Android:Linux上编译OpenCV的Android库，从源码编译出一个轻量级的OpenCV安卓库-Toy模板网

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（原文在这里，我根据这篇文章终于也能编译成功可以使用的OpenCV库文件了：
Linux上编译OpenCV的Android库
https://zhuanlan.zhihu.com/p/301203711
整个编译过程只用下载Android NDK和OpenCV源码。工具链android.toolchain.cmake，是NDK：android-ndk-r19c-linux-x86_64自带的，不用自己编译了。使用WSL Ubuntu记得每行命令前都要加sudo权限，不然就会有很多莫名其妙的错误
）

背景

最近需要在Android应用程序上使用OpenCV，官方提供的预编译库实在是太大了，有100多MB。因为我们只用到了OpenCV中有限的函数，于是决定从源码编译出一个轻量级的OpenCV安卓库。

安装依赖

Android NDK

wget https://dl.google.com/android/repository/android-ndk-r19c-linux-x86_64.zip
unzip android-ndk-r19c-linux-x86_64.zip
export ANDROID_NDK=$(pwd)/android-ndk-r19c（这行命令我好像没有用）

OpenCV源码

git clone https://github.com/opencv/opencv
（我用的是opencv-4.6.0源码）

编译

1，使用cmake进行构建

这次先编译静态库，命令如下：
gemfield@ThinkPad-X1C:/app/gemfield/opencv-4.4.0/build$ cmake
-DBUILD_opencv_ittnotify=OFF
-DBUILD_ITT=OFF
-DWITH_CUDA=OFF
-DWITH_OPENCL=OFF
-DWITH_OPENCLAMDFFT=OFF
-DWITH_OPENCLAMDBLAS=OFF
-DWITH_VA_INTEL=OFF
-DCPU_BASELINE_DISABLE=ON
-DENABLE_SSE=OFF
-DENABLE_SSE2=OFF
-DBUILD_TESTING=OFF
-DBUILD_PERF_TESTS=OFF
-DBUILD_TESTS=OFF
-DCMAKE_BUILD_TYPE=RELEASE
-DBUILD_EXAMPLES=OFF
-DBUILD_DOCS=OFF
-DBUILD_opencv_apps=OFF
-DBUILD_SHARED_LIBS=OFF
-DOpenCV_STATIC=ON
-DWITH_1394=OFF
-DWITH_ARITH_DEC=OFF
-DWITH_ARITH_ENC=OFF
-DWITH_CUBLAS=OFF
-DWITH_CUFFT=OFF
-DWITH_FFMPEG=OFF
-DWITH_GDAL=OFF
-DWITH_GSTREAMER=OFF
-DWITH_GTK=OFF
-DWITH_HALIDE=OFF
-DWITH_JASPER=OFF
-DWITH_NVCUVID=OFF
-DWITH_OPENEXR=OFF
-DWITH_PROTOBUF=OFF
-DWITH_PTHREADS_PF=OFF
-DWITH_QUIRC=OFF
-DWITH_V4L=OFF
-DWITH_WEBP=OFF
-DBUILD_LIST=core,imgproc
-DANDROID_NDK=/app/gemfield/android-ndk-r19c
-DCMAKE_TOOLCHAIN_FILE=/app/gemfield/android-ndk-r19c/build/cmake/android.toolchain.cmake
-DANDROID_NATIVE_API_LEVEL=android-21
-DBUILD_JAVA=ON
-DBUILD_ANDROID_EXAMPLES=OFF
-DBUILD_ANDROID_PROJECTS=OFF
-DANDROID_STL=c++_shared
-DANDROID_ABI=arm64-v8a
-DBUILD_FAT_JAVA_LIB=ON
-DCMAKE_INSTALL_PREFIX=/app/gemfield/opencv-4.4.0/opencv_v8
…

（下面这些是我在WSL Ubuntu18下面的命令，设置了ANDROID_STL=c++_shared 不知道为什么编译出来的是静态库？明天再看看原因，晚了休息了

sudo cmake
-DBUILD_opencv_ittnotify=OFF
-DBUILD_ITT=OFF
-DWITH_CUDA=OFF
-DWITH_OPENCL=OFF
-DWITH_OPENCLAMDFFT=OFF
-DWITH_OPENCLAMDBLAS=OFF
-DWITH_VA_INTEL=OFF
-DCPU_BASELINE_DISABLE=ON
-DENABLE_SSE=OFF
-DENABLE_SSE2=OFF
-DBUILD_TESTING=OFF
-DBUILD_PERF_TESTS=OFF
-DBUILD_TESTS=OFF
-DCMAKE_BUILD_TYPE=RELEASE
-DBUILD_EXAMPLES=OFF
-DBUILD_DOCS=OFF
-DBUILD_opencv_apps=OFF
-DBUILD_SHARED_LIBS=OFF
-DOpenCV_STATIC=ON
-DWITH_1394=OFF
-DWITH_ARITH_DEC=OFF
-DWITH_ARITH_ENC=OFF
-DWITH_CUBLAS=OFF
-DWITH_CUFFT=OFF
-DWITH_FFMPEG=OFF
-DWITH_GDAL=OFF
-DWITH_GSTREAMER=OFF
-DWITH_GTK=OFF
-DWITH_HALIDE=OFF
-DWITH_JASPER=OFF
-DWITH_NVCUVID=OFF
-DWITH_OPENEXR=OFF
-DWITH_PROTOBUF=OFF
-DWITH_PTHREADS_PF=OFF
-DWITH_QUIRC=OFF
-DWITH_V4L=OFF
-DWITH_WEBP=OFF
-DBUILD_LIST=core,imgproc
-DANDROID_NDK=/mnt/c/michael/Software/android-ndk-r19c
-DCMAKE_TOOLCHAIN_FILE=/mnt/c/michael/Software/android-ndk-r19c/build/cmake/android.toolchain.cmake
-DANDROID_NATIVE_API_LEVEL=android-21
-DBUILD_JAVA=ON
-DBUILD_ANDROID_EXAMPLES=OFF
-DBUILD_ANDROID_PROJECTS=OFF
-DANDROID_STL=c++_shared
-DANDROID_ABI=arm64-v8a
-DBUILD_FAT_JAVA_LIB=ON
-DCMAKE_INSTALL_PREFIX=/mnt/c/michael/Software/opencv-4.6.0/opencv_v8
…）

上述参数的简单说明：

NDK 通过cmake-toolchains(cmake工具链文件)支持 CMake。工具链文件是用于自定义交叉编译工具链行为的 CMake 文件。用于 NDK 的工具链文件位于 NDK目录下的/build/cmake/android.toolchain.cmake，比如上面参数中的：
-DCMAKE_TOOLCHAIN_FILE=/app/gemfield/android-ndk-r19c/build/cmake/android.toolchain.cmake
DANDROID_ARM_NEON用来指定 armeabi-v7a 启用或停用 NEON。对其他 ABI 没有影响。对于 API 级别（minSdkVersion或ANDROID_PLATFORM）23 或更高级别，默认为 true，否则为 false。要强制 armeabi-v7a 始终使用 Neon 支持构建，请传递-DANDROID_ARM_NEON=TRUE ；
ANDROID_ABI，用来指定目标 ABI。
armeabi-v7a
armeabi-v7a with NEON 与 -DANDROID_ABI=armeabi-v7a -DANDROID_ARM_NEON=ON 相同。
arm64-v8a
x86
x86_64
ANDROID_PLATFORM，指定应用或库所支持的最低 API 级别。此值对应于应用的minSdkVersion。当直接调用 CMake 时，此值默认为所使用的 NDK 支持的最低 API 级别。例如，对于 NDK r20，此值默认为 API 级别 16；
ANDROID_STL，指定要为此应用使用的 STL。默认情况下将使用 c++_static ：
值 Gemfield的解释
c++_shared libc++ 的共享库变体
c++_static libc++ 的静态库变体
无不支持 C++ 标准库
系统系统 STL
上述参数中使用了：-DANDROID_STL=c++_shared。

2，cmake输出的摘要

比如编译器用的是clang++、使用C++11标准等：

– General configuration for OpenCV 4.4.0 ===================================== – Platform: – Host: Linux 5.4.0-42-syszux x86_64 – Target: Android 1 aarch64 – CMake: 3.16.3 – CMake generator: Unix Makefiles – CMake build tool: /usr/bin/make – Configuration: RELEASE

– CPU/HW features: – Baseline: NEON FP16 – disabled: ON SSE SSE2

– C/C++: – Built as dynamic libs?: NO – C++ standard: 11 – C++ Compiler: /app/gemfield/android-ndk-r19c/toolchains/llvm/prebuilt/linux-x86_64/bin/clang++ (ver 8.0) – C++ flags (Release): -g -DANDROID -fdata-sections -ffunction-sections -funwind-tables -fstack-protector-strong -no-canonical-prefixes -fno-addrsig -Wa,–noexecstack -Wformat -Werror=format-security -stdlib=libc++ -fsigned-char -W -Wall -Werror=return-type -Werror=non-virtual-dtor -Werror=address -Werror=sequence-point -Wformat -Werror=format-security -Wmissing-declarations -Wmissing-prototypes -Wstrict-prototypes -Wundef -Winit-self -Wpointer-arith -Wshadow -Wsign-promo -Wuninitialized -Winit-self -Winconsistent-missing-override -Wno-delete-non-virtual-dtor -Wno-unnamed-type-template-args -Wno-comment -fdiagnostics-show-option -Qunused-arguments -fvisibility=hidden -fvisibility-inlines-hidden -O2 -DNDEBUG -DNDEBUG – C++ flags (Debug): -g -DANDROID -fdata-sections -ffunction-sections -funwind-tables -fstack-protector-strong -no-canonical-prefixes -fno-addrsig -Wa,–noexecstack -Wformat -Werror=format-security -stdlib=libc++ -fsigned-char -W -Wall -Werror=return-type -Werror=non-virtual-dtor -Werror=address -Werror=sequence-point -Wformat -Werror=format-security -Wmissing-declarations -Wmissing-prototypes -Wstrict-prototypes -Wundef -Winit-self -Wpointer-arith -Wshadow -Wsign-promo -Wuninitialized -Winit-self -Winconsistent-missing-override -Wno-delete-non-virtual-dtor -Wno-unnamed-type-template-args -Wno-comment -fdiagnostics-show-option -Qunused-arguments -fvisibility=hidden -fvisibility-inlines-hidden -O0 -fno-limit-debug-info -DDEBUG -D_DEBUG – C Compiler: /app/gemfield/android-ndk-r19c/toolchains/llvm/prebuilt/linux-x86_64/bin/clang – C flags (Release): -g -DANDROID -fdata-sections -ffunction-sections -funwind-tables -fstack-protector-strong -no-canonical-prefixes -fno-addrsig -Wa,–noexecstack -Wformat -Werror=format-security -fsigned-char -W -Wall -Werror=return-type -Werror=non-virtual-dtor -Werror=address -Werror=sequence-point -Wformat -Werror=format-security -Wmissing-declarations -Wmissing-prototypes -Wstrict-prototypes -Wundef -Winit-self -Wpointer-arith -Wshadow -Wsign-promo -Wuninitialized -Winit-self -Winconsistent-missing-override -Wno-delete-non-virtual-dtor -Wno-unnamed-type-template-args -Wno-comment -fdiagnostics-show-option -Qunused-arguments -fvisibility=hidden -fvisibility-inlines-hidden -O2 -DNDEBUG -DNDEBUG – C flags (Debug): -g -DANDROID -fdata-sections -ffunction-sections -funwind-tables -fstack-protector-strong -no-canonical-prefixes -fno-addrsig -Wa,–noexecstack -Wformat -Werror=format-security -fsigned-char -W -Wall -Werror=return-type -Werror=non-virtual-dtor -Werror=address -Werror=sequence-point -Wformat -Werror=format-security -Wmissing-declarations -Wmissing-prototypes -Wstrict-prototypes -Wundef -Winit-self -Wpointer-arith -Wshadow -Wsign-promo -Wuninitialized -Winit-self -Winconsistent-missing-override -Wno-delete-non-virtual-dtor -Wno-unnamed-type-template-args -Wno-comment -fdiagnostics-show-option -Qunused-arguments -fvisibility=hidden -fvisibility-inlines-hidden -O0 -fno-limit-debug-info -DDEBUG -D_DEBUG – Linker flags (Release): -Wl,–exclude-libs,libgcc.a -Wl,–exclude-libs,libatomic.a -Wl,–build-id -Wl,–warn-shared-textrel -Wl,–fatal-warnings -Wl,–no-undefined -Qunused-arguments -Wl,-z,noexecstack -Wl,-z,relro -Wl,-z,now -Wl,–as-needed – Linker flags (Debug): -Wl,–exclude-libs,libgcc.a -Wl,–exclude-libs,libatomic.a -Wl,–build-id -Wl,–warn-shared-textrel -Wl,–fatal-warnings -Wl,–no-undefined -Qunused-arguments -Wl,-z,noexecstack -Wl,-z,relro -Wl,-z,now -Wl,–as-needed – Extra dependencies: /app/gemfield/android-ndk-r19c/toolchains/llvm/prebuilt/linux-x86_64/sysroot/usr/lib/aarch64-linux-android/libz.a dl m log – 3rdparty dependencies: libcpufeatures tegra_hal

– OpenCV modules: – To be built: core imgproc – Disabled: world – Disabled by dependency: calib3d features2d flann gapi highgui imgcodecs java_bindings_generator ml objdetect photo stitching video videoio – Unavailable: dnn java js python2 python3 ts

– Android NDK: /app/gemfield/android-ndk-r19c (ver 19.2.5345600) – Android ABI: arm64-v8a – NDK toolchain: aarch64-linux-android-clang – STL type: c++_shared – Native API level: 21 – Android SDK: not used, projects are not built

– Media I/O: – ZLib: /app/gemfield/android-ndk-r19c/toolchains/llvm/prebuilt/linux-x86_64/sysroot/usr/lib/aarch64-linux-android/libz.a (ver 1.2.7) – JPEG: build-libjpeg-turbo (ver 2.0.5-62) – PNG: build (ver 1.6.37) – TIFF: build (ver 42 - 4.0.10) – JPEG 2000: NO – HDR: YES – SUNRASTER: YES – PXM: YES – PFM: YES

– – Other third-party libraries: – Custom HAL: YES (carotene (ver 0.0.1))

– Python (for build): /usr/bin/python2.7

– Java: export all functions – ant: NO – Java wrappers: NO – Java tests: NO

– Install to: /app/gemfield/opencv-4.4.0/opencv_v8
可以看到NDK默认是加上了debug flag "-g"的，哪怕是release。

3，编译的三方库和opencv的模块（就2个：core和imgproc）

如下所示：

3rdparty/libjpeg-turbo
3rdparty/libtiff
3rdparty/libpng
3rdparty/carotene
3rdparty/ade
modules/core
modules/imgproc

4，真正开始编译

使用make命令：

gemfield@ThinkPad-X1C:/app/gemfield/opencv-4.4.0/build$ make VERBOSE=1
5，安装

gemfield@ThinkPad-X1C:/app/gemfield/opencv-4.4.0/build$ make install
将会安装在/app/gemfield/opencv-4.4.0/opencv_v8/目录下。有所需的头文件和编译好的静态库：

./sdk/native/staticlibs/arm64-v8a/libopencv_core.a
./sdk/native/staticlibs/arm64-v8a/libopencv_imgproc.a
./sdk/native/3rdparty/libs/arm64-v8a/libtegra_hal.a
./sdk/native/3rdparty/libs/arm64-v8a/liblibtiff.a
./sdk/native/3rdparty/libs/arm64-v8a/libcpufeatures.a
./sdk/native/3rdparty/libs/arm64-v8a/liblibpng.a
./sdk/native/3rdparty/libs/arm64-v8a/liblibjpeg-turbo.a
./sdk/native/3rdparty/libs/arm64-v8a/libade.a
这样编译出来的库的大小有50多MB，不符合Gemfield的初心。

降低库的大小

上述步骤编译出来的opencv库很大，一大原因是因为NDK默认加了debug flag导致的，另一大原因是没有strip符号导致的。

我们先手工去掉-g flag，使用如下的临时解决方案：

-DCMAKE_CXX_FLAGS_RELEASE=-g0
整体命令如下（注意，ANDROID_STL改为默认值，也就是static的了）：

gemfield@ThinkPad-X1C:/app/gemfield/opencv-4.4.0/build$ cmake
-DBUILD_opencv_ittnotify=OFF
-DBUILD_ITT=OFF
-DWITH_CUDA=OFF
-DWITH_OPENCL=OFF
-DWITH_OPENCLAMDFFT=OFF
-DWITH_OPENCLAMDBLAS=OFF
-DWITH_VA_INTEL=OFF
-DCPU_BASELINE_DISABLE=ON
-DENABLE_SSE=OFF
-DENABLE_SSE2=OFF
-DBUILD_TESTING=OFF
-DBUILD_PERF_TESTS=OFF
-DBUILD_TESTS=OFF
-DCMAKE_BUILD_TYPE=RELEASE
-DCMAKE_CXX_FLAGS_RELEASE=-g0
-DBUILD_EXAMPLES=OFF
-DBUILD_DOCS=OFF
-DBUILD_opencv_apps=OFF
-DBUILD_SHARED_LIBS=ON
-DOpenCV_STATIC=OFF
-DWITH_1394=OFF
-DWITH_ARITH_DEC=OFF
-DWITH_ARITH_ENC=OFF
-DWITH_CUBLAS=OFF
-DWITH_CUFFT=OFF
-DWITH_FFMPEG=OFF
-DWITH_GDAL=OFF
-DWITH_GSTREAMER=OFF
-DWITH_GTK=OFF
-DWITH_HALIDE=OFF
-DWITH_JASPER=OFF
-DWITH_NVCUVID=OFF
-DWITH_OPENEXR=OFF
-DWITH_PROTOBUF=OFF
-DWITH_PTHREADS_PF=OFF
-DWITH_QUIRC=OFF
-DWITH_V4L=OFF
-DWITH_WEBP=OFF
-DBUILD_LIST=core,imgproc
-DANDROID_NDK=/app/gemfield/android-ndk-r19c
-DCMAKE_TOOLCHAIN_FILE=/app/gemfield/android-ndk-r19c/build/cmake/android.toolchain.cmake
-DANDROID_NATIVE_API_LEVEL=android-21
-DBUILD_JAVA=ON
-DBUILD_ANDROID_EXAMPLES=OFF
-DBUILD_ANDROID_PROJECTS=OFF
-DANDROID_ABI=arm64-v8a
-DCMAKE_INSTALL_PREFIX=/app/gemfield/opencv-4.4.0/opencv_v8
…
编译好后，我们可以看到库的大小（这个章节Gemfield使用了共享库编译，静态库类似，不再重复）：

gemfield@ThinkPad-X1C:/app/gemfield/opencv-4.4.0/opencv_v8$ find . -type f -name “lib*.so” -exec ls -lh {} +
-rw-r–r-- 1 gemfield gemfield 8.9M 11月 19 18:39 ./sdk/native/libs/arm64-v8a/libopencv_core.so
-rw-r–r-- 1 gemfield gemfield 3.6M 11月 19 18:41 ./sdk/native/libs/arm64-v8a/libopencv_imgproc.so
再strip下：

gemfield@ThinkPad-X1C:/app/gemfield/opencv-4.4.0/opencv_v8$ /app/gemfield/android-ndk-r19c/toolchains/llvm/prebuilt/linux-x86_64/aarch64-linux-android/bin/strip ./sdk/native/libs/arm64-v8a/libopencv_core.so
gemfield@ThinkPad-X1C:/app/gemfield/opencv-4.4.0/opencv_v8$ /app/gemfield/android-ndk-r19c/toolchains/llvm/prebuilt/linux-x86_64/aarch64-linux-android/bin/strip ./sdk/native/libs/arm64-v8a/libopencv_imgproc.so
看起来只有2、3个MB了：

gemfield@ThinkPad-X1C:/app/gemfield/opencv-4.4.0/opencv_v8$ find . -type f -name lib*.so -exec ls -lh {} +
-rw-r–r-- 1 gemfield gemfield 3.4M 11月 19 18:49 ./sdk/native/libs/arm64-v8a/libopencv_core.so
-rw-r–r-- 1 gemfield gemfield 2.9M 11月 19 18:49 ./sdk/native/libs/arm64-v8a/libopencv_imgproc.so
还可以看这两个共享库的依赖：

gemfield@ThinkPad-X1C:/app/gemfield/opencv-4.4.0/opencv_v8$ /app/gemfield/android-ndk-r19c/toolchains/llvm/prebuilt/linux-x86_64/arm-linux-androideabi/bin/readelf -a ./sdk/native/libs/arm64-v8a/libopencv_core.so | grep “Shared library:”
0x0000000000000001 (NEEDED) Shared library: [libdl.so]
0x0000000000000001 (NEEDED) Shared library: [libm.so]
0x0000000000000001 (NEEDED) Shared library: [liblog.so]
0x0000000000000001 (NEEDED) Shared library: [libc.so]

gemfield@ThinkPad-X1C:/app/gemfield/opencv-4.4.0/opencv_v8$ /app/gemfield/android-ndk-r19c/toolchains/llvm/prebuilt/linux-x86_64/arm-linux-androideabi/bin/readelf -a ./sdk/native/libs/arm64-v8a/libopencv_imgproc.so | grep “Shared library:”
0x0000000000000001 (NEEDED) Shared library: [libopencv_core.so]
0x0000000000000001 (NEEDED) Shared library: [libm.so]
0x0000000000000001 (NEEDED) Shared library: [libc.so]
当然，共享库是要包含在apk中的，会增加apk的大小，推荐使用静态库，自己酌情考虑吧。文章来源地址https://www.toymoban.com/news/detail-454573.html

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