Function to allocate memory for image processing with PHP in a smart way.

image-allocate-memory.php

<?php

/**
 * Dynamically allocate memory based on image dimensions, bit-depth and channels
 * Shamelessly stolen somewhere online years ago.
 * Probably from https://alvarotrigo.com/blog/allocate-memory-on-the-fly-PHP-image-resizing/
 *
 * @param string $filename Full path to a file supported by getimagesize() function
 * @param int $tweak_factor Multiplier for tweaking required memory. 1.8 seems fine. More info: http://php.net/imagecreatefromjpeg#76968
 * @param string $original_name Used purely for reporting actual file name instead of uploaded temp file (e.g. /tmp/RaNd0m.tmp)
 *
 * @return bool true on success or if no memory increase required, false if required memory amount is too large
 */
function setMemoryLimit($filename, $tweak_factor = 1.8, $original_name = null) {

    $maxMemoryUsage = 512 * 1024 * 1024; // 512MB
    $width = 0;
    $height = 0;
    $memory_limit = return_bytes(ini_get('memory_limit'));

    $memory_baseline_usage = memory_get_usage(true);

    // Getting the image info
    $info = @getimagesize($filename);
    if( empty($info) ) {
        throw new Exception( sprintf('ERROR: getimagesize("%s") returned: %s', $filename, print_r($info, true)) );
        return false;
    }

    !empty($original_name) ? $filename = $original_name : $original_name;

    $channels = isset($info['channels']) ? $info['channels'] : 3;
    $width = $info[0];
    $height = $info[1];

    if($info['mime'] == 'image/png') {
        $channels = 4;
    }

    if(!isset($info['bits'])) {
        $info['bits'] = 16;
    }
    $bytes_per_channel = ( ($info['bits'] / 8) * $channels );

    // Calculating the needed memory
    $new_limit = $memory_baseline_usage + ($width * $height * $bytes_per_channel * $tweak_factor + 1048576);

    if( $new_limit <= $memory_limit ) {
        return true;
    }

    /* We don't want to allocate an extremely large amount of memory
    so it's a good practice to define a limit and bail out if new limit is more than that */
    if ($new_limit > $maxMemoryUsage) {
        throw new Exception( sprintf( "Failed increasing memory limit to %dMB (max=%dMB) for file '%s' (%d x %d)", ceil( $new_limit / 1048576 ), ceil( $maxMemoryUsage / 1048576 ), $filename, $width, $height ) );
        return false;
    }

    $new_limit = ceil( $new_limit / 1048576 );

    // Updating the default value
    ini_set('memory_limit', $new_limit.'M');
    return true;
}