由于项目需要使用安卓平台下opencv的扩展库，对于通用的opencv库， opencv官网提供了android的SDK

但未能提供扩展库，因此需要自己进行源码编译。本文记录android平台下opencv及其扩展库的交叉编译。

前提：主机已安装android-ndk交叉编译器

安装依赖环境

sudo apt-get install build-essential libgtk2.0-dev libavcodec-dev libavformat-dev libjpeg-dev libswscale-dev libtiff5-dev
sudo apt-get install libgtk2.0-dev
sudo apt-get install pkg-config

1、源码下载

下载opencv，可手动下载源码和拓展模块源码，解压后分别命名opencv和opencv_contrib文件

Releases - OpenCV

GitHub - opencv/opencv at 4.8.0

GitHub - opencv/opencv_contrib: Repository for OpenCV's extra modules

也可利用以下setup.sh脚本下载，默认下载版本为3.1.0，自动命名opencv和opencv_contrib文件

#!/bin/bash

OPENCV_VERSION=3.1.0

if [ ! -z "$1" ]
  then
    OPENCV_VERSION="$1"
fi

echo "Opnecv version ${OPENCV_VERSION}"

SCRIPT=$(readlink -f $0)
WD=`dirname $SCRIPT`

cd "${WD}"
if [ ! -d "${WD}/opencv" ]; then
    echo 'Cloning opencv'
    git clone https://github.com/opencv/opencv.git
fi
cd opencv
git checkout -b "${OPENCV_VERSION}" "${OPENCV_VERSION}"

cd "${WD}"
if [ ! -d "${WD}/opencv_contrib" ]; then
    echo 'Cloning opencv_contrib'
    git clone https://github.com/opencv/opencv_contrib.git
fi
cd opencv_contrib
git checkout -b "${OPENCV_VERSION}" "${OPENCV_VERSION}"

cd "${WD}"

指定脚本下载，下载完成后出现opencv和opencv_contrib文件

sh setup.sh 4.8.0

2、源码编译

设置编译脚本build-opencv-for-android.sh

#!/bin/bash
NDK_ROOT="${1:-${ANDROID_NDK_HOME}}"
SHELL_PATH=$(pwd)

echo $NDK_ROOT

### ABIs setup
declare -a ANDROID_ABI_LIST=("arm64-v8a")

### path setup
INSTALL_DIR="${SHELL_PATH}/android_opencv"
rm -rf "${INSTALL_DIR}/opencv"

### Make each ABI target iteratly and sequentially
API_LEVEL=21
for i in "${ANDROID_ABI_LIST[@]}"
do
    ANDROID_ABI="${i}"
    echo "Start building ${ANDROID_ABI} version"

    TEMP_BUILD_DIR="${SHELL_PATH}/build/android_${ANDROID_ABI}"
    # ### Remove the build folder first, and create it
    rm -rf "${TEMP_BUILD_DIR}"
    mkdir -p "${TEMP_BUILD_DIR}"
    cd "${TEMP_BUILD_DIR}"

    OPENCV_PATH="${SHELL_PATH}/opencv"
    OPENCV_CONTRIB_PATH="${SHELL_PATH}/opencv_contrib"
    INSTALL_PATH=${SHELL_PATH}/out/
    mkdir -p "${INSTALL_PATH}"

    /usr/cmake-3.23.0-rc2-linux-x86_64/bin/cmake -DCMAKE_BUILD_WITH_INSTALL_RPATH=ON \
          -DCMAKE_TOOLCHAIN_FILE="${NDK_ROOT}/build/cmake/android.toolchain.cmake" \
          -DANDROID_TOOLCHAIN=clang++ \
          -DANDROID_NDK="${NDK_ROOT}" \
          -DANDROID_NATIVE_API_LEVEL=${API_LEVEL} \
          -DANDROID_ABI="${ANDROID_ABI}" \
          -DOPENCV_EXTRA_MODULES_PATH=${OPENCV_CONTRIB_PATH}/modules \
          -DCMAKE_INSTALL_PREFIX=${INSTALL_PATH} \
          -D BUILD_ANDROID_PROJECTS=OFF\
          -D WITH_CUDA=OFF \
          -D WITH_MATLAB=OFF \
          -D BUILD_ANDROID_EXAMPLES=ON \
          -D BUILD_DOCS=OFF \
          -D BUILD_PERF_TESTS=OFF \
          -D BUILD_TESTS=OFF \
          ${OPENCV_PATH}
    # # Build it
    make -j4
    # # Install it
    make install/strip
    # ### Remove temp build folder
    cd "${SHELL_PATH}"
    # rm -rf "${TEMP_BUILD_DIR}"
    echo "end building ${INSTALL_PATH} version"
done

将build-opencv-for-android.sh、opencv和opencv_contrib文件放置于同一目录下

导出NDK安装路径环境变量

export ANDROID_HOME=/usr/android-ndk-r25c/
export ANDROID_NDK_HOME=/usr/android-ndk-r25c/
./build-opencv-for-android.sh

等待编译完成，完成后，编译成功如下，库文件在 ./out/sdk/native/staticlibs/

本文在编译脚本中只设置了安卓arm64-v8a硬件平台的编译，如有需要可自行修改。

参考

GitHub - ShikinChen/build-opencv-for-android: 编译opencv的Android库的脚本

GitHub - tzutalin/build-opencv-for-android: An interactive script to download and build OpenCV and OpenCV contrib for Android