How to properly connect the Denoise node in Compositor?

Question

After enabling Denoising Data pass, there are now two image outputs:

• Image
• Noisy Image

Which should I use with the Denoise node? Blender Manual doesn't cover it.

Answer 1

The Noisy Image output is meant for the Denoise node.
But with very low samples, the Image output may give better results.

Image output

• this output comes pre-denoised by the Internal denoiser, if it's enabled
• this may lead to some lost detail if it's then denoised egain

Noisy Image output

• this is the intended output for the Denoise node
• the output has been Despeckled to remove fireflies
• however this may cause bad shadow artifacts for extra low sample counts

_{Further Reading:
Denoise node in Blender Manual
How to use Intel denoiser in Blender
Blenderartists.org discussion from Aug 2019
intel openimage denoise}