Thumbnail quality setting is wrong/undocumented

[gas85]

It is true what you say, and was good investigated here:

Understanding and improving Nextcloud Previews

Hi, I have been playing with the preview generation process to try to speed up things for low end devices (mainly for NextCloudPi) In case you are interested I would love some feedback https://ownyourbits.com/2019/06/29/understanding-and-improving-nextcloud-previews/