Uses to much Memory

The program currently uses far too much memory.
For each open window there are at least three, sometimes even six threads which use 100 times as much memory as the filesize.
Arbitrary rotating is only possible without zoom.
Even with that much caching, the program is often slow.
Fully entering full screen takes often more than half a minute.

Jojo Design about Xee³: Image Viewer and Browser, v3.5.1