I have applied Roger’s technique to my M81/M82 image – I found that if I transferred TIF file from Nebulosity after stacking to GIMP and used that rather than BMP/PNG file then I could pull out more detail.
I needed to use additional layering and masking to protect detail in galaxies and then allow me to darken remainder of sky.
My newly processed image:
Finder chart for M81/M82 area from Starry Night planetarium software:
Results of uploading my image to astrometry.net for plate solving: