce physically plausible lighting without extensive manual tuning. Real-time or interactive applications have traditionally used approximations through rasterization or biased global illumination, but advances in hardware acceleration and denoising have enabled increasingly credible real-time path-tracing demonstrations.