OpenCV ERROR - <unknown> is not a numpy array

Question

I get this error:

<unknown> is not a numpy array

when executing this code:

import cv2
import numpy as np

try:

    cap = cv2.VideoCapture(0)

    while (cap.isOpened()):
        ret,img=cap.read()
        cv2.imshow('output',img)
        img2=cv2.cvtColor(img,cv2.COLOR_BGR2GRAY) 
        cv2.imshow('gray_scale',img2)
        imgthreshold=cv2.inRange(img,cv2.cv.Scalar(3,3,125),cv2.cv.Scalar(40,40,255),)
        cv2.imshow('thresholded',imgthreshold)

        k=cv2.waitKey(10)
        if k==27:
            break

    cap.release()
    cv2.destroyAllWindows()


except Exception as inst:

    cap.release()
    cv2.destroyAllWindows()
    print("Eroor!!")
    print(inst)
    raise

Here's the traceback:

Traceback (most recent call last):
    File "C:\Users\... ...\camara.py", line 14, in <module>
        imgthreshold=cv2.inRange(img,cv2.cv.Scalar(3,3,125),cv2.cv.Scalar(40,40,255),)
TypeError: <unknown> is not a numpy array

I hope you can help me to solve this. I already check all the dependencies and they work fine also if I delete the line

imgthreshold=cv2.inRange(img,cv2.cv.Scalar(3,3,125),cv2.cv.Scalar(40,40,255),)

and the next one, the program work without problems

You have a comma at the end of your cv2.inRange(...) function call, turning the three arguments into a single tuple. Try removing that trailing comma. — user707650
– user707650, Commented Sep 6, 2015 at 22:37
@Evert, adding a trailing comma in a function call will not cause the arguments to be packed into a single tuple. — donkopotamus
– donkopotamus, Commented Sep 6, 2015 at 22:44
Thanks for the answer but it didn't work, the problem remains the same — Cesar Troya Sherdek
– Cesar Troya Sherdek, Commented Sep 6, 2015 at 22:44
@jojonas here it is: Traceback (most recent call last): File "C:\Users\... ...\camara.py", line 14, in <module> imgthreshold=cv2.inRange(img,cv2.cv.Scalar(3,3,125),cv2.cv.Scalar(40,40,255),) TypeError: <unknown> is not a numpy array — Cesar Troya Sherdek
– Cesar Troya Sherdek, Commented Sep 6, 2015 at 22:50

jojonas · Accepted Answer · 2015-09-06 23:02:24Z

1

You need to check the status returned by the VideoCapture::read function. It returns a boolean flag indicating whether the returned image is valid at all.

import cv2
import numpy as np

try:

    cap = cv2.VideoCapture(0)

    while (cap.isOpened()):
        ret,img=cap.read()
        if not ret:
            continue

        cv2.imshow('output',img)
        img2=cv2.cvtColor(img,cv2.COLOR_BGR2GRAY) 
        cv2.imshow('gray_scale',img2)
        imgthreshold=cv2.inRange(img,cv2.cv.Scalar(3,3,125),cv2.cv.Scalar(40,40,255),)
        cv2.imshow('thresholded',imgthreshold)

        k=cv2.waitKey(10)
        if k==27:
            break

    cap.release()
    cv2.destroyAllWindows()


except Exception as inst:

    cap.release()
    cv2.destroyAllWindows()
    print("Eroor!!")
    print(inst)
    raise

answered Sep 6, 2015 at 23:02

jojonas

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1 Comment

Cesar Troya Sherdek Over a year ago

The VideoCapture function is working without any problem, as I say if, you delete the trouble line, the program show tow displays with the correct image capture

Cesar Troya Sherdek · Accepted Answer · 2015-09-07 02:36:20Z

1

I find the solution, it is to convert the top parameters of colors to find into a numpy array -->

imgthreshold=cv2.inRange(img,np.array(cv2.cv.Scalar(3,3,125)),np.array(cv2.cv.Scalar(40,40,255)),)

answered Sep 7, 2015 at 2:36

Cesar Troya Sherdek

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