Render noise

Render noise is the grainy, speckled look on surfaces that ought to be smooth. Path tracing follows random light paths for each pixel and averages the results. With few samples that average has not settled yet, neighbouring pixels land on different values, and the image looks sandy. More samples reduce noise, but with diminishing returns: halving the noise takes roughly four times as many samples.

Where noise builds up

• Dark interiors lit through a small window
• Corners and ceilings lit only by bounced light
• Blurred reflections, glass, refraction and caustics
• Small but very bright light sources

Dealing with noise

More samples is the first fix, but not the only one. Light portals sample window light more efficiently, larger light sources produce less noise, and correct exposure stops dark areas from being pushed harder than they need. Denoisers take a partly cleaned image and finish the job in seconds. The best results usually come from a sensible sample count combined with a denoiser.

For step-by-step fixes, see how to reduce render noise.