code: public static void writeToFile(Bitmap bitmap, String dir, String filename) throws FileNotFoundException, IOException {
  		File sdCard = Environment.getExternalStorageDirectory();
  		File dirFile = new File (sdCard.getAbsolutePath() + "/" + dir);
  		dirFile.mkdirs();
  		File f = new File(dirFile, filename);
  		FileOutputStream fos = new FileOutputStream(f, false);
  		bitmap.compress(CompressFormat.PNG, 100 /*ignored for PNG*/, fos);
  		fos.flush();
  		fos.close();
  	}
docs: Write the given bitmap to a file in the external storage. Requires
  "android.permission.WRITE_EXTERNAL_STORAGE" permission.