MareArts Computer Vision Study.: 2016.06

6/20/2016

Matlab vector index shuffle

V1 =[ 10 20 30 40 50 60 70];
V2 = V1( :, randperm( length(V1) ));

V2 =

60 10 20 30 50 40 70

6/09/2016

OpenCV Mat and Matrix operation examples

example code.

...

Mat Ma = Mat::eye(3, 3, CV_64FC1);
 cout << Ma << endl;
 double dm[3][3] = { { 1, 2, 3 }, { 4, 5, 6 }, { 7, 8, 9 } };
 Mat Mb = Mat(3, 3, CV_64F, dm);
 cout << Mb << endl;
 
 //Matrix - matrix operations :
 Mat Mc;
 cv::add(Ma, Mb, Mc); // Ma+Mb   -> Mc
 cout << Ma+Mb << endl;
 cout << Mc << endl;
 cv::subtract(Ma, Mb, Mc);      // Ma-Mb   -> Mc
 cout << Ma - Mb << endl;
 cout << Mc << endl;
 Mc = Ma*Mb; //Ma*Mb;
 cout << Mc << endl;
 
 //Elementwise matrix operations :
 cv::multiply(Ma, Mb, Mc);   // Ma.*Mb   -> Mc
 cout << Mc << endl;
 Mc = Ma.mul(Mb);
 cout << Mc << endl;
 cv::divide(Ma, Mb, Mc);      // Ma./Mb  -> Mc
 cout << Mc << endl;
 Mc = Ma + 10; //Ma + 10 = Mc
 cout << Mc << endl;

 //Vector products :
 double va[] = { 1, 2, 3 };
 double vb[] = { 0, 0, 1 };
 double vc[3];

 Mat Va(3, 1, CV_64FC1, va);
 Mat Vb(3, 1, CV_64FC1, vb);
 Mat Vc(3, 1, CV_64FC1, vc);

 double res = Va.dot(Vb); // dot product:   Va . Vb -> res
 Vc = Va.cross(Vb);    // cross product: Va x Vb -> Vc
 cout << res << " " << Vc << endl;


 //Single matrix operations :
 Mc = Mb.t();      // transpose(Ma) -> Mb (cannot transpose onto self)
 cout << Mc << endl;
 cv::Scalar t = trace(Ma); // trace(Ma) -> t.val[0] 
 cout << t.val[0] << endl; 
 double d = determinant(Ma); // det(Ma) -> d
 cout << d << endl;
 Mc = Ma.inv();         // inv(Mb) -> Mc
 invert(Ma, Mc);
 cout << Mc << endl;


 //Inhomogeneous linear system solver :
 double dm2[3][3] = { { 1, 2, 3 }, { 4, 5, 6 }, { 7, 8, 9 } };
 Mat A(3, 3, CV_64FC1, dm2);
 Mat x(3, 1, CV_64FC1);
 double vvb[] = { 14, 32, 52 };
 Mat b(3, 1, CV_64FC1, vvb);
 cv::solve(A, b, x, DECOMP_SVD); //// solve (Ax=b) for x
 cout << x << endl;


 //Eigen analysis(of a symmetric matrix) :
 float f11[] = { 1, 0.446, -0.56, 0.446, 1, -0.239, -0.56, 0.239, 1 };
 Mat data(3, 3, CV_32F, f11);
 Mat value, vector;
 eigen(data, value, vector);
 cout << "Eigenvalues" << value << endl;
 cout << "Eigenvectors" << endl;
 cout << vector << endl;


 //Singular value decomposition :
 Mat w, u, v;
 SVDecomp(data, w, u, v); // A = U W V^T
 //The flags cause U and V to be returned transposed(does not work well without the transpose flags).
 cout << w << endl;
 cout << u << endl;
 cout << v << endl;

...

OpenCV image and video write

image write

..

Mat img = imread("ss.jpg");
 vector< Mat> rgbMat(3);
 cv::split(img, rgbMat);

 namedWindow("img", 0); //make window
 imshow("img", rgbMat[2]); //show
 waitKey(0);

 imwrite("r.jpg", rgbMat[2]);
 imwrite("g.bmp", rgbMat[1]);
 imwrite("b.tif", rgbMat[0]);

...

video write
http://study.marearts.com/2013/09/opencv-video-writer-example-source-code.html

OpenCV Mat copyTo, Clone, ROI example code

OpenCV Mat copyTo, Clone, ROI example code

...

Mat img = imread("ss.jpg");
 
 Rect r(img.cols / 4, img.rows / 4, img.cols / 4 * 2, img.rows / 4 * 2);

 //clone #1
 Mat img2 = img.clone();
 bitwise_not(img2, img2);

 //clone #2
 Mat img5 = img(r).clone();


 //copyTo #1
 Mat cimg;
 img.copyTo(cimg);

 //copyTo #2
 Mat cimg2;
 img(r).copyTo(cimg2);

 //copyTo #3
 Mat cimg3( Size(img.cols*2, img.rows), img.type() );
 cimg3.setTo(255);
 img.copyTo(cimg3(Range::all(), Range(0, img.cols)));
 img2.copyTo(cimg3(Range::all(), Range(img2.cols, img2.cols * 2)));

 //set roi
 Mat roi(img, r);
 //invert color
 bitwise_not(roi, roi);


 namedWindow("img2", 0); //make window
 imshow("img2", cimg); //show
 namedWindow("img3", 0); //make window
 imshow("img3", cimg2); //show
 namedWindow("img4", 0); //make window
 imshow("img4", cimg3); //show
 namedWindow("img5", 0); //make window
 imshow("img5", img5); //show
 namedWindow("img", 0); //make window
 imshow("img", img); //show
 
 waitKey(0);

...

OpenCV Pixel Access, at, ptr, data, iteration (example)

I once wrote the following article.
http://study.marearts.com/2014/04/opencv-study-mat-point-access-method.html
This article is a sample code.

..

#include "opencv2/opencv.hpp"

using namespace cv;
using namespace std;

int main(int, char)
{
    namedWindow("img", 1);
    Mat img = imread("anapji.jpg");
    
    if (img.depth() == CV_8U)
        printf("8bit unsigend\n");

    img.

    /*
    cout << img.elemSize() << endl;
    cout << img.channels() << endl;
    cout << img.rows << endl;
    cout << img.step << endl;
    */

    //using data
    //for (int i = img.rows / 10 * 7; i < img.rows / 10 * 8; i++) {

    //for (int i = 0; i < img.rows ; i++) {

    for (int i = img.rows / 10 * 7; i < img.rows / 10 * 8; i++) {
        for (int j = 0; j < img.cols; j++) {


            unsigned char r, g, b;

            b = img.data[i * img.step + j * img.elemSize() + 0];
            g = img.data[i * img.step + j * img.elemSize() + 1];
            r = img.data[i * img.step + j * img.elemSize() + 2];

            img.data[i * img.step + j * img.elemSize() + 0] = unsigned char(255 - b);
            img.data[i * img.step + j * img.elemSize() + 1] = unsigned char(255 - g);
            img.data[i * img.step + j * img.elemSize() + 2] = unsigned char(255 - r);

        }
    }




    

    //using at
    for (int i = img.rows / 10 * 2; i < img.rows / 10 * 3; ++i)
    {
        for (int j = 0; j < img.cols; ++j)
        {
            //Vec3b means 'uchar 3ch'
            unsigned char b = img.at< cv::Vec3b>(i, j)[0];
            unsigned char g = img.at< cv::Vec3b>(i, j)[1];
            unsigned char r = img.at< cv::Vec3b>(i, j)[2];

            //printf("%d %d %d\n", b, g, r);

            img.at< cv::Vec3b>(i, j)[0] = unsigned char(255 - b); //b
            img.at< cv::Vec3b>(i, j)[1] = unsigned char(255 - g); //g
            img.at< cv::Vec3b>(i, j)[2] = unsigned char(255 - r); //r
        }
    }


    
    //using ptr
    for (int i = img.rows / 10 * 5; i < img.rows / 10 * 6; i++) {

        cv::Vec3b* ptr = img.ptr< cv::Vec3b >(i);

        for (int j = 0; j < img.cols; j++) {

            unsigned char b1 = (ptr[j][0]);
            unsigned char g1 = (ptr[j][1]); //note!!
            unsigned char r1 = (ptr[j][2]);


            cv::Vec3b bgr = ptr[j];
            unsigned char b2 = (bgr[0]);
            unsigned char g2 = (bgr[1]); //note!!
            unsigned char r2 = (bgr[2]);

            

            ptr[j] = cv::Vec3b(255 - b1, 255 - g1, 255 - r1);

        }
    }



    

    //using iteration
    cv::MatIterator_< cv::Vec3b> itd = img.begin< cv::Vec3b>(), itd_end = img.end< cv::Vec3b>();

    for (int i = 0; itd != itd_end; ++itd, ++i) {

        cv::Vec3b bgr = (*itd);

        (*itd)[0] = 255 - bgr[0];
        (*itd)[1] = 255 - bgr[1];
        (*itd)[2] = 255 - bgr[2];
    }

    

    imshow("img", img); //show
    waitKey(0);

    destroyAllWindows();

    return 0;
}

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output

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