Using a handwritten signature in Okular

Hi,
I found how to define a handwritten signature in Okular (Annotations > Stamp).
But it appears very small and jaggy if you expand it.
It doesn’t help making it bigger, with higher resolution (png) or using a svg (which is strange, I wouldn’t expect jaggy edges in a svg).

I found this topic Using Okular to sign documents with handwritten signatures and it amazes me the small size isn’t experienced.