Hi,
I'm trying to detect the following card
And warp it, rotate it, to be centered on the screen.
I tried the following approach but it doesn't work at all.
#include "opencv2/imgproc.hpp"
#include "opencv2/imgcodecs.hpp"
#include "opencv2/highgui.hpp"
#include <iostream>
using namespace cv;
using namespace std;
#define EPSILON 1E-5
//! Return the maximum of the provided numbers
static double maximum(double number1, double number2, double number3) {
return std::max(std::max(number1, number2), number3);
}
//! Check if the two numbers are equal (almost)
/*!
* The expression for determining if two real numbers are equal is:
* if (Abs(x - y) <= EPSILON * Max(1.0f, Abs(x), Abs(y))).
*
* @param number1 First number
* @param number2 Second number
*/
static bool almostEqual(double number1, double number2) {
return (std::abs(number1 - number2) <= (EPSILON * maximum(1.0, std::abs(number1), std::abs(number2))));
}
//! Determine the intersection point of two lines, if this point exists
/*! Two lines intersect if they are not parallel (Parallel lines intersect at
* +/- infinity, but we do not consider this case here).
*
* The lines are specified by a pair of points each. If they intersect, then
* the function returns true, else it returns false.
*
* Lines can be specified in the following form:
* A1x + B1x = C1
* A2x + B2x = C2
*
* If det (= A1*B2 - A2*B1) == 0, then lines are parallel
* else they intersect
*
* If they intersect, then let us denote the intersection point with P(x, y) where:
* x = (C1*B2 - C2*B1) / (det)
* y = (C2*A1 - C1*A2) / (det)
*
* @param a1 First point for determining the first line
* @param b1 Second point for determining the first line
* @param a2 First point for determining the second line
* @param b2 Second point for determining the second line
* @param intersection The intersection point, if this point exists
*/
static bool lineIntersection(const cv::Point2f &a1, const cv::Point2f &b1, const cv::Point2f &a2,
const cv::Point2f &b2, cv::Point2f &intersection) {
double A1 = b1.y - a1.y;
double B1 = a1.x - b1.x;
double C1 = (a1.x * A1) + (a1.y * B1);
double A2 = b2.y - a2.y;
double B2 = a2.x - b2.x;
double C2 = (a2.x * A2) + (a2.y * B2);
double det = (A1 * B2) - (A2 * B1);
if (!almostEqual(det, 0)) {
intersection.x = static_cast<float>(((C1 * B2) - (C2 * B1)) / (det));
intersection.y = static_cast<float>(((C2 * A1) - (C1 * A2)) / (det));
return true;
}
return false;
}
struct vector_sorter
{
bool operator ()(const std::vector<cv::Point>& a, const std::vector<cv::Point> & b)
{
double dist_a = norm(a[0] - a[1]);
double dist_b = norm(b[0] - b[1]);
return dist_a > dist_b;
}
};
void sortCorners(std::vector<cv::Point2f>& corners)
{
std::vector<cv::Point2f> top, bot;
cv::Point2f center;
// Get mass center
for (int i = 0; i < corners.size(); i++)
center += corners[i];
center *= (1. / corners.size());
for (int i = 0; i < corners.size(); i++)
{
if (corners[i].y < center.y)
top.push_back(corners[i]);
else
bot.push_back(corners[i]);
}
corners.clear();
if (top.size() == 2 && bot.size() == 2) {
cv::Point2f tl = top[0].x > top[1].x ? top[1] : top[0];
cv::Point2f tr = top[0].x > top[1].x ? top[0] : top[1];
cv::Point2f bl = bot[0].x > bot[1].x ? bot[1] : bot[0];
cv::Point2f br = bot[0].x > bot[1].x ? bot[0] : bot[1];
corners.push_back(tl);
corners.push_back(tr);
corners.push_back(br);
corners.push_back(bl);
}
}
int main(int argc, char** argv)
{
bool showsteps = true; // set it to false to see only result;
Mat src, src_copy, edges;
src = imread("15017897249107145.jpg");
namedWindow("edges", WINDOW_AUTOSIZE);
Mat dst;
if (src.empty())
{
src = Mat(400, 400, CV_8UC3, Scalar(127, 127, 127));
rectangle(src, Rect(20, 200, 150, 50), Scalar(0, 0, 255), 8);
rectangle(src, Rect(200, 200, 50, 50), Scalar(0, 0, 255), 8);
}
src_copy = src.clone();
cvtColor(src, edges, COLOR_BGR2GRAY);
GaussianBlur(edges, edges, Size(5, 5), 1.5, 1.5);
erode(edges, edges, Mat());// these lines may need to be optimized
dilate(edges, edges, Mat());
dilate(edges, edges, Mat());
erode(edges, edges, Mat());
Canny(edges, edges, 10, 150, 3); // canny parameters may need to be optimized
if (showsteps)
{
namedWindow("edges", WINDOW_AUTOSIZE);
imshow("edges", edges);
}
vector<Point> selected_points;
vector<vector<Point> > contours;
std::cout << "1. findcontours\n"; // add this line
findContours(edges, contours, RETR_LIST, CHAIN_APPROX_SIMPLE);
std::cout << "1. findcontours...OK\n"; // add this line
for (size_t i = 0; i < contours.size(); i++)
{
Rect minRect = boundingRect(contours[i]);
if ((minRect.width > src.cols / 6) | (minRect.height > src.rows / 6)) // this line also need to be optimized
{
selected_points.insert(selected_points.end(), contours[i].begin(), contours[i].end());
if (showsteps)
{
drawContours(src_copy, contours, i, Scalar(0, 0, 255), 3);
}
}
}
if (showsteps) imshow("Selected contours", src_copy);
cv::waitKey(0); // add this line
vector<Point2f> selected_points_f;
vector<Point2f> corners;
Mat(selected_points).convertTo(selected_points_f, CV_32F);
Mat hull;
convexHull(selected_points_f, hull, true, true);
RotatedRect RRect = minAreaRect(hull);
std::vector<cv::Point2f> RR_corners;
Point2f four_points[4];
RRect.points(four_points);
RR_corners.push_back(four_points[0]);
RR_corners.push_back(four_points[1]);
RR_corners.push_back(four_points[2]);
RR_corners.push_back(four_points[3]);
for (int j = 0; j < 4; j++)
{
Point2f pt = RR_corners[j];
Point2f nearest_pt = hull.at<Point2f>(j, 0);
float dist = norm(pt - nearest_pt);
for (int k = 1; k < hull.rows; k++)
{
Point2f hull_point = hull.at<Point2f>(k, 0);
if (norm(pt - hull_point) < dist)
{
dist = norm(pt - hull_point);
nearest_pt = hull_point;
}
}
corners.push_back(nearest_pt);
}
sortCorners(corners);
Mat(corners).convertTo(selected_points, CV_32S);
Rect r = boundingRect(corners);
cv::Mat quad = cv::Mat::zeros(norm(corners[1] - corners[2]), norm(corners[2] - corners[3]), CV_8UC3);
std::vector<cv::Point2f> quad_pts;
quad_pts.push_back(cv::Point2f(0, 0));
quad_pts.push_back(cv::Point2f(quad.cols, 0));
quad_pts.push_back(cv::Point2f(quad.cols, quad.rows));
quad_pts.push_back(cv::Point2f(0, quad.rows));
cv::Mat transmtx = cv::getPerspectiveTransform(corners, quad_pts);
cv::warpPerspective(src, quad, transmtx, quad.size());
if (showsteps)
{
src_copy = src.clone();
polylines(src_copy, selected_points, true, Scalar(0, 0, 255), 3);
imshow("selected quadrilateral part", src_copy);
}
imshow("Result Image", quad);
cv::waitKey(0); // add this line
return 0;
}
