如何在从 Python 3.6 到 Java 1.8 JavaCV 的算法转换中找到轮廓

Question

我必须开发一个与Remove top section of image above border line to detection text document类似的算法，但在 Java 1.8 中使用 JavaCV。

Python中的方法签名是

cnts = cv2.findContours(thresh, cv2.RETR_EXTERNAL,cv2.CHAIN_APPROX_SIMPLE)

但是在Java中它似乎是：

MatVector mt = new MatVector();
findContours(dst, mt, RETR_EXTERNAL, CHAIN_APPROX_SIMPLE);

我一直在寻找轮廓并将它们从大到小排序。 我如何从最大到较低的轮廓进行排序？

我的代码：

         Mat image = imread(imagePath);
         Mat gray = new Mat();
         cvtColor(mat, gray, COLOR_BGR2GRAY);
         Mat grayImg = convertToGray(mat);
         GaussianBlur(grayImg, grayImg, new Size(3, 3), 0);
         Mat dst = new Mat();
         threshold(grayImg, dst, 0, 255,THRESH_BINARY + THRESH_OTSU);

        // Find contours and sort for largest contour
        MatVector mt = new MatVector();
        findContours(dst, mt, RETR_EXTERNAL, CHAIN_APPROX_SIMPLE);

如何从https://github.com/bytedeco/javacv/issues/1270访问轮廓建议：

    // accessing contours
MatVector contours = ...
for (int i = 0; i < contours.size(); ++i) {
    IntIndexer points = contours.get(i).createIndexer();
    int size = (int) points.size(0); // points are stored in a Mat with a single column and multiple rows, since size(0), each element has two channels - for x and y - so the type is CV_32SC2 for integer points
    
    for (int j = 0; j < size; ++j) {
        int x = points.get(2 * j);
        int y = points.get(2 * j + 1);

        // do something with x and y
    }
}

谢谢

Answer 1

正如@fmw42 所说，我重构了代码以查看轮廓区域（）。

见下文，

    Mat mask = new Mat();
    Mat gray = new Mat();
    Mat denoised = new Mat();
    Mat bin = new Mat();
    Mat hierarchy = new Mat();
    MatVector contours = new MatVector();

    cvtColor(mat, gray, COLOR_BGR2GRAY);
    //Normalize
    GaussianBlur(gray, denoised, new Size(5, 5), 0);
    threshold(denoised, mask, 0, 255, THRESH_BINARY_INV | THRESH_OTSU);
    normalize(gray, gray, 0, 255, NORM_MINMAX, -1, mask);
    // Convert image to binary
    threshold(gray, bin, 150, 255, THRESH_BINARY);
    // Find contours
    findContours(bin, contours, hierarchy, RETR_TREE, CHAIN_APPROX_NONE);
    long contourCount = contours.size();
    System.out.println("Countour count " + contourCount);

    double maxArea = 0;
    int maxAreaId = 0;
    for (int i = 0; i < contourCount; ++i) {
        // Calculate the area of each contour
        Mat contour = contours.get(i);
        double area = contourArea(contour);
        if(area > maxArea){
            maxAreaId = i;
            maxArea = area;
        }

    }