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I'm teaching myself OpenCV and wrote the following code today to track a ball rolling across my computer webcam feed and (attempt to) draw a filled in grey circle on to it's centroid:

#include <iostream>
#include <opencv2/opencv.hpp>

using namespace cv;
using namespace std;

Point getBlobCentroid(Mat blobImage);

int main()
{
    Mat bGround, fGround, diff;
    Point p = (500, 280);
    VideoCapture cap(0);

    while (true)
    {
        cap >> fGround; //assign frame from camera to newest image
        cvtColor(fGround, fGround, CV_BGR2GRAY); //convert to grayscale

        bGround.create(fGround.size(), fGround.type()); 
        absdiff(bGround, fGround, diff); //subtract current frame from old frame

        threshold(diff, diff, 50, 255, CV_THRESH_BINARY); //convert to binary
        erode(diff, diff, NULL, Point(-1,-1), 3, 0, BORDER_DEFAULT);

        imshow("Thresholded", diff);

        circle(fGround, getBlobCentroid(diff), 6, 127, -1, 8, 16);
        imshow("Natural Image with Tracking", fGround);

        fGround.copyTo(bGround); //move forward in time
        waitKey(1);
    }

    return 0;
}

Point getBlobCentroid(Mat blobImage)
{
    int rowSum=0, colSum=0, count = 1;

    for(int i=0; i<blobImage.rows; i++)
    {
        for (int j=0; j<blobImage.cols; j++)
        {
            if (blobImage.at<uchar>(i,j) == 255)
            {
                rowSum+=i;
                colSum+=j;
                count++;
            }
        }
    }
    Point centroid = (rowSum, colSum)/count;
    return centroid;
}

However, as evidenced by the attached image - the circle never moves away from the top of the screen - in other words, the centroid.y component is always zero. I wrote a bunch of steps of the calculation to the screen, and it appears as though the searching and additions to rowSum and count and such work - those are nonzero. However, as soon as you calculate the centroid or call it in the circle, that's a no go. Even weirder, I tried making a constant center for the circle Point p = (285, 285) and using that as an argument, and that was a no go as well. Help? Thanks!

-Tony

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1 回答 1

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fGround.copyTo(bGround); //move forward in time
// so, that's your idea. compare bg & fg, get the centroid of the diff.
// but then, if you follow your while loop there, (waitkey, back to the top ... )

bGround.create(fGround.size(), fGround.type()); 
// aww, so you're never using, what you copied before

absdiff(bGround, fGround, diff); 
// so, in the end, you're always comparing fGround to an empty bGround img
于 2013-02-13T20:15:57.197 回答