[PHP] PHP简单实现图片格式转换(jpg转png，gif转png等)

/**
 * 图片格式转换
 * @param string $image_path 文件路径或url
 * @param string $to_ext 待转格式，支持png,gif,jpeg,wbmp,webp,xbm
 * @param null|string $save_path 存储路径，null则返回二进制内容，string则返回true|false
 * @return boolean|string $save_path是null则返回二进制内容，是string则返回true|false
 * @throws Exception 
 * @author klinson <klinson@163.com>
 */
function transform_image($image_path, $to_ext = 'png', $save_path = null)
{
  if (! in_array($to_ext, ['png', 'gif', 'jpeg', 'wbmp', 'webp', 'xbm'])) {
  throw new \Exception('unsupport transform image to ' . $to_ext);
  }
  switch (exif_imagetype($image_path)) {
  case IMAGETYPE_GIF :
    $img = imagecreatefromgif($image_path);
    break;
  case IMAGETYPE_JPEG :
  case IMAGETYPE_JPEG2000:
    $img = imagecreatefromjpeg($image_path);
    break;
  case IMAGETYPE_PNG:
    $img = imagecreatefrompng($image_path);
    break;
  case IMAGETYPE_BMP:
  case IMAGETYPE_WBMP:
    $img = imagecreatefromwbmp($image_path);
    break;
  case IMAGETYPE_XBM:
    $img = imagecreatefromxbm($image_path);
    break;
  case IMAGETYPE_WEBP: //(从 PHP 7.1.0 开始支持)
    $img = imagecreatefromwebp($image_path);
    break;
  default :
    throw new \Exception('Invalid image type');
  }
  $function = 'image'.$to_ext;
  if ($save_path) {
  return $function($img, $save_path);
  } else {
  $tmp = __DIR__.'/'.uniqid().'.'.$to_ext;
  if ($function($img, $tmp)) {
    $content = file_get_contents($tmp);
    unlink($tmp);
    return $content;
  } else {
    unlink($tmp);
    throw new \Exception('the file '.$tmp.' can not write');
  }
  }
}

// 转换后保存在test.png
transform_image($url, 'png', './test.png');
transform_image($filepath, 'png', './test.png');
// 转换后二进制结果直接返回
transform_image($url, 'png');
transform_image($filepath, 'png');