使用 fitEllipse 对图像进行椭圆拟合 [英] Ellipse fitting for images using fitEllipse

问题描述

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

作为输入图像，我使用 AMD 14 目录中的图像，该目录分布在

Using OpenCV fitEllipse, I'd like to perform ellipse Fitting of 3900 × 3072 png images (Python 3.6.7).

As the input image, I'm using the images inside the AMD 14 directory, which is distributed at the following site.

Eventually I'd like to create a mask to crop the image from central region of interest (ROI), by fitting an ellipse shape to the largest connected region of non-zeros pixel values.

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)

Although I executed the above code, I got an error like the one below.

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'

解决方案

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

---

Here is a demo:

#!/usr/bin/python3
# 2018/12/25

import cv2
img = cv2.imread('test.jpg')
gray = cv2.cvtColor(img, cv2.COLOR_BGR2GRAY)
th, threshed = cv2.threshold(gray, 100, 255, cv2.THRESH_BINARY)

## findContours, then fitEllipse for each contour.
## 使用 cv2.findContours(...)[-2:] 对 2.x|3.x|4.x 兼容
cnts, hiers = cv2.findContours(threshed, cv2.RETR_EXTERNAL, cv2.CHAIN_APPROX_SIMPLE)[-2:]

for cnt in cnts:
    ellipse = cv2.fitEllipse(cnt)
    cv2.ellipse(img, ellipse, (255,0, 255), 1, cv2.LINE_AA)

cv2.imwrite("dst.png", img)

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