图像的路径不正确

Question

public function converter(){
        $pdf = "ci.pdf";
        $this->load->library('image_lib');

        $config = array(
                'image_library' => 'imagemagick',
                'library_path' => 'D:\Program Files\ImageMagick-6.9.3-Q16',
                'source_image' => " /theme/assets/pdf".$pdf,
                'new_image' => " /theme/assets/img/a.jpg",
                'maintain_ratio' => true,
                'width' => 980,
                'quality' => '90%',
             );

             $this->image_lib->initialize( $config );

        if (! $this->image_lib->resize()) {
                $error_msg = $this->image_lib->display_errors();
                print_r($error_msg);
        }
        else {
                echo "Done";
        }
}

Hi friends i'm trying to convert pdf file to jpg but while executing the controller it replies a message .

The path to the image is not correct. Image processing failed. Please verify that your server supports the chosen protocol and that the path to your image library is correct.

As i'm new to Codeigniter I was not able to achieve the result .could any one help me how to execute this code .