OpenCV在椭圆上获取像素

Question

我正在尝试从图像中获取椭圆的像素。

例如，我在随机图像上绘制一个椭圆（示例 geeksforgeeks 代码）：

import cv2
path = r'C:\Users\Rajnish\Desktop\geeksforgeeks\geeks.png'
image = cv2.imread(path)
window_name = 'Image'
center_coordinates = (120, 100)
axesLength = (100, 50)
angle = 0
startAngle = 0
endAngle = 360
color = (0, 0, 255)
thickness = 5
image = cv2.ellipse(image, center_coordinates, axesLength,
           angle, startAngle, endAngle, color, thickness)
cv2.imshow(window_name, image)

它给出如下输出：

现在，我想获取椭圆边界线的像素值。如果可能的话，我想使用 cv2.ellipse() 获取椭圆的像素作为坐标数组。
任何人都可以帮我解决这个问题吗？

Answer 1

如果要在椭圆上获取点（位置），则可以使用ellipse2poly（）函数。

---

如果ellipse2poly（）的参数类型是不便的，则自己计算是最方便的方法。

该示例代码为C ++，但计算出的是明确的。

//Degree -> Radian
inline double RadFromDeg( double Deg ){ return CV_PI*Deg/180.0; }

//Just calculate points mathematically.
//  Arguments are same as cv::ellipse2Poly (alothough ellipse parameters is cv::RotateRect).
void My_ellipse2Poly(
    const cv::RotatedRect &EllipseParam,
    double StartAngle_deg,
    double EndAngle_deg,
    double DeltaAngle_deg,
    std::vector< cv::Point2d > &DstPoints
)
{
    double Cos,Sin;
    {
        double EllipseAngleRad = RadFromDeg(EllipseParam.angle);
        Cos = cos( EllipseAngleRad );
        Sin = sin( EllipseAngleRad );
    }

    //Here, you will be able to reserve the destination vector size, but in this sample, it was omitted.
    DstPoints.clear();

    const double HalfW = EllipseParam.size.width * 0.5;
    const double HalfH = EllipseParam.size.height * 0.5;
    for( double deg=StartAngle_deg; deg<EndAngle_deg; deg+=DeltaAngle_deg )
    {
        double rad = RadFromDeg( deg );
        double u = cos(rad) * HalfW;
        double v = sin(rad) * HalfH;
        double x = u*Cos + v*Sin + EllipseParam.center.x;
        double y = u*Sin - v*Cos + EllipseParam.center.y;
        DstPoints.emplace_back( x,y );
    }
}

Answer 2

There is no direct OpenCV way probably to get these points of the ellipse but you can extract your points via indirect way like this:

mask = cv2.inRange(image, np.array(color), np.array(color))
contour = cv2.findContours(mask, cv2.RETR_EXTERNAL, cv2.CHAIN_APPROX_NONE)[-2][0]

contour will store the outer points of your red ellipse.
在这里，我所做的是创建椭圆形的掩码图像，并找到了所需的最外部轮廓点。