How to convert a BufferedImage to 8 bit?

Question

I was looking at the ImageConverter class, trying to figure out how to convert a BufferedImage to 8-bit color, but I have no idea how I would do this. I was also searching around the internet and I could find no simple answer, they were all talking about 8 bit grayscale images. I simply want to convert the colors of an image to 8 bit... nothing else, no resizing no nothing. Does anyone mind telling me how to do this.

Spokane

You probably have to choose a quantization algorithm, ie. something that transform the range of colors of your images into a 256 entry palette. – Vile

What do you mean by converting the colors of an image to 8-bit? I guess you want to reduce the color space? Do you want to perform Color quantization? – Overstride

Could you guys point me to a library/API of some sort? I have no idea what you're talking about. That also sounds like I would be able to create my own palette which would be event better if possible. – Spokane

Answer 1

This code snippet from the article "Transparent gifs in Java" at G-Man's Uber Software Engineering Blog works well:

public static void main(String[] args) throws Exception {
    BufferedImage src = convertRGBAToIndexed(ImageIO.read(new File("/src.jpg")));
    ImageIO.write(src, "gif", new File("/dest.gif"));
}

public static BufferedImage convertRGBAToIndexed(BufferedImage src) {
    BufferedImage dest = new BufferedImage(src.getWidth(), src.getHeight(), BufferedImage.TYPE_BYTE_INDEXED);
    Graphics g = dest.getGraphics();
    g.setColor(new Color(231, 20, 189));

    // fill with a hideous color and make it transparent
    g.fillRect(0, 0, dest.getWidth(), dest.getHeight());
    dest = makeTransparent(dest, 0, 0);

    dest.createGraphics().drawImage(src, 0, 0, null);
    return dest;
}

public static BufferedImage makeTransparent(BufferedImage image, int x, int y) {
    ColorModel cm = image.getColorModel();
    if (!(cm instanceof IndexColorModel))
        return image; // sorry...
    IndexColorModel icm = (IndexColorModel) cm;
    WritableRaster raster = image.getRaster();
    int pixel = raster.getSample(x, y, 0); // pixel is offset in ICM's palette
    int size = icm.getMapSize();
    byte[] reds = new byte[size];
    byte[] greens = new byte[size];
    byte[] blues = new byte[size];
    icm.getReds(reds);
    icm.getGreens(greens);
    icm.getBlues(blues);
    IndexColorModel icm2 = new IndexColorModel(8, size, reds, greens, blues, pixel);
    return new BufferedImage(icm2, raster, image.isAlphaPremultiplied(), null);
}

Oni

Worked great, just had to remove the transparency part. – Spokane

Answer 2

You can use JAI (Java Advanced Imaging), the official Sun (now Oracle) image library to do that.

The ColorQuantizerDescriptor shows the choice of quantization processes you can apply.

Vile

Do you have some sample code? #15313421 – Ingram

Answer 3

You can use the convert8 method in the ConvertUtil class.

For details have a look here.

Aleydis

I could not use ConvertUtil.convert8, so I would have to import that class, but I could not find what the import code was. Do you by chance do what/where it is? – Fuqua