Php 帮助修复图像库

我的图像库有问题。我想我知道这个问题，但我对图像知之甚少，希望有人能告诉我到底出了什么问题

我想做的是调整.png的大小并保持透明度。当我调整大小并保存.png图像时，它会失去透明度并变为黑色

我认为问题在于resize函数中的

imagecreatetruecolor

函数。文档表明这会返回一个黑色图像。我想这不是我想要的

有人能不能多管闲事，告诉我问题是否真的出在resize函数上，以及如何解决这个问题

谢谢

class ResizeImage {

    // Load Image
    function load($filename) {
        $image_info = getimagesize($filename);
        $this->image_type = $image_info[2];

        if( $this->image_type == IMAGETYPE_JPEG ) {
            $this->image = imagecreatefromjpeg($filename);
        } elseif( $this->image_type == IMAGETYPE_GIF ) {
            $this->image = imagecreatefromgif($filename);
        } elseif( $this->image_type == IMAGETYPE_PNG ) {
            $this->image = imagecreatefrompng($filename);
            imagealphablending($this->image, true);
            imagesavealpha($this->image, true);
        }
    }

        // Resize the image
        function resize($width,$height) {
        $new_image = imagecreatetruecolor($width, $height);
        imagecopyresampled($new_image, $this->image, 0, 0, 0, 0, $width, $height, $this->getWidth(), $this->getHeight());
        $this->image = $new_image;
    }

        // Save the image
    function save($filename, $image_type='', $compression=100, $permissions=null) {
        if ($image_type != '') {
            $this->image_type = $image_type;
        }

        if( $this->image_type == IMAGETYPE_JPEG ) {
            imagejpeg($this->image,$filename,$compression);
        } elseif( $this->image_type == IMAGETYPE_GIF ) {
            imagegif($this->image,$filename);
        } elseif( $this->image_type == IMAGETYPE_PNG ) {
            imagepng($this->image,$filename);
        }
        if( $permissions != null) {
            chmod($filename,$permissions);
        }
    }

尝试使用，例如：

function resize($width,$height) {
        $new_image = imagecreatetruecolor($width, $height);
        imagesavealpha($new_image, true);
        imagecopyresampled($new_image, $this->image, 0, 0, 0, 0, $width, $height, $this->getWidth(), $this->getHeight());
        $this->image = $new_image;
    }

尝试使用。检查