private BufferedImage createThumbNailImage(Dimension imgSize, ProgressMonitor pm) {
      Assert.notNull(pm, "pm");

      String thumbNailBandName = getThumbnailBandName();
      Band thumbNailBand = product.getBand(thumbNailBandName);

      Debug.trace(
          "ProductSubsetDialog: Reading thumbnail data for band '" + thumbNailBandName + "'...");
      pm.beginTask("Creating thumbnail image", 5);
      BufferedImage image = null;
      try {
        MultiLevelSource multiLevelSource =
            BandImageMultiLevelSource.create(thumbNailBand, SubProgressMonitor.create(pm, 1));
        final ImageLayer imageLayer = new ImageLayer(multiLevelSource);
        final int imageWidth = imgSize.width;
        final int imageHeight = imgSize.height;
        final int imageType = BufferedImage.TYPE_3BYTE_BGR;
        image = new BufferedImage(imageWidth, imageHeight, imageType);
        Viewport snapshotVp = new DefaultViewport(isModelYAxisDown(imageLayer));
        final BufferedImageRendering imageRendering = new BufferedImageRendering(image, snapshotVp);

        final Graphics2D graphics = imageRendering.getGraphics();
        graphics.setColor(getBackground());
        graphics.fillRect(0, 0, imageWidth, imageHeight);

        snapshotVp.zoom(imageLayer.getModelBounds());
        snapshotVp.moveViewDelta(snapshotVp.getViewBounds().x, snapshotVp.getViewBounds().y);
        imageLayer.render(imageRendering);

        pm.worked(4);
      } finally {
        pm.done();
      }
      return image;
    }
  private static RasterDataNode[] getReferencedNodes(final RasterDataNode node) {
    final Product product = node.getProduct();
    if (product != null) {
      final List<String> expressions = new ArrayList<String>(10);
      if (node.getValidPixelExpression() != null) {
        expressions.add(node.getValidPixelExpression());
      }
      final ProductNodeGroup<Mask> overlayMaskGroup = node.getOverlayMaskGroup();
      if (overlayMaskGroup.getNodeCount() > 0) {
        final Mask[] overlayMasks =
            overlayMaskGroup.toArray(new Mask[overlayMaskGroup.getNodeCount()]);
        for (final Mask overlayMask : overlayMasks) {
          final String expression;
          if (overlayMask.getImageType() == Mask.BandMathsType.INSTANCE) {
            expression = Mask.BandMathsType.getExpression(overlayMask);
          } else if (overlayMask.getImageType() == Mask.RangeType.INSTANCE) {
            expression = Mask.RangeType.getExpression(overlayMask);
          } else {
            expression = null;
          }
          if (expression != null) {
            expressions.add(expression);
          }
        }
      }
      if (node instanceof VirtualBand) {
        final VirtualBand virtualBand = (VirtualBand) node;
        expressions.add(virtualBand.getExpression());
      }

      final ArrayList<Term> termList = new ArrayList<Term>(10);
      for (final String expression : expressions) {
        try {
          final Term term = product.parseExpression(expression);
          if (term != null) {
            termList.add(term);
          }
        } catch (ParseException e) {
          // @todo se handle parse exception
          Debug.trace(e);
        }
      }

      final Term[] terms = termList.toArray(new Term[termList.size()]);
      final RasterDataSymbol[] refRasterDataSymbols = BandArithmetic.getRefRasterDataSymbols(terms);
      return BandArithmetic.getRefRasters(refRasterDataSymbols);
    }
    return new RasterDataNode[0];
  }