In OpenCV 1 there used to be an option of cvFindContours (using CV_CHAIN_CODE) to obtain a contour from an image in Freeman chain code. However, I cannot find it in OpenCV 3. Has it been removed as option? I know I could develop my own function to generate Freeman chain code from a contour given as a sequence of points, but I thought there was a ready-made function already available.
Since OpenCV 3.2.0 source image is not modified by findContour therefore the chain code is no more returned.
Unfortunately this information is in the master doc but not in 3.2.0 doc.
See news: findcontours doesn't alter the input image and and this comment on issue #8225
just tested an answer on SO
it seems calling findContours with CV_CHAIN_CODE returns useless data and old C API still useful.
#include "opencv2/imgproc.hpp"
#include "opencv2/highgui.hpp"
#include "opencv2/imgproc/imgproc_c.h"
#include <iostream>
using namespace std;
using namespace cv;
int main() {
cv::Mat img = cv::Mat::zeros(100, 100, CV_8UC1);
cv::line(img, Point(50,50), Point(60,60), cv::Scalar(255), 1);
cv::line(img, Point(40, 60), Point(60, 60), cv::Scalar(255), 1);
cv::line(img, Point(40, 60), Point(50, 50), cv::Scalar(255), 1);
imshow("Test", img);
vector<vector<Point> > contours;
findContours(img, contours, RETR_EXTERNAL, CV_CHAIN_CODE);
cout << Mat(contours[0]) << endl;
findContours(img, contours, RETR_EXTERNAL, CHAIN_APPROX_SIMPLE);
cout << "CHAIN_APPROX_SIMPLE" << endl;
cout << Mat(contours[0]) << endl;
CvChain* chain = 0;
CvMemStorage* storage = 0;
storage = cvCreateMemStorage(0);
cvFindContours(&IplImage(img), storage, (CvSeq**)(&chain), sizeof(*chain), CV_RETR_EXTERNAL, CV_CHAIN_CODE);
for (; chain != NULL; chain = (CvChain*)chain->h_next)
{
//chain=(CvChain*)chain ->h_next;
//if(chain==NULL){break;}
CvSeqReader reader;
int i, total = chain->total;
cvStartReadSeq((CvSeq*)chain, &reader, 0);
printf("--------------------chain\n");
for (i = 0; i<total; i++)
{
char code;
CV_READ_SEQ_ELEM(code, reader);
printf("%d", code);
}
}
waitKey();
return 0;
}
Hi, I used the same code as of above for my vertices data, but failed to get the freeman chain code.Please help me.
My dataset is as follows:
0 0
0 0.00144928
0.00144928 0.00144928
0.00289855 0.00144928
0.00724638 0.00434783
0.015942 0.00434783
0.0275362 0.00434783
0.0434783 0.00434783
0.0637681 0.00434783
0.0782609 0.00434783
0.0869565 0.00434783
0.102899 0.0057971
0.111594 0.0057971
0.126087 0.0057971
0.136232 0.0057971
0.15942 0.0057971
0.172464 0.0057971
0.182609 0.00434783
0.198551 0.00434783
0.214493 0.00434783
0.23913 0.00434783
0.250725 0.00434783
0.269565 0.00434783
0.284058 0.00434783
0.305797 0.00434783
0.331884 0.00434783
0.344928 0.00434783
0.371014 0.0057971
0
Asked: 2017-03-29 11:05:42 -0600
Seen: 3,779 times
Last updated: Mar 31 '17
In opencv 3.2 doc CHAIN_APPROX_SIMPLE is very similar to freeman code (direction is equal to end-begin and number of code is equal to difference?).
CHAIN_APPROX_SIMPLE does not give directional codes; it gives you characteristic points sufficient to describe elements in the contour. The Freeman code gives directional codes from one point to the next, including all points in the contour. I still use the Freeman code; based on it I have developed a differential chain code and the two together are a good description of the general shape of the contour, that is why I am still using it.