Helplessly Lost With OpenCV And HoughCircles

I'm trying to detect this black circle here. Shouldn't be too difficult but for some reason I just get 0 circles or approximately 500 circles everywhere, depending on the arguments

Solution 1:

There are few minor mistakes in your approach.

Here is the code I used from the documentation:

img = cv2.imread('temp.png',0)
img = cv2.medianBlur(img,5)
cimg = cv2.cvtColor(img,cv2.COLOR_GRAY2BGR)
cimg1 = cimg.copy() 

circles = cv2.HoughCircles img,cv2.HOUGH_GRADIENT,1,20,param1=50,param2=30,minRadius=0,maxRadius=0)

circles = np.uint16(np.around(circles))
for i in circles[0,:]:
    # draw the outer circle
    cv2.circle(cimg,(i[0],i[1]),i[2],(0,255,0),2)
    # draw the center of the circle
    cv2.circle(cimg,(i[0],i[1]),2,(0,255,255),3)

cv2.imshow('detected circles.jpg',cimg)

joint = np.hstack([cimg1, cimg])  #---Posting the original image along with the image having the detected circle
cv2.imshow('detected circle and output', joint )