How to extract lines from each contour in OpenCV for Android? -

i'd examine each canny detected edge , main lines in (to check if seem shape rectangle, example if 2 pairs of lines parallel etc.).

imgproc.houghlinesp want, gives lines whole image, , want know lines come same edges.

i tried findcontours, , looking main lines in each contour approxpolydp, doesn't adapted because there gaps in canny detected edges. gives contours of edges , not edges themselves.

here test image example :

how can set of lines each shape ?

if you're using opencv 3.0.0 can use linesegmentdetector, , "and" detected lines contours.

i provide sample code below. it's c++ (sorry that), can translate in java. @ least see how use linesegmentdetector , how extract common lines each contour. you'll see lines on same contour same color.

#include <opencv2/opencv.hpp> using namespace cv; using namespace std;  int main() {     rng rng(12345);     mat3b img = imread("path_to_image");     mat1b gray;     cvtcolor(img, gray, color_bgr2gray);      mat3b result;     cvtcolor(gray, result, color_gray2bgr);      // detect lines     ptr<linesegmentdetector> detector = createlinesegmentdetector();     vector<vec4i> lines;     detector->detect(gray, lines);      // draw lines     mat1b linemask(gray.size(), uchar(0));     (int = 0; < lines.size(); ++i)     {         line(linemask, point(lines[i][0], lines[i][1]), point(lines[i][2], lines[i][3]), scalar(255), 2);     }      // compute edges     mat1b edges;     canny(gray, edges, 200, 400);      // find contours     vector<vector<point>> contours;     findcontours(edges.clone(), contours, cv_retr_external, cv_chain_approx_none);      (int = 0; < contours.size(); ++i)     {         // draw each contour         mat1b contourmask(gray.size(), uchar(0));         drawcontours(contourmask, contours, i, scalar(255), 2); // better use 1 here. 2 visualization purposes          // , contour , lines         mat1b bor;         bitwise_and(contourmask, linemask, bor);          // draw common pixels random color         vector<point> common;         findnonzero(bor, common);          vec3b color = vec3b(rng.uniform(0, 255), rng.uniform(0, 255), rng.uniform(0, 255));         (int j = 0; j < common.size(); ++j)         {             result(common[j]) = color;         }     }       imshow("result", result);     waitkey();      return 0; }