face.py

"""Raspberry Pi Face Recognition Treasure Box
Face Detection Helper Functions
Copyright 2013 Tony DiCola 

Functions to help with the detection and cropping of faces.
"""
import cv2

import config


haar_faces = cv2.CascadeClassifier(config.HAAR_FACES)


def detect_single(image):
	"""Return bounds (x, y, width, height) of detected face in grayscale image.
	   If no face or more than one face are detected, None is returned.
	"""
	faces = haar_faces.detectMultiScale(image, 
				scaleFactor=config.HAAR_SCALE_FACTOR, 
				minNeighbors=config.HAAR_MIN_NEIGHBORS, 
				minSize=config.HAAR_MIN_SIZE, 
				flags=cv2.CASCADE_SCALE_IMAGE)
	if len(faces) != 1:
		return None
	return faces[0]

def crop(image, x, y, w, h):
	"""Crop box defined by x, y (upper left corner) and w, h (width and height)
	to an image with the same aspect ratio as the face training data.  Might
	return a smaller crop if the box is near the edge of the image.
	"""
	crop_height = int((config.FACE_HEIGHT / float(config.FACE_WIDTH)) * w)
	midy = y + h/2
	y1 = max(0, midy-crop_height/2)
	y2 = min(image.shape[0]-1, midy+crop_height/2)
	return image[y1:y2, x:x+w]

def resize(image):
	"""Resize a face image to the proper size for training and detection.
	"""
	return cv2.resize(image, 
					  (config.FACE_WIDTH, config.FACE_HEIGHT), 
					  interpolation=cv2.INTER_LANCZOS4)