Aspect Ratio (ar)
Resizes and crops the Original image to match a specified aspect ratio. This parameter will work only when either fit=crop is set. Values for ar are expressed as W:H.
Default: no aspect ratio set. In crop mode, the image is resized to match specified w and h dimensions exactly, discarding image data as needed. If only one dimension is specified, the other dimension is calculated automatically, preserving the original aspect ratio.

Aspect ratio set. ar=10:3&fit=crop: A 1000×520 image cropped using the aspect ratio of 10:3 results in an output image sized 1000x300. (Note the same result can be achieved with w=1000&h=300&fit=crop.) By default, center crop is used; see crop mode for more on directional cropping.
