That looks to me like they are using deep learning with CNN for denoising. NVIDI...

		fxtentacle on Dec 30, 2021 \| parent \| context \| favorite \| on: iPhone camera app replaces person’s head with a le... That looks to me like they are using deep learning with CNN for denoising. NVIDIA OptiX can produce similar artifacts. However, it appears they forgot to add a loss term to penalize if the source and the denoised result image turn out too different. NVIDIA's denoiser has user-configurable parameters for this trade-off.

I think it would be impossible to train the model in the first place without that loss term.