将图像从android上传到php服务器无法正常工作

我正在尝试使用openurlconnection上传图片，但遇到了一些问题。这是我的java类：

public class Upload extends AppCompatActivity
{
    InputStream inputStream;

    @Override
    protected void onCreate(Bundle savedInstanceState)
   {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.activity_upload);

      StrictMode.enableDefaults();

      Bitmap bitmap = BitmapFactory.decodeResource(getResources(), R.drawable.sss);
      ByteArrayOutputStream stream = new ByteArrayOutputStream();
      bitmap.compress(Bitmap.CompressFormat.PNG, 90, stream);
      byte [] byte_arr = stream.toByteArray();
      String encodedImage = Base64.encodeToString(byte_arr, Base64.DEFAULT);
      String msj = downloadImage(encodedImage);
      Toast.makeText(getBaseContext(), "mensaje "+msj, Toast.LENGTH_SHORT).show();
    }


    public String downloadImage(String tabla)
    {
      String urlG = "http://192.168.43.98/jober/";

      try {
          URL url = new URL(urlG+"upload.php");
          HttpURLConnection conn = (HttpURLConnection) url.openConnection();
          conn.setRequestMethod("POST");

          // para activar el metodo post
          conn.setDoOutput(true);
          conn.setDoInput(true);
          DataOutputStream wr = new DataOutputStream(
                  conn.getOutputStream());
          wr.writeBytes("image="+tabla);
          wr.flush();
          wr.close();

          InputStream is = conn.getInputStream();
          BufferedReader rd = new BufferedReader(new InputStreamReader(is));
          String line;
          StringBuffer response = new StringBuffer();
          while((line = rd.readLine()) != null) {
              response.append(line);
              response.append('\r');
          }
          rd.close();
          return response.toString();
       }
        catch(Exception e){ return "error";}
    }
}

和PHP代码是：

<?php   
    $base=$_REQUEST['image'];
    $binary=base64_decode($base);
    header('Content-Type: bitmap; charset=utf-8');
    $file = fopen('uploaded_image.png', 'wb');
    fwrite($file, $binary);
    fclose($file);
    echo 'Image upload complete!!, Please check your php file directory……';
?>

唯一的问题是当我检查文件并看起来像：

我一直在寻找错误，但我无法。