...though when I tested imagemagick from the command line I could generate an image fine. I would use GD2 instead (which I was using fine in 7.2.2) but since upgrading to 7.3, using GD2 I keep getting a message "fatal error: Allowed memory size of 33554432 bytes exhausted" which I have noticed a few other users posting too. Even though the files were well under 33554432 bytes and the permissions allowed for fair sized images.
Anyway, I would rather get ImageMagick working than GD2 if possible.