opencv 3.0 旋转矩阵ROI 直方图分析

使用Mat  mask的方式是解决特殊形状ROI的较好方法

一般需要使用支持mask的函数解决

这里是一个旋转矩形mask

opencv 不能直接绘制填充的旋转矩形，所以我使用的是填充矩形，外加旋转。

也可以用 fillPoly 绘制填充多边形

 

ROI操作是做直方图。

 注意：calcHist函数的输入变量hranges，它的最大值范围 需要 +1

例如

// hue varies from 0 to 179, see cvtColor

float hranges[] = { 0, 180 };

// saturation varies from 0 (black-gray-white) to

// 255 (pure spectrum color)

float sranges[] = { 0, 256 };

 

void test_rotate_rect_contour()
{
    Mat image(240, 320, CV_8U, Scalar(0));
    RotatedRect rRect = RotatedRect(Point2f(100,100), Size2f(100,50), 30);

    Point2f vertices[4];
    rRect.points(vertices);
    for (int i = 0; i < 4; i++)
        line(image, vertices[i], vertices[(i+1)%4], Scalar(255));
    //画图：两个色块
    rectangle(image, Rect(70, 70, 20,10), Scalar(220), CV_FILLED);
    rectangle(image, Rect(110,100,10,10), Scalar(128), CV_FILLED);
    //计算旋转ROI的旋转Mask
    Mat mask(240, 320, CV_8U, Scalar(0));
    Point p1 = rRect.center;
    p1.x = p1.x - rRect.size.width/2;
    p1.y = p1.y - rRect.size.height/2;
    rectangle(mask, Rect(p1, rRect.size), Scalar(255), CV_FILLED);
//     imshow("mask", mask);
//     waitKey(0);

    Mat R = getRotationMatrix2D(rRect.center, -rRect.angle, 1.0);
    Mat imgR;
    warpAffine(mask, imgR, R, Size(320, 240));
    threshold(imgR,imgR,254,255,THRESH_BINARY); //二值化
    erode(imgR,imgR, Mat(2,2,CV_8U,Scalar(1))); //小一圈，不算边缘
//     imshow("maskR", imgR);
//     waitKey();

    //直方图分析
    int histSize[1] = {32};     //32分隔
    int channels[1] = {0};      //第一通道
    float hranges[2];           //取值范围
    const float *ranges[1] = {hranges};
    double elem_min, elem_max;
    Mat hist;
    minMaxLoc(image, &elem_min, &elem_max, &Point(), &Point(), mask);
    
    hranges[0] = elem_min;
    hranges[1] = elem_max + 1;  //最大值范围 需要 +1
    cout << elem_min << "," << elem_max << endl;

    calcHist(&image, 1, channels, imgR, hist, 1, histSize, ranges);

    int maxNO = 0;      //最大直条编号
    float maxL = 0;     //最大直条的内个数
    for (int i = 0; i < histSize[0]; i++)
    {
        cout << "list" << i << " = " << hist.at<float>(i) << endl;
        if (maxL < hist.at<float>(i))
        {
            maxL  = hist.at<float>(i);
            maxNO = i;
        }
    }
    cout << ((elem_max - elem_min + 1)*(maxNO + 0.5)/histSize[0] + elem_min) << endl;

//     imshow("mask", mask);
    imshow("maskR", imgR);
    imshow("rectangles", image);
    waitKey();
}

旋转ROI 的mask

直方图统计的图像

输出结果