thumb.php

<?php

// resize an image by the width
$image->resize($width)->url();

// resize by width and height. The bigger one will be downscaled
$image->resize($width, $height)->url();

// adjust the jpeg compression
$image->resize($width, $height, $quality)->url();

// pass null as second argument if you only want to specify the width but also change the quality
$image->resize($width, null, $quality)->url();

// crop an image: by defining only the width the crop will be square
$image->crop($width)->url();

// speificy a width and height to get non-square crops
$image->crop($width, $height)->url();

// adjust the jpeg compression 
$image->crop($width, $height, $quality)->url();

// pass null again for the height if you want a square crop but also adjust the quality
$image->crop($width, null, $quality)->url();

Both methods return a Kirby media object which has tons of additional methods. So you can also do stuff like this:

echo $image->resize(300)->height();

echo $image->resize(300)->niceSize();

echo $image->resize(300)->ratio();

echo $image->resize(300)->orientation();

// etc. 

You can find more about it here: http://getkirby.com/docs/toolkit/api#media

@bastianallgeier is there still an equivalent of 'grayscale' => true with this new syntax?