Opencv: Train SVM with FAST keypoints and BRIEF features

Opencv: Train SVM with FAST keypoints and BRIEF features

By : user2953136
Date : November 20 2020, 01:01 AM
this will help To train a SVM you would need a matrix X with your features and a vector y with your labels. It should look like this for 3 images and two features:
code :
>>> from sklearn import svm
>>> X = [[0, 0],   <- negative 0
         [1, 3],   <- positive 1
          2, 5]]   <- negative 0
>>> y = [0,   
>>> model = svm.SVC()
>>> model.fit(X, y) 

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How to train a Support Vector Machine(svm) classifier with openCV with facial features?

How to train a Support Vector Machine(svm) classifier with openCV with facial features?

By : Ravi Raj
Date : March 29 2020, 07:55 AM
Hope this helps the machine learning algos in opencv all come with a similar interface. to train it, you pass a NxM Mat offeatures (N rows, each feature one row with length M) and a Nx1 Mat with the class-labels. like this:
code :
//traindata      //trainlabels

f e a t u r e    1 
f e a t u r e    -1
f e a t u r e    1
f e a t u r e    1
f e a t u r e    -1
Mat trainData; // start empty
Mat labels;

for all facial_point_vecs:
    for( size_t i=0; i<16; i++ )
    labels.push_back(label); // 1 or -1
// now here comes the magic:
// reshape it, so it has N rows, each being a flat float, x,y,x,y,x,y,x,y... 32 element array
trainData = trainData.reshape(1, 16*2); // numpoints*2 for x,y

// we have to convert to float:

SVM svm; // params omitted for simplicity (but that's where the *real* work starts..)
svm.train( trainData, labels );

//later predict:
vector<Point> points;
Mat testData = Mat(points).reshape(1,32); // flattened to 1 row
testData.convertTo(testData ,CV_32F);
float p = svm.predict( testData );
OpenCV FAST - too many features

OpenCV FAST - too many features

By : Maryam Raja
Date : March 29 2020, 07:55 AM
this will help If you look at the documentation, you will see that you can set a threshold for your FAST detector:
code :
FastFeatureDetector( int threshold=1, bool nonmaxSuppression=true, type=FastFeatureDetector::TYPE_9_16 );
fast = cv2.FastFeatureDetector(40)
train classifier to detect only eyelashes/nose features dlib and opencv?

train classifier to detect only eyelashes/nose features dlib and opencv?

By : eworker2003
Date : March 29 2020, 07:55 AM
I wish did fix the issue. For Dlib python api starting point should be this sample http://dlib.net/face_landmark_detection.py.html
As you see - it has face detection and shape prediction:
code :
dets = detector(img, 1)
shape = predictor(img, d)
with open("sample_file.txt", "w") as f:
    for i in range(30, 32):
       f.write("{};{}\n".format(i, shape.part(i)))
OpenCV - FAST+BRIEF: How to draw keypoints with DrawMatchesFlags::DRAW_RICH_KEYPOINTS?

OpenCV - FAST+BRIEF: How to draw keypoints with DrawMatchesFlags::DRAW_RICH_KEYPOINTS?

By : usrgz
Date : March 29 2020, 07:55 AM
may help you .
I have to implement a feature detector using FAST+BRIEF (which is the manual implementation of ORB if I understand correctly).
code :
#include <iostream>
#include <opencv2/highgui/highgui.hpp>
#include <opencv2/core/core.hpp>
#include <opencv2/imgproc/imgproc.hpp>
#include <opencv2/features2d/features2d.hpp>
#include <opencv2/xfeatures2d/nonfree.hpp>  

int main(int argc, char** argv)

    // Load image
    cv::Mat img = cv::imread("MT189.jpg", CV_LOAD_IMAGE_GRAYSCALE);
    if (!img.data) {
        std::cout << "Error reading image" << std::endl;
        return EXIT_FAILURE;
    cv::Mat output;

    // Detect FAST keypoints
    std::vector<cv::KeyPoint> keypoints_fast, keypoints_sift;
    cv::Ptr<cv::FastFeatureDetector> fast = cv::FastFeatureDetector::create();
    fast->detect(img, keypoints_fast);
    for (size_t i = 0; i < 100; ++i) {
        std::cout << "FAST Keypoint #:" << i;
        std::cout << " Size " << keypoints_fast[i].size << " Angle " << keypoints_fast[i].angle << " Response " << keypoints_fast[i].response << " Octave " << keypoints_fast[i].octave << std::endl;

    // Detect SIFT keypoints
    cv::Ptr<cv::xfeatures2d::SiftFeatureDetector> sift = cv::xfeatures2d::SiftFeatureDetector::create();
    sift->detect(img, keypoints_sift);

    for (size_t i = 0; i < 100; ++i) {
        std::cout << "SIFT Keypoint #:" << i;
        std::cout << " Size " << keypoints_sift[i].size << " Angle " << keypoints_sift[i].angle << " Response " << keypoints_sift[i].response << " Octave " << keypoints_sift[i].octave << std::endl;

    // Draw SIFT keypoints
    cv::drawKeypoints(img, keypoints_sift, output, cv::Scalar::all(-1), cv::DrawMatchesFlags::DRAW_RICH_KEYPOINTS);
    cv::imshow("Output", output);

How do I train an SVM classifier using HOG features in OpenCV 3.0 in Python?

How do I train an SVM classifier using HOG features in OpenCV 3.0 in Python?

By : DeepThought
Date : March 29 2020, 07:55 AM
seems to work fine Currently I have the same issue and I have seen the following document from OpenCV:
OCR of Hand-written Data using SVM
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