no result after hough filter

Question

In the program I use a canny filter like this:

circles = cv2.HoughCircles(cannyresult,cv2.cv.CV_HOUGH_GRADIENT,1,10)
    if circles is None:
        print'no '

Then the terminal prints no which means there is no result back, and the cannyresult is a picture with a lot of circles. Can someone help me on this please?

is the image an `8-bit, single-channel, grayscale input image.` ? — Awalias, Mar 15 '13 at 17:10
see my answer, the function doesn't 'return' a result, you pass it a vector as an argument (`vector circles`), and it fills the vector out with the circles it finds. — Awalias, Mar 16 '13 at 16:12
Please review the answers, up vote those who have been helpful to you, and if one of them lead you to solve the problem you should click on the checkbox near it to select it as the official answer. By doing these things you are helping future visitors. — karlphillip, Mar 31 '13 at 18:58

Awalias · Answer 1 · 2013-03-16T16:15:44.917

from the documentation the usage is:

 Python: cv2.HoughCircles(image, method, dp, minDist[, circles[,
    param1[, param2[, minRadius[, maxRadius]]]]]) → circles

where

 circles – Output vector of found circles. Each vector is encoded as a
 3-element floating-point vector (x, y, radius)

with example usage:

#include <cv.h>
#include <highgui.h>
#include <math.h>

using namespace cv;

int main(int argc, char** argv)
{
    Mat img, gray;
    if( argc != 2 && !(img=imread(argv[1], 1)).data)
        return -1;
    cvtColor(img, gray, CV_BGR2GRAY);
    // smooth it, otherwise a lot of false circles may be detected
    GaussianBlur( gray, gray, Size(9, 9), 2, 2 );
    vector<Vec3f> circles;
    HoughCircles(gray, circles, CV_HOUGH_GRADIENT,
                 2, gray->rows/4, 200, 100 );
    for( size_t i = 0; i < circles.size(); i++ )
    {
         Point center(cvRound(circles[i][0]), cvRound(circles[i][1]));
         int radius = cvRound(circles[i][2]);
         // draw the circle center
         circle( img, center, 3, Scalar(0,255,0), -1, 8, 0 );
         // draw the circle outline
         circle( img, center, radius, Scalar(0,0,255), 3, 8, 0 );
    }
    namedWindow( "circles", 1 );
    imshow( "circles", img );
    return 0;
}

the important bit to notice is that instead of:

circles = HoughCircles(gray, CV_HOUGH_GRADIENT...

you need to pass it a vector:

    vector<Vec3f> circles;

    HoughCircles(gray, circles, CV_HOUGH_GRADIENT,
                 2, gray->rows/4, 200, 100 );

This is more of a C style of programming

score 0 · Accepted Answer · edited May 23 '17 at 12:28

0

It's all about parameters, it always is. The parameters used in HoughCircles play a fundamental role.

I wish I could help you more, but without an input image to work with my hands are tied. The last reference I shared with you provides links to other answers with actual source code that demonstrates the importance of tweaking the function parameters until they work for you.

edited May 23 '17 at 12:28

Community

1
1

answered Mar 15 '13 at 19:28

karlphillip

92,053
36
243
426

for the input image, i use a 8 bit, sigle channel, grayscale, the others i don't know if they can be a problem. Still no result now. – user1510711 Mar 16 '13 at 10:10

no result after hough filter

2 Answers2