I am painting some images for printed banners. They need to be very large, maybe even up to 10,000pixels wide. At this image size, Krita starts to slow down a bit, especially when toggling layer visibility or doing lots of Undos. What can I do to help improve performance at these sizes? What settings are going to be the bottleneck? I am only working on a small area of the canvas at a time. Is there a way to select just a certain area and have Krita ignore any operations outside of it while i’m painting?
Unfortunately at that resolution Krita will slowdown, It needs RAM and CPU and for such large image it would need greater than normal PC. I do some illustrations for hoarding and banners too, and I had this experience too.
A work around that I do is to save a sequential copy and then merge unnecessary layers, Sometimes I also work on an image in a bit lower dimension and scale it later.
Use b) Basic 1 brush, it is made on Quick Brush engine so it should be much faster. The more advanced the brush it, the slower will it be rendered. In Pixel Brush engine, the fastest brush tips are circle ones, in which Default is the fastest and Gaussian is the slowest. Color Smudge Brush is ~2x slower than Pixel Brush. Masked Brush in Pixel Brush engine, any texture etc. will also make a difference in performance. Also check out “Precision” and “Spacing” options in brushes you use.
Also go to Performance tab, make sure you give as much RAM as you can (maybe not 100%, but for example maxRAM-1 or -2 or similar value). Make sure Krita can use all of your CPU cores. Make sure you have Graphic Canvas Acceleration turned on and that you don’t have any additional logging (Performance -> Advanced).
Try both turned on and off Instant Preview in brush editor.
There are also other things you can do while painting to make sure you always use the smallest image and smallest brushes you can: for example start with small image, make sure you don’t have any unneeded layers (and limit the needed ones), don’t use filter layers etc.