Is there an easy way to install OpenCV on Raspberry pi - opencv

Question

There are many steps while installing OpenCV on Raspberry pi . Is there any chance to install by using a single command. I tried sudo apt-get install python3-opencv but that doesn't work.

Answer 1

The main one liner is with pip The Python Package Installer but to make it work you also need some dependencies that may or may not be installed already from other related tools.
$ pip3 install opencv-python
$ sudo apt-get install libatlas-base-dev libjasper-dev libqtgui4 python3-pyqt5 libqt4-test libilmbase-dev libopenexr-dev libgstreamer1.0-dev libavcodec58 libavformat58 libswscale5
In addition with the current newest version you need to set an env variable to run it, LD_PRELOAD=/usr/lib/arm-linux-gnueabihf/libatomic.so.1.2.0 referenced issue
$ LD_PRELOAD=/usr/lib/arm-linux-gnueabihf/libatomic.so.1.2.0 python3
Python 3.7.3 (default, Apr 3 2019, 05:39:12)
[GCC 8.2.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import cv2
>>>
If you are really opposed to that you can use a previous version that doesn't have this issue. Don't forget to uninstall the other version if you already installed it pip3 uninstall opencv-python
$ pip3 install opencv-python==4.1.0.25
On a newly flashed 2019-09-26-raspbian-buster-lite img after adding ssh access and connecting that way.
system update and install pip3
$ sudo apt-get update
$ sudo apt-get upgrade
$ sudo apt-get install python3-pip
version check
$ python3 --version
Python 3.7.3
$ pip3 --version
pip 18.1 from /usr/lib/python3/dist-packages/pip (python 3.7)
install openCV and check version
$ pip3 install opencv-python
$ pip3 freeze | grep opencv-python
opencv-python==4.1.1.26
test and fail,
$ python3
Python 3.7.3 (default, Apr 3 2019, 05:39:12)
[GCC 8.2.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import cv2
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/home/pi/.local/lib/python3.7/site-packages/cv2/__init__.py", line 3, in <module>
from .cv2 import *
ImportError: libwebp.so.6: cannot open shared object file: No such file or directory
install dependencies
$ sudo apt-get install libatlas-base-dev libjasper-dev libqtgui4 python3-pyqt5 libqt4-test libilmbase-dev libopenexr-dev libgstreamer1.0-dev libavcodec58 libavformat58 libswscale5
test with env variable set
$ LD_PRELOAD=/usr/lib/arm-linux-gnueabihf/libatomic.so.1.2.0 python3
Python 3.7.3 (default, Apr 3 2019, 05:39:12)
[GCC 8.2.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import cv2
>>>

Answer 2

The easiest way to do this is using .whl files. When you want to install a package with pip, it searches for a precompiled version of that package that is compatible with your system.
In your case, pip is looking for an OpenCV Python package compatible with armv7l platform, if it cannot find a precompiled .whl file to install, it tries to download the source as .tar.gz and compile it by itself on Raspberry Pi (which is a real pain.)
armv7l compatible .whl files are available for OpenCV Python now and you can use pip to install it directly with pip install opencv-python command but sometimes pip tries to install the latest package and sometimes it is not armv7l compatible. I suggest you check packages and put version specifications to the command.
To handle this situation a lot easier with installations of prerequisites and preparation of the installation environment; you can use complete guides like in this blog post for beginners