jfreechart 生成JPEG格式圖檔出現不正常的背景色

版本1：jfreechart-1.0.9

生成圖檔代碼如下：

Java代碼 

1. ChartUtilities.writeChartAsJPEG(out, chart, 500, 400);  

得到的圖檔顯示如下，出現不正常的紅色背景

jfreechart-1.0.9生成圖檔各主要代碼如下：

JFreeChart類

Java代碼 

1. public BufferedImage createBufferedImage(int width, int height, ChartRenderingInfo info)  
2. {  
3.      return createBufferedImage(width, height, 2, info);  
4. }  
5. public BufferedImage createBufferedImage(int width, int height, int imageType, ChartRenderingInfo info)  
6. {  
7.      BufferedImage image = new BufferedImage(width, height, imageType);  
8.      Graphics2D g2 = image.createGraphics();  
9.      draw(g2, new Rectangle2D.Double(0.0D, 0.0D, width, height), null, info);  
10.      g2.dispose();  
11.      return image;  
12. }  

如上所述，建立BufferedImage的時候，使用的iamgeType是2，也就是BufferedImage.TYPE_INT_ARGB格式。

解決方法一：手動設定imageType為1（即BufferedImage.TYPE_INT_RGB），如下代碼：

Java代碼 

1. BufferedImage bi = chart.createBufferedImage(500, 400, 1, null);  
2. ImageIO.write(bi, "jpeg", out);  

解決方法二：更新jfreechart到1.0.10，該版本中JFreeChart中的createBufferedImage代碼如下：

Java代碼 

1. public static void writeChartAsJPEG(OutputStream out, float quality, JFreeChart chart, int width, int height, ChartRenderingInfo info)  
2.   throws IOException                                                                                                                    
3. {                                                                                                                                       
4.   if (chart == null) {                                                                                                                  
5.     throw new IllegalArgumentException("Null 'chart' argument.");                                                                       
6.   }                                                                                                                                     
7.   BufferedImage image = chart.createBufferedImage(width, height, 1, info);                                                                                                                                          
8.   EncoderUtil.writeBufferedImage(image, "jpeg", out, quality);                                                                          
9. }  

 1.0.10版本在調用JFreeChart的createBufferedImage預設使用了imageType為BufferedImage.TYPE_INT_RGB

調整後生成的圖檔如下：