如何为Android平台编译 opencv3 和 opencv

编译出来的opencv库有问题，正在调试中 ......

本文以编译opencv 3.3.0 和 opencv_contrib 3.3.0为例，系统为 Linux x64 (Fedora 21)，具体步骤如下：

1. 下载 Source code zip 压缩包

从下面网址，选择 opencv 3.3.0 Source code 下载
https://github.com/opencv/opencv/releases

从下面网址，选择下载与
opencv
3.3.0 对应的
opencv_contrib
3.3.0
https://github.com/opencv/opencv_contrib/releases

注意：opencv和opencv_contrib
版本必须保持一致，否则可能会出现编译错误。

2.
下载
build-opencv-for-android
开源代码

$ cd /mnt/work

$ git clone https://github.com/tzutalin/build-opencv-for-android.git

$ cd build-opencv-for-android

3. 解压源码包并重命名

将opencv-3.3.0.zip 和 opencv_contrib-3.3.0.zip 都解压到下载的build-opencv-for-android 开源代码所在目录 /mnt/work/build-opencv-for-android 。

$ unzip opencv-3.3..zip -d /mnt/work/build-opencv-for-android

$ unzip opencv_contrib-3.3..zip -d /mnt/work/build-opencv-for-android

$ cd /mnt/work/build-opencv-for-android

$ mv opencv-3.3. opencv

$ mv opencv_contrib-3.3. opencv_contrib

4. 修改 build-opencv-for-android 开源代码中 build-android-opencv.sh

修改内容如下：

修改第 6 行代码：

declare -a ANDROID_ABI_LIST=("x86" "x86_64" "armeabi" "arm64-v8a" "armeabi-v7a" "mips" "mips64")

为

declare -a ANDROID_ABI_LIST=("armeabi-v7a")

最终代码，如下：

 #!/bin/bash

 NDK_ROOT="${1:-${NDK_ROOT}}"

 ### ABIs setup

 #declare -a ANDROID_ABI_LIST=("x86" "x86_64" "armeabi-v7a with NEON" "arm64-v8a")

 declare -a ANDROID_ABI_LIST=("armeabi-v7a")

 ### path setup

 SCRIPT=$(readlink -f $0)

 WD=`dirname $SCRIPT`

 OPENCV_ROOT="${WD}/opencv"

 N_JOBS=${N_JOBS:-4}

 ### Download android-cmake

 if [ ! -d "${WD}/android-cmake" ]; then

     echo 'Cloning android-cmake'

     git clone https://github.com/taka-no-me/android-cmake.git

 fi

 INSTALL_DIR="${WD}/android_opencv"

 rm -rf "${INSTALL_DIR}/opencv"

 ### Make each ABI target iteratly and sequentially

 for i in "${ANDROID_ABI_LIST[@]}"

 do

     ANDROID_ABI="${i}"

     echo "Start building ${ANDROID_ABI} version"

     if [ "${ANDROID_ABI}" = "armeabi" ]; then

         API_LEVEL=19

     else

         API_LEVEL=21

     fi

     temp_build_dir="${OPENCV_ROOT}/platforms/build_android_${ANDROID_ABI}"

     ### Remove the build folder first, and create it

     rm -rf "${temp_build_dir}"

     mkdir -p "${temp_build_dir}"

     cd "${temp_build_dir}"

     cmake -DCMAKE_BUILD_WITH_INSTALL_RPATH=ON \

           -DCMAKE_TOOLCHAIN_FILE="${WD}/android-cmake/android.toolchain.cmake" \

           -DANDROID_NDK="${NDK_ROOT}" \

           -DANDROID_NATIVE_API_LEVEL=${API_LEVEL} \

           -DANDROID_ABI="${ANDROID_ABI}" \

           -D WITH_CUDA=OFF \

           -D WITH_MATLAB=OFF \

           -D BUILD_ANDROID_EXAMPLES=OFF \

           -D BUILD_DOCS=OFF \

           -D BUILD_PERF_TESTS=OFF \

           -D BUILD_TESTS=OFF \

           -DOPENCV_EXTRA_MODULES_PATH="${WD}/opencv_contrib/modules/"  \

           -DCMAKE_INSTALL_PREFIX="${INSTALL_DIR}/opencv" \

           ../..

     # Build it

     make -j${N_JOBS}

     # Install it

     make install/strip

     ### Remove temp build folder

     cd "${WD}"

     rm -rf "${temp_build_dir}"

     echo "end building ${ANDROID_ABI} version"

 done

说明：

1). 由于目前大多数 android 平台使用arm cpu, 采用armeabi-v7 指令集，为了减少编译时间，所有我只保留 "armeabi-v7a" ，其他删除，如果需要也可保留。
2). armeabi-v7 代表 arm EABI version 7 指令集, EABI 为嵌入应用二进制接口 (Embedded Application Binary Interface) 。

5. 执行脚本 build-android-opencv.sh

$ ./build-android-opencv.sh /mnt/work/android/android-sdk-linux/ndk-bundle

注：build-android-opencv.sh脚本的通用的执行命令格式为“./build-android-opencv.sh [NDK_ROOT]”，其中，参数NDK_ROOT是可选的，表示Android Native Development Kit (NDK) 顶层目录，如果没有提供，则会试图寻找环境变量 ANDROID_NDK。

6. 查看编译结果

编译成功后，会在 build-opencv-for-android 目录，即build-android-opencv.sh脚本所在目录，生成 android_opencv目录，其目录结构如下：

$ tree -d android_opencv

android_opencv

└── opencv

├── apk

└── sdk

├── etc

│   ├── haarcascades

│   └── lbpcascades

└── native

├── 3rdparty

│   └── libs

│   └── armeabi-v7a

├── jni

│   ├── abi-armeabi-v7a

│   └── include

│   ├── opencv

│   └── opencv2

│   ├── aruco

│   ├── bioinspired

│   ├── calib3d

│   ├── ccalib

│   ├── core

│   │   ├── cuda

│   │   │   └── detail

│   │   ├── hal

│   │   └── utils

│   ├── datasets

│   ├── dnn

│   ├── face

│   ├── features2d

│   ├── flann

│   ├── fuzzy

│   ├── highgui

│   ├── imgcodecs

│   ├── img_hash

│   ├── imgproc

│   │   ├── detail

│   │   └── hal

│   ├── line_descriptor

│   ├── ml

│   ├── objdetect

│   ├── optflow

│   ├── phase_unwrapping

│   ├── photo

│   ├── reg

│   ├── rgbd

│   ├── saliency

│   ├── shape

│   ├── stereo

│   ├── stitching

│   │   └── detail

│   ├── structured_light

│   ├── superres

│   ├── surface_matching

│   ├── text

│   ├── tracking

│   ├── video

│   ├── videoio

│   ├── videostab

│   ├── xfeatures2d

│   ├── ximgproc

│   └── xphoto

└── libs

└── armeabi-v7a

 directories

问题与解决方法

问题一

$ ./build-android-opencv.sh

Start building armeabi-v7a version

CMake Error at /mnt/work/video/res/opencv/build-opencv-for-android-master/android-cmake/android.toolchain.cmake: (message):

Could not find neither Android NDK nor Android standalone toolchain.

You should either set an environment variable:

export ANDROID_NDK=~/my-android-ndk

export ANDROID_STANDALONE_TOOLCHAIN=~/my-android-toolchain

or put the toolchain or NDK in the default path:

sudo ln -s ~/my-android-ndk /opt/android-ndk

sudo ln -s ~/my-android-toolchain /opt/android-toolchain

Call Stack (most recent call first):

/usr/share/cmake/Modules/CMakeDetermineSystem.cmake: (include)

CMakeLists.txt: (project)

CMake Error: Error required internal CMake variable not set, cmake may be not be built correctly.

Missing variable is:

CMAKE_CXX_COMPILER_ENV_VAR

CMake Error: Error required internal CMake variable not set, cmake may be not be built correctly.

Missing variable is:

CMAKE_CXX_COMPILER

CMake Error: Could not find cmake module file: /mnt/work/video/res/opencv/build-opencv-for-android-master/opencv/platforms/build_android_armeabi-v7a/CMakeFiles/3.0./CMakeCXXCompiler.cmake

CMake Error: Error required internal CMake variable not set, cmake may be not be built correctly.

Missing variable is:

CMAKE_C_COMPILER_ENV_VAR

CMake Error: Error required internal CMake variable not set, cmake may be not be built correctly.

Missing variable is:

CMAKE_C_COMPILER

CMake Error: Could not find cmake module file: /mnt/work/video/res/opencv/build-opencv-for-android-master/opencv/platforms/build_android_armeabi-v7a/CMakeFiles/3.0./CMakeCCompiler.cmake

CMake Error at CMakeLists.txt: (project):

No CMAKE_CXX_COMPILER could be found.

Tell CMake where to find the compiler by setting the CMake cache entry

CMAKE_CXX_COMPILER to the full path to the compiler, or to the compiler

name if it is in the PATH.

CMake Error at CMakeLists.txt: (project):

No CMAKE_C_COMPILER could be found.

Tell CMake where to find the compiler by setting the CMake cache entry

CMAKE_C_COMPILER to the full path to the compiler, or to the compiler name

if it is in the PATH.

CMake Error: CMAKE_CXX_COMPILER not set, after EnableLanguage

CMake Error: CMAKE_C_COMPILER not set, after EnableLanguage

-- Configuring incomplete, errors occurred!

make: *** No targets specified and no makefile found. Stop.

make: *** No rule to make target 'install/strip'. Stop.

end building armeabi-v7a version

解决方法

方法一（推荐方法）

从命令行传入 NDK_ROOT 目录，如下：

$ ./build-android-opencv.sh /mnt/work/android/android-sdk-linux/ndk-bundle/

方法二，

根据提示，设置环境变量 ANDROID_NDK，如下

$ export ANDROID_NDK=/mnt/work/android/android-sdk-linux/ndk-bundle/

$ env | grep ANDROID_NDK

ANDROID_NDK=/mnt/work/android/android-sdk-linux/ndk-bundle/

$ ./build-android-opencv.sh

参考资料

[1] Build and install OpenCV and contrib lib on Ubuntu / Android 链接一链接二（转载）

[2] 如何编译 opencv3 和 opencv_contrib（Linux）