How to get rid of excessive noise?

Subtle high-frequency noise is normal for Corona and other path-tracing renderers, especially at the beginning of the rendering process. But strong noise that won't go away after many passes, or after long rendering time, may suggest that the rendering engine encountered some problems in your scene setup. Starting from Corona 1.4 you can use the denoising feature to get rid of the noise by smartly blurring it. It is however recommended to make sure that there are no mistakes in the render setup, or the scene itself.

To efficiently get rid of problematic noise, you need to find out where it comes from. Most common causes of persistent noise include:

Wrong material setup:

This is usually manifested by noise visible only in specific parts of the scene (some objects or some materials).

  • How to create basic materials? (3ds Max | C4D)
  • Unrealistic material albedo - see: What is Albedo? (3ds Max | C4D)
  • Wrong glass type - see: What type of glass should I use? (3ds Max | C4D)
  • Too many mirror-like materials in scene - see: How to set up realistic glass / metal materials? (3ds Max | C4D)
  • Misuse of Corona Light material or self-illumination- see: Should I use Corona Light material or self illumination? (3ds Max | C4D)

Scene lighting:
Noise is visible in strongly lit areas, on edges of light spots or shadows, or when light bounces off objects.

Wrong render settings:

Noise is visible in the whole image or in specific areas like direct light or light bouncing off objects.

Note: you can easily reset all Corona render settings to their default values - see: How to reset settings to their default values?

Fireflies in corners:

Single bright pixels visible in corners of the room or on geometry without thickness.

Noise caused by anti-aliasing or image filtering:
Noise is visible in high-frequency textures or detailed geometry. For information on supersampling in Corona, see: Where are supersampling / antialiasing controls in Corona?
  • If you can see sharp or "jagged" edges, especially around lights, windows or other bright parts of your scene, see: I can see jagged edges!

Noise in camera effects:
Noise is visible in areas affected by depth of field or motion blur effects.

Flickering/splotches in animation when using legacy HD cache GI solver:

Splotches in static image when using legacy HD cache GI solver:

Apart from user errors, there are some physically-correct phenomena that can also cause "noise" effect in real life (for example in photography). This includes:

To determine the cause of noise, it may be sometimes useful to enable material override (see: How to create clay renders? ). If the noise is still visible after applying the diffuse grey material to all objects, it indicates that most probably it is not caused by scene materials. 

Too much noise may also indicate that the rendering process is abnormally slow. To find out about common causes of performance problems, see performance debugging.