How to use the Fireflies Filter in 3ds Max?

Corona includes a Fireflies Filter to remove single bright pixels—often called “fireflies”—during both production and interactive rendering. This filter targets only isolated fireflies while preserving most of the image’s detail, avoiding the blur or smearing that denoising can introduce. You can apply the Fireflies Filter on its own or use it alongside denoising for even cleaner results. It is useful in static images and animations. 

There are two modes available:

• Simple - faster and more aggressive at identifying and removing fireflies
• Accurate - more accurately preserves highlights, which are not fireflies, at some performance cost

You can find the option under Render Setup > Scene > Fireflies Filter:

Note: using high strength values can make the whole image appear darker. 

Examples

The below examples show how the Fireflies Filter works and how it compares to denoising:

Original image with no Fireflies Filter or denoising applied:

Fireflies appear most clearly on the glass tabletop. This happens because the sun—a small but very bright light source—shines through multiple glass layers and then reflects off the surface below. In this scenario, it’s challenging for the renderer to sample light accurately, which leads to bright fireflies. 

Fireflies Filter disabled. Visible fireflies. 

Fireflies Filter enabled.

Mode: simple

Strength: 0.5

Most of the fireflies disappeared from the glass tabletop. There are still some places where a bright spot can be seen - for example on the wine glasses or on the grass in the background.

Click here to view interactive comparison.

Fireflies Filter enabled. Mode: simple. Strength: 0.5. Some fireflies still visible. 

Fireflies Filter enabled.

Mode: simple

Strength: 1 (default value)

Even less fireflies are visible. 

Click here to view interactive comparison.

Fireflies Filter enabled. Mode: simple. Strength: 1. Less fireflies visible. 

Fireflies Filter enabled.

Mode: simple

Strength: 2

Almost no fireflies visible. Note that some areas appear darker - for example the reflections on the glass tabletop.

Click here to view interactive comparison.

Fireflies Filter enabled. Mode: simple. Strength: 2. Almost no fireflies visible.

Fireflies Filter enabled.

Mode: accurate

Strength: 1

With the accurate mode enabled, more highlights, which are not fireflies, are preserved. Also, less clamping (darkening) occurs in the image. 

Click here to view interactive comparison.

Fireflies Filter enabled. Mode: accurate. Strength: 1. More highlights are preserved than in the case of the simple mode.

Fireflies Filter vs Denoising

Both Fireflies Filter and denoising enabled.

Fireflies Filter Mode: simple

Strength: 1

Denoising: Intel AI

When both the Fireflies Filter and denoising are enabled, you get the best of both: denoising handles most of the noise, while the Fireflies Filter takes care of the brightest spots resulting in a cleaner image.

Click here to view interactive comparison.

Fireflies Filter and Intel AI denoising enabled. Mode: simple. Strength: 1.

Other examples of Fireflies Filter vs Denoising: 

• Fireflies Filter (mode: simple, strength: 1) vs "Only firefly removal" denoising.
  Click here to view interactive comparison. 
  
  
• Fireflies Filter (mode: simple, strength: 1) vs Corona High Quality denoising.
  Click here to view interactive comparison. 
  
  
• Fireflies Filter (mode: simple, strength: 1) vs Intel AI denoising.
  Click here to view interactive comparison. 

Fireflies Filter in Animations

The Fireflies Filter can also be used to mitigate the "dancing fireflies" effect, which can sometimes appear in animations when there are metallic or refractive objects and strong light sources.