Want to Find Contours -> Valueerror: Not Enough Values to Unpack (Expected 3, Got 2), This Appears

Want to find contours - ValueError: not enough values to unpack (expected 3, got 2), this appears

the function cv2.findContours() has been changed to return only the contours and the hierarchy and not ret

you should change it to:

contours,hierachy=cv2.findContours(thresh,cv2.RETR_TREE,cv2.CHAIN_APPROX_SIMPLE)

ValueError: not enough values to unpack (expected 3, got 2) (OpenCV)

findContours method returns two values: contours and hierarchy but you're expecting three: _,cnts,_. Change to this:

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

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

on Google Colab with pyhton: ValueError: not enough values to unpack (expected 3, got 2)

To make it easier to answer your question it would be very useful to have the full stack trace so that we can see clearly in which line the code fails.

But, I assume that the error is raised in (new, cnts, _) = cv2.findContours(...) because cv2.findContours() only returns a tuple of two (contours and hierarchy). You can see this in the documentation and a use case in their guide.

ValueError in python OpenCV - not enough values to unpack (expected 3, got 2)

As you can see here findContours only returns the contours and the hierarchy, but not the image itself, as in

contour, hierarchy = cv2.findContours(imthres, cv2.RETR_EXTERNAL, cv2.CHAIN_APPROX_NONE)

That's what this error message means.

Python ValueError: not enough values to unpack (expected 3, got 2)

According to cv2.findContours documentation, the function return only 2 values. You try to unpack 3.

Remove the first _ (unwanted value) from the second line to match the signature from the documentation.

_, threshold = cv2.threshold(gray_roi, 3, 255, cv2.THRESH_BINARY_INV)
contours, _ = cv2.findContours(threshold, cv2.RETR_TREE, cv2.CHAIN_APPROX_SIMPLE)
contours = sorted(contours, key=lambda x: cv2.contourArea(x), reverse=True)

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Generally speaking, when you get this Python error message:

ValueError: not enough values to unpack (expected x got y)

Search where you try to unpack y elements, and try to fix it by unpacking x elements.

ValueError: not enough values to unpack (expected 3, got 2) using Contour in OpenCV

In openCV4, cv2.findContours() returns 2 values contours, hierarchy, so it should be:

contours, hierarchy = cv2.findContours(edged, cv2.RETR_LIST, cv2.CHAIN_APPROX_NONE)

How to fix ValueError: not enough values to unpack (expected 3, got 2) in python

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

findContours returns a tuple of two objects (contours and hierachy). You are trying to unpack three values (even if you discard the first and third).

I imagine from the name you've used, you want

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

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