Looks like you checked 'merge filter'
Doesn't happen here as long as merge filter isn't checked, there is only one layer after edge detect. Then invert and all is ok.
If you want your colors reversed you can do it in the gimp plugin GMIC, under contours - 'edges' and check negative colors. Make sure you have the output as in place, if you dont want two layers
In Gimp only
If you want to make the grey/black darker you could try contrast/lavels/curves
Maybe don't desaturate first.
Doesn't happen here as long as merge filter isn't checked, there is only one layer after edge detect. Then invert and all is ok.
If you want your colors reversed you can do it in the gimp plugin GMIC, under contours - 'edges' and check negative colors. Make sure you have the output as in place, if you dont want two layers
In Gimp only
If you want to make the grey/black darker you could try contrast/lavels/curves
Maybe don't desaturate first.
