Legacy ImageMagick Discussions Archive

I'm on Debian "Sid". And interestingly, I just completed a system update, and now the command works fine. So perhaps it was a bug that's been fixed.

Now I'm running ImageMagick 6.8.9-6 Q16 x86_64 2014-09-06. Don't know what I was running just before the update.

I finally found a magick incantation that works well:
@fmw42: Those commands generated colour pictures with lots of speckle-y artifacts.

I am trying to convert galaxy images to greyscale, but I need to preserve most of the detail of the spiral "arms". I have read ImageMagick tutorials, and tried loads of different filters, thresholds, other options etc., but I'm not having any luck. Can anyone offer any suggestions? Here is a sample ...