/** Adds the image in 'ip' to the end of the stack. */
 public void addSlice(String sliceLabel, ImageProcessor ip) {
   if (ip.getWidth() != width || ip.getHeight() != height)
     throw new IllegalArgumentException("Dimensions do not match");
   if (nSlices == 0) {
     cm = ip.getColorModel();
     min = ip.getMin();
     max = ip.getMax();
   }
   addSlice(sliceLabel, ip.getPixels());
 }