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    <p>It is an interesting question... It is late, I will experiment tomorrow. I will first try and use a BufferedImage.TYPE_BYTE_INDEXED (perhaps after drawing) to see if Java is smart enough to generate an 8bit PNG.<br> Or perhaps some image library can allow that.</p> <p>[EDIT] Some years later... Actually, I made the code at the time, but forgot to update this thread... I used <a href="http://gman.eichberger.de/2007/07/transparent-gifs-in-java.html" rel="nofollow noreferrer">the code pointed at by Kat</a>, with a little refinement on the handling of transparency, and saving in PNG format instead of Gif format. It works in making a 8-bit PNG file with all-or-nothing transparency.</p> <p>You can find a working test file at <a href="http://bazaar.launchpad.net/~philho/+junk/Java/view/head:/Tests/src/org/philhosoft/tests/image/AddTransparency.java" rel="nofollow noreferrer">http://bazaar.launchpad.net/~philho/+junk/Java/view/head:/Tests/src/org/philhosoft/tests/image/AddTransparency.java</a> using my <a href="http://bazaar.launchpad.net/~philho/+junk/Java/view/head:/Utilities/src/org/philhosoft/util/ImageUtil.java" rel="nofollow noreferrer">ImageUtil</a> class.</p> <p>Since the code isn't that big, for posterity sake, I post it here, without the JavaDoc to save some lines.</p> <pre><code>public class ImageUtil { public static int ALPHA_BIT_MASK = 0xFF000000; public static BufferedImage imageToBufferedImage(Image image, int width, int height) { return imageToBufferedImage(image, width, height, BufferedImage.TYPE_INT_ARGB); } public static BufferedImage imageToBufferedImage(Image image, int width, int height, int type) { BufferedImage dest = new BufferedImage(width, height, type); Graphics2D g2 = dest.createGraphics(); g2.drawImage(image, 0, 0, null); g2.dispose(); return dest; } public static BufferedImage convertRGBAToIndexed(BufferedImage srcImage) { // Create a non-transparent palletized image Image flattenedImage = transformTransparencyToMagenta(srcImage); BufferedImage flatImage = imageToBufferedImage(flattenedImage, srcImage.getWidth(), srcImage.getHeight(), BufferedImage.TYPE_BYTE_INDEXED); BufferedImage destImage = makeColorTransparent(flatImage, 0, 0); return destImage; } private static Image transformTransparencyToMagenta(BufferedImage image) { ImageFilter filter = new RGBImageFilter() { @Override public final int filterRGB(int x, int y, int rgb) { int pixelValue = 0; int opacity = (rgb &amp; ALPHA_BIT_MASK) &gt;&gt;&gt; 24; if (opacity &lt; 128) { // Quite transparent: replace color with transparent magenta // (traditional color for binary transparency) pixelValue = 0x00FF00FF; } else { // Quite opaque: get pure color pixelValue = (rgb &amp; 0xFFFFFF) | ALPHA_BIT_MASK; } return pixelValue; } }; ImageProducer ip = new FilteredImageSource(image.getSource(), filter); return Toolkit.getDefaultToolkit().createImage(ip); } public static BufferedImage makeColorTransparent(BufferedImage image, int x, int y) { ColorModel cm = image.getColorModel(); if (!(cm instanceof IndexColorModel)) return image; // No transparency added as we don't have an indexed image IndexColorModel originalICM = (IndexColorModel) cm; WritableRaster raster = image.getRaster(); int colorIndex = raster.getSample(x, y, 0); // colorIndex is an offset in the palette of the ICM' // Number of indexed colors int size = originalICM.getMapSize(); byte[] reds = new byte[size]; byte[] greens = new byte[size]; byte[] blues = new byte[size]; originalICM.getReds(reds); originalICM.getGreens(greens); originalICM.getBlues(blues); IndexColorModel newICM = new IndexColorModel(8, size, reds, greens, blues, colorIndex); return new BufferedImage(newICM, raster, image.isAlphaPremultiplied(), null); } } </code></pre>
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    1. POIn java, how do you write a java.awt.image.BufferedImage to an 8-bit png file?
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    1. CO4 years later, still waiting for this to be an answer rather than another question.
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    2. COI don't see a question on my response, although honestly I don't see an answer either (hey, I was new on SO at the time...). Anyway, despite the tone, thanks for the heads up.
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    3. COSorry for the tone, it wasn't supposed to sound aggressive. SO asks you to specify why you're down-voting so I was just answering that question.
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