Python openCV 3中contourArea的兼容性问题
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compatibility issue with contourArea in openCV 3
提问by YNWA
I am trying to do a simple area calculation of contours I get from findContours. My openCv version is 3.1.0
我正在尝试对从 findContours 获得的轮廓进行简单的面积计算。我的 openCv 版本是 3.1.0
My code is:
我的代码是：
cc = cv2.findContours(im_bw.copy(), cv2.RETR_TREE, cv2.CHAIN_APPROX_SIMPLE)
cv2.contourArea(cc[0])
error: 'C:\builds\master_PackSlaveAddon-win32-vc12-static\opencv\modules\imgproc\src\shapedescr.cp...: error: (-215) npoints >= 0 && (depth == CV_32F || depth == CV_32S) in function cv::contourArea\n'
Cant seem to solve it, I have a feeling its just typecasting altough I expect the findContours result to match the type of contourArea
似乎无法解决它，我有一种感觉它只是类型转换，尽管我希望 findContours 结果与 contourArea 的类型相匹配
Thanks :)
谢谢 ：）
EDIT: turns out I need to take the 2nd argument of findContours
编辑：原来我需要采用 findContours 的第二个参数
im2, cc, hierarchy = cv2.findContours(im_bw.copy(), cv2.RETR_TREE, cv2.CHAIN_APPROX_SIMPLE)
回答by ZdaR
回答by Qin Heyang
This problem is caused by the different return value of cv2.findContours in different OpenCV versions.
这个问题是由于不同OpenCV版本中cv2.findContours的返回值不同造成的。
In OpenCV 4.0.0, this error may looks like cv2.error: OpenCV(4.0.0) C:\projects\opencv-python\opencv\modules\imgproc\src\convhull.cpp:137: error: (-215:Assertion failed) total >= 0 && (depth == CV_32F || depth == CV_32S) in function 'cv::convexHull'
在 OpenCV 4.0.0 中，这个错误可能看起来像 cv2.error: OpenCV(4.0.0) C:\projects\opencv-python\opencv\modules\imgproc\src\convhull.cpp:137: error: (-215:Assertion failed) total >= 0 && (depth == CV_32F || depth == CV_32S) in function 'cv::convexHull'
You can find a detailed explanation and solutions here: How to use `cv2.findContours` in different OpenCV versions?
你可以在这里找到详细的解释和解决方案：如何在不同的 OpenCV 版本中使用 `cv2.findContours`？
回答by nathancy
Depending on the OpenCV version, cv2.findContours()has varying return signatures.
根据 OpenCV 版本，cv2.findContours()具有不同的返回签名。
In OpenCV 3.4.X, cv2.findContours()returns 3 items
在 OpenCV 3.4.X 中，cv2.findContours()返回 3 个项目
image, contours, hierarchy = cv.findContours(image, mode, method[, contours[, hierarchy[, offset]]])
In OpenCV 2.X and 4.1.X, cv2.findContours()returns 2 items
在 OpenCV 2.X 和 4.1.X 中，cv2.findContours()返回 2 个项目
contours, hierarchy = cv.findContours(image, mode, method[, contours[, hierarchy[, offset]]])
You can easily obtain the contours regardless of the version like this:
无论版本如何，您都可以轻松获得轮廓：
cnts = cv2.findContours(image, cv2.RETR_EXTERNAL, cv2.CHAIN_APPROX_SIMPLE)
cnts = cnts[0] if len(cnts) == 2 else cnts[1]
回答by Hosein Basafa
Thanks for @ZdaR; By the way, you can do the following in OpenCV 4.1:
感谢@ZdaR；顺便说一句，您可以在 OpenCV 4.1 中执行以下操作：
contours, hierarchy = cv2.findContours(im_bw.copy(), cv2.RETR_TREE, cv2.CHAIN_APPROX_SIMPLE)
