opencv::图像矩(Image Moments)

矩的概念介绍

　1、几何矩

　

　2、中心距

　3、中心归一化距

4、图像中心Center(x0, y0)

计算矩
moments(
    InputArray  array,           // 输入数据
    bool   binaryImage=false     // 是否为二值图像
)

contourArea(
    InputArray  contour,   // 输入轮廓数据
    bool   oriented        // 默认false、返回绝对值
)

arcLength(
    InputArray  curve,   // 输入曲线数据
    bool   closed        // 是否是封闭曲线
)

步骤
    提取图像边缘
    发现轮廓
    计算每个轮廓对象的矩
    计算每个对象的中心、弧长、面积

Mat src, gray_src;
int threshold_value = ;
int threshold_max = ;
const char* output_win = "image moents demo";
RNG rng();
void Demo_Moments(int, void*);
int main(int argc, char** argv) {
    src = imread(STRPAHT3);
    if (!src.data) {
        printf("could not load image...\n");
        return -;
    }
    cvtColor(src, gray_src, CV_BGR2GRAY);
    GaussianBlur(gray_src, gray_src, Size(, ), , );

    char input_win[] = "input image";
    namedWindow(input_win, CV_WINDOW_AUTOSIZE);
    namedWindow(output_win, CV_WINDOW_AUTOSIZE);
    imshow(input_win, src);

    createTrackbar("Threshold Value : ", output_win, &threshold_value, threshold_max, Demo_Moments);
    Demo_Moments(, );

    waitKey();
    return ;
}

void Demo_Moments(int, void*) {
    Mat canny_output;
    vector<vector<Point>> contours;
    vector<Vec4i> hierachy;

    //提取图像边缘
    Canny(gray_src, canny_output, threshold_value, threshold_value * , , false);
    //发现轮廓
    findContours(canny_output, contours, hierachy, RETR_TREE, CHAIN_APPROX_SIMPLE, Point(, ));

    vector<Moments> contours_moments(contours.size());
    vector<Point2f> ccs(contours.size());
    for (size_t i = ; i < contours.size(); i++) {
        contours_moments[i] = moments(contours[i]);
        ccs[i] = Point(static_cast<float>(contours_moments[i].m10 / contours_moments[i].m00), static_cast<float>(contours_moments[i].m01 / contours_moments[i].m00));
    }

    Mat drawImg;// = Mat::zeros(src.size(), CV_8UC3);
    src.copyTo(drawImg);
    for (size_t i = ; i < contours.size(); i++) {
        if (contours[i].size() < ) {
            continue;
        }
        Scalar color = Scalar(rng.uniform(, ), rng.uniform(, ), rng.uniform(, ));
        printf("center point x : %.2f y : %.2f\n", ccs[i].x, ccs[i].y);
        printf("contours %d area : %.2f   arc length : %.2f\n", i, contourArea(contours[i]), arcLength(contours[i], true));
        drawContours(drawImg, contours, i, color, , , hierachy, , Point(, ));
        circle(drawImg, ccs[i], , color, , );
    }

    imshow(output_win, drawImg);
    return;
}