To change the X-axis starting value of graph in Jfreechart

Question

I am calculating histogram of red component of the image and stored it in redhisto[]. The index of the array represent the intensity(0 to 255) and the value represent the number of pixel with that intensity. Then plotting those values with JFreeChart.

My question is:

1. How to make X-axis value start from 0. Now its starting from negative number.

2. Can we change the color of the bars in the graph code is :

    public class Histogram extends ApplicationFrame {
      public Histogram(final String title) throws IOException {
       super(title);
       IntervalXYDataset dataset = createDataset();
       JFreeChart chart = createChart(dataset);
       final ChartPanel chartPanel = new ChartPanel(chart);
       chartPanel.setPreferredSize(new java.awt.Dimension(500, 270));
       setContentPane(chartPanel);
      }
   
     private IntervalXYDataset createDataset() throws IOException {
      BufferedImage imageA = ImageIO.read(new File("XYZ.bmp"));
      int[] red = new int[imageA.getHeight()*imageA.getWidth()];
      int[] redhisto = new int[256];
      int[] pixel;
      int k= 0;
      for (int y = 0; y < imageA.getHeight(); y++) {
         for (int x = 0; x < imageA.getWidth(); x++) {
           pixel = imageA.getRaster().getPixel(x, y, new int[3]);       
           red[k] = pixel[0];
           k++;
         }
      }        
   
      for(int x=0;x<red.length;x++){
          int y = red[x];
          redhisto[y]++;
       }
   
     final XYSeries series = new XYSeries("No of pixels");
     for(int i=0; i<redhisto.length;i++)
       series.add(i,redhisto[i]);
   
     final XYSeriesCollection dataset = new XYSeriesCollection(series);
     return dataset;
    }
   
    private JFreeChart createChart(IntervalXYDataset dataset) {
     final JFreeChart chart = ChartFactory.createXYBarChart("Color Intensity   Histogram","X",false,"Y",dataset,PlotOrientation.VERTICAL,true,true,false);
     XYPlot plot = (XYPlot) chart.getPlot();
     return chart;    
    }
   
    public static void main(final String[] args) throws IOException {
     final Histogram demo = new Histogram("Image Histogram");
     demo.pack();
     RefineryUtilities.centerFrameOnScreen(demo);
     demo.setVisible(true);
    }
   }
   

Answer 1

You can change the lower bound of the domain axis and set the series paint as shown below. The default XYBarPainter has a gradient color highlight, so I used a StandardXYBarPainter.

XYPlot plot = (XYPlot) chart.getPlot();
ValueAxis axis = plot.getDomainAxis();
axis.setLowerBound(0);
XYBarRenderer r = (XYBarRenderer) plot.getRenderer();
r.setBarPainter(new StandardXYBarPainter());
r.setSeriesPaint(0, Color.blue);

Answer 2

    XYPlot plot = (XYPlot) chart.getPlot();  

    //To change the lower bound of X-axis
    NumberAxis xAxis = (NumberAxis) plot.getDomainAxis();
    xAxis.setLowerBound(0);

    //To change the lower bound of Y-axis       
    NumberAxis yAxis = (NumberAxis) plot.getRangeAxis();
    yAxis.setLowerBound(0);

    // To change the color
    XYItemRenderer renderer = plot.getRenderer();
    renderer.setSeriesPaint(0, Color.green);