PNG - Is it possible to reduce the palette using Java 2D?

Question

If I have a PNG image opened as a BufferedImage, can I reduce the palette in the PNG image so that there is less color (fewer bits per pixel / color depth)?

For example, if you look at Color Depth on Wikipedia, I would like to use 16 colors in my PNG image (3rd image down the right side).

If this is not possible with Java 2D, is there a library out there that will allow me to do this efficiently?

Answer 1

I think Martijn Courteaux was right:

Here is an example implementation:

import java.awt.Graphics2D; import java.awt.image.BufferedImage; import java.awt.image.IndexColorModel; import java.io.File; import java.io.IOException; import javax.imageio.ImageIO; public class ImagingTest2 { public static void main(String[] args) throws IOException { BufferedImage src = ImageIO.read(new File("in.png")); // 71 kb // here goes custom palette IndexColorModel cm = new IndexColorModel( 3, // 3 bits can store up to 8 colors 6, // here I use only 6 // RED GREEN1 GREEN2 BLUE WHITE BLACK new byte[]{-100, 0, 0, 0, -1, 0}, new byte[]{ 0, -100, 60, 0, -1, 0}, new byte[]{ 0, 0, 0, -100, -1, 0}); // draw source image on new one, with custom palette BufferedImage img = new BufferedImage( src.getWidth(), src.getHeight(), // match source BufferedImage.TYPE_BYTE_INDEXED, // required to work cm); // custom color model (ie palette) Graphics2D g2 = img.createGraphics(); g2.drawImage(src, 0, 0, null); g2.dispose(); // output ImageIO.write(img, "png", new File("out.png")); // 2,5 kb } } 

Answer 2

Create a new BufferedImage with a lower palette and use createGraphic() to get a Graphics2D object. Draw the original image on the graph. dispose() graphics and here you are.

 BufferedImage img = new BufferedImage(orig.getWidth(), orig.getHeight(), BufferedImage.TYPE_USHORT_555_RGB);