How to resize an image with imagemagick to show a horizontal margin if required

Question

I'm using imagemagick to resize photographs in my app, but I'm having trouble getting it to work as I need it to.

Can someone please help me come up with the right combination of option configurations to meet the following requirements:

• Images should be resized to 320x213:
  • Set the height to exactly 213px
  • If the image is smaller than 320x213, enlarge it
  • If the image is larger than 320x213, make it smaller
  • Preserve the aspect ratio of the image
• If the resized image is narrower than 320px:
  • center the image horizontally
  • add a background colour to the back of the image
  • preserve the aspect ratio of the image
• If the resized image is wider than 320px:
  • trim the additional pixels evenly from both sides

Answer 1

In ImageMagick, try

convert image -resize x213 -gravity center -background white -extent 320x213 result