pb.add((int) (dy < 0 ? -dy : 0));
pb.add(BorderExtender.createInstance(BorderExtender.BORDER_ZERO));
RenderedOp border = JAI.create("Border", pb, JAIContext.noCacheHint);
pb = new ParameterBlock();
pb.addSource(border);
pb.add((float) back.getMinX());
pb.add((float) back.getMinY());
pb.add((float) back.getWidth());
pb.add((float) back.getHeight());
RenderedOp crop = JAI.create("Crop", pb, JAIContext.noCacheHint);