Python 3 OpenCV Detect Face Tilt in Degrees From Live Webcam

pip install opencv-python

pip install numpy

import cv2 as cv
import numpy as np


# 0 for webcam feed ; add "path to file"
# for detection in video file
capture = cv.VideoCapture(0)
face_cascade = cv.CascadeClassifier('haarcascade_frontalface_default.xml')
eye_cascade = cv.CascadeClassifier("haarcascade_eye.xml")

while True:
 ret, frame = capture.read()
 gray = cv.cvtColor(frame, cv.COLOR_BGR2GRAY)
 faces = face_cascade.detectMultiScale(gray, 1.1, 5)
 x, y, w, h = 0, 0, 0, 0
 for (x, y, w, h) in faces:
  cv.rectangle(frame, (x, y), (x + w, y + h), (0, 255, 0), 2)
  cv.circle(frame, (x + int(w * 0.5), y +
      int(h * 0.5)), 4, (0, 255, 0), -1)
 eyes = eye_cascade.detectMultiScale(gray[y:(y + h), x:(x + w)], 1.1, 4)
 index = 0
 eye_1 = [None, None, None, None]
 eye_2 = [None, None, None, None]
 for (ex, ey, ew, eh) in eyes:
  if index == 0:
   eye_1 = [ex, ey, ew, eh]
  elif index == 1:
   eye_2 = [ex, ey, ew, eh]
  cv.rectangle(frame[y:(y + h), x:(x + w)], (ex, ey),
     (ex + ew, ey + eh), (0, 0, 255), 2)
  index = index + 1
 if (eye_1[0] is not None) and (eye_2[0] is not None):
  if eye_1[0] < eye_2[0]:
   left_eye = eye_1
   right_eye = eye_2
  else:
   left_eye = eye_2
   right_eye = eye_1
  left_eye_center = (
   int(left_eye[0] + (left_eye[2] / 2)),
  int(left_eye[1] + (left_eye[3] / 2)))
  
  right_eye_center = (
   int(right_eye[0] + (right_eye[2] / 2)),
  int(right_eye[1] + (right_eye[3] / 2)))
  
  left_eye_x = left_eye_center[0]
  left_eye_y = left_eye_center[1]
  right_eye_x = right_eye_center[0]
  right_eye_y = right_eye_center[1]

  delta_x = right_eye_x - left_eye_x
  delta_y = right_eye_y - left_eye_y
  
  # Slope of line formula
  angle = np.arctan(delta_y / delta_x)
  
  # Converting radians to degrees
  angle = (angle * 180) / np.pi

  # Provided a margin of error of 10 degrees
  # (i.e, if the face tilts more than 10 degrees
  # on either side the program will classify as right or left tilt)
  if angle > 10:
   cv.putText(frame, 'RIGHT TILT :' + str(int(angle))+' degrees',
     (20, 30), cv.FONT_HERSHEY_SIMPLEX, 1,
     (0, 255, 0), 2, cv.LINE_4)
  elif angle < -10:
   cv.putText(frame, 'LEFT TILT :' + str(int(angle))+' degrees',
     (20, 30), cv.FONT_HERSHEY_SIMPLEX, 1,
     (0, 255, 0), 2, cv.LINE_4)
  else:
   cv.putText(frame, 'STRAIGHT :', (20, 30),
     cv.FONT_HERSHEY_SIMPLEX, 1,
     (0, 255, 0), 2, cv.LINE_4)

 cv.imshow('Frame', frame)

 if cv.waitKey(1) & 0xFF == 27:
  break
capture.release()
cv.destroyAllWindows()