Tutorial: Setting Up OpenCV for Android

Hey everyone,
Welcome!
My goal with this tutorial is to make it super easy for you to create an Android application using the OpenCV library.

Before we dive in, it’s helpful to check the tool versions I used to avoid any compatibility issues.

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Tools Version

OS: Windows 10

Getting Started

First things first—download these:

• OpenCV Android SDK
• Android NDK (Native Development Kit)

Extract the Files

• Extract the NDK to a directory without spaces in the path, e.g. C:\work\android-ndk-r12b
• Extract the OpenCV SDK to a location near the NDK (though its exact location doesn’t really matter)

Setting Up Environment Variables (Java & NDK)

1. Right-click This PC → Properties → click Advanced system settings
2. In the window that appears, go to the Advanced tab and click Environment Variables
3. Under User variables, find the PATH variable and click Edit
4. Click New, then add the path to your Java bin folder
   Example: C:\Program Files\Java\jdk1.8.0_40\bin\
5. Add the NDK root path in the same way
   Example: C:\work\android-ndk-r12b
6. Done!

Installing CMake (Required for Native Code)

1. Open Android Studio and go to Settings
2. Navigate to Appearance & Behavior → System Settings → Android SDK
3. Go to the SDK Tools tab and make sure CMake is checked and installed
   If it’s not, check it and click Apply

Creating Your Android Project

Let’s build your first project:

1. Open Android Studio → click New Project
2. Fill in the Application Name and Company Domain
3. Important: Check the box for Include C++ Support
4. Proceed with the default settings
   On the final screen before clicking Finish, set the C++ standard. I recommend using Toolchain Default

Note:
If you encounter this error:
Error: NDK not configured. Download it with SDK manager.
Follow these steps:

• Go to File → Project Structure
• Set the correct NDK path under Android NDK location

Import the OpenCV Java Module

1. Go to File → New → Import Module
2. Navigate to {YOUR_OPENCV_SDK_DIR}\sdk\ and select the java folder
3. Click OK, then Next, then Finish
4. Open your app-level build.gradle file and add this under dependencies:

implementation project(':openCVLibrary320')

openCVLibrary320 is the default module name. Yours might differ depending on the SDK version.

Add jniLibs Folder

1. Right-click the app module → New → Folder → JNI Folder
2. Check Change Folder Location
3. Change the directory from src/main/jni/ to src/main/jniLibs/
4. Click Finish

Add Native Libraries

You’ll need native libraries for each processor architecture you want to support. Luckily, OpenCV provides them all!

• They’re located in \sdk\native\libs inside the OpenCV SDK
• Copy only the folders you need (or all of them) into your project’s jniLibs directory

Pro tip: Only include the architectures you plan to support to reduce app size.

Create and Configure Android.mk

1. Inside jniLibs, create a new file named Android.mk
2. Add the following content:

LOCAL_PATH := $(call my-dir)
include $(CLEAR_VARS)
OPENCV_LIB_TYPE := SHARED
OPENCV_CAMERA_MODULES := on
OPENCV_INSTALL_MODULES := on
include {OpenCV.mk_DIR}
LOCAL_SRC_FILES  := native-lib.cpp
LOCAL_C_INCLUDES += {INCLUDE_DIR}
LOCAL_LDLIBS     += -llog -ldl
LOCAL_CFLAGS     += -DOPENCV_OLDER_VERSION
LOCAL_CPP_FEATURES += exceptions
LOCAL_CPPFLAGS += -fexceptions
LOCAL_MODULE     := native-lib
include $(BUILD_SHARED_LIBRARY)

Notes:

• {OpenCV.mk_DIR} → path to OpenCV.mk, usually:
  \sdk\native\jni\OpenCV.mk
• {INCLUDE_DIR} → path to OpenCV’s include directory:
  \sdk\native\jni\include
• LOCAL_MODULE → name of your native C++ source file (native-lib.cpp)

Optional Configs:

• OPENCV_CAMERA_MODULES and OPENCV_INSTALL_MODULES:
  Set to off if you want the app to require the OpenCV Manager app on the user’s device

That’s It!

You’re now all set to start building your Android OpenCV app with native C++ support.