Opencv Python: Cv2.Findcontours - Valueerror: Too Many Values to Unpack

OpenCV Python: cv2.findContours - ValueError: too many values to unpack

I got the answer from the OpenCV Stack Exchange site. Answer

THE ANSWER:

I bet you are using the current OpenCV's master branch: here the return statements have changed, see http://docs.opencv.org/modules/imgproc/doc/structural_analysis_and_shape_descriptors.html?highlight=findcontours.

Thus, change the corresponding line to read:

_, contours, _= cv2.findContours(skin_ycrcb, cv2.RETR_EXTERNAL, cv2.CHAIN_APPROX_SIMPLE)

Or: since the current trunk is still not stable and you probably will run in some more problems, you may want to use OpenCV's current stable version 2.4.9.

too many values to unpack calling cv2.findContours

It appears that you're using OpenCV version 3.x, while writing code intended for the 2.x branch. There were some API changes between those two branches. Since you're using Python, you have a handy help available -- make sure to use it, along with the documentation.

OpenCV 2.x:

>>> import cv2
>>> help(cv2.findContours)
Help on built-in function findContours in module cv2:

findContours(...)
    findContours(image, mode, method[, contours[, hierarchy[, offset]]]) -> contours, hierarchy

OpenCV 3.x:

>>> import cv2
>>> help(cv2.findContours)
Help on built-in function findContours:

findContours(...)
    findContours(image, mode, method[, contours[, hierarchy[, offset]]]) -> image, contours, hierarchy

This means that in your script the correct way to call findContours when using OpenCV 3.x would be something like

(_, cnts, _) = cv2.findContours(closed.copy(), cv2.RETR_EXTERNAL, cv2.CHAIN_APPROX_SIMPLE)

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UPDATE (Dec 2018)

In OpenCV 4.x, findContours returns 2 values only.

>>> help(cv2.findContours)
Help on built-in function findContours:

findContours(...)
    findContours(image, mode, method[, contours[, hierarchy[, offset]]]) -> contours, hierarchy
    .   @brief Finds contours in a binary image.

Python / Contour OpenCV returns too many values to unpack

You'll need to change it to

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

Or, if you only care about the contours:

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

The function has changed in OpenCV 3.

ValueError: too many values to unpack in OpenCV project

Depending on the cv2 version, this function may return a different number of elements.
The problem is that you are using cv2 version 3, and not version 2.

First of all, what is your version?

Use:

import cv2
cv2.__version__

To solve the error try first this:

(_, cnts, _)  = cv2.findContours(closed.copy(), cv2.RETR_EXTERNAL, cv2.CHAIN_APPROX_SIMPLE)

Documentation 3.4.1

ValueError: too many values to unpack (expected 2) in openCV while trying to detect nameplates of cars

There was a change in cv 3.0
Has to do with .findContours returns 3 values now.

https://docs.opencv.org/3.1.0/d4/d73/tutorial_py_contours_begin.html

import cv2 
image = cv2.imread("path")
gray=cv2.cvtColor(image,cv2.COLOR_BGR2GRAY)
edged = cv2.Canny(image, 10, 250)

#old way
#(cnts, _) = cv2.findContours(edged.copy(), cv2.RETR_EXTERNAL, cv2.CHAIN_APPROX_SIMPLE)

# 3.0 way
_, cnts, hierarchy = cv2.findContours(edged, cv2.RETR_EXTERNAL, cv2.CHAIN_APPROX_SIMPLE)

idx = 0
for c in cnts:
    x,y,w,h = cv2.boundingRect(c)
    if w>50 and h>50:
        idx+=1
        new_img=image[y:y+h,x:x+w]
        cv2.imwrite(str(idx) + '.png', new_img)
cv2.imshow("im",image)
cv2.waitKey(0)

usage of findContours causes ValueError: not enough values to unpack (expected 3, got 2)

This is a version change. Prior to OpenCV 4.4, findCounters did return three things. Newer versions return 2: contours and hierarchy.

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

cv.findContours() - ValueError: not enough values to unpack (expected 3, got 2)

"findContours" returns a tuple of two values. The correct usage is:

contours, _ = cv.findContours(canny_output, cv.RETR_TREE, cv.CHAIN_APPROX_SIMPLE)

Error ValueError: too many values to unpack (expected 4) on official structured edge detection and edgeboxes example

The method returns (boxes, scores), not just the boxes. That seems to have been changed between 2017 and 2019.

You should use this code:

(boxes, scores) = edge_boxes.getBoundingBoxes(edges, orimap)

Then the loop will work.

You encountered this issue because you're using an outdated link to that example. The link you have shows a version from 2017. That old code would work with a 2017/2018 release of OpenCV.

The current version of the example, from 2019, corresponds to the current API. The current example shows the proper usage for the current API.

Here is the change: https://github.com/opencv/opencv_contrib/commit/6ae9809b2e464b72810298b10c6cf4935886a0f1

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