从String到BufferedImage再返回到String会给出不同的字符串

Question

我有一个base64编码的图像字符串，我将其转换为byte []和bufferedImage，然后再返回该字符串。我得到的两个字符串是不同的。我得到类似expected:<...1HAwCAAAAC0lEQVR42mP[4/x8AAwAB/2+Bq7Y]AAAAASUVORK5CYII=> but was:<...1HAwCAAAAC0lEQVR42mP[8/x8AAwMCAO+ip1s]AAAAASUVORK5CYII=>的信息。我不确定是什么原因造成的。任何帮助表示赞赏！

// a 1x1 pixel white png image
String imageString = "iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAQAAAC1HAwCAAAAC0lEQVR42mP8/x8AAwMCAO+ip1sAAAAASUVORK5CYII=";
byte[] bytes = Base64.decode(imageString);
String newString = toBase64String(toImage(bytes), "png");
Assert.assertEquals(imageString, newString); // not equal

public static BufferedImage toImage(final byte[] bytes) {
  BufferedImage image = null;

  try {
    image = ImageIO.read(new ByteArrayInputStream(bytes));
  } catch (IOException e) {
    e.printStackTrace();
  }

  return image;
}

public static String toBase64String(final BufferedImage image, final String formatName) {
  ByteArrayOutputStream baos = new ByteArrayOutputStream();

  try {
    ImageIO.write(image, formatName, baos);
    return Base64.encodeBase64String(baos.toByteArray());
  } catch (IOException e) {
    e.printStackTrace();
  }

  return "";
}