imagecreatetruecolor php占用了太多内存

我有一个通过ajax调用获取其值的php代码。这些值由用户用于裁剪图像的裁剪模块提供。

<?php
ini_set('Memory_limit', -1);
$imgUrl = $_POST['imgUrl'];
// original sizes
$imgInitW = $_POST['imgInitW'];
$imgInitH = $_POST['imgInitH'];
// resized sizes
$imgW = $_POST['imgW'];
$imgH = $_POST['imgH'];
// offsets
$imgY1 = $_POST['imgY1'];
$imgX1 = $_POST['imgX1'];
// crop box
$cropW = $_POST['cropW'];
$cropH = $_POST['cropH'];
// rotation angle
$angle = $_POST['rotation'];
$jpeg_quality = 100;
$uniquename=uniqid().time();
$output_filename = "croppedimages/".$uniquename;
// uncomment line below to save the cropped image in the same location as the original image.
//$output_filename = dirname($imgUrl). "/croppedImg_".rand();
$what = getimagesize($imgUrl);
switch(strtolower($what['mime']))
{
    case 'image/png':
        $img_r = imagecreatefrompng($imgUrl);
        $source_image = imagecreatefrompng($imgUrl);
        $type = '.png';
        break;
    case 'image/jpeg':
        $img_r = imagecreatefromjpeg($imgUrl);
        $source_image = imagecreatefromjpeg($imgUrl);
        error_log("jpg");
        $type = '.jpeg';
        break;
    case 'image/gif':
        $img_r = imagecreatefromgif($imgUrl);
        $source_image = imagecreatefromgif($imgUrl);
        $type = '.gif';
        break;
    default: die('image type not supported');
}

//Check write Access to Directory
if(!is_writable(dirname($output_filename))){
    $response = Array(
        "status" => 'error',
        "message" => 'Can`t write cropped File'
    );  
}else{
    // resize the original image to size of editor
    $resizedImage = imagecreatetruecolor($imgW, $imgH);
    imagecopyresampled($resizedImage, $source_image, 0, 0, 0, 0, $imgW, $imgH, $imgInitW, $imgInitH);
    // rotate the rezized image
    $rotated_image = imagerotate($resizedImage, -$angle, 0);
    // find new width & height of rotated image
    $rotated_width = imagesx($rotated_image);
    $rotated_height = imagesy($rotated_image);
    // diff between rotated & original sizes
    $dx = $rotated_width - $imgW;
    $dy = $rotated_height - $imgH;
    // crop rotated image to fit into original rezized rectangle
    $cropped_rotated_image = imagecreatetruecolor($imgW, $imgH);
    imagecolortransparent($cropped_rotated_image, imagecolorallocate($cropped_rotated_image, 0, 0, 0));
    imagecopyresampled($cropped_rotated_image, $rotated_image, 0, 0, $dx / 2, $dy / 2, $imgW, $imgH, $imgW, $imgH);
    // crop image into selected area
    $final_image = imagecreatetruecolor($cropW, $cropH);
    imagecolortransparent($final_image, imagecolorallocate($final_image, 0, 0, 0));
    imagecopyresampled($final_image, $cropped_rotated_image, 0, 0, $imgX1, $imgY1, $cropW, $cropH, $cropW, $cropH);
    // finally output png image
    //imagepng($final_image, $output_filename.$type, $png_quality);
    imagejpeg($final_image, $output_filename.$type, $jpeg_quality);
    $response = Array(
        "status" => 'success',
        "url" => $output_filename.$type,
    );
}
print json_encode($response);

这里裁剪W和cropH值是裁剪图像的值。但是这对于低分辨率图像工作正常，但是当使用高分辨率图像时，控制台显示imagecreatetruecolor功能错误。

致命错误：允许的内存大小 134217728 字节已耗尽

现在，即使我按ini_set('Memory_limit', -1);设置内存使用情况，它仍然向我显示此错误。原因可能是什么，解决方案是什么？

注意：我知道设置ini_set('Memory_limit', -1);是个坏主意。