How to install OpenCV in Python

1. Know What OpenCV Is

OpenCV, or Open Source Computer Vision Library, is an open-source library for computer vision, image processing, and machine learning. It is widely used in Python for image and video processing and performing advanced computer vision tasks.

2. Prerequisites

Before installing OpenCV, ensure the following:

• Python is installed (version 3.x recommended).
• pip, Python’s package manager, is installed and updated. You can update pip using:

python -m pip install --upgrade pip

3. Install OpenCV via pip

The easiest way to install OpenCV is by pip. OpenCV has two main packages available on PyPI:

• opencv-python: Contains the main modules.
• opencv-contrib-python: This package includes all the main modules plus additional ones, such as SIFT, SURF, etc.

Steps:

1. Open your terminal or command prompt.
2. Run the following command:

• For the core library:

pip install opencv-python

• For the full library with extra modules:

pip install opencv-contrib-python

3. Verify the installation:

python -c "import cv2; print(cv2.__version__)"

This should print the installed OpenCV version, confirming the installation.

4. Using Virtual Environments (Recommended)

To avoid conflicts with other packages or projects, it’s a good practice to use a virtual environment:

1. Create a virtual environment:

python -m venv myenv

2. Activate the virtual environment:

• Windows:

myenv\Scripts\activate

• macOS/Linux:

source myenv/bin/activate

3. Install OpenCV inside the virtual environment:

pip install opencv-python

5. Installing OpenCV with Additional Dependencies

By default, opencv-python provides precompiled binaries. However, some functionalities may require additional libraries or system dependencies:

• On Linux, you may need to install system-level dependencies:

sudo apt-get update
sudo apt-get install libopencv-dev python3-opencv

• On macOS, using brew to manage dependencies can help:

brew install opencv

• On Windows, the pip installation usually handles most dependencies.

6. Common Installation Issues and Solutions

Problem: “No module named ‘cv2′”

• Ensure you have installed OpenCV in the appropriate Python environment.
• Check your Python path or activate the virtual environment.

Issue: Version Conflicts

• If there’s a version mismatch or issues with existing installations, use:

pip uninstall opencv-python opencv-contrib-python
pip install opencv-contrib-python

Issue: Missing Dependencies

• Some OpenCV features may require external libraries (e.g., video codecs). Install missing system dependencies or consider using a full-featured distribution like Anaconda.

7. Advanced Installation (Optional)

In case you require a finer level of control during the installation, you can compile OpenCV from source. It is a bit more complex, but it enables you to specifically include or exclude modules and perform certain optimizations.

1. Install system prerequisites (cmake, git, etc.).
2. OpenCV repository cloning:

git clone https://github.com/opencv/opencv.git
git clone https://github.com/opencv/opencv_contrib.git

3. Build OpenCV using cmake with desired flags.