OpenCV三角检测不起作用

Question

我正在使用opencv进行多边形检测，我似乎无法检测到以下三角形。这是三角形图像。

以下是我用来检测三角形的方法

int vertices = 3;
Mat blurred(image);
medianBlur(image, blurred, 9);

Mat gray0(blurred.size(), CV_8U), gray;
vector<vector<Point> > contours;

for (int c = 0; c < 3; c++)
{
    int ch[] = {c, 0};
    mixChannels(&blurred, 1, &gray0, 1, ch, 1);

    const int threshold_level = 2;
    for (int l = 0; l < threshold_level; l++)
    {
        if (l == 0)
        {
            Canny(gray0, gray, 10, 20, 3);
            dilate(gray, gray, Mat(), Point(-1,-1));
        }
        else
        {
            gray = gray0 >= (l+1) * 255 / threshold_level;
        }

        findContours(gray, contours, CV_RETR_LIST, CV_CHAIN_APPROX_SIMPLE);

        vector<Point> approx;
        for (size_t i = 0; i < contours.size(); i++)
        {
            approxPolyDP(Mat(contours[i]), approx, arcLength(Mat(contours[i]), true)*0.02, true);

            if (approx.size() == vertices && 
                fabs(contourArea(Mat(approx))) > 1000 &&
                isContourConvex(Mat(approx)))
            {
                double maxCosine = 0;

                for (int j = 2; j < 5; j++)
                {
                    double cosine = fabs(angle(approx[j%4], approx[j-2], approx[j-1]));
                    maxCosine = MAX(maxCosine, cosine);
                }

                if (maxCosine < 0.3)
                    polygons.push_back(approx);
            }
        }
    }
}

任何帮助将不胜感激。谢谢。 问候，C。