I need to install opencv and use it via java in Maven+IntelliJ (on Windows and macOS/OSX).

Question

I need to install opencv and use it via java in Maven+IntelliJ (on Windows and macOS/OSX). What is the "standard" or easy way?

Answer 1

I googled extensively and did look at How to use OpenCV with IntelliJ IDEA 12. Here is what worked for me and it looks simple enough. Please comment if there is a "better" and/or "standard" way. Wish list: I would like to be able to remove opencv easily from my computer if not needed anymore (some of my laptops run out of disk space).

The following is done on macOS Sierra (10.12.1)

Step1: download and install opencv via command-line (i.e. Terminal on macOS/OSX): see http://docs.opencv.org/2.4/doc/tutorials/introduction/linux_install/linux_install.html

UPDATE 17-Nov-2016: http://docs.opencv.org/3.0-beta/doc/tutorials/introduction/linux_install/linux_install.html

$ mkdir ~/dev/lib/opencv/github_opencv_161101
$ cd ~/dev/lib/opencv/github_opencv_161101
$ git clone https://github.com/opencv/opencv.git

I used ~/dev/lib/opencv/github_opencv_161101 as my install directory, so I could remove it easily if needed, and to remind myself when I installed it.

Step 2: build. Note, the last command below $ sudo make install will copy all libs to /usr/local. However, I tried to install opencv via at least two other ways (via brew and http://opencv.org/platforms/android.html), so I am not sure which libraries are which in /usr/local.

$ cd opencv
$ mkdir release
$ cd release
$ cmake -D CMAKE_BUILD_TYPE=RELEASE -D CMAKE_INSTALL_PREFIX=/usr/local .. 
$ make
$ sudo make install

Notes on used tools: You also need JavaSDK installed. My cmake is

$ cmake -version
cmake version 3.6.2

If you do not have cmake installed, use brew (or install from http://brew.sh/ )

$ brew install cmake

You may also need to install Command Line Tools not working - OS X El Capitan/ macOS-sierra via

$ xcode-select --install

Step 3: Running HelloCV.java in IntelliJ. Start IntelliJ. Create New Project. Select Maven

Continue until you get Enable auto-import!

Create new class HelloCV and type (from https://github.com/opencv-java/opencv-java-tutorials/blob/master/docs/source/02-first-java-application-with-opencv.rst):

public class HelloCV {
    public static void main(String[] args){
            System.loadLibrary(Core.NATIVE_LIBRARY_NAME);
            Mat mat = Mat.eye(3, 3, CvType.CV_8UC1);
            System.out.println("mat = " + mat.dump());
    }
}

You should get something like:

Now, finally the payload ;-) Select File->Project Structure:

Select Libraries (or Global libraries), and add java library:

From https://stackoverflow.com/a/24853043/1006226: Navigate to ~/dev/lib/opencv/github_opencv_161101/opencv/release/bin in my case, or ~/path_to_your_dir/opencv/release/bin.

You can now compile and run your HelloCV.java:

import org.opencv.core.Core;
import org.opencv.core.CvType;
import org.opencv.core.Mat;

public class HelloCV {
    public static void main(String[] args){
        System.loadLibrary(Core.NATIVE_LIBRARY_NAME);
        Mat mat = Mat.eye(3, 3, CvType.CV_8UC1);
        System.out.println("mat = " + mat.dump());
    }
}

But you will get the following runtime error:

Exception in thread "main" java.lang.UnsatisfiedLinkError: no opencv_java310 in java.library.path
    at java.lang.ClassLoader.loadLibrary(ClassLoader.java:1864)
    at java.lang.Runtime.loadLibrary0(Runtime.java:870)
    at java.lang.System.loadLibrary(System.java:1122)
    at org.dak.HelloCV.main(HelloCV.java:9)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:497)
    at com.intellij.rt.execution.application.AppMain.main(AppMain.java:144)

Process finished with exit code 1

Go back to Menu->File->Project Structure, select Libraries and add ~/dev/lib/opencv/github_opencv_161101/opencv/release/lib in my case, or ~/path_to_your_dir/opencv/release/lib

Now, you are linked to the native libs via JNI. Run HelloCV and you should get:

mat = [  1,   0,   0;
   0,   1,   0;
   0,   0,   1]

Process finished with exit code 0