Detecting 16 squares in a live video in Python

edit

the question seems finding Rubics cube asked before,

i did some modifications on my code of previous answer like below and get this result image...

#include "opencv2/imgproc.hpp"
#include "opencv2/highgui.hpp"

using namespace cv;
using namespace std;

// helper function:
// finds a cosine of angle between vectors
// from pt0->pt1 and from pt0->pt2
static double angle(Point pt1, Point pt2, Point pt0)
{
    double dx1 = pt1.x - pt0.x;
    double dy1 = pt1.y - pt0.y;
    double dx2 = pt2.x - pt0.x;
    double dy2 = pt2.y - pt0.y;
    return (dx1*dx2 + dy1*dy2) / sqrt((dx1*dx1 + dy1*dy1)*(dx2*dx2 + dy2*dy2) + 1e-10);
}

static void drawSquares(Mat& image, const vector<vector<Point> >& squares)
{
    Mat canvas(image.size(), CV_8SC3, Scalar(0, 0, 0));
    for (size_t i = 0; i < squares.size(); i++)
    {
        const Point* p = &squares[i][0];
        int n = (int)squares[i].size();

        Rect r = boundingRect(squares[i]);
        r.x = r.x + r.width / 4;
        r.y = r.y + r.height / 4;
        r.width = r.width / 2;
        r.height = r.height / 2;

        Mat roi = image(r);
        Scalar color = mean(roi);
        polylines(image, &p, &n, 1, true, color, 2);
        polylines(canvas, &p, &n, 1, true, color, 2);

        Point center(r.x + r.width / 2, r.y + r.height / 2);
        ellipse(image, center, Size(r.width / 2, r.height / 2), 0, 0, 360, color, 2, LINE_AA);
        ellipse(canvas, center, Size(r.width / 2, r.height / 2), 0, 0, 360, color, 2, LINE_AA);
    }
    imshow("canvas", canvas);
}

// returns sequence of squares detected on the image.
// the sequence is stored in the specified memory storage
static void findSquares(const Mat& image, vector<vector<Point> >& squares, bool inv = false)
{
    squares.clear();

    Mat gray, gray0;

    vector<vector<Point> > contours;

    cvtColor(image, gray0, COLOR_BGR2GRAY);
    GaussianBlur(gray0, gray0, Size(5, 5), 1.5, 1.5);
    Canny(gray0, gray, 0, 30, 3);
    dilate(gray, gray, Mat());
    imshow("canny", gray);
    // find contours and store them all as a list
    findContours(gray, contours, RETR_EXTERNAL, CHAIN_APPROX_SIMPLE);

    vector<Point> approx;

    // test each contour
    for (size_t i = 0; i < contours.size(); i++)
    {
        // approximate contour with accuracy proportional
        // to the contour perimeter
        approxPolyDP(Mat(contours[i]), approx, 9, true);

        // square contours should have 4 vertices after approximation
        // relatively large area (to filter out noisy contours)
        // and be convex.
        // Note: absolute value of an area is used because
        // area may be positive or negative - in accordance with the
        // contour orientation
        if (approx.size() == 4 &&
            fabs(contourArea(Mat(approx))) > 5 &&
            isContourConvex(Mat(approx)))
        {
            double maxCosine = 0;

            for (int j = 2; j < 5; j++)
            {
                // find the maximum cosine of the angle between joint edges
                double cosine = fabs(angle(approx[j % 4], approx[j - 2], approx[j - 1]));
                maxCosine = MAX(maxCosine, cosine);
            }

            // if cosines of all angles are small
            // (all angles are ~90 degree) then write quandrange
            // vertices to resultant sequence
            if (maxCosine < 0.3)
                squares.push_back(approx);
        }
    }
}

int main(int argc, char** argv)
{
    Mat frame;
    vector<vector<Point> > squares;

        frame =imread(argv[1]);

        if (frame.empty())
        {
            return -1;
        }
        findSquares(frame, squares);
        drawSquares(frame, squares);
        imshow("result", frame);
        waitKey(0);

    return 0;
}