How can I modify the map of a Java IndexColorModel?

Question

I want to change one single color (yellow, to be somewhat specific) to another color in a BufferedImage which was loaded from a .GIF file. I should be able to do it easily enough with getRGB and setRGB, but it would much more efficient if I could just change the color that the IndexColorModel's 'yellow' index is referring to. Failing that, is it possible to create a new IndexColorModel which has the altered map?

Answer 1

Maybe something like this:

     BufferedImage bi = javax.imageio.ImageIO.read(new File("pathToGif"));
     
     if(bi.getColorModel() instanceof IndexColorModel) {
         IndexColorModel colorModel = (IndexColorModel)bi.getColorModel();
         int colorCount = colorModel.getMapSize();
         byte[] reds = new byte[colorCount];
         byte[] greens = new byte[colorCount];
         byte[] blues = new byte[colorCount];
         colorModel.getReds(reds);
         colorModel.getGreens(greens);
         colorModel.getBlues(blues);
         Color yellow = Color.YELLOW;
         Color blue = Color.BLUE;
         for(int i = 0; i < reds.length; i++) {
            Color newColor = new Color(reds[i]&0xff, greens[i]&0xff, blues[i]&0xff);
            if(newColor.equals(yellow)) {
                reds[i] = (byte)blue.getRed();
                greens[i] = (byte)blue.getGreen();
                blues[i] = (byte)blue.getBlue();
                break;
            }
         }
         
     }

This changed the yellow color to blue color, you can then use the changed color model to create a new BufferedImage and save it.