如何将图像从不规则矩形更改为矩形？

Question

我想要做的是将图像左侧的矩阵改为右侧。据我所知，我们不能只用基本的转换方法改变。

真正的问题是我在下图中有一个矩形。我需要将不规则矩形更改为常规矩形。

Answer 1

所以，第一个问题是拐角顺序。它们在两个向量中的顺序必须相同。因此，如果在第一个向量中您的顺序是:(左上角，左下角，右下角，右上角），它们必须在另一个向量中的顺序相同。

其次，要使结果图像仅包含感兴趣的对象，必须将其宽度和高度设置为与生成的矩形宽度和高度相同。别担心，warpPerspective中的src和dst图像可以有不同的大小。

第三，表现关注。虽然你的方法是绝对准确的，因为你只做仿射变换（旋转，调整大小，去歪斜），在数学上，你可以使用你的函数的仿射对应。它们要快得多。

getAffineTransform()
warpAffine().

重要提示：getAffine转换需要并且只需要3个点，结果矩阵是2乘3，而不是3乘3。

如何使结果图像具有与输入不同的大小：

cv::warpPerspective(src, dst, dst.size(), ... );
use

cv::Mat rotated;
cv::Size size(box.boundingRect().width, box.boundingRect().height);
cv::warpPerspective(src, dst, size, ... );

所以你在这里，你的编程任务结束了。

void main()
{
    cv::Mat src = cv::imread("r8fmh.jpg", 1);


    // After some magical procedure, these are points detect that represent 
    // the corners of the paper in the picture: 
    // [408, 69] [72, 2186] [1584, 2426] [1912, 291]

    vector<Point> not_a_rect_shape;
    not_a_rect_shape.push_back(Point(408, 69));
    not_a_rect_shape.push_back(Point(72, 2186));
    not_a_rect_shape.push_back(Point(1584, 2426));
    not_a_rect_shape.push_back(Point(1912, 291));

    // For debugging purposes, draw green lines connecting those points 
    // and save it on disk
    const Point* point = &not_a_rect_shape[0];
    int n = (int)not_a_rect_shape.size();
    Mat draw = src.clone();
    polylines(draw, &point, &n, 1, true, Scalar(0, 255, 0), 3, CV_AA);
    imwrite("draw.jpg", draw);

    // Assemble a rotated rectangle out of that info
    RotatedRect box = minAreaRect(cv::Mat(not_a_rect_shape));
    std::cout << "Rotated box set to (" << box.boundingRect().x << "," << box.boundingRect().y << ") " << box.size.width << "x" << box.size.height << std::endl;

    Point2f pts[4];

    box.points(pts);

    // Does the order of the points matter? I assume they do NOT.
    // But if it does, is there an easy way to identify and order 
    // them as topLeft, topRight, bottomRight, bottomLeft?

    cv::Point2f src_vertices[3];
    src_vertices[0] = pts[0];
    src_vertices[1] = pts[1];
    src_vertices[2] = pts[3];
    //src_vertices[3] = not_a_rect_shape[3];

    Point2f dst_vertices[3];
    dst_vertices[0] = Point(0, 0);
    dst_vertices[1] = Point(box.boundingRect().width-1, 0); 
    dst_vertices[2] = Point(0, box.boundingRect().height-1);

    Mat warpAffineMatrix = getAffineTransform(src_vertices, dst_vertices);

    cv::Mat rotated;
    cv::Size size(box.boundingRect().width, box.boundingRect().height);
    warpAffine(src, rotated, warpAffineMatrix, size, INTER_LINEAR, BORDER_CONSTANT);

    imwrite("rotated.jpg", rotated);
}