使用codeigniter的图像裁剪没有GD库-GD2

我目前正在为一个网站开发媒体库，其中一个功能是用户可以创建他们上传的图像的裁剪版本。

然而，我的问题是，当我尝试裁剪图像时，我会出现以下错误，

The path to the image is not correct.

这是我的代码，

$config['image_library'] = 'gd2';
    $config['source_image'] = "/media/images/products/".$this->data['image'];
    //die($config['source_image']);
    $config['maintain_ratio'] = FALSE;
    $config['x_axis'] = $this->input->post('x');
    $config['y_axis'] = $this->input->post('y');
    $config['width'] = $this->input->post('w');
    $config['height'] = $this->input->post('h');
    $config['dynamic_output'] = FALSE;
    $config['create_thumb'] = TRUE;
    $this->load->library('image_lib', $config);
    if(!$this->image_lib->crop()) {
        if($this->input->post('isAjax') == "1") {
            echo json_encode($this->image_lib->display_errors());
        } else {
            $this->data['image_error'] = $this->image_lib->display_errors();
            $this->template->build('/admin/media/crop', $this->data);
        }       
    } else {
        $filename = base_url()."media/images/products/".$this->data['image'];
        $extension_pos = strrpos($filename, '.'); // find position of the last dot, so where the extension starts
        $thumb = substr($filename, 0, $extension_pos) . '_thumb' . substr($filename, $extension_pos);
        if($this->input->post('isAjax') == 1) {
            echo json_encode($success = array('message' => 'Image Cropped'));
        } else {
            $this->data['success'] = "Image Cropped";
            $this->template->build('/admin/media/crop', $this->data);
        }   
    }

所以我想我会把$config['source_image']改成下面的

$config['source_image'] = "./media/images/products/".$this->data['image'];

然而，这只会留下这个信息，

Your server does not support the GD function required to process this type of image.

我是不是做错了什么？我只是想裁剪一个简单的.png，这个文件肯定存在于我的服务器上，而且我最确定的是安装了GD2。