如何在 opencv 4.4.0 版上正确使用 cv2.findContours()? [英] How to properly use cv2.findContours() on opencv version 4.4.0.?

问题描述

我正在尝试在 opencv 4.4.0 版上使用 cv2.findContours().(我使用的是 Python 3.8.5 版)但它抛出了一个错误，我无法弄清楚.我不确定代码有什么问题.这是一些背景:

Im trying to use cv2.findContours() on opencv version 4.4.0. (Im using Python version 3.8.5) but it throws an error, I cant figure out. Im not sure whats wrong with the code. Here's some background:

• 根据 OpenCV，cv2.findContours() 的语法如下:Python:轮廓，层次= cv.findContours(图像，模式，方法[，轮廓[，层次[，偏移]]])

• According to OpenCV the syntax for cv2.findContours() is as follows: Python: contours, hierarchy = cv.findContours( image, mode, method[, contours[, hierarchy[, offset]]] )

我找了一些例子来确保如何正确实现它，这是我发现的:示例 1_, 轮廓, _ = cv2.findContours(binary_image,cv2.RETR_LIST,cv2.CHAIN_APPROX_SIMPLE)

I looked for some examples to make sure how to properly implement it, heres what I found: example 1 _, contours, _ = cv2.findContours(binary_image,cv2.RETR_LIST,cv2.CHAIN_APPROX_SIMPLE)

示例 2(_, cnts, _) = cv2.findContours(thresholded.copy(), cv2.RETR_EXTERNAL, cv2.CHAIN_APPROX_SIMPLE)

example 2 (_, cnts, _) = cv2.findContours(thresholded.copy(), cv2.RETR_EXTERNAL, cv2.CHAIN_APPROX_SIMPLE)

那些是我在网上找到的工作项目，有很多这样的例子.所以，我试图实现我从视频中获得的一些代码以对该主题有一些了解，但它似乎对我不起作用，我找不到原因.代码如下:

Those are from working projects I found online, there are plenty examples like those. So, Im trying to implement some code I got from a video to gain some understanding on the topic but it does not seem to work for me and I cant find why. Heres the code:

import cv2 
import numpy as np 

imagen =cv2.imread('lettuce.jpg')
gray = cv2.cvtColor(imagen,cv2.COLOR_BGR2GRAY)
_,binary = cv2.threshold(gray,100,255,cv2.THRESH_BINARY)

image,contours,hierarchy = cv2.findContours(binary,cv2.RETR_LIST,cv2.CHAIN_APPROX_SIMPLE)

cv2.drawContours(image,contours, -1, (0,255,0),3)

错误:回溯(最近一次调用最后一次):第 8 行，在图像，轮廓，层次结构 = cv2.findContours(二进制，cv2.RETR_LIST，cv2.CHAIN_APPROX_SIMPLE)值错误:没有足够的值来解包(预期为 3，得到 2)

Error: Traceback (most recent call last): line 8, in image,contours,hierarchy = cv2.findContours(binary,cv2.RETR_LIST,cv2.CHAIN_APPROX_SIMPLE) ValueError: not enough values to unpack (expected 3, got 2)

推荐答案

在 Python/OpenCV 4.4.0 中，findContours 仅返回 2 个值，您列出了 3 个.

In Python/OpenCV 4.4.0, findContours returns only 2 values, you list 3.

你展示:

image,contours,hierarchy = cv2.findContours(binary,cv2.RETR_LIST,cv2.CHAIN_APPROX_SIMPLE)

OpenCV 4.4.0，列表:

OpenCV 4.4.0, lists:

contours, hierarchy = cv.findContours(image, mode, method[, contours[, hierarchy[, offset]]])

请务必查看文档.见

https://docs.opencv.org/4.4.0/d3/dc0/group__imgproc__shape.html#gadf1ad6a0b82947fa1fe3c3d497f260e0

一种以独立于版本的方式处理这个问题的方法，如果你想要的只是轮廓，是(归功于@nathancy):

One way to handle this in a version independent way, if all you want are the contours, is (credit to @nathancy):

contours = cv2.findContours(binary, cv2.RETR_LIST, cv2.CHAIN_APPROX_SIMPLE)
contours = contours[0] if len(contours) == 2 else contours[1]

如果您不想要所有嵌套轮廓，则使用 RETR_EXTERNAL 而不是 RETR_LIST.

If you do not want all nested contours, then use RETR_EXTERNAL and not RETR_LIST.

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