static IIntegralImage iiPad(IIntegralImage etc inner, int left, int top, int right, int bottom) {
  int[] padColor = {0, 0, 0}; // black
  IIntegralImage img = inner;
  
  // add top border
  if (top > 0)
    img = IIVerticalSplit(IISingleColor(img.getWidth(), top, padColor), img);
  
  // add bottom border
  if (bottom > 0)
    img = IIVerticalSplit(img, IISingleColor(img.getWidth(), bottom, padColor));
    
  // add left border
  if (left > 0)
    img = IIHorizontalSplit(IISingleColor(left, img.getHeight(), padColor), img);
  
  // add right border
  if (right > 0)
    img = IIHorizontalSplit(img, IISingleColor(right, img.getHeight(), padColor));
    
  ret img;
}