TypeError: function takes exactly 3 arguments (1 given) ,python

Question

I'm trying to create a trackbar for contours but when I run the code I get this error:

TypeError: thresh_callback() takes exactly 3 arguments (1 given)

the code:

def thresh_callback(thresh,blur,img):
    edges = cv.Canny(blur,thresh,thresh*2)
    drawing = np.zeros(img.shape,np.uint8)     # Image to draw the contours
    contours,hierarchy = cv.findContours(edges,cv.RETR_TREE,cv.CHAIN_APPROX_SIMPLE)
    for cnt in contours:
        color = np.random.randint(0,255,(3)).tolist()  # Select a random color
        cv.drawContours(drawing,[cnt],0,color,2)
        cv.imshow('output',drawing)
    cv.imshow('input',img)

def Pics():
    vc = cv.VideoCapture(2)
    retVal, frame = vc.read();
    while True :
        if frame is not None:
            imgray = cv.cvtColor(frame,cv.COLOR_BGR2GRAY)
            blur = cv.GaussianBlur(imgray,(5,5),0)
            thresh = 100
            max_thresh = 255
            cv.createTrackbar('canny thresh:','input',thresh,max_thresh,thresh_callback)
            thresh_callback(thresh,blur,frame)
        rval, frame = vc.read()
        if cv.waitKey() & 0xFF == 27:
            break
    cv1.DestroyAllWindows()

Answer 1

您正在将函数thresh_callback作为回调传递给cv.createTrackbar( 。看起来该方法期望单参数函数调用某个事件。

Answer 2

You're passing thresh_callback into cv.createTrackbar , and it is somewhere in there that your function is getting called with only one argument. I assume that you still want to use the blur and frame that you determine in your code, so trying using functools.partial to set those for you:

import functools

...

        partialed_callback = functools.partial(thresh_callback, blur=blur, img=frame)
        cv.createTrackbar('canny thresh:','input',thresh,max_thresh,partialed_callback)

This creates a version of your function for which blur and frame are already set, so your thresh_callback function will be called with the frame and blur defined in the loop and the thresh provided from within createTrackbar .

Also, you probably don't want to be calling thresh_callback(thresh,blur,frame) in the line after calling cv.createTrackbar , as that will mean it gets called twice and always with thresh=100 the second time.