An example how to resize images in Kirby with SimpleImage class. SimpleImage class is now built in to make thumbnail creation work. Probably only work with Kirby 2.1+.
Here is some information of how to use it:
$image = new abeautifulsite\SimpleImage( $load_image_path );
$image->fit_to_width( 300 )->save( $save_image_path );
More options and full documentation…
It can be useful if you don’t like the Kirby thumbnail function and want to do it your own way.