If anyone finds "The other parameter will be calculated if 0 is passed as either param. " to be a bit confusing, it means approximately this:
<?php
$im = new Imagick('example.jpg');
$im->scaleImage(300, 0);
?>
This scales the image such that it is now 300 pixels wide, and automatically calculates the height to keep the image at the same aspect ratio.
<?php
$im = new Imagick('example.jpg');
$im->scaleImage(0, 300);
?>
Similarly, this example scales the image to make it 300 pixels tall, and the method automatically recalculates the image's height to maintain the aspect ratio.
