用imagick php掩盖文本

Question

The following code is a very basic example of imagick's Imagick::annotateImage() function. How would I go about masking the top half of the text while retaining the background image?

<?php
/* Create some objects */
$image = new Imagick('bg.jpg');
$draw = new ImagickDraw();
$pixel = new ImagickPixel( 'transparent' );

/* New image */
$image->newImage(800, 75, $pixel);

/* Black text */
$draw->setFillColor('black');

/* Font properties */
$draw->setFont('Bookman-DemiItalic');
$draw->setFontSize( 30 );

/* Create text */
$image->annotateImage($draw, 10, 45, 0, 'The quick brown fox jumps over the lazy dog');

/* Give image a format */
$image->setImageFormat('png');

/* Output the image with headers */
header('Content-type: image/png');
echo $image;

?>