Opencv TypeError: points is not a numpy array, neither a scalar

Question

Basically, I have this code that detects changes in background and boxed them. When I run the code, I get this error:

Traceback (most recent call last):
  File "cam2.py", line 28, in <module>
    vertices = cv2.boundingRect(list(contours))
TypeError: points is not a numpy array, neither a scalar

Code:

import cv2
import numpy as np

c = cv2.VideoCapture(0)
_,f = c.read()

avg1 = np.float32(f)

while(1):
    _,f = c.read()

    cv2.accumulateWeighted(f,avg1,0.1)

    res1 = cv2.convertScaleAbs(avg1)

    absdiff = cv2.absdiff(f,res1)

    graydiff = cv2.cvtColor(absdiff, cv2.COLOR_BGR2GRAY)

    retval, mask = cv2.threshold(graydiff, 50,255,cv2.THRESH_BINARY) 

    mask = cv2.dilate(mask, None, 18)
    mask = cv2.erode(mask, None, 10) 

    contours = cv2.findContours(mask, cv2.RETR_LIST, cv2.CHAIN_APPROX_NONE) #not right

    while contours:
        vertices = cv2.boundingRect(list(contours))
        interest = vertices

        point1 = (interest[0], interest[1])

        point2 = (interest[0] + interest[2], interest[1] + interest[3])
        cv2.rectangle(f, point1, point2, cv2.RGB(255,0,0), 1)
        cv2.rectangle(mask, point1, point2, cv2.RGB(255,255,255), 1)

        contours = contours.h_next()

    cv2.imshow('mask',mask)

    cv2.imshow('img',f)
    cv2.imshow('avg1',res1)

    k = cv2.waitKey(20)

    if k == 27:
        break

cv2.destroyAllWindows()
c.release()

How do i solve this? Thanks.

Did you trace your code!? What was the value for contours list? — Hadi
– Hadi, Commented Apr 16, 2014 at 4:06
the value is a very long array heres a snippet: [[ 995, 1018]], [[ 995, 1019]], [[ 995, 1020]], [[ 995, 1021]], — alex
– alex, Commented Apr 16, 2014 at 15:45
It seems you have 4 contours that each of them contains just a point!? — Hadi
– Hadi, Commented Apr 16, 2014 at 17:00

Hadi · Accepted Answer · 2015-06-04 00:23:25Z

4

According to the findContour doc it returns two things:

cv2.findContours(image, mode, method[, contours[, hierarchy[, offset]]]) → contours, hierarchy

Change the line to:

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

That may works!

edited Jun 4, 2015 at 0:23

answered Apr 16, 2014 at 17:34

Hadi

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1 Comment

berak Over a year ago

ah ofc. , missed that.

berak · Accepted Answer · 2014-04-15 19:19:47Z

1

contours is actually a double-array. the outer one is the list of contours, the inner ones are the points of a single contour.

so, replace:

while contours:
    vertices = cv2.boundingRect(list(contours))

with:

for cnt in contours:
    vertices = cv2.boundingRect(cnt)

and drop the

contours = contours.h_next()

line (you probably confused cv2 with the old c-api/cv approach, which was using linked lists under the hood)

answered Apr 15, 2014 at 19:19

berak

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3 Comments

alex Over a year ago

Hmmm... Still not working (same error). But thank you for informing me with the last comment.

berak Over a year ago

you probably got a different err now.

alex Over a year ago

I wish :( TypeError: points is not a numpy array, neither a scalar

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