How to build a custom opencv 3.4.0 for Android

OpenCV is an awesome library with the enumerous built-in modules which support us a lot in the image processing. But sometimes, we don't need to import all of these modules to archive what we want. This could make the application size pretty big. We just need some very specific modules such as core lib and imgproc. And in this tutorial, I'm gonna show you how to custom the opencv build for Android steps-by-steps.

Environments

Install Docker latest version

Setup Build Environment Steps

Step 1. Clone the repository and build the opencv_env image.

cd ~
git clone git@github.com:hzung/custom-build-opencv-android.git
cd ~/custom-build-opencv-android
docker image build -t hungtv/opencv_env:v01 .

Step 2. Clone opencv into custom-build-opencv-android/opencv and check out to the version 3.4.1.

cd ~/custom-build-opencv-android && git clone git@github.com:opencv/opencv.git
cd ~/custom-build-opencv-android/opencv && git checkout 3.4.0

Step 3. Download and unzip android-ndk-r14b into custom-build-opencv-android/android-ndk-r14b After unzipping the android-ndk-r14b,

3.1. Open the file ~/custom-build-opencv-android/android-ndk-r14b/build/tools/make_standalone_toolchain.py

3.2. Goto the line 402 and edit the line to fix the issue for creating the toolchain for the chip x86 and x86_64.

assert len(dirs) == 1

to

assert len(dirs) >= 1

Step 4. Download and unzip android-sdk-linux into custom-build-opencv-android/android-sdk-linux

Step 5. Start the container using the image opencv_env:v01

cd ~/custom-build-opencv-android
docker container run \
-v $(pwd)/android-sdk-linux:/android-sdk-linux \
-v $(pwd)/android-ndk-r14b:/android-ndk-r14b \
-v $(pwd)/opencv:/opencv \
-v $(pwd)/toolchains:/toolchains \
-v $(pwd)/builds:/builds \
--name opencv_env \
-td hungtv/opencv_env:v01

Step 6. Install platform-tools,build-tools-23.0.3,android-25

docker exec -it opencv_env /bin/bash
android update sdk --no-ui --all --filter platform-tools,build-tools-23.0.3,android-25

Note: You can list for other packages using this command: android list sdk --all --extended

Here is the result directory structure. Make sure that the structure is correct.

├── Dockerfile
├── README.md
├── android-ndk-r14b
│   ├── CHANGELOG.md
│   ├── build
│   ├── ndk-build
│   ├── ndk-depends
│   ├── ...
├── android-sdk-linux
│   ├── add-ons
│   ├── build-tools
│   ├── ...
├── builds
├── env_var_setup
├── opencv
│   ├── 3rdparty
│   ├── CMakeLists.txt
│   ├── CONTRIBUTING.md
│   ├── ...
└── toolchains

Build Steps For armeabi-v7a/arm64-v8a

Step 1. Access to the bash shell of the opencv_env container and export ONE of the environment variables.

For arm chipset

docker exec -it opencv_env /bin/bash
export ANDROID_STANDALONE_TOOLCHAIN=/toolchains/arm-toolchain
export TOOLCHAIN_ARCH=arm
export BUILD_OUTPUT_ARCH=armeabi-v7a
export BUILD_OUTPUT_DIR=/builds/${BUILD_OUTPUT_ARCH}

For arm64 chipset

docker exec -it opencv_env /bin/bash
export ANDROID_STANDALONE_TOOLCHAIN=/toolchains/arm64-toolchain
export TOOLCHAIN_ARCH=arm64
export BUILD_OUTPUT_ARCH=arm64-v8a
export BUILD_OUTPUT_DIR=/builds/${BUILD_OUTPUT_ARCH}

For x86 chipset

docker exec -it opencv_env /bin/bash
export ANDROID_STANDALONE_TOOLCHAIN=/toolchains/x86-toolchain
export TOOLCHAIN_ARCH=x86
export BUILD_OUTPUT_ARCH=x86
export BUILD_OUTPUT_DIR=/builds/${BUILD_OUTPUT_ARCH}

For x86_64 chipset

docker exec -it opencv_env /bin/bash
export ANDROID_STANDALONE_TOOLCHAIN=/toolchains/x86_64-toolchain
export TOOLCHAIN_ARCH=x86_64
export BUILD_OUTPUT_ARCH=x86_64
export BUILD_OUTPUT_DIR=/builds/${BUILD_OUTPUT_ARCH}

Step 2. Create the toolchain.

/android-ndk-r14b/build/tools/make_standalone_toolchain.py --arch ${TOOLCHAIN_ARCH} --api 23 --install-dir ${ANDROID_STANDALONE_TOOLCHAIN}

Extra step for x86_64 only.

cp ${ANDROID_STANDALONE_TOOLCHAIN}/x86_64-linux-android/lib64/{*++.a,libgnustl_shared.so} ${ANDROID_STANDALONE_TOOLCHAIN}/x86_64-linux-android/lib/

Step 4. Create a build directory for arm64-v8

mkdir ${BUILD_OUTPUT_DIR}

Step 5. Start configurations for compiling.

cd ${BUILD_OUTPUT_DIR}
cmake \
  -DCMAKE_TOOLCHAIN_FILE=/opencv/platforms/android/android.toolchain.cmake \
  -DWITH_CAROTENE=OFF \
  -DANDROID_STL=gnustl_static \
  -DANDROID_NATIVE_API_LEVEL=23 \
  -DWITH_OPENCL=OFF \
  -DWITH_CUDA=OFF \
  -DWITH_IPP=OFF \
  -DBUILD_EXAMPLES=OFF \
  -DBUILD_TESTS=OFF \
  -DBUILD_PERF_TESTS=OFF \
  -DBUILD_ANDROID_EXAMPLES=OFF \
  -DINSTALL_ANDROID_EXAMPLES=OFF \
  -DANDROID_ABI=${BUILD_OUTPUT_ARCH} \
  -DWITH_TBB=ON \
  -DWITH_ITT=OFF \
  /opencv

Wait until the configuration steps is completed. Using a text editor to open the file ${BUILD_OUTPUT_DIR}/modules/java/CMakeFiles/opencv_java.dir/cmake_clean.cmake and remove these lines.

"CMakeFiles/opencv_java.dir/generator/src/cpp/Mat.cpp.o"
"CMakeFiles/opencv_java.dir/generator/src/cpp/converters.cpp.o"
"CMakeFiles/opencv_java.dir/generator/src/cpp/jni_part.cpp.o"
"CMakeFiles/opencv_java.dir/generator/src/cpp/listconverters.cpp.o"
"CMakeFiles/opencv_java.dir/generator/src/cpp/utils.cpp.o"
"CMakeFiles/opencv_java.dir/__/core/misc/java/src/cpp/core_manual.cpp.o"
"CMakeFiles/opencv_java.dir/__/dnn/misc/java/src/cpp/dnn_converters.cpp.o"
"CMakeFiles/opencv_java.dir/__/features2d/misc/java/src/cpp/features2d_converters.cpp.o"
"CMakeFiles/opencv_java.dir/gen/core.cpp.o"
"CMakeFiles/opencv_java.dir/gen/imgproc.cpp.o"
"CMakeFiles/opencv_java.dir/gen/ml.cpp.o"
"CMakeFiles/opencv_java.dir/gen/objdetect.cpp.o"
"CMakeFiles/opencv_java.dir/gen/photo.cpp.o"
"CMakeFiles/opencv_java.dir/gen/video.cpp.o"
"CMakeFiles/opencv_java.dir/gen/dnn.cpp.o"
"CMakeFiles/opencv_java.dir/gen/imgcodecs.cpp.o"
"CMakeFiles/opencv_java.dir/gen/videoio.cpp.o"
"CMakeFiles/opencv_java.dir/gen/features2d.cpp.o"
"CMakeFiles/opencv_java.dir/gen/calib3d.cpp.o"

This configuration prevent the compiling process removing these above files. We're gonna need these files when manually linking library (step 9).

Step 6. Start compiling with 4 compiling jobs. Pick the greater number for faster compiling if your computer is trong.

cd ${BUILD_OUTPUT_DIR} && make -j 4

After this step, you can import the libopencv_java3.so into the Android project. It should work fine. But this is not what we want. We want to make the size of libopencv_java3.so smaller. The current size is pretty big for us.

Step 7. Let's re-bundle the build to make it contains only libopencv_core.a and libopencv_imgproc.a.

cd ${BUILD_OUTPUT_DIR}/lib/${BUILD_OUTPUT_ARCH}
${ANDROID_STANDALONE_TOOLCHAIN}/bin/*android*-g++ \
-shared -o libopencv_output.so \
--sysroot=${ANDROID_STANDALONE_TOOLCHAIN}/sysroot/ \
-Wl,--whole-archive \
libopencv_core.a \
libopencv_imgproc.a \
-Wl,--no-whole-archive

Step 8. Use this command to stripe the output library for smaller size.

${ANDROID_STANDALONE_TOOLCHAIN}/bin/*android*strip --strip-unneeded libopencv_output.so

Step 9. Linking other dependencies of the library. After this step, the build's output is ready for using.

cd ${BUILD_OUTPUT_DIR}/lib/${BUILD_OUTPUT_ARCH}
${ANDROID_STANDALONE_TOOLCHAIN}/bin/*android*-g++ \
-L ${BUILD_OUTPUT_DIR}/3rdparty/lib/${BUILD_OUTPUT_ARCH} \
-ldl \
-lm \
-llog \
-ljnigraphics \
-lz \
-lcpufeatures \
-fexceptions \
-frtti \
-fsigned-char \
-shared -Wl,-soname,libopencv_output.so \
-o libopencv_output.so \
../../modules/java/CMakeFiles/opencv_java.dir/generator/src/cpp/Mat.cpp.o \
../../modules/java/CMakeFiles/opencv_java.dir/generator/src/cpp/converters.cpp.o \
../../modules/java/CMakeFiles/opencv_java.dir/generator/src/cpp/jni_part.cpp.o \
../../modules/java/CMakeFiles/opencv_java.dir/generator/src/cpp/listconverters.cpp.o \
../../modules/java/CMakeFiles/opencv_java.dir/generator/src/cpp/utils.cpp.o \
../../modules/java/CMakeFiles/opencv_java.dir/__/core/misc/java/src/cpp/core_manual.cpp.o \
../../modules/java/CMakeFiles/opencv_java.dir/__/dnn/misc/java/src/cpp/dnn_converters.cpp.o \
../../modules/java/CMakeFiles/opencv_java.dir/__/features2d/misc/java/src/cpp/features2d_converters.cpp.o \
../../3rdparty/cpufeatures/CMakeFiles/libcpufeatures.dir/cpu-features.c.o \
../../modules/java/CMakeFiles/opencv_java.dir/gen/core.cpp.o \
../../modules/java/CMakeFiles/opencv_java.dir/gen/imgproc.cpp.o \
--sysroot=${ANDROID_STANDALONE_TOOLCHAIN}/sysroot \
-Wl,--whole-archive \
libopencv_core.a \
libopencv_imgproc.a \
-Wl,--no-whole-archive

Step 10. After the above step, the size of libopencv_output.so is increased a little bit. In this final step, let's stripe the file libopencv_output.so for smaller size.

${ANDROID_STANDALONE_TOOLCHAIN}/bin/*android*strip --strip-unneeded libopencv_output.so

We're ready to intergrate this file ${BUILD_OUTPUT_DIR}/lib/${BUILD_OUTPUT_ARCH}/libopencv_output.so the Android project now.

In Java, loading library by the code:

System.loadLibrary("opencv_output");

Done!

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Repository files navigation

How to build a custom opencv 3.4.0 for Android

Environments

Setup Build Environment Steps

Build Steps For armeabi-v7a/arm64-v8a

About

Releases

Packages

Languages

Name		Name	Last commit message	Last commit date
Latest commit History 17 Commits
builds		builds
toolchains		toolchains
.dockerignore		.dockerignore
.gitignore		.gitignore
Dockerfile		Dockerfile
README.md		README.md
env_var_setup		env_var_setup

hzung/custom-build-opencv-android

Folders and files

Latest commit

History

Repository files navigation

How to build a custom opencv 3.4.0 for Android

Environments

Setup Build Environment Steps

Build Steps For armeabi-v7a/arm64-v8a

About

Resources

Stars

Watchers

Forks

Releases

Packages 0

Languages

Packages