The correct manner to install OpenCV in RaspberryPi to use it with Python

Question

So far I have followed this tutorial to install OpenCV in RaspberryPi for Python. It says simply to run:

sudo apt-get install libopencv-dev python-opencv

But I've looked around internet and I've found there are more libraries to install than that, as in these two similar tutorials:

1) http://denis.doublebuffer.net/lablog/2012/08/10/setting-everything-up-for-opencv-raspberry-pi/

2) http://eduardofv.com/read_post/185-Installing-OpenCV-on-the-Raspberry-Pi

Doubts about my incorrect installation of OpenCV are based on the delay in the visualisation of the sequence with this following simple code. It just gets the frames from the camera (RPi camera module) and shows them:

import cv2

cap = cv2.VideoCapture(0)
while True:
    b,frame = cap.read()
    cv2.imshow("frame", frame)
    cv2.waitKey(1)

As I said above the visualization is flowing but delayed.

Community · Accepted Answer · 2017-04-13 12:56:22Z

2

If you're able to import it, then I would guess that you've installed it correctly. If you're in doubt, you can install it from the source, although it takes a while on the Raspi.

Try this code:

import cv2
import cv2.cv as cv
import numpy


class test():
    def __init__(self):
        cv.NamedWindow("w1", cv.CV_WINDOW_NORMAL)

        self.capture = cv.CreateCameraCapture(-1)
        self.vid()

    def vid(self):


      while True:

          self.frame = cv.QueryFrame(self.capture)


          aframe = numpy.asarray(self.frame[:,:])

          cv2.imshow("w1", aframe)

          c = cv.WaitKey(5)

      if c == 110:
        exit()

p = test()

Also, see the answer to this question (assuming you're using the Raspicam)

edited Apr 13, 2017 at 12:56

CommunityBot

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answered Nov 21, 2014 at 21:05

Ryan

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4 Comments

cyberdyne Over a year ago

Yes, I've already read that discussion and indeed I've set it in that manner. Your code works in real time. Thanks! Two questions: Therefore to speed up I have always to convert the output of cv.QueryFrame() in an array, right? What is the main difference between cv2.VideoCapture (or cv.CaptureFromCAM) and cv.CreateCameraCapture?

cyberdyne Over a year ago

There is a big problem: changing the resolution by cv.SetCaptureProperty introduces the delay again. So it works in real-time only for small resolution. Can I do anything for it?

Ryan Over a year ago

Might be worth it to try overclocking the device and see if it improves performance

cyberdyne Over a year ago

I do not think is a CPU problem (RPi has 700MHz) since commands like raspistill or raspivid work in real-time with the highest resolution. Therefore I wonder, if this is a simple acquisition and visualisation by OpenCV and it is not in real-time, what could happen if I begin a processing? Lags added to lags ?

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