Only shrink larger images using ImageMagick to a ratio

Question

Using ImageMagick, I can easily have a screenshot of what I want, but I'd like to resize it for using less space. I found this :

convert screen.jpg    -resize 1280x1024\!  screen.jpg

But I'd like to resize it based on the most bigger size (width OR height) and the other one (height OR width) will be proportionnaly resized too.

For example, say I want all my image to be resized to 600px at their most width/height size :

• 1920x1200 => width is the biggest : 600x375
• 600x1200 => height is the biggest : 300x600

How can I do that with ImageMagick? (or at least, defining one max size (only width for example)).

Thanks for your help!

Note: is it possible to implement it automatically with the import command?

Answer 1

To preserve aspect ratio:

convert -resize 600x600 screen.jpg:

• 1920x1200 => 600x375
• 600x1200 => 300x600
• 150x300 => 300x600
• 300x150 => 600x300

convert -resize 600x600\> screen.jpg:

• 1920x1200 => 600x375
• 600x1200 => 300x600
• 150x300 => 150x300 (is not resized to bigger size)
• 300x150 => 300x150 (is not resized to bigger size)

Answer 2

To preserve aspect ratio, you can shrink the image by a certain scale:

convert -resize 50% screen.jpg

Or use a pixel area:

convert -resize 180000@ screen.jpg

This would also blow up small images to the specified area. If you want ImageMagick to shrink your large images but keep small images untouched, use the ">" operator:

convert -resize '180000@>' screen.jpg

Note that you then need to quote the geometry argument in order to prevent your shell interpreting the ">" sign as a file redirectors.

See ImageMagick documentation for these and other options: http://www.imagemagick.org/script/command-line-processing.php#geometry