// Like the Process/Math/Gamma command, this script
// allows you to interactively adjust the gamma of an image

   img = IJ.openImage("http://imagej.nih.gov/ij/images/boats.gif");
   img.show();
   ip = img.getProcessor();
   ip.snapshot();
   dialog = GenericDialog("Gamma Adjuster");
   dialog.addSlider("Gamma:", 0.05, 5.0, 1);
   listener = new DialogListener ({
      dialogItemChanged : function(gd, event) {
         gamma = gd.getNextNumber();
         ip.reset();
         ip.snapshot();
         ip.gamma(gamma);
         img.updateAndDraw();
         return true;
      }
   });
   dialog.addDialogListener(listener);
   dialog.showDialog();
   if (dialog.wasCanceled()) {
      ip.reset();
      img.updateAndDraw();
   }