ALFaceDetection Tutorial

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NAOqi People Perception - Overview | API | Tutorial


This tutorial explains how to run the ALFaceDetection module using Python. We use the following approach: we regularly check the ALMemory’s result variable. Information about the detected faces is printed on the screen.

Getting a proxy to ALFaceDetection

After some initialization steps, we first instantiate a proxy to the ALFaceDetection module.

             # This test demonstrates how to use the ALFaceDetection module.
# Note that you might not have this module depending on your distribution
# - We first instantiate a proxy to the ALFaceDetection module
#     Note that this module should be loaded on the robot's NAOqi.
#     The module output its results in ALMemory in a variable
#     called "FaceDetected"
# - We then read this ALMemory value and check whether we get
#   interesting things.
import time
from naoqi import ALProxy

# Replace this with your robot's IP address
IP = ""
PORT = 9559

# Create a proxy to ALFaceDetection
  faceProxy = ALProxy("ALFaceDetection", IP, PORT)
except Exception, e:
  print "Error when creating face detection proxy:"
  print str(e)

# Subscribe to the ALFaceDetection proxy
# This means that the module will write in ALMemory with
# the given period below
period = 500
faceProxy.subscribe("Test_Face", period, 0.0 )


Reading the results in the ALMemory variable

Now we need to get a proxy to ALMemory and check the ALFaceDetection output variable.

             # ALMemory variable where the ALFaceDetection module
# outputs its results.
memValue = "FaceDetected"

# Create a proxy to ALMemory
  memoryProxy = ALProxy("ALMemory", IP, PORT)
  except Exception, e:
  print "Error when creating memory proxy:"
  print str(e)

# A simple loop that reads the memValue and checks whether faces are detected.
for i in range(0, 20):
  val = memoryProxy.getData(memValue, 0)
  print ""
  print "\*****"
  print ""

# Check whether we got a valid output: a list with two fields.
if(val and isinstance(val, list) and len(val) == 2):
  # We detected faces !
  # For each face, we can read its shape info and ID.
  # First Field = TimeStamp.
  timeStamp = val[0]
  # Second Field = array of face_Info's.
  faceInfoArray = val[1]

  # Browse the faceInfoArray to get info on each detected face.
    for faceInfo in faceInfoArray:
    # First Field = Shape info.
    faceShapeInfo = faceInfo[0]
    # Second Field = Extra info (empty for now).
    faceExtraInfo = faceInfo[1]
    print "  alpha %.3f - beta %.3f" % (faceShapeInfo[1], faceShapeInfo[2])
    print "  width %.3f - height %.3f" % (faceShapeInfo[3], faceShapeInfo[4])
  except Exception, e:
    print "faces detected, but it seems getData is invalid. ALValue ="
    print val
    print "Error msg %s" % (str(e))
  print "Error with getData. ALValue = %s" % (str(val))
  # Unsubscribe the module.

print "Test terminated successfully."



Here is what you get when you execute the above script. We get different results as we occult or present new faces to the robot.

alpha 0.243 - beta 0.005
width 0.167 - height 0.167
alpha 0.243 - beta 0.005
width 0.167 - height 0.167
alpha 0.243 - beta 0.005
width 0.167 - height 0.167