const extendTransforms = (builtins) => {
  const getBase64 = async (image) => {
    const img = image.resize({ width: 10 });
    const buf = await img.toBuffer();
    const mt = await img.metadata();
    return `data:image/${mt.format};base64,${buf.toString("base64")}`;
  };

  function base64(config, ctx) {
    if (config.width != "10") return;
    return async (image) => {
      setMetadata(image, "base64", await getBase64(image));
      return image;
    };
  }

  return [base64, ...builtins];
};

imagetools({ extendTransforms })