Question

I am trying to obtain RGB values from an ImagePlus object. I am getting an exception error when I attempt to do this:

import ij.IJ;
import ij.ImagePlus;
import ij.plugin.filter.PlugInFilter;
import ij.process.ColorProcessor;
import ij.process.ImageProcessor;
import java.awt.image.IndexColorModel;

public class ImageHelper implements PlugInFilter {

    public int setup(String arg, ImagePlus img) {
        return DOES_8G + NO_CHANGES;
    }

    public void run(ImageProcessor ip) {

        final int r = 0;
        final int g = 1;
        final int b = 2;

        int w = ip.getWidth();
        int h = ip.getHeight();

        ImagePlus ips = new ImagePlus("C:\\Lena.jpg");
        int width = ips.getWidth();
        int height = ips.getHeight();
        System.out.println("width of image: " + width + " pixels");
        System.out.println("height of image: " + height + " pixels");

        // retrieve the lookup tables (maps) for R,G,B
        IndexColorModel icm = (IndexColorModel) ip.getColorModel();

        int mapSize = icm.getMapSize();
        byte[] Rmap = new byte[mapSize];
        icm.getReds(Rmap);
        byte[] Gmap = new byte[mapSize];
        icm.getGreens(Gmap);
        byte[] Bmap = new byte[mapSize];
        icm.getBlues(Bmap);

        // create new 24-bit RGB image
        ColorProcessor cp = new ColorProcessor(w, h);
        int[] RGB = new int[3];
        for (int v = 0; v < h; v++) {
            for (int u = 0; u < w; u++) {
                int idx = ip.getPixel(u, v);
                RGB[r] = Rmap[idx];
                RGB[g] = Gmap[idx];
                RGB[b] = Bmap[idx];
                cp.putPixel(u, v, RGB);
            }
        }
        ImagePlus cwin = new ImagePlus("RGB Image", cp);
        cwin.show();
    }
}

The exception is comming from this line:

 IndexColorModel icm = (IndexColorModel) ip.getColorModel();

Exception:

Exception in thread “main” java.lang.ClassCastException:
java.awt.image.DirectColorModel cannot be cast to
java.awt.image.IndexColorModel

…Any ideas? ^_^

Answer 1

The error occurs beccause ip.getColorModel() does not return a IndexColorModel object, but a ColorModel object.

To get the IndexColorModel object, you should use the following code:

IndexColorModel icm = ip.getDefaultColorModel();

That should give you a IndexColorModel, according to the ImageJ API.