Artifacts in result sketch
Hi

Thanks for your great work.

When I test on my own dataset, sometimes it will show some artifacts in darkness place.
Do you have any good suggestions to fix it? 
![artifact](https://user-images.githubusercontent.com/68932652/159424037-c43c3e38-2f2c-4c5f-a981-53e5d9c2a981.jpg)

