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Using OpenCV Java with Eclipse

, Monday, 29 July 2013
For some time OpenCV supports Java. This is a blessing, I have been waiting this for years. I am quite fond of Java, for such an old language they got lots of things right at the time (C# is better in a sense, they avoided the mistakes of Java). Anyway, here I will explain how to setup development environment for using OpenCV Java with Eclipse, so you can enjoy the benefits of garbage collected, very refactorable (rename variable, extract method and whatnot) modern language that enables you to write code with less effort and make less mistakes. Here we go.

First obtain a fresh release of OpenCV here and extract it under a simple location like C:\OpenCV-2.4.6\. I am using version 2.4.6, but the steps are more or less the same for other versions.

First we will define OpenCV as a user library in Eclipse, so we can reuse the configuration for any project. Launch Eclipse and select Window->Preferences from the menu.


Navigate under Java->Build Path->User Libraries and click New....


Enter a name, e.g. OpenCV-2.4.6, for your new library.


Now select your new user library and click "Add External JARs...".


Browse through C:\OpenCV-2.4.6\build\java\ and select opencv-246.jar. After adding the jar, extend the opencv-246.jar and select Native library location and press Edit....


Select External Folder... and browse to select the folder C:\OpenCV-2.4.6\build\java\x64. If you have a 32-bit system you need to select the x86 folder instead of x64.


Your user library configuration should look like this:


Now start creating a new Java project.


On the Java Settings step, under Libraries tab, select Add Library... and select OpenCV-2.4.6, then click Finish.




Libraries should look like this:


Now you have created and configured a new Java project it is time to test it. Create a new java file. Here is a starter code for your convenience:
import org.opencv.core.Core;
import org.opencv.core.CvType;
import org.opencv.core.Mat;

public class Hello
{
 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() );
 }
}

When you run the code you should see 3x3 identity matrix as output.


That is it, enjoy your powerful, less painful development environment :)

2 comments:

  1. Hello,

    thanks for this post.
    But when I run this code I get this error.
    Exception in thread "main" java.lang.UnsatisfiedLinkError: no opencv_java246 in java.library.path
    at java.lang.ClassLoader.loadLibrary(ClassLoader.java:1874)
    at java.lang.Runtime.loadLibrary0(Runtime.java:849)
    at java.lang.System.loadLibrary(System.java:1087)
    at Main.main(Main.java:7)

    (my OS is UBUNTU)

    Do you know where is the problem and how to fix them.
    Thanks.

    ReplyDelete
  2. There are some examples of how to capture the webcam with this api without using javacv?

    ReplyDelete