Imagick::appendImages

# How to combine a multi-page pdf file into a single long image:

<?php
$im1 = new Imagick();   
$im1->readImage('multi-page-pdf.pdf');
$im1->resetIterator();
# Combine multiple images into one, stacked vertically. 
$ima = $im1->appendImages(true);
$ima->setImageFormat("png");
header("Content-Type: image/png");
echo $ima;
?>

# change $ima to $ima->getimagesblob()

<?php
$im1 = new Imagick();  
$im1->readImage('multi-page-pdf.pdf');
$im1->resetIterator();
# Combine multiple images into one, stacked vertically.
$ima = $im1->appendImages(true);
$ima->setImageFormat("png");
header("Content-Type: image/png");
echo $ima->getimagesblob();
?>

Sometimes when running this code on a long running apache24 instance on a server with minimal memory the final "echo $ima;" returns an empty string.

Doing an "apache graceful" seems to clear this up.  There appears to be no other way to correct OR DETECT this problem. Suckky.