想要减少图像RGB级别的位大小

Question

我想将图像颜色量化从16位减少到8位。到目前为止这是我的代码。它只会使图像透明。根据我所学到的，我应该采用每个像素并除以比特尺寸减小的因子。我在这里做错了什么？

    import java.awt.*;
    import java.awt.image.BufferedImage;
    import java.io.*;
    import javax.imageio.ImageIO;
    import javax.swing.JFrame;
    import java.util.Scanner;

    public class ConvertImage{
        public static void main(String args[])throws IOException{
            BufferedImage image = null;
            File f = null;

            try {

                       f = new File("lennapng.png");
                         image = ImageIO.read(f);
                       }catch(IOException e){
                         System.out.println(e);
                       }

                     //get width and height
                     int width = image.getWidth();
                     int height = image.getHeight();


                     width = image.getWidth();
                     height = image.getHeight();
                     for(int y = 0; y < height; y++) {
                         for(int x = 0; x <height; x++) {
                             int p = image.getRGB(x, y);
                           // System.out.println("rgb "+ rgb);

                              int a = (p>>24) & 0xff;
                              int r = (p>>16) & 0xff;
                              int g = (p>>8) & 0xff;
                              int b = p&0xff;


                              r= r*16/256;
                              g= g*16/256;
                              b = b*16/256;

                                //set new RGB
                              p = (a<<12) | (r<<8) | (g<<4) | b;

                              image.setRGB(x, y, p);

                                        }
                    }

                      try{
                         f = new File("output.png");
                         ImageIO.write(image, "png", f);
                       }catch(IOException e){
                         System.out.println(e);
                       }


                  } 



               }