Opencv Js Detect Rectangle


Define a detection window on image with mouse through Python 3 and OpenCV 3 For image recognition or object tracking, we often need to define a target window to locate the area interested as below. OpenCV-Python Tutorials. I'm new to image processing in general and I have recently started using opencv. To validate OpenCV* installation, run the OpenCV deep learning module with the Inference Engine backend. OpenCV already contains many pre-trained classifiers for face, eyes, smiles, etc. This article will go through the most basic implementations of face detection including Cascade Classifiers, HOG windows and Deep Learning. But we could not identify the shape of the object there. After of several days struggling I am still unable to do this. detecting rectangle in real images. OpenCV provides some pre-trained models for different use cases such as face detection, eye detection, full body detection and others. html with HTML used to serve the video feed. Pre-Requisites: Basic knowledge of coding in Python and C++, OpenCV, Python and C++ installed on the machine, a code editor. So if we find a contour in a binary image, we are finding the boundaries of objects in an image. We're going to look into two commonly used edge detection schemes - the gradient (Sobel - first order. Andrew, I wonder how could you figure out the question was about shape recognition? Frankly, I could not see that. In this post, I would like to introduce how to do this in OpenCV. JavaScript preprocessors can help make authoring JavaScript easier and more convenient. Once we have at least one face rectangle, either using a CIDetector or an OpenCV CascadeClassifier, we can try to identify the person in the image. Detect 80 common objects in context including car, bike, dog, cat etc. 그리고 python 스크립트를 짜기 위해 파일을 만든다. Under Linux we have to build OpenCV from source manually or using the auto build script. drawContours ( im ,[ box ], 0 ,( 0 , 0 , 255 ), 2 ). BoxPoints(rect) instead of cv2. Simple Rectangle Detection Using OpenCV on Android. Recently I have added the face recognition algorithms from OpenCV contrib to opencv4nodejs, an npm package, which allows you to use OpenCV in your Node. Search for jobs related to Object detection google vision api opencv or hire on the world's largest freelancing marketplace with 15m+ jobs. Instead of a chess board, which has well-defined areas of contrasting colors, the edge of a floor, where there is lots of "noise" that will give rise to many features which just approximate a straight line, from which we want to then derive the straight line, which as I understand it is the whole point of the Hough transform, or am I misunderstanding what Sobel does?. js — OpenCV tutorial. Few dependencies OpenCV (>=2. Face detection network gets BGR image as input and produces set of bounding boxes that might contain faces. How to Use OpenCV in React Native for Image OpenCV Processing If you have ever wondered how to process your images using OpenCV with React Native, then you're in the right place. js nodejs OCR OpenCV PHP Python raspberrypi Raspberry Pi react native Scanning SDK source control TFS Hosting TWAIN TWAIN scanning SDK ubuntu Version Control web WebAssembly Webcam. 10 20:23 색깔있는 도형에 도형의 색 이름을 표시해주는 예제 코드입니다. Welcome back to yet another Node. Canny Edge Detection is used to detect the edges in a picture. OpenCV Linking Guide First, install OpenCV library and link it with C compiler ( I am using Microsoft Visual studio in Windows platform). videoio package contains classes and methods to capture video using the system camera. YOLO object detection using Opencv with Python; Simple shape detection - Opencv with Python 3; YOLO V3 - Install and run Yolo on Nvidia Jetson Nano (with GPU) Find and Draw Contours - OpenCV 3. Connaissant très peu OpenCV, quelle est le meilleur moyen de traiter ce problème ?. Computer vision is widely used, for example for motion tracking in security cameras, control of autonomous vehicles, identification of /searching for objects in a picture/video. Detecting Rectangle using OpenCV Java We are dealing with image processing it often comes that how to detect particular shape in image. Generally you will have a simple generic shape that covers the entity known as a "hitbox" so even though collision may not be pixel perfect, it will look good enough and be performant. It's free to sign up and bid on jobs. Simple Rectangle Detection Using OpenCV on Android. Code example about selecting the rectangle region of interest inside the image and cut or display part of the image from the bigger picture. The objective of this post is to demonstrate how to detect and count faces in an image, using OpenCV and Python. Real time face detection in webcam using Python 3 will show you how your working webcam detects your face and draws a rectangle around your face. This code is supposed to grab live camera feed, display feed in a window, mark in rectangles all detected faces, get the biggest detected face (by total area), display it in separate window, conver. There are opencv samples to do this. js nodejs OCR OpenCV PHP Python raspberrypi Raspberry Pi react native Scanning SDK source control TFS Hosting TWAIN TWAIN scanning SDK ubuntu Version Control web WebAssembly Webcam. I have also more trained version also on 300 people. The question is very basic, it can be solved in two or three steps: 1. OpenCV is the most popular computer-vision library with a comprehensive set of vision functions and a large developer community. Following is the syntax of this method −. Learn how to detect lines in an image. Hello, there is a program I would like to make with a face detector using OpenCV. Here they hardcoded the values for detecting the people in the video. Object detection using OpenCV dnn module with a pre-trained YOLO v3 model with Python. The auto build script comes in form of the opencv-build npm package, which will run by default when installing opencv4nodejs. Now I want to convert dlib::rectangle to cv::Rect to use for futher purpose, but I don't know how to do that. The thing is that up until two hours ago I had no idea what OpenCV is and I have never even remotely did anything involving image processing. Opencv rectangle drawing tutorial by example in C++. There is nothing what is difficult about this. It was developed by John F. package gocv. /** * Simple shape detector program. Some time back I learned about the OpenCV’s User Interface module and I always wanted a quick way of dragging a rectangle on an image using OpenCV. Canny Edge Detection is a popular edge detection algorithm. Face Detection using HTML5, Javascript, Webrtc, Websockets, Jetty and OpenCV. Traverse these Contours and check whether it satisfies your requirement (You will get all the verti. So basically you would have an image A (could be a video) that when a face is close enough to the camera, slowly morphs into an image B. OpenCV Drawing Example, (line, circle, rectangle, ellipse, polyline, fillConvexPoly, putText, drawContours). Instead of a chess board, which has well-defined areas of contrasting colors, the edge of a floor, where there is lots of "noise" that will give rise to many features which just approximate a straight line, from which we want to then derive the straight line, which as I understand it is the whole point of the Hough transform, or am I misunderstanding what Sobel does?. BoxPoints(rect) instead of cv2. 4' into merge-3. Histograms in OpenCV. Haar-cascade Detection in OpenCV. It detects facial features and ignores anything else, such as buildings, trees and bodies. Your tutorial (Android eye detection updated for OpenCV 2. That callback function will be called every time, mouse events occur. In this project, we are going to demonstrate how one can drive a car by just detecting hand gestures on the steering wheel. A simple python script to detect and count faces in an image using python's opencv. js in a nodejs as well as browser environment. js provides javascript bindings for opencv, bringing the powerful image processing operations to javascripts. org; You’ll quickly come across the term cascades. Video processing (asm. if you are after edge detection you can use sobel function. Here is a list of algorithms you can experiment on to make OpenCV handy. You initialize your code with the cascade you want, and then it does the work for you. Learning OpenCV is a good asset to the developer to improve aspects of coding and also helps in building a software development. What is the best algorithm for rectangle detection? Hey all, I want to detect and track rectangle pattern. OpenCV’s deployed uses span the range from stitching streetview images together, detecting intrusions in surveillance video in Israel, monitoring mine equipment in China, helping robots navigate and pick up objects at Willow Garage, detection of swimming pool drowning accidents in Europe, running interactive art in Spain and New York, checking runways for debris in Turkey, inspecting labels on products in factories around the world on to rapid face detection in Japan. Python版OpenCVでは、「cv2. People are using node-opencv to fly control quadrocoptors, detect faces from webcam images and annotate video streams. Andrew, I wonder how could you figure out the question was about shape recognition? Frankly, I could not see that. Here we will deal with detection. I'm new to image processing in general and I have recently started using opencv. Detecting cats in images with OpenCV. Java Project Tutorial - Make Login and Register Form Step by Step Using NetBeans And MySQL Database - Duration: 3:43:32. Including jsfeat, clmtrackr, js-objectdetect, JSARToolkit, oflow, and tracking. Below is an example with a short description of different nodes. That is why, OpenCV doc says, " The contours are a useful tool for shape analysis and object detection and recognition ". Image Transforms in OpenCV. Haar Cascade based Face Detector was the state-of-the-art in Face Detection for many years since 2001, when it was introduced by Viola and Jones. How to Use OpenCV in React Native for Image OpenCV Processing If you have ever wondered how to process your images using OpenCV with React Native, then you're in the right place. OpenCV 3 is a state-of-the-art computer vision library that allows a great variety of image and video processing operations. The smile/happiness. The similar tutorial we will use here to detect your face and draw a rectangle around it to indicated your face. If you want to train your own classifier for any object like a car, planes, etc. js) Video processing (wasm) Face detection (asm. We're going to look into two commonly used edge detection schemes - the gradient (Sobel - first order. by GleasonK @ GleasonK 0. Object Detection and Recognition has been of prime importance in Computer Vision. Canny Edge Detection is used to detect the edges in a picture. Simple Rectangle Detection Using OpenCV on Android. Edge Detection is an image processing technique to find boundaries of objects in the image. It can be embedded using a script tag and it is ready for use! For the demonstration a simple image is taken and the various stages of processing are shown:. Insert a checkbox to select the Haar Classifier, detect and track a face, and draw a green rectangle around the detected face. The objective of this post is to demonstrate how to detect and count faces in an image, using OpenCV and Python. Example of Python with Opencv and camera face detection - python_opencv_camera_haar. The program grabs each frame from the video, then uses the classifier to detect faces. js provides javascript bindings for opencv, bringing the powerful image processing operations to javascripts. OpenCV typically assumes that the top and left boundary of the rectangle are inclusive, while the right and bottom boundaries are not. In the next few sections, we will cover steps that led to the development of Faster R-CNN object detection architecture. I used someone's code from internet. and <=0 is just habit failsafe code, of course an array cant be less than 0 but you know. I will be able more than 10 hours on the platform, so if you will have any thing to ask, don't hesitate to ask me. Using the OpenCV library, you can make use of the HAAR cascade filters to do this efficiently. Prepare the image data. A face detection library for node. Installing OpenCV via Auto Build Script. This example shows how to find circular blobs in an grayscale image. If you have only these regular shapes, there is a simple procedure as follows : 1. In this tutorial, we'll see how to create and launch a face detection algorithm in Python using OpenCV. js) Face detection (wasm). cv2: This is the OpenCV module for Python used for face detection and face recognition. Another problem is the rotation of the barcode. The tracking. The copyMakeBorder() Method. But OpenCV only has C++, C, Python and Java interfaces so how are these demos working with just JavaScript?. The objective of this post is to demonstrate how to detect and count faces in an image, using OpenCV and Python. If your image is relatively clean, you have obvious rectangles without a lot of breaks the alternative to a Hough transform is to create contours and reduce them until they form a 4 sided contour = your rectangle. js right in a browser. boxPoints ( rect ) box = np. we need to remove the code like AvgX,closestToLeft and closestToRight like these. Available in vivo models of primed adaptation that contain a plasmid-borne PPS or phage-borne PPS are limited due to difficulties in detecting bidirectional spacer acquisition or by high rates of. dst − An object of the class Mat representing the destination (output) image. Introduction. If you want to unleash the awesomeness of neural nets to. It may be too sensitive for other applications with many close to each other rectangles. Object detection using custom Haar Cascade on an image with OpenCV - run-custom-cascade. First I would recommend filling in the contour of the toy - in case it looks like the one in the second image. We want to strictly separate front-end and back-end in order to make it reusable. xml), which is stored in ~/. minNeighbors: parameter specifying how many neighbors each candidate rectangle should have to retain it. After searching the internet I have concluded that the best tool for this is OpenCV. The similar tutorial we will use here to detect your face and draw a rectangle around it to indicated your face. Prepare the image data. 4 0cf479d Jul 25, 2019. Face Detection using Haar Cascades. To validate OpenCV* installation, run the OpenCV deep learning module with the Inference Engine backend. Classifiers have been trained to detect faces using thousands to millions of images in order to get more accuracy. ) and the position. OpenCV provides some pre-trained models for different use cases such as face detection, eye detection, full body detection and others. Let (x,y) be the top-left coordinate of the rectangle and (w,h) be its width and height. Face detection network gets BGR image as input and produces set of bounding boxes that might contain faces. Following is the syntax Home. Training an object detector is bit of a complicated task. js like Fourier Transform, Cosine Transform etc. OpenCV Example Code It is very simple to do that. The thing is that up until two hours ago I had no idea what OpenCV is and I have never even remotely did anything involving image processing. Python OpenCV library will use to teach multiple face recognition software development. Why? Code: from time import sleep from picamera. OpenCV together with React Native enables you to process images on mobile devices (most likely you'd like to process images taken by your device's camera). If OpenCV detects a face it will track it and calculate its center's X,Y coordinates. Below are the codes I've made so far. This tutorial will teach you how to train your own Support Vector Machine (SVM) from a set of training images for image classification with OpenCV and JavaScript. Hardware acceleration. Processing 2. OpenCV - Face Detection in a Picture - The VideoCapture class of the org. Detect 80 common objects in context including car, bike, dog, cat etc. After these process, I try to find the. Opencv C++ Code with Example for Feature Extraction and Detection using SURF Detector This OpenCV C++ Tutorial is about feature detection using SURF Detector. •All original functions and classes of the C standard OpenCV components in the Bradski book are still available and current. In the next few sections, we will cover steps that led to the development of Faster R-CNN object detection architecture. Face Detection in Video Capture. CascadeClassifier」が実装されています。 今回はそれを使っておなじみの人の顔を検出するのに参考になったサイトをまとめてみました。. Object detection without Machine Learning When objects are of similar size and shape, like these rainbow donuts, they can be detected using simple template matching in OpenCV: Template matching is a method for finding the location of a template image in a larger image. js is a JavaScript binding for selected subset of OpenCV functions for the web platform. This was used to increase the dimensionality of the set of features in an attempt to improve the detection of objects in images. This is my first time making something that I'd actually consider using, and my first time posting to Code Review SE. Therefore I'd like to implement it within a Runnable class but I'm not having much luck. I have just installed opencv and am following this tutorial to detect faces while displaying a stream. Instead of a chess board, which has well-defined areas of contrasting colors, the edge of a floor, where there is lots of "noise" that will give rise to many features which just approximate a straight line, from which we want to then derive the straight line, which as I understand it is the whole point of the Hough transform, or am I misunderstanding what Sobel does?. Github Link. The objective of this post is to demonstrate how to detect and count faces in an image, using OpenCV and Python. Detect 80 common objects in context including car, bike, dog, cat etc. The objective of this post is to demonstrate how to detect and count faces in an image, using OpenCV and Python. The GUI functions, imread() and imshow() are used for such communication. Find Contours (by any method you find suitable/comfortable with using it) 2. It accepts a grayscale image as input and it uses a multi-stage algorithm. In order to do object recognition/detection with cascade files, you first need cascade files. Deteksi bentuk lingkaran, kotak, segitiga, dan lainx menggunakan WebCAM. Face Detection Using OpenCV In Python | How To Setup OpenCV Python Opencv is the most popular computer vision library, and today we are going to learn how to setup opencv, how to access your webcam and how easily we can write a face detection program with just a few lines of code. Introduction. nerds_thesis_clartips_OpencvClass. OpenCV HOG Detector: Result Clustering 07 Nov 2013. OpenCV’s deployed uses span the range from stitching streetview images together, detecting intrusions in surveillance video in Israel, monitoring mine equipment in China, helping robots navigate and pick up objects at Willow Garage, detection of swimming pool drowning accidents in Europe, running interactive art in Spain and New York, checking runways for debris in Turkey, inspecting labels on products in factories around the world on to rapid face detection in Japan. Contribute to opencv/opencv development by creating an account on GitHub. Face Detection using Haar-Cascade Classifier in OpenCV, OpenCV Object Detection, objects – Vector of rectangles where each rectangle contains the detected object. cv2 module in the root of Python's site-packages), remove it before installation to avoid conflicts. Detect and Track Objects With OpenCV (computers) These tutorials introduce you into the detection and tracking objects with OpenCV when you’re using computers. Today we are going to take a look at OpenCV’s Deep Neural Networks module. It is obtained by the function cv2. (4) Translate back by adding c to each coordinate. Object Detection & Tracking in OpenCV with Visual Studio 2015 in Windows 10. Results are also same, but with a slight difference. This was used to increase the dimensionality of the set of features in an attempt to improve the detection of objects in images. Traverse these Contours and check whether it satisfies your requirement (You will get all the verti. This process can run in any environment where OpenCV can be installed and doesn't depend on the hassle of installing deep learning libraries with GPU support. All of the new developments and algorithms in OpenCV are now developed in the C++ interface. these pattern I want to set on object which moving and captured using webcam. Calculate Object Distance From Camera Opencv Android. io/x/gocv" Package gocv is a wrapper around the OpenCV 3. But OpenCV only has C++, C, Python and Java interfaces so how are these demos working with just JavaScript?. Edge detection is one of the fundamental operations when we perform image processing. This is merely detection that there is a face in a given image. This is my first time making something that I'd actually consider using, and my first time posting to Code Review SE. Detecting Rectangle using OpenCV Java We are dealing with image processing it often comes that how to detect particular shape in image. Computer vision is widely used, for example for motion tracking in security cameras, control of autonomous vehicles, identification of /searching for objects in a picture/video. Find Contours (by any method you find suitable/comfortable with using it) 2. Face detection using haar-cascades. Learning the basic concepts behind computer vision algorithms, models,. If someone having no hands on a. So remember, object to be found should be white and background should be black. OpenCV Python Tutorial. OpenCV on Wheels. After searching the internet I have concluded that the best tool for this is OpenCV. The program grabs each frame from the video, then uses the classifier to detect faces. Face and Eye Detection With Raspberry Pi Zero and Opencv: In this instructable i'm going to show how you can detect face and eye using raspberry pi and opencv. 0 – module object has no attribute ‘xfeatures2d’ I have shifted from OpenCV 2. OpenCV Facerecog. detecting faces from an image) with Ruby. and <=0 is just habit failsafe code, of course an array cant be less than 0 but you know. So remember, object to be found should be white and background should be black. jsis a javascript module, built on top of tensorflow. In OpenCV, finding contours is like finding white object from black background. 0 version so any way I can detect rectangles using openCV 2. It provides a Go language interface to the latest version of OpenCV. This example will switch on the default webcam to capture the live video and perform a blur and Canny edge detection. package gocv. I'm new to image processing in general and I have recently started using opencv. It will then call the sketch. Template Matching. py file will use OpenCV to access our web camera, perform motion detection via SingleMotionDetector, and then serve the output frames to our web browser via the Flask web framework. Calculate Object Distance From Camera Opencv Android. (4) Translate back by adding c to each coordinate. 1BestCsharp blog 6,075,516 views. js to help developers create CV code in JS interactively and see the results immediately, all in the browser on any device, including on smart phones. I am using Processing with the OpenCV Lib and wanted to rewrite the example Code from the creators Git so that instead of doing Face Detection on a Camera Capture I'll load a video (. Your browser does not support the video tag. OpenCV is a library of programming functions mainly aimed at real-time computer vision. A Haar Cascade is an object detection method used to locate an object of interest in images. If you take a look at the OpenCV repository, specifically within the haarcascades directory (where OpenCV stores all its pre-trained Haar classifiers to detect various objects, body parts, etc. For example, there are several transforms in OpenCV, some of which are very usable to detect dominant straight lines in the picture. learn the basics of face detection using Haar Feature-based Cascade Classifiers; extend the same for eye detection etc. Face detection network gets BGR image as input and produces set of bounding boxes that might contain faces. To add a person to the database, you need to create a subfolder with the person's name. How to detect multiple faces using opencv in order to generate an output of flickering LED lights. Object Detection without color in OpenCV (Java) (A pre requisite to Object tracking OpenCV tutorial I published earlier) , so I decided to make a small tutorial. OpenCV 3 is a state-of-the-art computer vision library that allows a great variety of image and video processing operations. Learn how to detect lines in an image. In the face detector code, inside the detectfaces function, there is a cvrectangle() used to construct rectangle around the detected face. In this tutorial, we’ll make use of OpenCV in Python to detect circle-shaped objects in a webcam stream and replace them with 3D Earth in Three. Welcome back to yet another Node. The copyMakeBorder () Method. OpenCV Shape Detection - PyImageSearch - Free download as PDF File (. Your browser does not support the video tag. This process can run in any environment where OpenCV can be installed and doesn't depend on the hassle of installing deep learning libraries with GPU support. minNeighbors: This is a detection algorithm that uses a moving window to detect objects, it does so by defining how many objects are found near the current one before it can declare the face found. While many object detection algorithms like YOLO, SSD, RCNN, Fast R-CNN and Faster R-CNN have been researched a lot to great success but still pedestrian detection in crowded scenes remains an open challenge. The question is very basic, it can be solved in two or three steps: 1. Face detection network gets BGR image as input and produces set of bounding boxes that might contain faces. OpenCV and the Viola-Jones Object. Code example about selecting the rectangle region of interest inside the image and cut or display part of the image from the bigger picture. Where these thresholds comes? Why on the tree there are a right or left part?. On Jul 2 @KirkDBorne tweeted: "From Books To Tutorials — Top 7 Resource. OpenCV - Drawing a Rectangle - You can draw a rectangle on an image using the method rectangle() of the imgproc class. In this simple example, we will use a Haar feature-based cascade classifier. This means if the computer is presented with two pictures of me, it would not only recognize what part of the picture is my face, it would also recognize that I am the one in. Facial Recognition. Otherwise, other preprocessing methods should be done to make barcode horizontal. I’ve colored the results blue or red based on whether they represent a true positive or a false positive. XML file to the classifier's constructor (the HAAR_FRONTALFACE_ALT constant). nerds_thesis_clartips_OpencvClass. opencv / samples / dnn / js_face_recognition. js and OpenCV communicate through the use of the canvas object. Evidence is collected in a 3D accumulator array for the presence of circles with different centers and radii. I followed many tutorials to set up open cv in raspberry but every time struck with some errors. rectangleの型に変換します。. The similar tutorial we will use here to detect your face and draw a rectangle around it to indicated your face. Detecting and tracking a face with Python and OpenCV At work, I was asked whether I wanted to help out on a project dealing with a robot that could do autonomous navigation and combine this with both speech recognition and most importantly: face recognition. js to help developers create CV code in JS interactively and see the results immediately, all in the browser on any device, including on smart phones. Before we dive into the details, please check previous posts listed below on Object Tracking to understand the basics of single object trackers implemented in OpenCV. Joseph provides computer vision expertise through his company, Nummist Media. OpenCV uses two types of classifiers, LBP (Local Binary Pattern) and Haar Cascades. In my previous tutorial we have seen how you see yourself in webcam using Python. Deteksi bentuk lingkaran, kotak, segitiga, dan lainx menggunakan WebCAM. js or WebAssembly targets, and provides a JavaScript APIs for web application to access them Emscripten is an LLVM-to-JavaScript. OpenCV tutorial: Computer vision with Node. Haar-feature Object Detection in C# I don't understand the classification part. We can use skimage here to directly overlay the dlib rectangle object on the image. Facial Recognition. 其中detect_rect是opencv类型,dets是dlib类型; 参考. i need some one how can do opencv algorithms code detection on live video and hide it. It helps you to write computer vision programs (e. Joseph provides computer vision expertise through his company, Nummist Media. This tutorial will show us how to run deep learning models using OpenCV. Canny in 1986. It is obtained by the function cv2. js in a browser window while using WebSockets to join this all together. In addition to counting the cars as they are detected, you'll also count them as they cross a "finish line" for each lane and show cars per second. 4' into merge-3. This is a default interpretation of Rect_::x and Rect_::y in OpenCV. and then take picture. Edge Detection is an image processing technique to find boundaries of objects in the image. The detect-multi-scale method then let’s us analyze the image and know if a person exists using the classification result from our SVM. Soon, it was implemented in OpenCV and face detection became synonymous with Viola and Jones algorithm. int0 ( box ) im = cv2. top − A variable of integer the type integer representing the length of the border at the top. We're going to look into two commonly used edge detection schemes - the gradient (Sobel - first order. I following some guide on the internet in how to detect document in an image in OpenCV and Java. Learning the basic concepts behind computer vision algorithms, models,. All you have do is to define a callback function in the OpenCV C++ code attaching to the OpenCV window. So, you want to see some real life examples on what tracking. Part 2 was all about grabbing frames from video file. Display Image OpenCV; Drawing Functions in Java; Draw rectangle on image; Drawing Shapes (Line, Circle, , etc) in C++; Edge detection; Image Content Modification; Image Processing; Loading and Saving Various Media Formats; Object Detection; OpenCV initialization in Android; OpenCV Installation; Pixel Access; Using Cascade Classifiers In Java. The objective of this post is to demonstrate how to detect and count faces in an image, using OpenCV and Python.