def update_mark_alpha_channel(
mark: torch.Tensor,
mark_background_color: torch.Tensor | None = None
) -> torch.Tensor:
if mark_background_color is None:
return mark
mark = mark.clone()
mark_background_color = mark_background_color.view(-1, 1, 1)
mark[-1] = ~mark[:-1].isclose(mark_background_color,
atol=1e-3).all(dim=0)
return mark
