cv2.counterArea在OpenCV 4.0中不再起作用

Question

我正在尝试从图像中提取一只手。我正在使用OpenCV 4.0和Python 3.6。

cnts = cv2.findContours(thresholded.copy(), cv2.RETR_EXTERNAL, cv2.CHAIN_APPROX_SIMPLE)

    # return None, if no contours detected
    if len(cnts) == 0:
        return
    else:
        # based on contour area, get the maximum contour which is the hand
        segmented = max(cnts, key=cv2.contourArea)

这给了我这个错误：

Traceback (most recent call last):
  File "test.py", line 85, in <module>
    hand = segment(gray)
  File "test.py", line 37, in segment
    segmented = max(cnts, key=cv2.contourArea)
TypeError: Expected cv::UMat for argument 'contour'

自从半年前开始工作以来，我假设该错误是由于某种模块更改而发生的。怎么解决？

Answer 1

您没有注意cv2.findContours的输出。对于任何OpenCV版本> = 4.0，它都是

contours, hierarchy = cv2.findContours(...)

我做了一个例子：

import cv2
import numpy as np

# Set up dummy image
image = np.zeros((400, 400), np.uint8)
cv2.circle(image, (150, 250), 100, 255, cv2.FILLED)

# Find contours: OpenCV 4.x
cnts, _ = cv2.findContours(image, cv2.RETR_EXTERNAL, cv2.CHAIN_APPROX_SIMPLE)

if len(cnts) == 0:
    # return None, if no contours detected
    segmented = None
else:
    # based on contour area, get the maximum contour which is the hand
    segmented = max(cnts, key=cv2.contourArea)

print('Number of contour points:', segmented.shape[0])
cv2.imshow('image', image)
cv2.waitKey(0)
cv2.destroyAllWindows()

示例图片如下：

输出：

Number of contour points: 292

希望有帮助！