protected void scroll(int sx, int sy) {
   int ox = xSrcStart + (int) (sx / magnification); // convert to offscreen coordinates
   int oy = ySrcStart + (int) (sy / magnification);
   // IJ.log("scroll: "+ox+" "+oy+" "+xMouseStart+" "+yMouseStart);
   int newx = xSrcStart + (xMouseStart - ox);
   int newy = ySrcStart + (yMouseStart - oy);
   if (newx < 0) newx = 0;
   if (newy < 0) newy = 0;
   if ((newx + srcRect.width) > imageWidth) newx = imageWidth - srcRect.width;
   if ((newy + srcRect.height) > imageHeight) newy = imageHeight - srcRect.height;
   srcRect.x = newx;
   srcRect.y = newy;
   // IJ.log(sx+"  "+sy+"  "+newx+"  "+newy+"  "+srcRect);
   imp.draw();
   Thread.yield();
 }
    public BandAdjuster() {

      super("Threshold Colour");
      if (instance != null) {
        instance.toFront();
        return;
      }
      imp = WindowManager.getCurrentImage();
      if (imp == null) {
        IJ.beep();
        IJ.showStatus("No image");
        return;
      }
      IJ.run("Select None");
      thread = new Thread(this, "BandAdjuster");
      WindowManager.addWindow(this);
      instance = this;
      IJ.register(PasteController.class);

      ij = IJ.getInstance();
      Font font = new Font("SansSerif", Font.PLAIN, 10);
      GridBagLayout gridbag = new GridBagLayout();
      GridBagConstraints c = new GridBagConstraints();
      setLayout(gridbag);

      int y = 0;
      c.gridx = 0;
      c.gridy = y;
      c.gridwidth = 1;
      c.weightx = 0;
      c.insets = new Insets(5, 0, 0, 0);
      labelh = new Label("Hue", Label.CENTER);
      add(labelh, c);

      c.gridx = 1;
      c.gridy = y++;
      c.gridwidth = 1;
      c.weightx = 0;
      c.insets = new Insets(7, 0, 0, 0);
      labelf = new Label("Filter type", Label.RIGHT);
      add(labelf, c);

      // plot
      c.gridx = 0;
      c.gridy = y;
      c.gridwidth = 1;
      c.fill = c.BOTH;
      c.anchor = c.CENTER;
      c.insets = new Insets(0, 5, 0, 0);
      add(plot, c);

      // checkboxes
      panelh = new Panel();
      filterTypeH = new CheckboxGroup();
      bandPassH = new Checkbox("Pass");
      bandPassH.setCheckboxGroup(filterTypeH);
      bandPassH.addItemListener(this);
      panelh.add(bandPassH);
      bandStopH = new Checkbox("Stop");
      bandStopH.setCheckboxGroup(filterTypeH);
      bandStopH.addItemListener(this);
      panelh.add(bandStopH);
      bandPassH.setState(true);
      c.gridx = 1;
      c.gridy = y++;
      c.gridwidth = 2;
      c.insets = new Insets(5, 0, 0, 0);
      add(panelh, c);

      // minHue slider
      minSlider = new Scrollbar(Scrollbar.HORIZONTAL, 0, 1, 0, sliderRange);
      c.gridx = 0;
      c.gridy = y++;
      c.gridwidth = 1;
      c.weightx = IJ.isMacintosh() ? 90 : 100;
      c.fill = c.HORIZONTAL;
      c.insets = new Insets(5, 5, 0, 0);

      add(minSlider, c);
      minSlider.addAdjustmentListener(this);
      minSlider.setUnitIncrement(1);

      // minHue slider label
      c.gridx = 1;
      c.gridwidth = 1;
      c.weightx = IJ.isMacintosh() ? 10 : 0;
      c.insets = new Insets(5, 0, 0, 0);
      label1 = new Label("       ", Label.LEFT);
      label1.setFont(font);
      add(label1, c);

      // maxHue sliderHue
      maxSlider = new Scrollbar(Scrollbar.HORIZONTAL, 0, 1, 0, sliderRange);
      c.gridx = 0;
      c.gridy = y;
      c.gridwidth = 1;
      c.weightx = 100;
      c.insets = new Insets(5, 5, 0, 0);
      add(maxSlider, c);
      maxSlider.addAdjustmentListener(this);
      maxSlider.setUnitIncrement(1);

      // maxHue slider label
      c.gridx = 1;
      c.gridwidth = 1;
      c.gridy = y++;
      c.weightx = 0;
      c.insets = new Insets(5, 0, 0, 0);
      label2 = new Label("       ", Label.LEFT);
      label2.setFont(font);
      add(label2, c);

      // =====
      c.gridx = 0;
      c.gridy = y++;
      c.gridwidth = 1;
      c.weightx = 0;
      c.insets = new Insets(10, 0, 0, 0);
      labels = new Label("Saturation", Label.CENTER);
      add(labels, c);

      // plot
      c.gridx = 0;
      c.gridy = y;
      c.gridwidth = 1;
      c.fill = c.BOTH;
      c.anchor = c.CENTER;
      c.insets = new Insets(0, 5, 0, 0);
      add(splot, c);

      // checkboxes
      panels = new Panel();
      filterTypeS = new CheckboxGroup();
      bandPassS = new Checkbox("Pass");
      bandPassS.setCheckboxGroup(filterTypeS);
      bandPassS.addItemListener(this);
      panels.add(bandPassS);
      bandStopS = new Checkbox("Stop");
      bandStopS.setCheckboxGroup(filterTypeS);
      bandStopS.addItemListener(this);
      panels.add(bandStopS);
      bandPassS.setState(true);
      c.gridx = 1;
      c.gridy = y++;
      c.gridwidth = 2;
      c.insets = new Insets(5, 0, 0, 0);
      add(panels, c);

      // minSat slider
      minSlider2 = new Scrollbar(Scrollbar.HORIZONTAL, 0, 1, 0, sliderRange);
      c.gridx = 0;
      c.gridy = y++;
      c.gridwidth = 1;
      c.weightx = IJ.isMacintosh() ? 90 : 100;
      c.fill = c.HORIZONTAL;
      c.insets = new Insets(5, 5, 0, 0);
      add(minSlider2, c);
      minSlider2.addAdjustmentListener(this);
      minSlider2.setUnitIncrement(1);

      // minSat slider label
      c.gridx = 1;
      c.gridwidth = 1;
      c.weightx = IJ.isMacintosh() ? 10 : 0;
      c.insets = new Insets(5, 0, 0, 0);
      label3 = new Label("       ", Label.LEFT);
      label3.setFont(font);
      add(label3, c);

      // maxSat slider
      maxSlider2 = new Scrollbar(Scrollbar.HORIZONTAL, 0, 1, 0, sliderRange);
      c.gridx = 0;
      c.gridy = y++;
      c.gridwidth = 1;
      c.weightx = 100;
      c.insets = new Insets(5, 5, 0, 0);
      add(maxSlider2, c);
      maxSlider2.addAdjustmentListener(this);
      maxSlider2.setUnitIncrement(1);

      // maxSat slider label
      c.gridx = 1;
      c.gridwidth = 1;
      c.weightx = 0;
      c.insets = new Insets(5, 0, 0, 0);
      label4 = new Label("       ", Label.LEFT);
      label4.setFont(font);
      add(label4, c);

      // =====
      c.gridx = 0;
      c.gridwidth = 1;
      c.gridy = y++;
      c.weightx = 0;
      c.insets = new Insets(10, 0, 0, 0);
      labelb = new Label("Brightness", Label.CENTER);
      add(labelb, c);

      c.gridx = 0;
      c.gridwidth = 1;
      c.gridy = y;
      c.fill = c.BOTH;
      c.anchor = c.CENTER;
      c.insets = new Insets(0, 5, 0, 0);
      add(bplot, c);

      // checkboxes
      panelb = new Panel();
      filterTypeB = new CheckboxGroup();
      bandPassB = new Checkbox("Pass");
      bandPassB.setCheckboxGroup(filterTypeB);
      bandPassB.addItemListener(this);
      panelb.add(bandPassB);
      bandStopB = new Checkbox("Stop");
      bandStopB.setCheckboxGroup(filterTypeB);
      bandStopB.addItemListener(this);
      panelb.add(bandStopB);
      bandPassB.setState(true);
      c.gridx = 1;
      c.gridy = y++;
      c.gridwidth = 2;
      c.insets = new Insets(5, 0, 0, 0);
      add(panelb, c);

      // minBri slider
      minSlider3 = new Scrollbar(Scrollbar.HORIZONTAL, 0, 1, 0, sliderRange);
      c.gridx = 0;
      c.gridy = y++;
      c.gridwidth = 1;
      c.weightx = IJ.isMacintosh() ? 90 : 100;
      c.fill = c.HORIZONTAL;
      c.insets = new Insets(5, 5, 0, 0);
      add(minSlider3, c);
      minSlider3.addAdjustmentListener(this);
      minSlider3.setUnitIncrement(1);

      // minBri slider label
      c.gridx = 1;
      c.gridwidth = 1;
      c.weightx = IJ.isMacintosh() ? 10 : 0;
      c.insets = new Insets(5, 0, 0, 0);
      label5 = new Label("       ", Label.LEFT);
      label5.setFont(font);
      add(label5, c);

      // maxBri slider
      maxSlider3 = new Scrollbar(Scrollbar.HORIZONTAL, 0, 1, 0, sliderRange);
      c.gridx = 0;
      c.gridy = y++;
      c.gridwidth = 1;
      c.weightx = 100;
      c.insets = new Insets(5, 5, 0, 0);
      add(maxSlider3, c);
      maxSlider3.addAdjustmentListener(this);
      maxSlider3.setUnitIncrement(1);

      // maxBri slider label
      c.gridx = 1;
      c.gridwidth = 1;
      c.weightx = 0;
      c.insets = new Insets(5, 0, 0, 0);
      label6 = new Label("       ", Label.LEFT);
      label6.setFont(font);
      add(label6, c);

      // =====
      panelt = new Panel();
      threshold = new Checkbox("Threshold");
      threshold.addItemListener(this);
      panelt.add(threshold);

      invert = new Checkbox("Invert");
      invert.addItemListener(this);
      panelt.add(invert);

      c.gridx = 0;
      c.gridy = y++;
      c.gridwidth = 2;
      c.insets = new Insets(0, 0, 0, 0);
      add(panelt, c);

      // buttons
      panel = new Panel();
      // panel.setLayout(new GridLayout(2, 2, 0, 0));
      originalB = new Button("Original");
      originalB.setEnabled(false);
      originalB.addActionListener(this);
      originalB.addKeyListener(ij);
      panel.add(originalB);

      filteredB = new Button("Filtered");
      filteredB.setEnabled(false);
      filteredB.addActionListener(this);
      filteredB.addKeyListener(ij);
      panel.add(filteredB);

      stackB = new Button("Stack");
      stackB.addActionListener(this);
      stackB.addKeyListener(ij);
      panel.add(stackB);

      helpB = new Button("Help");
      helpB.addActionListener(this);
      helpB.addKeyListener(ij);
      panel.add(helpB);

      c.gridx = 0;
      c.gridy = y++;
      c.gridwidth = 2;
      c.insets = new Insets(0, 0, 0, 0);
      add(panel, c);

      panelMode = new Panel();

      sampleB = new Button("Sample");
      sampleB.addActionListener(this);
      sampleB.addKeyListener(ij);
      panelMode.add(sampleB);

      colourMode = new CheckboxGroup();
      hsb = new Checkbox("HSB");
      hsb.setCheckboxGroup(colourMode);
      hsb.addItemListener(this);
      panelMode.add(hsb);
      hsb.setState(true);
      rgb = new Checkbox("RGB");
      rgb.setCheckboxGroup(colourMode);
      rgb.addItemListener(this);
      panelMode.add(rgb);

      c.gridx = 0;
      c.gridy = y++;
      c.gridwidth = 2;
      c.insets = new Insets(0, 0, 0, 0);
      add(panelMode, c);

      addKeyListener(ij); // ImageJ handles keyboard shortcuts
      pack();
      GUI.center(this);
      setVisible(true);

      ip = setup(imp);
      if (ip == null) {
        imp.unlock();
        IJ.beep();
        IJ.showStatus("RGB image cannot be thresholded");
        return;
      }
      thread.start();
    }