Adding Opencv to Native C Code Through Cmake on Android Studio

Adding OpenCV to Native C code through CMake on Android Studio

UPDATE 21-Oct-19: Deprecated Git/Simpler Way in favor of new AndroidOpenCVGradlePlugin

UPDATE 22-May-18: Added missing step number 6.

UPDATE 10-May-17: New solution provides proper integration of OpenCV into application with CMake and Android Gradle plugin 2.3.1. Tested using Android Studio 2.3.1.

UPDATE 11-May-17: An additional solution has been provided

There are two ways of including OpenCV.

Using AndroidOpenCVGradlePlugin

Visit https://github.com/ahasbini/AndroidOpenCVGradlePlugin for more details.

Git/Simpler Way

Visit https://github.com/ahasbini/Android-OpenCV for more details.

Manual/Advanced Way

To include OpenCV libraries into Android Studio Project, its best to create a new Library Module in the project and port the files from OpenCV Android SDK bundle into it:

1. Create a new module by selecting File>New Module.
2. Select "Android Library", and then enter the details:
   
   
   • Library name: OpenCV
   • Module name: opencv
   • Package name: org.opencv
3. Once the new module created, copy the contents of path_to_opencv_sdk/sdk/java/src directory into path_to_your_project/opencv/src/main/java.
4. Under main, create the following directly path: aidl/org/opencv/engine and move main/java/org/opencv/engine/OpenCVEngineInterface.aidl into it.
5. Copy the contents of path_to_opencv_sdk/sdk/java/res into path_to_your_project/opencv/src/main/res.
6. Create sdk folder inside path_to_your_project/opencv/src/ and copy path_to_opencv_sdk/sdk/native folder into it.
7. Within the opencv module, create CMakeLists.txt file and add the following lines in the following order:

---

cmake_minimum_required(VERSION 3.4.1)
set(OpenCV_DIR "src/sdk/native/jni")
find_package(OpenCV REQUIRED)
message(STATUS "OpenCV libraries: ${OpenCV_LIBS}")
include_directories(${OpenCV_INCLUDE_DIRS})

---

8. Within the opencv module, edit the build.gradle file as such:

---

...
android {
    ...

    defaultConfig {
        minSdkVersion 8
        targetSdkVersion 25
        versionCode 3200
        versionName "3.2.0"

        ...

        externalNativeBuild {
            cmake {
                cppFlags "-frtti -fexceptions"
            }
        }
    }
    buildTypes {
        ...
    }
    externalNativeBuild {
        cmake {
            path "CMakeLists.txt"
        }
    }
    sourceSets {
        main {
            jni.srcDirs = [jni.srcDirs, 'src/sdk/native/jni/include']
            jniLibs.srcDirs = [jniLibs.srcDirs, 'src/sdk/native/3rdparty/libs', 'src/sdk/native/libs']
        }
    }
}
...

---

9. Within the app (application module, could be another name) module, create/edit CMakeLists.txt file and add the following lines in the following order (Note the different path set to OpenCV_DIR):

---

set(OpenCV_DIR "../opencv/src/sdk/native/jni")
find_package(OpenCV REQUIRED)
message(STATUS "OpenCV libraries: ${OpenCV_LIBS}")
target_link_libraries(YOUR_TARGET_LIB ${OpenCV_LIBS})

---

10. Within the app (application module, could be another name) module, edit the build.gradle file as such:

---

...    
android {
    ...
    defaultConfig {
        ...
        externalNativeBuild {
            cmake {
                cppFlags "-frtti -fexceptions"
        }
    }
    buildTypes {
        ...
    }
    externalNativeBuild {
        cmake {
            path "CMakeLists.txt"
        }
    }
}

dependencies {
    ...
    compile project(':opencv')
}

---

11. Do a gradle sync, and now the OpenCV native libs, header files and Java wrapper classes are included.

When project is built and apk is launched, you could inspect the packaged apk under path_to_project/path_to_app_module/build/output/ (drag the apk onto the text editor tabs of Android Studio)

You should see a libopencv_java3.so under each abi architecture folder.

Initialize the OpenCV SDK in your java class :

public class MyClass {

    static {
        if (BuildConfig.DEBUG) {
            OpenCVLoader.initDebug();
        }
    }

    ...
}

And you should see within logcat messages specifying the OpenCV has been loaded (the first error is normal):

05-10 10:42:31.451 D/OpenCV/StaticHelper: Trying to get library list
05-10 10:42:31.452 E/OpenCV/StaticHelper: OpenCV error: Cannot load info library for OpenCV
05-10 10:42:31.452 D/OpenCV/StaticHelper: Library list: ""
05-10 10:42:31.452 D/OpenCV/StaticHelper: First attempt to load libs
05-10 10:42:31.452 D/OpenCV/StaticHelper: Trying to init OpenCV libs
05-10 10:42:31.452 D/OpenCV/StaticHelper: Trying to load library opencv_java3
05-10 10:42:32.031 D/OpenCV/StaticHelper: Library opencv_java3 loaded
05-10 10:42:32.031 D/OpenCV/StaticHelper: First attempt to load libs is OK
05-10 10:42:32.045 I/OpenCV/StaticHelper: General configuration for OpenCV 3.2.0 =====================================
05-10 10:42:32.045 I/OpenCV/StaticHelper:   Version control:               3.2.0
05-10 10:42:32.045 I/OpenCV/StaticHelper:   Platform:
05-10 10:42:32.045 I/OpenCV/StaticHelper:     Timestamp:                   2016-12-23T13:04:49Z
05-10 10:42:32.045 I/OpenCV/StaticHelper:     Host:                        Linux 4.8.0-25-generic x86_64
05-10 10:42:32.045 I/OpenCV/StaticHelper:     Target:                      Linux 1 x86_64
05-10 10:42:32.045 I/OpenCV/StaticHelper:     CMake:                       2.8.12.2
05-10 10:42:32.045 I/OpenCV/StaticHelper:     CMake generator:             Ninja
05-10 10:42:32.045 I/OpenCV/StaticHelper:     CMake build tool:            /usr/bin/ninja
05-10 10:42:32.045 I/OpenCV/StaticHelper:     Configuration:               Release
05-10 10:42:32.045 I/OpenCV/StaticHelper:   C/C++:
05-10 10:42:32.045 I/OpenCV/StaticHelper:     Built as dynamic libs?:      NO
05-10 10:42:32.045 I/OpenCV/StaticHelper:     C++ Compiler:                /usr/bin/ccache /opt/android/android-ndk-r10e/toolchains/x86_64-4.9/prebuilt/linux-x86_64/bin/x86_64-linux-android-g++ (ver 4.9)

How to compile and share two c++ libraries on an android build using CMake

the error you get is telling you that it cannot find opencv include file:

#include <opencv2/core.hpp>

you need to locate the opencv2 folder, and pass it to cmake as an additional include directory:

https://cmake.org/cmake/help/v3.0/command/include_directories.html

example: Adding OpenCV to Native C code through CMake on Android Studio

cmake_minimum_required(VERSION 3.4.1)
set(OpenCV_DIR "src/sdk/native/jni")
find_package(OpenCV REQUIRED)
message(STATUS "OpenCV libraries: ${OpenCV_LIBS}")
include_directories(${OpenCV_INCLUDE_DIRS})

or you can use this approach:
https://github.com/ahasbini/Android-OpenCV/blob/master/app/CMakeLists.txt

How to add native OpenCV in Android Studio 3.1.2?

This problem is being tracked on OpenCV GitHub: OpenCV doesn't link on Android x86/x86_64 with ndk 16.0.4442984 with R_386_GOTOFF error (closed).

TL;NR: the prebuilt binaries of OpenCV-android-sdk, and in particular the x86/libippicv.a, is not compatible with the latest NDK r16. The easiest workaround is to use an older NDK version. If you cannot, the patch which excludes libippicv.a should do the job:

set(CMAKE_SHARED_LINKER_FLAGS "${CMAKE_SHARED_LINKER_FLAGS} -Wl,--exclude-libs,libippicv.a -Wl,--exclude-libs,libippiw.a")

CMake error while adding opencv 4.5.2 into my android studio project

The key is "not" to rename the sdk folder. It is because OpenCV hardcoded the path with the name of “sdk” in the native/jni/OpenCVConfig.cmake.

How can I integrate OpenCV 4.0 into a pure C++ Android NDK project?

1. Download opencv Android package (e.g. opencv-4.0.1-android-sdk) and unpack to, say, ~/android.

2. To the bottom of CMakeLists.txt, add

   set( OpenCV_DIR "~/android/OpenCV-android-sdk/sdk/native/jni" )
   find_package( OpenCV REQUIRED )
   target_link_libraries(game opencv_java)
   

The package will define the following variables:

OpenCV_LIBS : The list of all imported targets for OpenCV modules.

OpenCV_INCLUDE_DIRS : The list of OpenCV include directories. With CMake >= 2.8.11 you don't even need to write

include_directories(${OpenCV_INCLUDE_DIRS})

This version of prebuilt OpenCV SDK defines also

OpenCV_VERSION : The version of this OpenCV build: "4.0.1"

OpenCV_ANDROID_NATIVE_API_LEVEL : Minimum required level of Android API: "16".

This means that your app manifest needs minSdkVersion 16 or higher (the original sample needs a fix here).

Instead of the shared library that contains all OpenCV functionality, you can use static libraries (opencv_imgcodecs, opencv_stitching, et al). These static libraries assume the default ANDROID_STL=c++_static.

For best results, use NDK r.18 or r.19.

UPDATE: NDK r.21 works well for opencv 4.3.0.

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