Zooming gif files

[sphh]

I use the Camera Roll to display pictures coming in via E-Mail. I use K-9 Mail.

I can display gif files, but have a problem zooming: The zoomed picture becomes granulated. Best to show it in an example:
Original file:

Files opened and displayed in landscape:

Picture zoomed in:

If I rotate the phone to portrait, the effect is even more pronounced.

jpeg pictures are displayed well and I can zoom in without loosing quality.

My system:
Android v8.1.0
Camera Roll v1.0.6 (installed via F-Droid)

If you need more information, I am happy to supply it. Just please tell me what you need.