java - 在Jfreechart中更改图形的X轴起始值

Question

我正在计算图像红色分量的直方图并将其存储在 redhisto[] 中。数组的索引代表强度(0到255)该值表示具有该强度的像素数。然后使用 JFreeChart 绘制这些值。

我的问题是:

1. 如何让X轴的值从0开始，现在是从负数开始。

2. 我们可以更改图中条形的颜色吗 代码是:

    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

您可以更改域轴的下限并设置系列绘制，如下所示。默认的 XYBarPainter 具有渐变色突出显示，因此我使用了 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);