gscan2pdf: scanimage; libimage-sane-perl; scanadf

[Duliwi]

When I use gscan2pdf (this is a default scanning programme in MX Linux) with the setting "scanimage" together with my HPLIP printer all works as expected.

But when I choose libimage-sane-perl or scanadf, then gscan2pdf is very sluggish. For every little thing ...
-(e.g. pressing a button in the button bar immediately brings a core of my CPU to 100% for about 30 seconds. (The same, when I want to close the programme.)
-After scanning, it takes a long time to process the scan (again, related to the load of one of the cpu cores at 100%).

1. Question: Is this normal?
2. What is the difference between scanimage; libimage-sane-perl; scanadf ?

Thank you.

Edit:
I was wrong: Also with "scanimage" it is very sluggish compared with simple-scan. Is this normal?

What did I scan?
Answer: A4, grey scale, 300 dpi