Building on Linux

Prerequisites

Install the required packages with apt:

# Update package index
sudo apt-get update

# Core build tools (choose one compiler)
sudo apt-get install -y build-essential cmake git pkg-config

# Optional: use Ninja for faster builds
sudo apt-get install -y ninja-build

# Required media/codec libraries
sudo apt-get install -y \
  libgtk2.0-dev \
  libavcodec-dev \
  libavformat-dev \
  libswscale-dev

# Python 3 bindings
sudo apt-get install -y \
  python3-dev \
  python3-numpy

# Image format libraries
sudo apt-get install -y \
  libjpeg-dev \
  libpng-dev \
  libtiff-dev \
  libopenexr-dev

# Optional performance libraries
sudo apt-get install -y \
  libtbb2 \
  libtbb-dev \
  libeigen3-dev

# Optional camera support
sudo apt-get install -y \
  libdc1394-dev \
  libgstreamer1.0-dev \
  libgstreamer-plugins-base1.0-dev

Step-by-Step Build

Clone the three repositories:

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

Create a build directory:
Terminal window
```
mkdir opencv/build
cd opencv/build
```

Configure with CMake (development / debug build):

cmake \
  -DCMAKE_BUILD_TYPE=Debug \
  -DBUILD_TESTS=ON \
  -DBUILD_PERF_TESTS=ON \
  -DBUILD_EXAMPLES=ON \
  -DOPENCV_EXTRA_MODULES_PATH=../../opencv_contrib/modules \
  -DOPENCV_TEST_DATA_PATH=../../opencv_extra/testdata \
  ..

Build using all available CPU cores:

cmake --build . -j$(nproc)
# Or using make directly:
make -j$(nproc)

Verify the build:

# Check build info from the command line
./bin/opencv_version

# Check from Python (no install needed with PYTHONPATH set)
export PYTHONPATH=$(pwd)/python_loader:$(pwd)/lib/python3/
export LD_LIBRARY_PATH=$(pwd)/lib:$LD_LIBRARY_PATH
python3 -c "import cv2; print(cv2.getBuildInformation())"

Using OpenCV from the Build Directory (No Install)

Downstream CMake projects can use the build directory directly by setting OpenCV_DIR:

# In your own project's CMakeLists.txt:
# find_package(OpenCV REQUIRED)
# ...then configure pointing to the build dir:

cmake -DOpenCV_DIR=/path/to/opencv/build ..

Ninja Build (Faster Alternative)

cmake -G Ninja \
  -DCMAKE_BUILD_TYPE=Debug \
  -DBUILD_TESTS=ON \
  -DOPENCV_EXTRA_MODULES_PATH=../../opencv_contrib/modules \
  ..

ninja -j$(nproc)

Release vs Debug vs RelWithDebInfo

Build Type	GCC Flags	Use Case
`Debug`	`-g -O0`	Full symbols, no optimization — step through code in a debugger
`Release`	`-O3 -DNDEBUG`	Maximum performance, no debug info
`RelWithDebInfo`	`-O2 -g -DNDEBUG`	Optimized + symbols — best for profiling
`MinSizeRel`	`-Os -DNDEBUG`	Smallest binary size

Disabling Specific Modules

# Build only specific modules (auto-resolves dependencies)
cmake -DBUILD_LIST=core,imgproc,imgcodecs ..

# Disable individual modules
cmake -DBUILD_opencv_java=OFF \
      -DBUILD_opencv_gapi=OFF \
      ..

# Disable OpenCV's internal test apps
cmake -DBUILD_opencv_apps=OFF ..