The Missing Documentation: Using Face Detector with Files

FaceDetectionExample.java

int rotateAngle; 

void rotatePhoto(){
   rotateAngle += 90f;
    if (rotateAngle == 360f) { 
      rotateAngle = 0;
    }
    photoImageView.setRotation(rotateAngle); // just rotate the image view for the user
}

int detectFaces(File photoFile){
  BitmapFactory.Options options=new BitmapFactory.Options();
  options.inPreferredConfig = Bitmap.Config.RGB_565; // we need to set it to this otherwise FaceDetector won't work
  Bitmap photoBitmap = BitmapFactory.decodeFile(photoFile.getPath(), options);
  
  FaceDetector faceDetector = new FaceDetector(photoBitmap.getWidth(), photoBitmap.getHeight(), 1);
  FaceDetector.Face[] faces = new FaceDetector.Face[1];//array to pass into face detector...faces will be stored in it (creepy, i know)
  return faceDetector.findFaces(photoBitmap, faces);
}

File rotatePhoto(File photoFile){
  File rotatedPhotoFile = ...; // just create a temp file however you want
  
  Bitmap photoBitmap = BitmapFactory.decodeFile(photoFile.getPath()); // we don't need to set it to RGB_565 for rotation
  
  Matrix matrix = new Matrix();
  matrix.postRotate(rotateAngle);
  photoBitmap = Bitmap.createBitmap(photoBitmap, 0, 0, photoBitmap.getWidth(), photoBitmap.getHeight(), matrix, true);
  
  try {
    tempPhotoFile.createNewFile(); //saves the file in the cache dir
    FileOutputStream fos = new FileOutputStream(tempPhotoFile);
    photoBitmap.compress(Bitmap.CompressFormat.JPEG, 90, fos);//jpeg format
    fos.close();
    photoFile = tempPhotoFile;
  } catch (Exception e) {
    // do something...
  }
}

void uploadPhoto(File photoFile){
  // we need to detect faces before we upload, FaceDetector won't work on photos in which faces aren't upright
  int faces = detectFaces(photoFile);
  File uploadFile = rotatePhoto(photoFile);
  
  uploadPhotoToServer(uploadFile, faces);
}