v4lvj drawing lines on top of webcam image

Question

I am following a tutorial on the v4lvj library that allows access to webcams on a linux. link to source I wrote the example program that basically displays the video feed of your webcamera. Everything works just as the program described. The problem comes in when I try to alter the program by adding a green line ontop of the video feed. I simply grab the graphics the same way, set the line color and then draw the line.

@Override
        public void nextFrame(VideoFrame frame) {
                // This method is called when a new frame is ready.
                // Don't forget to recycle it when done dealing with the frame.

                // draw the new frame onto the JLabel
                label.getGraphics().drawImage(frame.getBufferedImage(), 0, 0, width, height, null);
                label.getGraphics().setColor(Color.GREEN); //this line causes exceptions
                label.getGraphics().drawLine(0, 0, 640, 480); //this line causes exceptions 

                // recycle the frame
                frame.recycle();
        }

When I do that though, I get some exceptions preceded by "It seems your JVM is unable to decode this image. Supported image types: BMP bmp jpg JPG..." and then

javax.imageio.IIOException: Unsupported marker type 0x5a
    at com.sun.imageio.plugins.jpeg.JPEGImageReader.readImage(Native Method)
    at com.sun.imageio.plugins.jpeg.JPEGImageReader.readInternal(JPEGImageReader.java:1176)
    at com.sun.imageio.plugins.jpeg.JPEGImageReader.read(JPEGImageReader.java:984)
    at javax.imageio.ImageIO.read(ImageIO.java:1438)
    at javax.imageio.ImageIO.read(ImageIO.java:1342)
    at au.edu.jcu.v4l4j.JPEGVideoFrame.refreshBufferedImage(Unknown Source)
    at au.edu.jcu.v4l4j.BaseVideoFrame.getBufferedImage(Unknown Source)
    at SimpleViewer.nextFrame(SimpleViewer.java:143)
    at au.edu.jcu.v4l4j.PushSource.run(Unknown Source)
    at java.lang.Thread.run(Thread.java:679)
au.edu.jcu.v4l4j.exceptions.V4L4JException: Exception received while grabbing next frame
    at au.edu.jcu.v4l4j.PushSource.run(Unknown Source)
    at java.lang.Thread.run(Thread.java:679)
Caused by: au.edu.jcu.v4l4j.exceptions.UnsupportedMethod: Unable to decode the image
    at au.edu.jcu.v4l4j.JPEGVideoFrame.refreshBufferedImage(Unknown Source)
    at au.edu.jcu.v4l4j.BaseVideoFrame.getBufferedImage(Unknown Source)
    at SimpleViewer.nextFrame(SimpleViewer.java:143)
    ... 2 more
Caused by: javax.imageio.IIOException: Unsupported marker type 0x5a
    at com.sun.imageio.plugins.jpeg.JPEGImageReader.readImage(Native Method)
    at com.sun.imageio.plugins.jpeg.JPEGImageReader.readInternal(JPEGImageReader.java:1176)
    at com.sun.imageio.plugins.jpeg.JPEGImageReader.read(JPEGImageReader.java:984)
    at javax.imageio.ImageIO.read(ImageIO.java:1438)
    at javax.imageio.ImageIO.read(ImageIO.java:1342)
    ... 5 more

Could anyone tell me why and help me draw a line ontop of a video feed. Thank you.

Answer 1

You should do your painting by overriding paint(Graphics g) method of JLabel, then do a cast Graphics2D g2d = (Graphics2D) g; and use Graphics2D for painting.

It is incorrect way you use JLabel in your code.

You could use also BufferedImage you received from frame, get their Graphics and draw on it