Scale factor is available in the annotation screenshot dialog, but setting >1 value corrupts the rendering:

(Slicer-4.11.20200930 on Windows, Intel integrated graphics)

Did you try both CPU and GPU volume rendering?

Higher-resolution rendering fails the same way with CPU and GPU volume rendering (looks like in the screenshot above).

Interesting, I believe CPU used to work. It looks like a row-length issue. I wonder if we can snap the row to a multiple of 8 or something similar (just an even number?) as a workaround.

Full layout capture works, but it is just "digital zoom" (image is rendered at screen resolution and then it is resized to the requested size), so it does not improve image quality.

We can give it a try after the VTK9 upgrade. Maybe the issue is resolved in VTK and if not then we can report it to VTK developers.

If the problem gets fixed then it would be useful to use it also in ScreenCapture module. That would also make it easily accessible in Python (as requested here).

This came up again on discourse: https://discourse.slicer.org/t/annotation-screenshot-scale-factor/29091/2