Yes, the mageMagick issue #1819 (https://github.com/ImageMagick/ImageMagick/issues/1819) discusses performance also. See the following quotes: "...the dithering step takes so long that I haven't had the patience to let it finish yet...", "...Not sure why it is doing very slow dithering...", "...The IM developers will have to look into the slow dithering..."
What version of gscan2pdf and imagemagick are you using to reproduce the problem? It has to be recent versions on Debian 11 and the scan or image also needs to be 600dpi (300 dpi is fast). I can still reproduce it on a fresh install done today: apt search gscan2pdf gscan2pdf/testing,now 2.9.1-1 all ... apt search imagemagick imagemagick/testing,now 8:6.9.11.24+dfsg-1+b1 amd64 ... Steps to reproduce, even without a scanner: GIMP > File > New Change "px" to "in" Set Width: 8.5" Height: 11" Advanced > Set X & Y resolution to 600 "pixels/in" Click OK File > Export As: "Untitled.jpg" Leave all other settings on their defaults gscan2pdf > File > Open: "Untitled.jpg" Tools > Threshold > 50% Takes very long, eg 2 minutes. Tools > User-defined > "mogrify -threshold 50% %i" (manually configured previously) Take about 3 seconds. Threshold was working normally before. Sent with ProtonMail Secure Email. ‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐ On Friday, September 4, 2020 5:14 PM, Jeff <jf...@posteo.net> wrote: > Thanks for the report. > > https://github.com/ImageMagick/ImageMagick/issues/1819 > > doesn't mention performance problems, just corruption in the image. > > I can't reproduce your problem. The threshold tool works fine for me > with or without conversion to PNG first. > > Please start gscan2pdf from the command line with the --log=log option, > reproduce the problem, quit, and post the log file, which gscan2pdf > should have compressed to log.xz.
