Color detection on HoughCircles using OpenCV

I have detected 22 balls and am struggling to find a way to run a color detection algorithm on these circles to get their colors. I am using HoughCircles to detect the circles but don't know how to check what color these circles are? Source Code:

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

int main(int argc, char** argv)
{
    //load image from directory
    IplImage* img = cvLoadImage("C:\\Users\\Nathan\\Desktop\\SnookerPic.png");


    IplImage* gray = cvCreateImage(cvGetSize(img), IPL_DEPTH_8U, 1);
    CvMemStorage* storage = cvCreateMemStorage(0);

    //covert to grayscale
    cvCvtColor(img, gray, CV_BGR2GRAY);

    // This is done so as to prevent a lot of false circles from being detected
    cvSmooth(gray, gray, CV_GAUSSIAN, 7, 7);

    IplImage* canny = cvCreateImage(cvGetSize(img),IPL_DEPTH_8U,1);
    IplImage* rgbcanny = cvCreateImage(cvGetSize(img),IPL_DEPTH_8U,3);
    cvCanny(gray, canny, 50, 100, 3);

    //detect circles
    CvSeq* circles = cvHoughCircles(gray, storage, CV_HOUGH_GRADIENT, 1, 35.0, 75, 60,0,0);
    cvCvtColor(canny, rgbcanny, CV_GRAY2BGR);

    //draw all detected circles
    for (int i = 0; i < circles->total; i++)
    {
         // round the floats to an int
         float* p = (float*)cvGetSeqElem(circles, i);
         cv::Point center(cvRound(p[0]), cvRound(p[1]));
         int radius = cvRoun开发者_StackOverflow中文版d(p[2]);
         cvScalar c = cvGet2D(center.x, center.y);//colour of circle

         // draw the circle center
         cvCircle(img, center, 3, CV_RGB(0,255,0), -1, 8, 0 );

         // draw the circle outline
         cvCircle(img, center, radius+1, CV_RGB(0,0,255), 2, 8, 0 );

         //display coordinates
         printf("x: %d y: %d r: %d\n",center.x,center.y, radius);
    }

    //create window
    cvNamedWindow("circles", 1);
    cvNamedWindow("SnookerImage", 1);
    //show image in window
    cvShowImage("circles", rgbcanny);
    cvShowImage("SnookerImage", img);

    cvSaveImage("out.png", rgbcanny);
    cvWaitKey(0);

    return 0;
}

If the balls each have a uniform color, you can check the color at the center:

CvMemStorage* storage = cvCreateMemStorage(0);
cvSmooth(image, image, CV_GAUSSIAN, 5, 5 );
CvSeq* results = cvHoughCircles(
image,
storage,
CV_HOUGH_GRADIENT,
2,
image->width/10
);
for( int i = 0; i < results->total; i++ ) 
{
float* p = (float*) cvGetSeqElem( results, i );
CvPoint center = cvPoint( cvRound( p[0] ), cvRound( p[1] ) );
CvScalar c = cvGet2D(image, center.x, center.y); //color of the center
}

Haven't tested the code but it should be ok.

EDIT:

Ooops, I forgot one parameter from the Get2D method, the actual image from which to get the color. Changed to the correct form.

We have written our own blob detection library in the open source vision framework: http://www.simplecv.org

The code to do what you want is as easy as:

img = Image("/path/to/image.png")
blobs = img.findBlobs()
circle_blobs = blobs.filter(blobs.isCircle() == True)
list_of_blobs_colors = circle_blobs.meanColor()