在Jfreechart中更改图形的X轴起始值

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);