JPEG Grabber - bug in JMF???

Question

Dear all.
I am trying to use a FrameGrabbingControl to grab JPEG images from a webcam.
Every so often, the BufferToImage.createImage(buf) <see below> fails, giving a null image. After it fails once, it never recovers, it will always fail - almost like the Player gets itself into an invalid state???
FrameGrabberException is an exception class I have defined. It never gets thrown!
Many thanks, I'm really stuck with this one.
Iain A. Mcleod
import javax.media.*;
import javax.media.control.*;
import javax.media.protocol.*;
import javax.media.util.*;
import javax.media.format.*;
public class FrameGrabber extends Thread {
private Player player;
public FrameGrabber(CaptureDeviceInfo cdi, Format format){
connectToPlayer(cdi,format);
start();
    private void connectToPlayer(CaptureDeviceInfo cdi, Format format) throws FrameGrabberException{
        /*  To use this device we need a MediaLocator  */
        MediaLocator loc = cdi.getLocator();
        if (loc == null) {
            throw new FrameGrabberException("Unable to get MediaLocator for video device");
        try{
            player = Manager.createRealizedPlayer(loc);
        }catch (Exception e){
            throw new FrameGrabberException("Could not get realized player for webcam: "+e.getMessage());
        player.start();
public void run(){
while(true){
                FrameGrabbingControl fgc = (FrameGrabbingControl)player.getControl("javax.media.control.FrameGrabbingControl");
                Buffer buf = fgc.grabFrame();
                // Convert it to an image
                BufferToImage btoi = new BufferToImage((VideoFormat)buf.getFormat());
                Image img = btoi.createImage(buf);
//FOR SOME REASON, IMG IS NULL HERE SOMETIMES???
                processImage(img);
try{Thread.sleep(1000);}
catch(InterruptedException ie) {ie.printStackTrace();}
public void processImage (Image img){
//STUB
}

Answer 1

As nobody answered to your question yet, I am just telling about another possibility to connect to a camera from a java application. The Morena Image Acquisition Frame is a commmercial package (with a trial version) http://www.gnome.sk, which enables you to connect to a camera or scanner from a java application in a very intuitive way. It can help much if you do not need to display live video or get many images in a short time interval.
If you just want to see how Morena works with your scanner or camera:
- java (1.2 or higher for Windows, 1.3 or higher for Mac OS X) has to be installed on your computer
- a scanner or camera has to be installed on your computer
- download the trial package from http://www.gnome.sk
- unzipp it
- go to the examples directory of the unzipped package
- in Windows: doubleclick the runExampleShow.bat
- in MacOS:
    - open the Terminal window
    - change the working directory to the examples
    - run .sh file (type ExampleShow.sh or sh ExampleShow.sh)
This will pop up the Twain Source Selection user interface. There, all your scanners and cameras which do have a twain driver should be listed. (About 90% of scanners and cameras on the market do have a twain driver for Windows, only a few do have a twain driver for MacOS.) Select one of them. The user interface of the selected scanner (camera) will appear. Confirm the scanning (you can set the scanning parameters first). The scanned image will be displayed in a separate window. To end the application, close that window.
Running different examples, you can test scanning with hidden UI, saving the scanned image, using ADF, taking images at regular intervals (ExampleCamera) ...
If there is any problem, do not hesitate to inquire about it at the technical support, email: [email protected] .