------------------------------------------------------------------------
magick one image format to another
------------------------------------------------------------------------

$ magick a.pdf a.png   #convert pdf to png

can also resize

$ magick image.jpg -resize dimensions newimage.jpg

dimension 
  e.g. 800x600 
       800x600! (exact)
       800 (preserve aspect ratio by letting program determine width)
     
$ magick image.jpg -rotate 90 newimage.jpg

See
https://www.lifewire.com/convert-linux-command-unix-command-4097060

------------------------------------------------------------------------
pngpngquant .. compress png file
------------------------------------------------------------------------

pngquant file.png 
(see -- help for options)