#OpenCV – Detect and blur faces 😁 using haar cascades in C#

#englishpost #csharp #facedetection

Hi !

NET is in anniversary mode, so I think it will be a good idea to share some camera samples in C#. For these demos I’m using C#, NET 6 and OpenCVSharp as OpenCV wrapper for .NET.

Today post: detect a face using haar cascades and blur the face area. This demo also show the detected face in a separated window (just for fun).

Code Sample

Easy to implement, and also easy to read:

	// Copyright (c) 2022
	// Author : Bruno Capuano
	// Create Time : 2022 Feb
	// Change Log :
	// - Open a camera feed from a local USB webcam and analyze each frame to detect faces using haar cascades
	// - When a face is detected, the app will blur the face zone in the main window
	// - When a face is detected, the app will show the original detected face in a separated window
	// - Press [F] to enable / disable the face detection process
	// - Press [Q] to quit the app
	//
	// The MIT License (MIT)
	//
	// Permission is hereby granted, free of charge, to any person obtaining a copy
	// of this software and associated documentation files (the "Software"), to deal
	// in the Software without restriction, including without limitation the rights
	// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
	// copies of the Software, and to permit persons to whom the Software is
	// furnished to do so, subject to the following conditions:
	//
	// The above copyright notice and this permission notice shall be included in
	// all copies or substantial portions of the Software.
	//
	// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
	// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
	// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
	// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
	// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
	// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
	// THE SOFTWARE.

	using OpenCvSharp;

	var faceCascade = new CascadeClassifier();
	faceCascade.Load("haarcascade_frontalface_default.xml");

	using var capture = new VideoCapture(0);
	{
	var image = new Mat();
	var showFace = true;
	var run = true;
	using var window = new Window("El Bruno - Blur Face");
	using var windowFace = new Window("El Bruno - Face");

	while (run)
	{
	capture.Read(image);
	if (image.Empty())
	break;

	var newSize = new Size(640, 480);
	using var smallFrame = new Mat();
	Cv2.Resize(image, smallFrame, newSize);

	if (showFace)
	{
	using var gray = new Mat();
	Cv2.CvtColor(smallFrame, gray, ColorConversionCodes.BGR2GRAY);

	var faces = faceCascade.DetectMultiScale(gray, 1.3, 5);
	foreach (var face in faces)
	{
	Cv2.Rectangle(smallFrame, face, Scalar.Red);

	// create a new Mat with the detected face
	var faceImg = new Mat(smallFrame,
	new OpenCvSharp.Range(face.Top, face.Top + face.Width),
	new OpenCvSharp.Range(face.Left, face.Left + face.Height));
	windowFace.Image = faceImg;

	// blur the face area in the original frame
	var faceBlur = new Mat();
	Cv2.GaussianBlur(faceImg, faceBlur, new Size(23, 23), 30);
	smallFrame[face] = faceBlur;
	}
	}

	window.Image = smallFrame;
	switch ((char)Cv2.WaitKey(100))
	{
	case (char)27: // ESC
	run = false;
	break;
	case 'f':
	showFace = !showFace;
	break;
	}
	}
	}