Age and Gender Detection using OpenCV in Python

Learn how to perform age and gender detection using OpenCV library in Python with camera or image input.
  · 8 min read · Updated sep 2021 · Machine Learning · Computer Vision

In this tutorial, we will combine gender detection and age detection tutorials to come up with a single code that detects both.

Let's get started. If you haven't OpenCV already installed, make sure to do so:

$ pip install opencv-python numpy

Open up a new file. Importing the libraries:

# Import Libraries
import cv2
import numpy as np

Next, defining the variables of weights and architectures for face, age, and gender detection models:

FACE_PROTO = "weights/deploy.prototxt.txt"
FACE_MODEL = "weights/res10_300x300_ssd_iter_140000_fp16.caffemodel"
# The gender model architecture
GENDER_MODEL = 'weights/deploy_gender.prototxt'
# The gender model pre-trained weights
GENDER_PROTO = 'weights/gender_net.caffemodel'
# Each Caffe Model impose the shape of the input image also image preprocessing is required like mean
# substraction to eliminate the effect of illunination changes
MODEL_MEAN_VALUES = (78.4263377603, 87.7689143744, 114.895847746)
# Represent the gender classes
GENDER_LIST = ['Male', 'Female']
# The model architecture
# download from:
AGE_MODEL = 'weights/deploy_age.prototxt'
# The model pre-trained weights
# download from:
AGE_PROTO = 'weights/age_net.caffemodel'
# Represent the 8 age classes of this CNN probability layer
AGE_INTERVALS = ['(0, 2)', '(4, 6)', '(8, 12)', '(15, 20)',
                 '(25, 32)', '(38, 43)', '(48, 53)', '(60, 100)']

Below are the necessary files to be included in the project directory:

  • gender_net.caffemodel: It is the pre-trained model weights for gender detection. You can download it here.
  • deploy_gender.prototxt: is the model architecture for the gender detection model (a plain text file with a JSON-like structure containing all the neural network layer’s definitions). Get it here.
  • age_net.caffemodel: It is the pre-trained model weights for age detection. You can download it here.
  • deploy_age.prototxt: is the model architecture for the age detection model (a plain text file with a JSON-like structure containing all the neural network layer’s definitions). Get it here.
  • res10_300x300_ssd_iter_140000_fp16.caffemodel: The pre-trained model weights for face detection, download here.
  • deploy.prototxt.txt: This is the model architecture for the face detection model, download here.

Next, loading the models:

# Initialize frame size
frame_width = 1280
frame_height = 720
# load face Caffe model
face_net = cv2.dnn.readNetFromCaffe(FACE_PROTO, FACE_MODEL)
# Load age prediction model
age_net = cv2.dnn.readNetFromCaffe(AGE_MODEL, AGE_PROTO)
# Load gender prediction model
gender_net = cv2.dnn.readNetFromCaffe(GENDER_MODEL, GENDER_PROTO)

Before trying to detect age and gender, we need a function to detect faces first:

def get_faces(frame, confidence_threshold=0.5):
    # convert the frame into a blob to be ready for NN input
    blob = cv2.dnn.blobFromImage(frame, 1.0, (300, 300), (104, 177.0, 123.0))
    # set the image as input to the NN
    # perform inference and get predictions
    output = np.squeeze(face_net.forward())
    # initialize the result list
    faces = []
    # Loop over the faces detected
    for i in range(output.shape[0]):
        confidence = output[i, 2]
        if confidence > confidence_threshold:
            box = output[i, 3:7] * \
                np.array([frame.shape[1], frame.shape[0],
                         frame.shape[1], frame.shape[0]])
            # convert to integers
            start_x, start_y, end_x, end_y = box.astype(
            # widen the box a little
            start_x, start_y, end_x, end_y = start_x - \
                10, start_y - 10, end_x + 10, end_y + 10
            start_x = 0 if start_x < 0 else start_x
            start_y = 0 if start_y < 0 else start_y
            end_x = 0 if end_x < 0 else end_x
            end_y = 0 if end_y < 0 else end_y
            # append to our list
            faces.append((start_x, start_y, end_x, end_y))
    return faces

The get_faces() function was grabbed from the face detection tutorial, so check it out if you want more information.

Below is a function for simply displaying an image:

def display_img(title, img):
    """Displays an image on screen and maintains the output until the user presses a key"""
    # Display Image on screen
    cv2.imshow(title, img)
    # Mantain output until user presses a key
    # Destroy windows when user presses a key

Below are is a function for dynamically resizing an image, we're going to need it to resize the input images when exceeding a certain width:

# from:
def image_resize(image, width = None, height = None, inter = cv2.INTER_AREA):
    # initialize the dimensions of the image to be resized and
    # grab the image size
    dim = None
    (h, w) = image.shape[:2]
    # if both the width and height are None, then return the
    # original image
    if width is None and height is None:
        return image
    # check to see if the width is None
    if width is None:
        # calculate the ratio of the height and construct the
        # dimensions
        r = height / float(h)
        dim = (int(w * r), height)
    # otherwise, the height is None
        # calculate the ratio of the width and construct the
        # dimensions
        r = width / float(w)
        dim = (width, int(h * r))
    # resize the image
    return cv2.resize(image, dim, interpolation = inter)

Now that everything is ready, let's define our two functions for age and gender detection:

def get_gender_predictions(face_img):
    blob = cv2.dnn.blobFromImage(
        image=face_img, scalefactor=1.0, size=(227, 227),
        mean=MODEL_MEAN_VALUES, swapRB=False, crop=False
    return gender_net.forward()

def get_age_predictions(face_img):
    blob = cv2.dnn.blobFromImage(
        image=face_img, scalefactor=1.0, size=(227, 227),
        mean=MODEL_MEAN_VALUES, swapRB=False
    return age_net.forward()

The get_gender_predictions() and get_age_predictions() perform prediction on the gender_net and age_net models to infer the gender and age of the input image respectively.

Finally, we write our main function:

def predict_age_and_gender(input_path: str):
    """Predict the gender of the faces showing in the image"""
    # Initialize frame size
    # frame_width = 1280
    # frame_height = 720
    # Read Input Image
    img = cv2.imread(input_path)
    # resize the image, uncomment if you want to resize the image
    # img = cv2.resize(img, (frame_width, frame_height))
    # Take a copy of the initial image and resize it
    frame = img.copy()
    if frame.shape[1] > frame_width:
        frame = image_resize(frame, width=frame_width)
    # predict the faces
    faces = get_faces(frame)
    # Loop over the faces detected
    # for idx, face in enumerate(faces):
    for i, (start_x, start_y, end_x, end_y) in enumerate(faces):
        face_img = frame[start_y: end_y, start_x: end_x]
        age_preds = get_age_predictions(face_img)
        gender_preds = get_gender_predictions(face_img)
        i = gender_preds[0].argmax()
        gender = GENDER_LIST[i]
        gender_confidence_score = gender_preds[0][i]
        i = age_preds[0].argmax()
        age = AGE_INTERVALS[i]
        age_confidence_score = age_preds[0][i]
        # Draw the box
        label = f"{gender}-{gender_confidence_score*100:.1f}%, {age}-{age_confidence_score*100:.1f}%"
        # label = "{}-{:.2f}%".format(gender, gender_confidence_score*100)
        yPos = start_y - 15
        while yPos < 15:
            yPos += 15
        box_color = (255, 0, 0) if gender == "Male" else (147, 20, 255)
        cv2.rectangle(frame, (start_x, start_y), (end_x, end_y), box_color, 2)
        # Label processed image
        font_scale = 0.54
        cv2.putText(frame, label, (start_x, yPos),
                    cv2.FONT_HERSHEY_SIMPLEX, font_scale, box_color, 2)

        # Display processed image
    display_img("Gender Estimator", frame)
    # uncomment if you want to save the image
    cv2.imwrite("output.jpg", frame)
    # Cleanup

The main function does the following:

  • First, it reads the image using the cv2.imread() method.
  • After the image is resized to the appropriate size, we use our get_faces() function to get all the detected faces from the image.
  • We iterate on each detected face image and call our get_age_predictions() and get_gender_predictions() to get the predictions.
  • We print the age and gender.
  • We draw a rectangle surrounding the face and also put the label that contains the age and gender text along with confidence on the image.
  • Finally, we show the image.

Let's call it:

if __name__ == "__main__":
    import sys
    input_path = sys.argv[1]

Done, let's run the script now (testing on this image):

$ python images/girl.jpg

Output in the console:

Male-99.1%, (4, 6)-71.9%
Female-96.0%, (4, 6)-70.9%

The resulting image:

Resulting ImageHere is another example:

Resulting image 2 on age & gender detection using OpenCVOr this:

Age & Gender detection tutorial resulting imageAwesome! If you see the text in the image is large or small, make sure to tweak the font_scale floating-point variable on your image in the predict_age_and_gender() function.

For more detail on how the gender and age prediction works, I suggest you check the individual tutorials:

If you want to use your camera, I made a Python script to read images from your webcam and perform inference in real-time.

Check the full code here.

Happy coding ♥

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