Native OpenCV with Android Studio

This application is a sample Android Studio project with native OpenCV.

It gets the camera frames, make JNI calls with its gray matrices references as parameters, add some random noise to the images from a C++ method, and render the generated frames.

It works with Android Studio 3+

Last included OpenCV version: 3.4

Usage

Here is how to use this project to run native OpenCV code.

• Make sure you have Android SDK up to date, with NDK installed and CMake
• Download latest OpenCV SDK for Android from OpenCV.org and decompress the zip file.
• Clone this project
• Create a symlink named jniLibs in app/src/main that points to YOUR_OPENCV_SDK/sdk/native/libs
• In app/CMakeLists.txt change line 9 to points to YOUR_OPENCV_SDK/sdk/native/jni/include
• Sync gradle
• Run the application

How to create the native OpenCV project from scratch

Here is how I made this project. If you simply want to run openCV with NDK support, use the previous Usage chapter. If you want to build the full project from scratch, you can follow the steps in this chapter.

• Make sure you have Android SDK up to date, with NDK installed

• Download latest OpenCV SDK for Android from OpenCV.org and decompress the zip file.

• Create a new Android Studio project

  • Check Include C++ Support
  • Choose empty Activity
  • In C++ Support, you can check -fexceptions and -frtti

• Import OpenCV library module

  • New -> Import Module
  • Choose the YOUR_OPENCV_SDK/sdk/java folder
  • Unckeck replace jar, unckeck replace lib, unckeck create gradle-style

• Set the OpenCV library module up to fit your SDK

  Edit openCVLibrary/build.gradle to fit your SDK:

    compileSdkVersion 27
    defaultConfig {
        minSdkVersion 19
        targetSdkVersion 27
    }
  

• Add OpenCV module dependency in your app module

  File -> Project structure -> Module app -> Dependencies tab -> New module dependency -> choose OpenCV library module

• Make a symlink named jniLibs in app/src/main that points to YOUR_OPENCV_SDK/sdk/native/libs

• Set the app build.gradle

  • Add abiFilters

        externalNativeBuild {
            cmake {
                cppFlags "-frtti -fexceptions"
                abiFilters 'x86', 'x86_64', 'armeabi-v7a', 'arm64-v8a'
            }
        }
    

  • Add openCV jniLibs directory to point to the symlink

    sourceSets {
        main {
            jniLibs.srcDirs = ['src/main/jniLibs']
        }
    }
    

  See build.gradle

• Configure the CMakeLists.txt file

  • After the cmake_minimum_required, add

    include_directories(YOUR_OPENCV_SDK/sdk/native/jni/include)
    add_library( lib_opencv SHARED IMPORTED )
    set_target_properties(lib_opencv PROPERTIES IMPORTED_LOCATION ${CMAKE_CURRENT_SOURCE_DIR}/src/main/jniLibs/${ANDROID_ABI}/libopencv_java3.so)
    

  • At the end of the file add lib_opencv to the target_link_libraries list

• Grant camera permission

  • Add the following lines in the AndroidManifest.xml file

    <uses-permission android:name="android.permission.CAMERA"/>
    <uses-feature android:name="android.hardware.camera"/>
    <uses-feature android:name="android.hardware.camera.autofocus"/>
    <uses-feature android:name="android.hardware.camera.front"/>
    <uses-feature android:name="android.hardware.camera.front.autofocus"/>
    

• Add OpenCV code

  • MainActivity.java
  • activity_main.xml
  • native-lib.cpp