Problem: ArrayIndexOutOfBoundsException while reading PNG image

Question

Hi all!
I have a problem I hope you can help me with.
I'm getting an ArrayIndexOutOfBoundsException when I try to do an ImageIO.read() on a particular PNG file. The file loads fine in a browser and I have examined the file and cannot find any faults in it although there may be.
Is it possible the PNGImageReader is broken?
I'd really appreciate any hint on what I can do to fix the problem.
I am using Java HotSpot(TM) Client VM (build 1.4.0-b92, mixed mode).
Offending code:
void imageCmd(DataInputStream imageData) throws IOException {
Image newImage;
newImage = ImageIO.read(imageData);
Stacktrace of the exception:
java.lang.ArrayIndexOutOfBoundsException
     at com.sun.imageio.plugins.png.PNGImageReader.parse_PLTE_chunk(PNGImageReader.java:347)
     at com.sun.imageio.plugins.png.PNGImageReader.readMetadata(PNGImageReader.java:635)
     at com.sun.imageio.plugins.png.PNGImageReader.readImage(PNGImageReader.java:1309)
     at com.sun.imageio.plugins.png.PNGImageReader.read(PNGImageReader.java:1530)
     at javax.imageio.ImageIO.read(ImageIO.java:1315)
     at javax.imageio.ImageIO.read(ImageIO.java:1203)
     at CFclient.imageCmd(CFclient.java:1126)
     at CFclient.evalSrvCmd(CFclient.java:1248)
     at ServerCon.readLine(ServerCon.java:105)
     at CFclient.readFromServer(CFclient.java:1217)
     at ReadServerLoop.run(CFclient.java:68)
The image can be found at
http://www.enus-quest.net/images/errorImage2545.png

Answer 1

How many colours are in the palette of your optimized PNG? I've also been having the same problem and I think I've narrowed down the cause. It seems that com.sun.imageio.plugins.png.PNGImageReader can't cope with PNGs with optimized palettes that have between 3 and 8 colours (inclusive).
This is the code in PNGImageReader::parse_PLTE_chunk which appears to be at the root of the problem:
        int paletteEntries;
        if (numEntries > 16) {
            paletteEntries = 256;
        } else if (numEntries > 8) {
            paletteEntries = 16;
        } else if (numEntries > 2) {
            paletteEntries = 4;
        } else {
            paletteEntries = 2;
        }It looks as though it might be missing a couple of lines:
       } else if (numEntries > 4) {
            paletteEntries =8;
       } All the PNGs I've tried that have 1, 2 or 9+ colours in their palette work without the exception being thrown.