[JAVA2D] Please help - very strange Image I/O problem

[John Donahue]

I am trying to use Image I/O to load some PNG images in an applet.  The
first time the applet calls the method that loads images, it works fine.
But every time this method is called after that, I get strange
IIOExceptions thrown.  I am using the JRE 1.4 release candidate VM.

Here is an example of the exceptions I get-

javax.imageio.IIOException: Unknown row filter type (= 255)!
     at com.sun.imageio.plugins.png.PNGImageReader.decodePass(Unknown Source)
     at com.sun.imageio.plugins.png.PNGImageReader.decodeImage(Unknown Source)
     at com.sun.imageio.plugins.png.PNGImageReader.readImage(Unknown Source)
     at com.sun.imageio.plugins.png.PNGImageReader.read(Unknown Source)
     at javax.imageio.ImageIO.read(Unknown Source)
     at javax.imageio.ImageIO.read(Unknown Source)
     at com.pfpc.checkimage.applet.CheckImageApplet$1.run(CheckImageApplet.java:94)
     at java.lang.Thread.run(Unknown Source)

javax.imageio.IIOException: Unknown row filter type (= 221)!
     at com.sun.imageio.plugins.png.PNGImageReader.decodePass(Unknown Source)
     at com.sun.imageio.plugins.png.PNGImageReader.decodeImage(Unknown Source)
     at com.sun.imageio.plugins.png.PNGImageReader.readImage(Unknown Source)
     at com.sun.imageio.plugins.png.PNGImageReader.read(Unknown Source)
     at javax.imageio.ImageIO.read(Unknown Source)
     at javax.imageio.ImageIO.read(Unknown Source)
     at com.pfpc.checkimage.applet.CheckImageApplet$1.run(CheckImageApplet.java:104)
     at java.lang.Thread.run(Unknown Source)

Here is the applet method that attempts to load the images (it is called from 
Javascript in my Web page )

    public void manipulateImages( String fbwImageName, String bbwImageName, String 
bgsImageName )
    {
        final JApplet thisApplet = this;
        final String fbwImage = fbwImageName;
        final String bbwImage = bbwImageName;
        final String bgsImage = bgsImageName;

        if ( civ != null && fbwName.equals( fbwImage ) && bbwName.equals( bbwImage ) 
&& bgsName.equals( bgsImage ) )
        { // civ is a CheckImageViewer (a JFrame that is extended to produce an image 
manipulation tool)
            civ.show();
            return;
        }
        else
        {
            fbwName = fbwImage;
            bbwName = bbwImage;
            bgsName = bgsImage;
        }

        Runnable r = new Runnable()
        {
            BufferedImage front=null, backBW=null, backGS=null;
            URL fbwURL = null, bbwURL = null, bgsURL = null;

            public void run()
            {
                thisApplet.showStatus( "loading image applet..." );

                if ( fbwImage != null )
                {
                    try
                    {
                        fbwURL = new URL( getDocumentBase(), fbwImage );
                    }
                    catch( MalformedURLException mfue1 )
                    { fbwURL = null; }
                }

                if ( bbwImage != null )
                {
                    try
                    {
                        bbwURL = new URL( getDocumentBase(), bbwImage );
                    }
                    catch( MalformedURLException mfue2 )
                    { bbwURL = null; }
                }

                if ( bgsImage != null )
                {
                    try
                    {
                        bgsURL = new URL( getDocumentBase(), bgsImage );
                    }
                    catch( MalformedURLException mfue3 )
                    { bgsURL = null; }
                }

                /* so that the applet doesn't try to write files to disk, which is a 
security violation */
                if ( ImageIO.getUseCache() )
                    ImageIO.setUseCache( false );

                //now, try to read each file if appropriate.

                if ( bbwURL != null )
                {
                    try
                    {
                        backBW = ImageIO.read( bbwURL );
                    }
                    catch( Exception e2 )
                    { backBW = null; }
                }

                if ( bgsURL != null )
                {
                    try
                    {
                        backGS = ImageIO.read( bgsURL );
                    }
                    catch( Exception e3 )
                    { backGS = null; }
                }

                if ( fbwURL != null )
                {
                    try
                    {
                        front = ImageIO.read( fbwURL );
                    }
                    catch( Exception e1 )
                    { front = null; }
                }

                if ( civ==null )
                {
                    civ = new CheckImageViewer( front, backBW, backGS );
                }
                else
                {
                    civ.replaceImages(  front, backBW, backGS );
                }

                thisApplet.showStatus( "" );
            }
        };

        Thread internalThread = new Thread( r );
        internalThread.start();

    }

The strange thing is that when this method is called the second time, it occasionally 
loads one of the images correctly, but this is a random
occurrence.  However,
if I close and restart my browser, the applet will always work fine on the next call 
to manipulateImages().

Am I doing anything wrong in my use of ImageIO.read() ?  Do I need to reset something 
between uses of the static method?

Please help me!  I'm going to get a concussion from banging my head against the wall 
:-(

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