How to use denoising in Corona Renderer for C4D?

How to use denoising?

Denoising has been introduced in Corona Renderer 1.4. It is a post-rendering effect which analyzes noise in the 3D space and smartly reduces it without producing splotches while maintaining sharp edges and texture details. Therefore it is not a strictly 2D post-process. The result can be interactively blended with the original non-denoised image directly in the VFB after the rendering is finished to achieve desired level of denoising. This is especially useful if the denoised image appears to be overprocessed (generally this should not happen but can sometimes be observed, for example in case of textures with very subtle patterns and rendering a small number of passes).

The main purpose of denoising, along with adaptivity, is reducing the number of passes needed to get a noise-free image. The reported render time reductions are between 50 and 70%. Denoising also attempts to remove fireflies (single bright pixels) from the image.

Denoising is applied after the rendering is finished. This can be done either by limiting the rendering, or by manually stopping it after desired time.

Note: clicking "Cancel" in the Corona VFB (from the dropdown under the “Stop” button) will DISCARD denoising, and it will not be applied to the final rendering! To stop rendering and apply denoising, you need to use the "Stop" button in the Corona VFB. 

How to use denoising?

Enabling denoising

Denoising can be enabled under Render Settings > Corona > General settings > Denoising:

Enabling denoising in render settings and available denoising modes. Click to enlarge.

Available denoising options include:

  • Denoise mode - none/only remove fireflies/full denoising/Gather data for later
  • Denoise amount - this can be seen as opacity of the denoised image being overlaid on top of the original one
  • Denoise radius - radius of the blurring filter. Increasing it may help reduce very strong noise. Decreasing can help prevent loss of fine details. Default value usually works best.

Saving a CXR file and denoising it later

The "Gather data for later" option can be used to skip the actual denoising process, but save the denoising data within the CXR file. Such file can be then denoised later using the Corona Image Editor. Since the denoising is calculated later, you can use this approach to try different Denoise radius values without re-rendering (otherwise, the Denoise radius is baked in at render time).

For more information about CXR file saving for later use, visit this link -> How to save a .CXR file from the VFB

Saving multiple versions of the rendering with different denoising amounts

Multiple "VirtualBeauty" passes can be used to save different versions of the same image at once with various amounts of denoising applied. This allows you to use masks (either generated from Corona or created manually) to blend between different denoising amounts in post, for example if you wish to preserve flakes in car paint or fine bump mapping in carpets that might need a lower denoising level than other parts of the image. Individual denoising amount is specified in the properties of each VirtualBeauty pass regardless of the in-VFB setting:

Multiple VirtualBeauty elements visible on the Corona Multi-Pass list. The denoising value of each of the passes is different than the currently set "denoise amount" in Corona VFB. Click to enlarge.

Denoising other passes

Denoising can be applied to other passes too by enabling the "Apply denoising also to this render element" option in each pass's settings.


Below are some examples where denoising greatly improves image quality:

1. Denoising on and off

1.1. Denoising on - interior scene - 10 minutes.

(click to enlarge)

1.2. Denoising off - interior scene - 10 minutes.

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1.3. Denoising on - strong DOF - 10 minutes.

(click to enlarge)

1.4. Denoising off - strong DOF - 10 minutes.

(click to enlarge)

2. Denoise radius

2.1. Denoise radius: 1
Denoise amount: 1

(default settings)

2.2. Denoise radius: 0,25
Denoise amount: 1
Note that the details are sharper than with default settings, but there are some artifacts visible.

2.3. Denoise radius: 4
Denoise amount: 1
Note how details get blurred.