Creating windows and capturing webcam with Java and OpenCV

As we saw here, we can load a picture and display it, all in java. Now we want to use OpenCV for some of this so that we can apply some signal processing to the image down the road... The trick is explained here... Basically how to "cast" the image from OpenCV (in Mat) in an Image object that works with drawImage.We found some answers in the topic but nothing was too clear:

1. Android has a library that allows from Bitmap to Mat and viceversa: org.opencv.android.Utils. This probably would work for us as finally we want to run this on Android, but still, not for the time being (we are in PC...).
2. http://stackoverflow.com/questions/14958643/converting-bufferedimage-to-mat-in-opencv
3. http://stackoverflow.com/questions/15670933/opencv-java-load-image-to-gui

Did a further search for "java opencv convert mat into image -android -IplImage" and got this two that match:

1. http://answers.opencv.org/question/10344/opencv-java-load-image-to-gui/
2. http://enfanote.blogspot.com/2013/06/converting-java-bufferedimage-to-opencv.html

That solved! Geeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee!! Somehow, seems to be done by hand conversion, which is not very nice, but looks like there is not library call for this...

UPDATE: please see the code on the first comment below, that ngeen left. I have not tried it in here, but I used it in this other example and it works nicely!!
UPDATE2: triggered by another nice way to do this Mat to BufferedImage conversion, I decided to benchmark all these methods. See here this post for the results.

 // Import the basic graphics classes.  
 // The problem here is that we read the image with OpenCV into a Mat object.  
 // But OpenCV for java doesn't have the method "imshow", so, we got to use  
 // java for that (drawImage) that uses Image or BufferedImage (?)  
 // So, how to go from one the other...  
 import java.awt.*;  
 import java.awt.image.BufferedImage;  
 import javax.swing.*;  
 //import org.opencv.core.Core;  
 import org.opencv.core.Mat;  
 import org.opencv.highgui.Highgui;  
 public class Panel extends JPanel{  
   private static final long serialVersionUID = 1L;  
   String pic_name="resources/DSC01638.jpg";  
   Mat picture;  
   BufferedImage image;  
   /**  
    * Converts/writes a Mat into a BufferedImage.  
    *  
    * @param matrix Mat of type CV_8UC3 or CV_8UC1  
    * @return BufferedImage of type TYPE_3BYTE_BGR or TYPE_BYTE_GRAY  
    */  
   public static BufferedImage matToBufferedImage(Mat matrix) {  
     int cols = matrix.cols();  
     int rows = matrix.rows();  
     int elemSize = (int)matrix.elemSize();  
     byte[] data = new byte[cols * rows * elemSize];  
     int type;  
     matrix.get(0, 0, data);  
     switch (matrix.channels()) {  
       case 1:  
         type = BufferedImage.TYPE_BYTE_GRAY;  
         break;  
       case 3:  
         type = BufferedImage.TYPE_3BYTE_BGR;  
         // bgr to rgb  
         byte b;  
         for(int i=0; i<data.length; i=i+3) {  
           b = data[i];  
           data[i] = data[i+2];  
           data[i+2] = b;  
         }  
         break;  
       default:  
         return null;  
     }  
     BufferedImage image = new BufferedImage(cols, rows, type);  
     image.getRaster().setDataElements(0, 0, cols, rows, data);  
     return image;  
   }  
   // Create a constructor method  
   public Panel(){  
     super(); // Calls the parent constructor  
     picture = Highgui.imread(pic_name);  
     // Got to cast picture into Image  
     image=matToBufferedImage(picture);  
   }  
   public void paintComponent(Graphics g){  
      g.drawImage(image,50,10,400,400, this);  
   }  
   public static void main(String arg[]){  
    // Load the native library.  
    System.loadLibrary("opencv_java245");    
    JFrame frame = new JFrame("BasicPanel");  
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);  
    frame.setSize(400,400);  
    Panel panel = new Panel();  
    frame.setContentPane(panel);       
    frame.setVisible(true);           
  }  
 }  

Then, we want to display the webcam. So, not read from file...

 // Import the basic graphics classes.  
 // The problem here is that we read the image with OpenCV into a Mat object.  
 // But OpenCV for java doesn't have the method "imshow", so, we got to use  
 // java for that (drawImage) that uses Image or BufferedImage.  
 // So, how to go from one the other... Here is the way...  
 import java.awt.*;  
 import java.awt.image.BufferedImage;  
 import javax.swing.*;  
 import org.opencv.core.Mat;  
 import org.opencv.highgui.VideoCapture;  
 public class Panel extends JPanel{  
   private static final long serialVersionUID = 1L;  
   private BufferedImage image;  
   // Create a constructor method  
   public Panel(){  
     super();  
   }  
   private BufferedImage getimage(){  
     return image;  
   }  
   private void setimage(BufferedImage newimage){  
     image=newimage;  
     return;  
   }  
   /**  
    * Converts/writes a Mat into a BufferedImage.  
    *  
    * @param matrix Mat of type CV_8UC3 or CV_8UC1  
    * @return BufferedImage of type TYPE_3BYTE_BGR or TYPE_BYTE_GRAY  
    */  
   public static BufferedImage matToBufferedImage(Mat matrix) {  
     int cols = matrix.cols();  
     int rows = matrix.rows();  
     int elemSize = (int)matrix.elemSize();  
     byte[] data = new byte[cols * rows * elemSize];  
     int type;  
     matrix.get(0, 0, data);  
     switch (matrix.channels()) {  
       case 1:  
         type = BufferedImage.TYPE_BYTE_GRAY;  
         break;  
       case 3:  
         type = BufferedImage.TYPE_3BYTE_BGR;  
         // bgr to rgb  
         byte b;  
         for(int i=0; i<data.length; i=i+3) {  
           b = data[i];  
           data[i] = data[i+2];  
           data[i+2] = b;  
         }  
         break;  
       default:  
         return null;  
     }  
     BufferedImage image2 = new BufferedImage(cols, rows, type);  
     image2.getRaster().setDataElements(0, 0, cols, rows, data);  
     return image2;  
   }  
   public void paintComponent(Graphics g){  
      BufferedImage temp=getimage();  
      g.drawImage(temp,10,10,temp.getWidth(),temp.getHeight(), this);  
   }  
   public static void main(String arg[]){  
    // Load the native library.  
    System.loadLibrary("opencv_java245");    
    JFrame frame = new JFrame("BasicPanel");  
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);  
    frame.setSize(400,400);  
    Panel panel = new Panel();  
    frame.setContentPane(panel);       
    frame.setVisible(true);       
    Mat webcam_image=new Mat();  
    BufferedImage temp;  
    VideoCapture capture =new VideoCapture(0);  
    if( capture.isOpened())  
     {  
      while( true )  
      {  
        capture.read(webcam_image);  
        if( !webcam_image.empty() )  
         {  
           frame.setSize(webcam_image.width()+40,webcam_image.height()+60);  
           temp=matToBufferedImage(webcam_image);  
           panel.setimage(temp);  
           panel.repaint();  
         }  
         else  
         {  
           System.out.println(" --(!) No captured frame -- Break!");  
           break;  
         }  
        }  
       }  
       return;  
   }  
 }  

And as we are here, let's finish with the tracking of face and eyes... Tomorrow :)
PS.: Click here to see the index of these series of posts on OpenCV