Example of convolveImage:
<?php
// run an edge detection filter on an image
$image = new imagick( "diana.png" );
$edgeArray = array(-1,-1,-1,-1,8,-1,-1,-1,-1);
$image->convolveImage ($edgeArray);
$image->thresholdImage(1);
header('Content-type: image/png');
echo $image;
?>