A path tracer is technically a type of ray tracer that accumulates indirect lighting via random sampling

The term ‘ray tracing’ is ambiguous: it covers a family of algorithms. A path tracer specifically fires rays that bounce randomly through the scene, accumulating indirect illumination over many samples per pixel. This is distinct from Whitted-style ray tracing, which traces mirror reflections and refractions deterministically. The Ray Tracing in One Weekend series builds a path tracer — the algorithm behind photorealistic film rendering — not a Whitted tracer. Conflating the two leads to misconceptions about performance and output quality. Path tracing is unbiased given enough samples; Whitted tracing handles only specular paths and misses diffuse indirect lighting entirely.

Examples

Book 1 of the series produces a path-traced image with soft indirect shadows and color bleeding — effects impossible with simple Whitted ray tracing.

Assessment

Name two visual phenomena that a path tracer produces that a Whitted ray tracer cannot; explain why the brute-force path tracer is called ‘unbiased’.