Path tracing
Also known as: full ray tracing, Monte Carlo path tracing
Path tracing is the most complete form of ray tracing: it follows light rays through many random bounces around a scene to calculate how all the light combines, including colour bleeding from one surface onto another.
It's how most animated films are rendered. While a few games now offer path-traced modes, they depend heavily on top-end graphics cards plus AI upscaling and frame generation to run smoothly.
Path tracing, explained at three levels
At home
Picture sunlight entering a room through one window. It hits the floor, bounces to a wall, then to the ceiling, and the whole room glows softly, picking up a little colour from each surface. Path tracing copies that chain of bounces. For each pixel, the computer follows light along a long, random path around the scene, then adds up what it finds, which is why the result looks so natural.
At work
Path tracing is the most complete form of ray tracing. Instead of ray tracing a few chosen effects, it calculates all the lighting in a scene, direct and bounced, with one physically based method. That matters to studios because lighting comes out correct by default. Artists no longer have to place hidden fake lights to imitate bounced light, which saves time and makes results more consistent from shot to shot.
At home
For each pixel, path tracing shoots a ray into the scene. When it hits a surface, it bounces in a random direction based on the material, rough walls scattering widely and mirrors reflecting sharply, and keeps going for several bounces. The light collected along that path becomes one sample. Average many samples and the pixel settles on the right colour. With too few samples the image looks grainy, so games run an AI denoiser to smooth it.
At work
Hybrid ray tracing adds selected effects to a rasterized image; path tracing replaces the lighting model entirely, so shadows, reflections, and bounce light come from one calculation. Offline renderers such as Pixar's RenderMan and Disney's Hyperion take hundreds or thousands of samples per pixel. Real-time modes, such as Cyberpunk 2077's Overdrive, take one or two, then rely on ReSTIR, which reuses good light paths between pixels and frames, plus denoising, upscaling, and frame generation.
At home
Path tracing is a Monte Carlo method: it estimates an answer by random sampling, like polling voters instead of counting everyone. The catch is that noise only falls with the square root of the sample count, so halving the grain takes four times the work. Smarter sampling, which sends rays toward bright lights and important directions, cuts that cost dramatically. While faster GPUs help, in my view the magic of real-time path tracing lies mostly in choosing which samples to take.
At work
In production, path tracing shifts cost from artist time to compute. Film pipelines render on farms, where convergence time per frame, denoiser artifacts on hair and glass, and consistent material definitions, often in OpenUSD and MaterialX, drive budgets. Games face a different limit: one or two samples per pixel at 60 frames per second, so quality depends on ReSTIR sampling and denoisers like Nvidia's Ray Reconstruction. Path-traced modes must ship alongside rasterized fallbacks, which doubles lighting QA.
Real-world examples
At home
Jerome upgraded his graphics card and tried a game's path-traced mode. Neon signs now lit wet streets and walls with coloured light, though he needed frame generation to keep the game smooth.
At work
Aisha is a lighting artist at a Vancouver animation studio. With a path-traced renderer, she spends less time placing fake bounce lights and more time on the mood of each scene.
How it compares
| feature | Path tracing | Hybrid ray tracing |
|---|---|---|
| Lighting model | All lighting simulated together | Selected effects ray traced |
| Realism | Highest | High |
| Performance cost | Very high | Moderate to high |
| Common use | Films, showcase game modes | Many current games |
Path tracing simulates all light. Hybrid ray tracing picks a few effects.
For analysts
For studios, path tracing can cut artist time spent faking lighting, but render costs rise. I'd compare total cost per finished frame, including artist hours, rather than render time alone.
History & origin
James Kajiya introduced the 'rendering equation' and path tracing in a 1986 paper, giving graphics a physically based model of light. Path tracing was too slow for decades except in research and offline rendering. In the 2010s, film studios switched to path-traced renderers, such as Pixar's RenderMan RIS and Disney's Hyperion. Nvidia's 2019 Quake II RTX demo showed a fully path-traced game. Cyberpunk 2077 added a path-traced 'Overdrive' mode in 2023, and Alan Wake 2 and others followed. In my opinion, path tracing is the long-term destination for real-time graphics, but for now it's a showcase feature for players with expensive hardware.