Path tracing

Path tracing is the member of the ray tracing family that handles light most completely. A ray leaves the camera, hits a surface and bounces off in a random direction chosen according to the material, and the path continues until it reaches a light or hits the bounce limit. Trace thousands of such paths for a pixel, average them, and the result is very close to how real light behaves.

Path tracing in architectural rendering

Interiors show why it matters. Sunlight through a window lands on the floor, bounces to the ceiling, then spreads across the walls; a timber floor leaves a faint warm tint on a white wall. Path tracing produces these effects naturally, without separate tricks, which is why most physically based engines are built on it.

Noise and render time

The price is noise. With few samples the image looks grainy, and it cleans up as samples accumulate. Denoisers shorten that wait dramatically, and graphics cards speed things up by computing thousands of paths in parallel. Scene choices such as light portals and correct exposure also give a cleaner result in the same time.

We look at the physics of light in more depth in what is path tracing.