1

I am currently doing real time object detection of an orange ball with Raspberry Pi 3 Model B. The code below is supposed to take a frame, then with the cv2.inRange() function, filter out the image using RGB (BGR). Then I apply dialation and erosion to remove noise. Then I find the contours and draw them. This code worked until now. However when I ran it today without changing it, I got the folowing error: 

 Traceback (most recent call last):
 File "/home/pi/Desktop/maincode.py", line 12, in <module>
   mask = cv2.inRange(frame, lower, upper)
error: /build/opencv-ISmtkH/opencv-2.4.9.1+dfsg/modules/core/src/arithm.cpp:2701: error: (-209) The lower bounary is neither an array of the same size and same type as src, nor a scalar in function inRange

Any help would be really awesome, because I was new to openCV and spent a lot of time proggraming this, and I have a competetion of robotics in 5 days.

Thank you in advance

            import cv2
            import cv2.cv as cv
            import numpy as np


            capture = cv2.VideoCapture(0)
            while capture.isOpened:
                    ret, frame = capture.read()
                    im = frame
                    lower = np.array([0, 100 ,150], dtype = 'uint8')
                    upper = np.array([10,180,255], dtype = 'uint8')
                    mask = cv2.inRange(frame, lower, upper)
                    eroded = cv2.erode(mask, np.ones((7, 7)))
                    dilated = cv2.dilate(eroded, np.ones((7, 7)))
                    contours, hierarchy =   cv2.findContours(dilated,cv2.RETR_TREE,cv2.CHAIN_APPROX_SIMPLE)

                    cv2.drawContours(im,contours,-1,(0,255,0),3)
                    cv2.imshow('colors',im)
                    cv2.waitKey(1)
Zvonko Bednarcik
  • 25
  • 6
  • 1
    Are you sure that the frame you are feeding in `mask = cv2.inRange(frame, lower, upper)` is not empty ? try printing `frame.shape` before this statement. – ZdaR Apr 01 '17 at 11:14

1 Answers1

2

The error you receive almost certainly means you have an empty image (or you mix up the sizes of your input image).

Webcam captures in OpenCV often start with one or a couple of black/emtpy images (crappy drivers). Since it goes too fast, that's why you don't notice this. However, this will have an influence on your application if you want to process the image. Therefore, I recommend you to check the image before proceeding with the calculations on them. Just add this after your capture.read() line:

if ret == True:

Note: make sure (by printing in the console or something) that this only happens when you start capturing. If this happens regularly (empty frames from your webcam), maybe there's something else wrong (or maybe with your webcam). Also check it on another computer.

Jurjen
  • 1,376
  • 12
  • 19
  • I hope this fixed your problem! If the problem only occurs on the first frames, don't worry about it. I have that with multiple webcams as well. If it still happens later, it could indeed be a hardware related issue. Make sure the Pi gets enough power. Also try to test it with another webcam or with your original webcam on another computer. See if the problem still occurs. Good luck with your competition! Also, if this answer solved your problem don't forget to accept it as answer! – Jurjen Apr 02 '17 at 12:35