将PDF转换为图像使用CI并且路径不正确

Question

function Upload_file(){
   $config = array(
        'image_library' => 'ImageMagick',
        'library_path' => '/usr/bin/convert',
        'source_image' => './files/test/images.pdf',
        'new_image' => './files/test/a.jpg',
        'maintain_ratio' => true,
        'quality' => '100%',
  );
   $this->image_lib->initialize($config);
   if ( !$this->image_lib->resize()){
      echo $this->image_lib->display_errors();
   } 
   $this->image_lib->clear();
}

您好我试图将pdf文件转换为jpg但控制器会回复消息 ＆＃34; imglib_invalid_image。  imglib_image_process_failed＆＃34; 任何人都可以帮助我如何执行此代码。