Hi, I’ve been away from Linux for a few months, but I’ve returned because Microsoft.
I was editing a tiff file with GIMP 2.10.14 and it’s being incredibly slow. Even just brushing on a mask, in a project with a single layer, the tool lags severely behind my cursor. Every tool is very slow to update the screen.
Back in summer is the last time I used GIMP and I really don’t remember it being this slow, quite the contrary, actually.
Don’t know the answer to your problem, sorry…
However, it would be helpful to try their latest version of GIMP, that is 2.10.18 (unless you have already done it…)
Perhaps they have already solved this problem…
In my experience GIMP is not particularly fast compared to other “similar” applications.
For instance it doesn’t take full advantage of your GPU (even though some code is implemented to do so: it is OpenCL stuff, from what I have cursory read…).
As usual, you need a very powerful hardware (CPU, RAM etc) to edit your pictures fast
later edit: I downloaded and installed the latest version and it’s basically the same.
What I did notice is that the bigger the brush is, the slower it is to update the screen. When the brush size is very small, the update is basically instant, when it’s a really big size, it updates almost 2 seconds later.
Even the interface is very sluggish, dragging and resizing panels is laggy as all hell.
Brushes are slow with gimp. In my experience they lag significantly behind the mouse pointer. Perhaps there are tweaks or hardware solutions but for me its just a downside of gimp.
For brush/pencil/eraser, the apparent slowness & lag can come from the “Smooth stroke” options.
Another reason for slowness is an insufficient tile cache. Go to Edit>Preferences>System resources>Resource consumption>Tile cache size and make sure the size is set to something reasonable (at least half you RAM). Otherwise Gimp self-limits the amount of RAM it uses and swaps to disk.