To trim image with 15% of fuzziness
<?php
$image = new Gmagick($image_path);
$max_quantum = 65535;
switch ($image->getQuantumDepth()['quantumDepthLong']) {
case 8: $max_quantum = 255; break;
case 16: $max_quantum = 65535; break;
case 32: $max_quantum = 4294967295; break;
}
$image->trimImage(0.15 * $max_quantum);