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Sometimes your scene is either too complicated, or you’re unsure where your noise is coming from, or you’re about to meet your deadline and need an easy way to get a clean render.

In this short tutorial we will study the case of a render that is mostly clean except for some caustics.

NOTE: This particular example has been set up to generate excessive noise and fireflies from specular surfaces.

Method #1: Using the Main and Caustics AOVs

To achieve our denoising goal with this method, all we need to do is enable the Caustics AOV and let Arion render until most of the image is clean:


The Main AOV.
The Main AOV.

The Cautics AOV.
The Caustics AOV.

By subtracting the Caustics AOV from the Main AOV, we get a clean render of the full GI, minus caustics:

Main minus Caustics
Main minus Caustics.

We can carefully denoise or despeckle the Caustics AOV to remove all the fireflies:

Denoised Caustics AOV
Denoised Caustics AOV.

Now we can add the despeckled Caustics AOV to the Main AOV and get the final (clean) image:

The denoised final rendering


Method #2: Using the Direct/Indirect AOVs


This method is similar to the previous one, but requires fewer editing steps.

Note that for this method, you may need to enable the Lights AOV as well, as direct vision of light sources is not included in the Direct/Indirect AOVs:


Direct AOV
The Direct AOV.

The Indirect AOV
The Indirect AOV.

 The Lights AOV
The Lights AOV.

Just like in the previous method, we carefully denoise or despeckle the Indirect AOV:

 Denoised Indirect AOV
The Indirect AOV after denoising.

Then we add it back to the Direct AOV, without forgetting to add the Lights AOV as well, in order to restore the full image:

The denoised final rendering


As you can see, using Arion’s AOVs, it is possible to get out of a difficult rendering situation without sacrificing quality, when the deadline is about to expire.

Note that, in both cases, denoising the Caustics/Indirect AOVs is virtually non-destructive to the final image, because most of the sharpness and evident details in the render are present in the Main/Direct AOVs, which remain intact through the process.

Note also that, strictly speaking, all these operations must happen in HDR (linear) space so addition and subtraction of AOVs is correct.