在python中使用cv2.approxPolyDP（）绘制轮廓

Question

我无法使用cv2.approxPolyDP()绘制完整的形状轮廓。

我得到以下结果：

但我想要这样的输出：

这是我的代码：

import cv2
im = cv2.imread('C:\Python27\Test\Targets\s1.jpg') # read picture

imgray = cv2.cvtColor(im, cv2.COLOR_BGR2GRAY) # BGR to grayscale

ret, thresh = cv2.threshold(imgray, 200, 255, cv2.THRESH_BINARY)

countours, hierarchy = cv2.findContours(thresh, cv2.RETR_TREE, cv2.CHAIN_APPROX_SIMPLE)

epsilon = 0.1 * cv2.arcLength(countours[0], True)
approx = cv2.approxPolyDP(countours[0], epsilon, True)

cv2.drawContours(im, approx, -1, (0, 255, 0), 3)
cv2.imshow("Contour", im)

cv2.waitKey(0)
cv2.destroyAllWindows()

Answer 1

cv2.CHAIN_APPROX_SIMPLE删除所有冗余点并压缩轮廓，从而节省内存。如果您转到findContours()函数cv2.CHAIN_APPROX_NONE参数而不是cv2.CHAIN_APPROX_SIMPLE，则问题将得到解决。 您的代码应更改如下：

_, countours, hierarchy = cv2.findContours(thresh, cv2.RETR_TREE, 
                                                 cv2.CHAIN_APPROX_NONE)

Answer 2

很久以前，但我建议您这样

contours,hierarchy = cv2.findContours(thresh, 1, 2)

contours_sizes= [(cv2.contourArea(cnt), cnt) for cnt in contours]
biggest_contour = max(contours_sizes, key=lambda x: x[0])[1]

countours = biggest_contour

这将找到图像的最大轮廓，而忽略了小点和噪点

Answer 3

我尝试了相同的代码。但我能够得到这个：

Answer 4

在Java中，这可以工作

MatOfPoint2f  newContour = new MatOfPoint2f();      
largestContour.convertTo(newContour, CvType.CV_32F);
double arcLength = Imgproc.arcLength(newContour, closed);
double epsilon = 0.2 * arcLength;
MatOfPoint2f approxCurve = new MatOfPoint2f();
Imgproc.approxPolyDP(newContour, approxCurve, epsilon, closed);

// convert back to form that can be plotted by drawContours
MatOfPoint largestOutline = new  MatOfPoint();
approxCurve.convertTo(largestOutline, CvType.CV_32S);