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    <p>Edit:</p> <p>Just to notify anyone visiting this site. I have written some sample code to perform face recognition in videos using my libfacerec library:</p> <ul> <li><a href="https://github.com/bytefish/libfacerec/blob/master/samples/facerec_video.cpp" rel="nofollow">https://github.com/bytefish/libfacerec/blob/master/samples/facerec_video.cpp</a></li> </ul> <p>Original post:</p> <p>I assume your problem is the following. You've used the Cascade Classifier <a href="http://opencv.willowgarage.com/documentation/cpp/objdetect_cascade_classification.html#cascadeclassifier" rel="nofollow">cv::CascadeClassifier</a> coming with OpenCV to detect and extract faces from images. Now you want to perform a face recognition on the images. </p> <p>You want to use the Eigenfaces for face recognition. So the first thing you have to do is to learn the Eigenfaces from the images you've gathered. I rewrote the <a href="https://github.com/bytefish/opencv/tree/master/eigenfaces" rel="nofollow">Eigenfaces class</a> for you to make it simpler. To learn the eigenfaces simply pass a vector with your face images and the corresponding labels (the subject) either to <a href="https://github.com/bytefish/opencv/blob/master/eigenfaces/include/eigenfaces.hpp#L48" rel="nofollow">Eigenfaces::Eigenfaces</a> or <a href="https://github.com/bytefish/opencv/blob/master/eigenfaces/include/eigenfaces.hpp#L53" rel="nofollow">Eigenfaces::compute</a>. Make sure all your images have the same size, you can use <a href="http://opencv.willowgarage.com/documentation/cpp/geometric_image_transformations.html#cv-resize" rel="nofollow">cv::resize</a> to ensure this.</p> <p>Once you have computed the Eigenfaces, you can get predictions from your model. Simply call <a href="https://github.com/bytefish/opencv/blob/master/eigenfaces/include/eigenfaces.hpp#L57" rel="nofollow">Eigenfaces::predict</a> on a computed model. The <a href="https://github.com/bytefish/opencv/blob/master/eigenfaces/src/main.cpp" rel="nofollow">main.cpp</a> shows you how to use the class and its methods (for prediction, projection, reconstruction of images), here's <a href="https://github.com/bytefish/opencv/blob/master/eigenfaces/src/main.cpp#L66" rel="nofollow">how to get a prediction for an image</a>.</p> <p>Now I see where your problem is. You are using the old OpenCV C API. That makes it's hard to interface with the new OpenCV2 C++ API my code is written in. Not to be offending, but if you want to interface with my code you better use the OpenCV2 C++ API. I can't give a guide on learning C++ and the OpenCV2 API here, there's a lot of documentation coming with OpenCV. A good start is the OpenCV C++ Cheat Sheet (also available at <a href="http://opencv.willowgarage.com/" rel="nofollow">http://opencv.willowgarage.com/</a>) or the OpenCV Reference Manual.</p> <p>For recognizing images from the Cascade Detector, I repeat: First learn the Eigenfaces model with the persons you want to recognize, it's shown in the example coming with my code. Then you need to get the Region Of Interest (ROI), that's the face, the Rectangle the Cascade Detector outputs. Finally you can get a prediction for the ROI from the Eigenfaces model (you have computed it above), it's shown in the example coming with my code. You probably have to convert your image to grayscale, but that's all. That's how it's done.</p>
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    1. CO@bytefish-Thanks for the answer:) I have used your code of Eigenfaces at https://github.com/bytefish/opencv/tree/master/eigenfaces.In this code you have passed a text file containing faces from ORL Face Database.Can i just change that text file and pass my extracted face?
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    2. CONo Problem. Yes of course, you can use any vector of [cv::Mat](http://opencv.willowgarage.com/documentation/cpp/core_basic_structures.html#mat) you want as long as the images have the same size. The CSV file is just an example how to load data, you can of course edit this file to pass your own images. If you still have problems, please edit your post and paste some code. Just as @BjörnPollex pointed out, it's hard to make assumptions without details. By the way, please accept if this is the answer to your question.
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    3. COIt's still work in progress, but I've started a guide on face recognition: [bytefish.de/pdf/facerec.pdf](http://www.bytefish.de/pdf/facerec.pdf). The code examples are available at [github.com/bytefish/facerecognition_guide](http://www.github.com/bytefish/facerecognition_guide).
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