https://github.com/yangxy/GPEN
https://github.com/yangxy/GPEN/raw/main/figs/real_00.png
https://github.com/yangxy/GPEN/raw/main/figs/real_01.png
https://github.com/yangxy/GPEN/raw/main/figs/real_02.png
https://github.com/yangxy/GPEN/raw/main/figs/real_03.png