Imagemagick is a powerful image manipulation program. This tutorial is about resizing image with Imagemagick.
Resize an image to 500px width.
mogrify -resize 500 image.pngResize an image to 500×300, with aspect ratio preserved.
mogrify -resize 500x300 image.pngForce resize an image to 500×300.
mogrify -resize 500x300! image.pngResize multiple images.
mogrify -resize 500x300 *.png
Hey. For Mac users, i wanna introduce an image resizng tool called PhotoMagic, which is powerful and easy to use. It can help you resize your images or photos for photo album, making wallpaper etc. Besides, it supports batch resize and batch saving. Are you a Mac user? if you are, hen go have a look.