What are the boundary artifacts?

[heyoon01]

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As shown in the ablation studies section, without symmetry loss, boundary artifacts become visible.

Can you give more explanation about what a boundary artifact is? Why it happens when not using sym loss?

I thought the symmetry loss was about regularizing self occluded parts when given a sided face as an input (e.g., profile face) but this effect was rather unexpected.

Thanks in advance. Appreciate sharing such a nice work.