How to build OpenCV from source with python binding? - python-3.x

Question

I need to build OpenCV from source and I have limited space, so, I have to build OpenCV on a module basis (https://docs.opencv.org/4.x/db/d05/tutorial_config_reference.html - Build limited set of modules). OK, cmake and make work fine.
Would be easier to use these OpenCV modules from python so I add cmake -D BUILD_opencv_python3=ON but make install does not create the prefix/lib/pythonX.Y/site-packages directory I expected. There is no python related option but only a CMake option as far as I understand the doc.
How to get python(3) binding for OpenCV when building it on a module basis ?
Once installed, how to set up environnement to get python -c "import cv2" to work with my custom-built OpenCV ?
UPDATE
Running ubuntu L4T on jetson. CMake outputs :
-- Python 3:
-- Interpreter: /usr/bin/python3 (ver 3.6.9)
-- Libraries: NO
-- numpy: /home/me/.local/lib/python3.6/site-packages/numpy/core/include (ver 1.19.5)
-- install path: -
So I guess empty install path hides a problem behind... But grep -ni OPENCV_PYTHON3_INSTALL_PATH CMakeCache.txt returns nothing.
At this point, I tried to add cmake -DOPENCV_PYTHON3_INSTALL_PATH=~/Programs/opencv/local/lib/python3.6/site-packages/, still nothing in cmake output (blank install path) but
grep -ni OPENCV_PYTHON3_INSTALL_PATH CMakeCache.txt
1076:OPENCV_PYTHON3_INSTALL_PATH:UNINITIALIZED=~/Programs/opencv/local/lib/python3.6/site-packages/
And after make install (without sudo - I don't have root privilege and need local install), I have no python binding in the local install.
... Any clue would be appreciated !
Note: compiling opencv-4.5.4 on L4T ubuntu

Answer 1

I wanted to add to CYL answer, I use that GitHub Gist and it works, but I have to drop all my junk cmake flags.
Here is what I ultimately end up with.
cmake \
-D CMAKE_BUILD_TYPE=RELEASE \
-D CMAKE_INSTALL_PREFIX=$(python3 -c "import sys; print(sys.prefix)") \
-D INSTALL_PYTHON_EXAMPLES=ON \
-D INSTALL_C_EXAMPLES=ON \
-D WITH_TBB=ON \
-D WITH_CUDA=OFF \
-D BUILD_opencv_cudacodec=OFF \
-D ENABLE_FAST_MATH=1 \
-D CUDA_FAST_MATH=1 \
-D WITH_CUBLAS=1 \
-D WITH_V4L=ON \
-D WITH_QT=OFF \
-D WITH_OPENGL=ON \
-D WITH_GSTREAMER=ON \
-D OPENCV_GENERATE_PKGCONFIG=ON \
-D OPENCV_PC_FILE_NAME=opencv.pc \
-D OPENCV_ENABLE_NONFREE=ON \
-D OPENCV_PYTHON3_INSTALL_PATH=$(python3 -c "from distutils.sysconfig import get_python_lib; print(get_python_lib())") \
-D OPENCV_EXTRA_MODULES_PATH=/tmp/opencv_contrib/modules \
-D PYTHON_EXECUTABLE=$(which python3) \
-D BUILD_EXAMPLES=ON ..
and this is the General Config output
-- General configuration for OpenCV 4.5.5 =====================================
-- Version control: 4.5.5
--
-- Extra modules:
-- Location (extra): /tmp/opencv_contrib/modules
-- Version control (extra): 4.5.5
--
-- Platform:
-- Timestamp: 2022-01-23T08:47:55Z
-- Host: Linux 5.11.0-41-generic x86_64
-- CMake: 3.18.2
-- CMake generator: Unix Makefiles
-- CMake build tool: /usr/bin/make
-- Configuration: RELEASE
--
-- CPU/HW features:
-- Baseline: SSE SSE2 SSE3
-- requested: SSE3
-- Dispatched code generation: SSE4_1 SSE4_2 FP16 AVX AVX2 AVX512_SKX
-- requested: SSE4_1 SSE4_2 AVX FP16 AVX2 AVX512_SKX
-- SSE4_1 (18 files): + SSSE3 SSE4_1
-- SSE4_2 (2 files): + SSSE3 SSE4_1 POPCNT SSE4_2
-- FP16 (1 files): + SSSE3 SSE4_1 POPCNT SSE4_2 FP16 AVX
-- AVX (5 files): + SSSE3 SSE4_1 POPCNT SSE4_2 AVX
-- AVX2 (33 files): + SSSE3 SSE4_1 POPCNT SSE4_2 FP16 FMA3 AVX AVX2
-- AVX512_SKX (8 files): + SSSE3 SSE4_1 POPCNT SSE4_2 FP16 FMA3 AVX AVX2 AVX_512F AVX512_COMMON AVX512_SKX
--
-- C/C++:
-- Built as dynamic libs?: YES
-- C++ standard: 11
-- C++ Compiler: /usr/bin/c++ (ver 9.3.0)
-- C++ flags (Release): -fsigned-char -ffast-math -W -Wall -Werror=return-type -Werror=non-virtual-dtor -Werror=address -Werror=sequence-point -Wformat -Werror=format-security -Wmissing-declarations -Wundef -Winit-self -Wpointer-arith -Wshadow -Wsign-promo -Wuninitialized -Wsuggest-override -Wno-delete-non-virtual-dtor -Wno-comment -Wimplicit-fallthrough=3 -Wno-strict-overflow -fdiagnostics-show-option -Wno-long-long -pthread -fomit-frame-pointer -ffunction-sections -fdata-sections -msse -msse2 -msse3 -fvisibility=hidden -fvisibility-inlines-hidden -O3 -DNDEBUG -DNDEBUG
-- C++ flags (Debug): -fsigned-char -ffast-math -W -Wall -Werror=return-type -Werror=non-virtual-dtor -Werror=address -Werror=sequence-point -Wformat -Werror=format-security -Wmissing-declarations -Wundef -Winit-self -Wpointer-arith -Wshadow -Wsign-promo -Wuninitialized -Wsuggest-override -Wno-delete-non-virtual-dtor -Wno-comment -Wimplicit-fallthrough=3 -Wno-strict-overflow -fdiagnostics-show-option -Wno-long-long -pthread -fomit-frame-pointer -ffunction-sections -fdata-sections -msse -msse2 -msse3 -fvisibility=hidden -fvisibility-inlines-hidden -g -O0 -DDEBUG -D_DEBUG
-- C Compiler: /usr/bin/cc
-- C flags (Release): -fsigned-char -ffast-math -W -Wall -Werror=return-type -Werror=address -Werror=sequence-point -Wformat -Werror=format-security -Wmissing-declarations -Wmissing-prototypes -Wstrict-prototypes -Wundef -Winit-self -Wpointer-arith -Wshadow -Wuninitialized -Wno-comment -Wimplicit-fallthrough=3 -Wno-strict-overflow -fdiagnostics-show-option -Wno-long-long -pthread -fomit-frame-pointer -ffunction-sections -fdata-sections -msse -msse2 -msse3 -fvisibility=hidden -O3 -DNDEBUG -DNDEBUG
-- C flags (Debug): -fsigned-char -ffast-math -W -Wall -Werror=return-type -Werror=address -Werror=sequence-point -Wformat -Werror=format-security -Wmissing-declarations -Wmissing-prototypes -Wstrict-prototypes -Wundef -Winit-self -Wpointer-arith -Wshadow -Wuninitialized -Wno-comment -Wimplicit-fallthrough=3 -Wno-strict-overflow -fdiagnostics-show-option -Wno-long-long -pthread -fomit-frame-pointer -ffunction-sections -fdata-sections -msse -msse2 -msse3 -fvisibility=hidden -g -O0 -DDEBUG -D_DEBUG
-- Linker flags (Release): -Wl,--exclude-libs,libippicv.a -Wl,--exclude-libs,libippiw.a -Wl,--gc-sections -Wl,--as-needed
-- Linker flags (Debug): -Wl,--exclude-libs,libippicv.a -Wl,--exclude-libs,libippiw.a -Wl,--gc-sections -Wl,--as-needed
-- ccache: NO
-- Precompiled headers: NO
-- Extra dependencies: dl m pthread rt
-- 3rdparty dependencies:
--
-- OpenCV modules:
-- To be built: aruco barcode bgsegm bioinspired calib3d ccalib core datasets dnn dnn_objdetect dnn_superres dpm face features2d flann fuzzy gapi hfs highgui img_hash imgcodecs imgproc intensity_transform line_descriptor mcc ml objdetect optflow phase_unwrapping photo plot python3 quality rapid reg rgbd saliency shape stereo stitching structured_light superres surface_matching text tracking ts video videoio videostab wechat_qrcode xfeatures2d ximgproc xobjdetect xphoto
-- Disabled: world
-- Disabled by dependency: -
-- Unavailable: alphamat cudaarithm cudabgsegm cudacodec cudafeatures2d cudafilters cudaimgproc cudalegacy cudaobjdetect cudaoptflow cudastereo cudawarping cudev cvv freetype hdf java julia matlab ovis python2 sfm viz
-- Applications: tests perf_tests examples apps
-- Documentation: NO
-- Non-free algorithms: YES
--
-- GUI: NONE
-- GTK+: NO
-- OpenGL support: NO
-- VTK support: NO
--
-- Media I/O:
-- ZLib: /usr/lib/x86_64-linux-gnu/libz.so (ver 1.2.11)
-- JPEG: /usr/lib/x86_64-linux-gnu/libjpeg.so (ver 80)
-- WEBP: build (ver encoder: 0x020f)
-- PNG: /usr/lib/x86_64-linux-gnu/libpng.so (ver 1.6.37)
-- TIFF: /usr/lib/x86_64-linux-gnu/libtiff.so (ver 42 / 4.1.0)
-- JPEG 2000: build (ver 2.4.0)
-- OpenEXR: build (ver 2.3.0)
-- HDR: YES
-- SUNRASTER: YES
-- PXM: YES
-- PFM: YES
--
-- Video I/O:
-- DC1394: NO
-- FFMPEG: YES
-- avcodec: YES (58.54.100)
-- avformat: YES (58.29.100)
-- avutil: YES (56.31.100)
-- swscale: YES (5.5.100)
-- avresample: YES (4.0.0)
-- GStreamer: YES (1.16.2)
-- v4l/v4l2: YES (linux/videodev2.h)
--
-- Parallel framework: TBB (ver 2020.1 interface 11101)
--
-- Trace: YES (with Intel ITT)
--
-- Other third-party libraries:
-- Intel IPP: 2020.0.0 Gold [2020.0.0]
-- at: /tmp/opencv/build/3rdparty/ippicv/ippicv_lnx/icv
-- Intel IPP IW: sources (2020.0.0)
-- at: /tmp/opencv/build/3rdparty/ippicv/ippicv_lnx/iw
-- VA: NO
-- Lapack: NO
-- Eigen: NO
-- Custom HAL: NO
-- Protobuf: build (3.19.1)
--
-- OpenCL: YES (no extra features)
-- Include path: /tmp/opencv/3rdparty/include/opencl/1.2
-- Link libraries: Dynamic load
--
-- Python 3:
-- Interpreter: /home/user/miniconda3/bin/python3 (ver 3.9.5)
-- Libraries: /home/user/miniconda3/lib/libpython3.9.so (ver 3.9.5)
-- numpy: /home/user/miniconda3/lib/python3.9/site-packages/numpy/core/include (ver 1.21.2)
-- install path: /home/user/miniconda3/lib/python3.9/site-packages/cv2/python-3.9
--
-- Python (for build): /home/user/miniconda3/bin/python3
--
-- Java:
-- ant: NO
-- JNI: NO
-- Java wrappers: NO
-- Java tests: NO
--
-- Install to: /home/user/miniconda3
-- -----------------------------------------------------------------
--
-- Configuring done
-- Generating done
-- Build files have been written to: /tmp/opencv/build
Just for documentation, this is what I install on the ubuntu 20.04.
apt-get update && apt-get install git openssh-client curl wget sudo \
build-essential pkg-config libboost-system-dev libboost-thread-dev libboost-program-options-dev libboost-test-dev \
libgl1-mesa-glx libglib2.0-0 \
libjpeg-dev libpng-dev libtiff-dev \
libavcodec-dev libavformat-dev libswscale-dev libavresample-dev \
libgstreamer1.0-dev libgstreamer-plugins-base1.0-dev \
libxvidcore-dev x264 libx264-dev libfaac-dev libmp3lame-dev libtheora-dev \
libfaac-dev libmp3lame-dev libvorbis-dev \
libtbb-dev libatlas-base-dev gfortran -y

Answer 2

To have py binding, make sure the cmake config output near the end has the Python 3 section i.e.
Python 3:
Interpreter: /home/user/anaconda3/envs/cv451/bin/python3 (ver 3.8.12)
Libraries: /home/user/anaconda3/envs/cv451/lib/libpython3.8.so (ver 3.8.12)
numpy: /home/user/anaconda3/envs/cv451/lib/python3.8/site-packages/numpy/core/include (ver 1.21.2)
install path: /home/user/anaconda3/envs/cv451/lib/python3.8/site-packages/cv2/python-3.8
For me that section was missing at first. My problem was python version mismatch between the lib (found from system) and the interpreter (from conda env).
Thus in my case the fix was:
Have cmake find the conda env's python instead of the system's python:
CMAKE_LIBRARY_PATH=/home/user/anaconda3/envs/cv451/lib cmake /path/to/opencv/arc
By default the binding is installed to system's python. To specify the python binding install path, use the cmake flag OPENCV_PYTHON3_INSTALL_PATH i.e.
-D OPENCV_PYTHON3_INSTALL_PATH=/home/user/anaconda3/envs/cv451/lib/python3.8/site-packages/
Remember to install after the compile
sudo make install
Ref:
https://gist.github.com/raulqf/f42c718a658cddc16f9df07ecc627be7
https://qengineering.eu/install-opencv-4.5-on-jetson-nano.html

Answer 3

cmake -DBUILD_LIST=python3 .. solved the problem: getting clean install directory including python site-packages directory.