Shows the camera view in fullscreen in gray. The color convertion done with native C++ OpenCV code.
Useful when creating a new project.

1. Download OpenCV for Android pack. Unzip to C:/ (or your opencv path)

2. New Android project with C++ support.

3. New->Import module: path: C:/OpenCV-android-sdk/sdk/java (or your opencv path/OpenCV-android-sdk/sdk/java)

4. Go to File->Project Structure. On the left, select app. On the top, select Dependencies. Add new Module dependency and select openCVLibrary.

5. App build gradle and OpenCV build gradle should have the same: compileSdkVersion buildToolsVerion minSdkVersion and targetSdkVersion.

6. Create new directory in the your project path/src/main folder named "jniLibs".

7. Copy into jniLibs all the folders (arm64-v8a,armeabi,etc.) from C:/OpenCV-android-sdk/sdk/native/libs (or your opencv path/OpenCV-android-sdk/sdk/java)

8. Modify CMakeLists.txt with the following lines: To the beginning:

    set(pathToOpenCV C:\\OpenCV-android-sdk (or *your opencv path*))
    set(pathToProject *your project path*)
   

   After "cmake_minimum_requires":

    #Two sets suggested by Bruno Alexandre Krinski 20160825
    set(CMAKE VERBOSE MAKEFILE on)
    set(CMAKE CXX FLAGS "{CMAKE CXX FLAGS} -std=gnu++11")
    
    include_directories(${pathToOpenCV}\\sdk\\native\\jni\\include)
   

   After "add_library":

    # Adding OpenCV
    add_library(lib_opencv SHARED IMPORTED)
    set_target_properties(lib_opencv PROPERTIES IMPORTED_LOCATION ${pathToProject}\\app\\src\\main\\jniLibs\\${ANDROID_ABI}\\libopencv_java3.so)
   

   Modify last command "target_link_libraries" to:

    target_link_libraries( # Specifies the target library.
                   native-lib
    
                   # Links the target library to the log library
                   # included in the NDK.
                   ${log-lib}
    
                    lib_opencv )
   

9. Try to Sync and Compile.

https://stackoverflow.com/questions/38958876/can-opencv-for-android-leverage-the-standard-c-support-to-get-native-build-sup
https://www.youtube.com/watch?v=Z2vrioEr9OI
https://www.youtube.com/watch?v=0fdIiOqCz3o