In John's human readable code version of Karolis code to dynimicly allocate need memory there are a few bugs. If you didn't compile with the "--enable-memory-limit" option, this script will error with a level E_ERROR. Bellow is a fixed version rapped as a function. To view replacement functions for memory_get_usage() look at http://us2.php.net/manual/en/function.memory-get-usage.php

<?php
function setMemoryForImage( $filename ){
    $imageInfo = getimagesize($filename);
    $MB = 1048576;  // number of bytes in 1M
    $K64 = 65536;    // number of bytes in 64K
    $TWEAKFACTOR = 1.5;  // Or whatever works for you
    $memoryNeeded = round( ( $imageInfo[0] * $imageInfo[1]
                                           * $imageInfo['bits']
                                           * $imageInfo['channels'] / 8
                             + $K64
                           ) * $TWEAKFACTOR
                         );
    //ini_get('memory_limit') only works if compiled with "--enable-memory-limit" also
    //Default memory limit is 8MB so well stick with that. 
    //To find out what yours is, view your php.ini file.
    $memoryLimit = 8 * $MB;
    if (function_exists('memory_get_usage') && 
        memory_get_usage() + $memoryNeeded > $memoryLimit) 
    {
        $newLimit = $memoryLimitMB + ceil( ( memory_get_usage()
                                            + $memoryNeeded
                                            - $memoryLimit
                                            ) / $MB
                                        );
        ini_set( 'memory_limit', $newLimit . 'M' );
        return true;
    }else
        return false;
    }
}
?>