Creating BufferedImage from int[] (not RGB's)

Question

Hi,
I have an int[] that contains how many intersections occur between each pixel and a series of overlapping rectangles. So the array would look like this:
int [] intersections = { 0,1,1,1,1,0,2,4,4...etc} each number representing the number of times each pixel intersects a rectangle.
What I would like to do is create a bufferedImage where each pixel in the image is a color based on the number of intersections from the array. 0 intersections is transparent, 1 intersection is a blue pixel , 2 intersections is green etc.
I implemented it first looping through the array and painting a 1X1 rectangle colored according to the number of intersections but it is slow. Can I use a ColorModel for this (never used one)?. If so, what is a good method to convert these integers that represent the number of intersections to the corresponding color in a BufferedImage? The maximum number of intersections would be far fewer than 256, probably in the range of 10-50. I would also like to create the image in grayscale, the larger number of intersections getting darker and as hues of one color where an index of 0 would be transparent and as the number of intersections got larger the color gets darker. It all works the way I did it but it is way too slow. Will a ColorModel do transparent pixels? Is MemorySourceImage a good way to do this? Any ideas?
Thanks very much!
Paul

Answer 1

You're more or less describing a IndexColorModel, except the data bank is usually a byte[]:
import java.awt.*;
import java.awt.image.*;
import java.util.*;
import javax.swing.*;
public class IndexColorModelTest {
    public static void main(String[] args) {
        int w = 300, h = 200;
        BufferedImage bi = createImage(w, h, createData(w, h));
        JLabel label = new JLabel(new ImageIcon(bi));
        label.setOpaque(true);
        label.setBackground(Color.RED);
        final JFrame f = new JFrame("IndexColorModelTest");
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.getContentPane().add(label);
        f.pack();
        SwingUtilities.invokeLater(new Runnable(){
            public void run() {
                f.setLocationRelativeTo(null);
                f.setVisible(true);
    static byte[] createData(int w, int h) {
        byte[] data = new byte[w*h];
        new Random().nextBytes(data);
        return data;
    static BufferedImage createImage(int w, int h, byte[] data) {
        //create a color model with grays
        int SIZE = 256;
        byte[] gray = new byte[SIZE];
        for(int i=0; i<256; ++i)
            gray[i] = (byte) i;
        ColorModel cm = new IndexColorModel(8, SIZE, gray, gray, gray, 0); //0 is transparent pixel
        DataBuffer db = new DataBufferByte(data, w*h);
        WritableRaster r = Raster.createInterleavedRaster(db, w, h, w, 1, new int[]{0}, null);
        return new BufferedImage(cm, r, false, null);
}