ImageJMask.java

import ij.ImagePlus;
import ij.io.FileSaver;
import ij.io.Opener;
import ij.process.ByteProcessor;
import ij.process.ColorProcessor;

/** ImageJ's actual byte-HSB conversion with explicit, inclusive thresholds. */
class ImageJMask {
    public static void main(String[] args) {
        ImagePlus input = new Opener().openImage(args[0]);
        if (input == null) throw new IllegalArgumentException("Unreadable image");
        ColorProcessor rgb = (ColorProcessor) input.getProcessor().convertToRGB();
        int size = rgb.getWidth() * rgb.getHeight();
        byte[] h = new byte[size], s = new byte[size], b = new byte[size], mask = new byte[size];
        rgb.getHSB(h, s, b);
        int[] limits = new int[6];
        for (int i = 0; i < 6; i++) limits[i] = Integer.parseInt(args[i + 2]);
        for (int i = 0; i < size; i++) {
            int hue = h[i] & 255, sat = s[i] & 255, bri = b[i] & 255;
            if (hue >= limits[0] && hue <= limits[1] && sat >= limits[2] && sat <= limits[3]
                    && bri >= limits[4] && bri <= limits[5]) mask[i] = (byte) 255;
        }
        ImagePlus output = new ImagePlus("Threshold mask", new ByteProcessor(rgb.getWidth(), rgb.getHeight(), mask));
        if (!new FileSaver(output).saveAsPng(args[1])) throw new IllegalStateException("Cannot save mask");
        System.out.println("ImageJ " + ij.IJ.getVersion());
    }
}