使用fitEllipse进行图像的椭圆拟合

Question

使用OpenCV fitEllipse，我想对3900×3072 png图像（Python 3.6.7）执行椭圆拟合。

作为输入图像，我使用的是AMD 14目录中的图像，该目录位于following site。

最终，我想通过将椭圆形状拟合到非零像素值的最大连接区域来创建一个遮罩，以从感兴趣的中心区域（ROI）裁剪图像。

import numpy as np
import cv2

def create_ellipse(thresh,cnt):
    ellipse = cv2.fitEllipse(cnt) #ここでエラーが出る
    thresh = cv2.ellipse(thresh,ellipse,(0,255,255),2) 
    return thresh

def rgb_to_gray(src):
     b, g, r = src[:,:,0], src[:,:,1], src[:,:,2]
     gray = 0.2989 * r + 0.5870 * g + 0.1140 * b
     return gray   


im = cv2.imread('AMD1.png')

gray = rgb_to_gray(im)
gray = cv2.convertScaleAbs(gray)

cv2.imwrite("gray.png", gray)

height = im.shape[0]
width = im.shape[1]
cnt = (width/2, height/2)

im = np.float32(im)
thresh = create_ellipse(im,cnt)

尽管我执行了上面的代码，但出现了类似以下的错误。

error                                     Traceback (most recent call last)
<ipython-input-46-9f83929ab8df> in <module>()
     37 im = np.float32(im)
---> 38 thresh = create_ellipse(im,cnt)

<ipython-input-46-9f83929ab8df> in create_ellipse(thresh, cnt)
      3 
      4 def create_ellipse(thresh,cnt):
----> 5     ellipse = cv2.fitEllipse(cnt) 
      6     
      7     #ex : cv2.ellipse(img, (width/2-200, height/2-300), (100, 50), 0, 0, 360, (0, 0, 255), 10)

error: OpenCV(3.4.3) /io/opencv/modules/imgproc/src/shapedescr.cpp:305: error: (-215:Assertion failed) n >= 0 && (depth == CV_32F || depth == CV_32S) in function 'fitEllipse'

Answer 1

Strategy Pattern

---

这是一个演示：

cv2.fitEllipse(...)
    fitEllipse(points) -> retval
    .   @brief Fits an ellipse around a set of 2D points.
    .
    .   The function calculates the ellipse that fits (in a least-squares sense) a set of 2D points best of
    .   all. It returns the rotated rectangle in which the ellipse is inscribed. The first algorithm described by @cite Fitzgibbon95
    .   is used. Developer should keep in mind that it is possible that the returned
    .   ellipse/rotatedRect data contains negative indices, due to the data points being close to the
    .   border of the containing Mat element.
    .
    .   @param points Input 2D point set, stored in std::vector\<\> or Mat