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Create transparent GIF with JAI

Posted on 2006-12-01
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Last Modified: 2008-01-09
Hello,
I'm trying to create a transparent GIF with JAI:

  private static void createImage(BufferedImage argBufferedImage, String argFileName) {
    ImageWriter gifWriter = null;
    IIOImage iioImage = null;
    IIOMetadata iioMetadata = null;

    IIOMetadataNode gifMetadataNode = null;
    IIOMetadataNode tmpNode = null;

    gifWriter = (ImageWriter) ImageIO.getImageWritersByFormatName("gif").next();
    try {
      gifWriter.setOutput(ImageIO.createImageOutputStream(new File(argFileName)));
      iioMetadata = gifWriter.getDefaultImageMetadata(new ImageTypeSpecifier(argBufferedImage), null);
      gifMetadataNode = (IIOMetadataNode) iioMetadata.getAsTree("javax_imageio_gif_image_1.0");
      tmpNode = (IIOMetadataNode) gifMetadataNode.getElementsByTagName("GraphicControlExtension").item(0);
      tmpNode.setAttribute("transparentColorIndex", "0");
      tmpNode.setAttribute("transparentColorFlag", "true");
      iioMetadata.setFromTree("javax_imageio_gif_image_1.0", gifMetadataNode);
      iioImage = new IIOImage(argBufferedImage, null, iioMetadata);
      gifWriter.write(iioImage);
      gifWriter.dispose();
    } catch (Exception e) {
      System.out.println("ex:" + e);
    }
  }

Unfortunately my code doesn't work. Any recommendations?
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Question by:egono
14 Comments
 
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Expert Comment

by:sciuriware
ID: 18055718
Any error messages?

;JOOP!
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Author Comment

by:egono
ID: 18055801
No - the background color is just not set transparent.

I get a

java.lang.NullPointerException
      at com.sun.media.imageioimpl.common.PaletteBuilder.findPaletteEntry(PaletteBuilder.java:349)
      at com.sun.media.imageioimpl.common.PaletteBuilder.getIndexColorModel(PaletteBuilder.java:335)
      at com.sun.media.imageioimpl.common.PaletteBuilder.getIndexedImage(PaletteBuilder.java:184)
      at com.sun.media.imageioimpl.common.PaletteBuilder.createIndexedImage(PaletteBuilder.java:116)
      at com.sun.media.imageioimpl.plugins.gif.GIFImageWriter.write(GIFImageWriter.java:602)
      at com.sun.media.imageioimpl.plugins.gif.GIFImageWriter.write(GIFImageWriter.java:530)
      at javax.imageio.ImageWriter.write(ImageWriter.java:573)

if I want to create a complete transparent gif. But this seems to be a known bug: http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6287936
Again - the NPE is *not* my problem.

regards
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Expert Comment

by:girionis
ID: 18060171
Can you try to upgrade/downgrade the library?
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Author Comment

by:egono
ID: 18067046
girionis - I could try this, but the environment is given because the jai libs are used for other things too.

the question is: is my code the right way to create a transparent gif?
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Expert Comment

by:girionis
ID: 18067127
Not sure tbh. But the exception you get means that something is not loaded up properly so I guess there is a problem either with some sort fo configuration or with the package itself.
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Author Comment

by:egono
ID: 18067178
girionis - no the exception is a know bug for complete transparent images, and again this is not my problem.

maybe I should change my question into: How to create a transparent gif with JAI?
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Expert Comment

by:girionis
ID: 18067210
This link: http://www.esri.com/software/arcexplorer/about/ae9_faq.html states that this is a limitation. Maybe you can create a transparent PNG and then convert it to GIF?
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by:egono
ID: 18067234
some more info. here is how I create my BufferedImage:

        bufferedImage = new BufferedImage(argWidth, argHeight, BufferedImage.TYPE_INT_ARGB);

        graphics2D = bufferedImage.createGraphics();
        if (colorIdx == 0) {
          graphics2D.setBackground(Color.WHITE);
        } else {
          graphics2D.setBackground(Color.BLACK);
        }
        graphics2D.clearRect(0, 0, argWidth, argHeight);
        graphics2D.setColor(Color.BLUE);
        graphics2D.fillRect(0, 0, 10, 10);
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Author Comment

by:egono
ID: 18067256
girionis - I'm not displaying the gif with jai, I just want to save it (I'm using Paint.Net to view it)
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Expert Comment

by:girionis
ID: 18067369
If you just want to save it just use one of the usual output stream methods that write the binary data on the disk. But I guess the problem is that the image is not what you want and therefore before you save it you need it to be transparent. Not sure how exactly you can do it, but from a quick search on jai-interest archives I found the following URL for GIF files: http://archives.java.sun.com/cgi-bin/wa?A2=ind9902&L=jai-interest&P=R5968&I=-3

You might also want to try this: http://archives.java.sun.com/cgi-bin/wa?S1=jai-interest and do a search for "GIF encoding".
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Author Comment

by:egono
ID: 18174435
Now here is a working solution. The trick is to use a IndexColorModel for the image. The createColorModel() method should create the desired color model, in my case a model with just 2 colors (first one is black).

create the image with

[...]
          bufferedImage = new BufferedImage(argWidth, argHeight, BufferedImage.TYPE_BYTE_INDEXED,                                             createColorModel(COLORS[colorIdx]));
[...]


private static IndexColorModel createColorModel(Color argColor) {
    IndexColorModel result = null;
    result = new IndexColorModel(1, 2,
                                 new byte[] {0, (byte)argColor.getRed()},
                                 new byte[] {0, (byte)argColor.getGreen()},
                                 new byte[] {0, (byte)argColor.getBlue()},
                                 0);
    return result;
 }

  private static void createImage(BufferedImage argBufferedImage, String argFileName) {
    ImageWriter gifWriter = null;
    IIOImage iioImage = null;
    IIOMetadata iioMetadata = null;
    gifWriter = (ImageWriter) ImageIO.getImageWritersByFormatName("gif").next();
    try {
      gifWriter.setOutput(ImageIO.createImageOutputStream(new File(argFileName)));
      iioMetadata = gifWriter.getDefaultImageMetadata(new ImageTypeSpecifier(argBufferedImage), null);
      iioImage = new IIOImage(argBufferedImage, null, iioMetadata);
      gifWriter.write(iioImage);
    } catch (Exception e) {
      System.out.println("ex:" + e);
    }

  }


that's it :-)
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Expert Comment

by:girionis
ID: 18185742
Fine by me.
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Accepted Solution

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DarthMod earned 0 total points
ID: 18221518
PAQd, 500 points refunded.

DarthMod
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