Java BufferedImage可以保存不需要的背景颜色

问题描述

提前感谢您的帮助

描述：
程序绘制，显示和保存图像。它的工作原理如下：对象本身扩展了Frame。在构造函数中，该对象创建一个BufferedImage，并调用一个绘制到该图像上的方法。然后，它将图像显示在帧上。最后，它将图像保存到文件中（我不关心它使用的是什么格式）。主程序创建了对象，剩下的就完成了。

Description:The program draws, displays, and saves an image. It works as following: the object itself extends Frame. In the constructor, the object creates a BufferedImage, and calls a method that draw onto that image. Then, it displays the image onto the Frame. Finally, it saves the image into a file (I don't care what format it uses). The main program creates the object, which does the rest.

问题：
保存的文件总是有彩色背景！由于显示的图像很好，这尤其奇怪。如果我在ImageIO.write（）中使用jpg格式，背景会偏红。如果我使用png格式，背景为深灰色。

Problem:The saved file always has a colored background! This is especially wierd since the displayed image is fine. If I use "jpg" format with ImageIO.write(), the background is reddish. If I use the "png" format, the background is dark grey.

我已经花了一段时间，我仍然不知道到底发生了什么！

I've spent a while on this, and I still have no idea what the hell is happening!

    import java.awt.Frame ;
    import java.awt.image.BufferedImage ;
    import java.io.IOException ;
    import java.awt.event.WindowEvent ;
    import java.awt.event.WindowAdapter ;
    import java.awt.Toolkit ;
    import java.awt.Graphics2D ;
    import java.awt.Graphics ;
    import java.awt.Color ;
    import java.awt.Dimension ;
    import javax.imageio.ImageIO ;
    import java.io.File ;
    import java.awt.geom.Rectangle2D;

    public class HGrapher extends Frame{
       private BufferedImage img ;
       private float colors[][] ; //the colors for every rectangle
       private double availWidth ;
       private double availHeight ;


       public HGrapher(String saveFileName, int numRects) throws IOException {
          //*add window closer
          addWindowListener(new WindowAdapter() {
             public void windowClosing(WindowEvent e) {
                System.exit(0);            }
          });

          //*get colors to use
          setColors( numRects) ;

          //*figure out the size of the image and frame
          this.availHeight = (3.0/4) * Toolkit.getDefaultToolkit().getScreenSize().height ;
          this.availWidth = (3.0/4) * Toolkit.getDefaultToolkit().getScreenSize().width ;

          //*create the image
          this.img = new BufferedImage( (int)availWidth, (int)availHeight, BufferedImage.TYPE_INT_ARGB);
          Graphics2D drawer = img.createGraphics() ;
          drawer.setBackground(Color.WHITE);

          this.makeImg( drawer) ;
          //*display the image
          this.setSize( new Dimension( (int)availWidth, (int)availHeight ) ) ;
          this.setVisible(true);

          //*save the image
          ImageIO.write(img, "jpg",new File( (saveFileName +".jpg") ) );
       }


       //*draws the image by filling rectangles whose color are specified by this.colors
       public void makeImg( Graphics2D drawer) {
          double rectWidth = this.availWidth / (double)colors.length ;
          for(int i = 0 ; i < colors.length ; i ++) {
             drawer.setColor( new Color( this.colors[i][0], this.colors[i][1], this.colors[i][2],
                                         this.colors[i][3] ) ) ;
             drawer.fill( new Rectangle2D.Double( rectWidth*i, 0, rectWidth, this.availHeight ) ) ;
          }
       }


       //*paint method
       public void paint(Graphics g) {
          Graphics2D drawer = (Graphics2D)g ;
          drawer.drawImage(img, 0, 0, null) ;
       }


       //*creates an array of the colors rectangles are filled with
       public void setColors( int numRects) {
          this.colors = new float[ numRects][4] ;
          //*make every 1st rect red
          for(int i = 0 ; i< colors.length ; i+= 3) {
             this.colors[i][0] = (float).8 ; this.colors[i][1] = (float).1 ; this.colors[i][2] = (float).1 ;
             this.colors[i][3] = (float).8 ;      }
          //*make every 2nd rect green
          for(int i = 1 ; i< colors.length ; i+= 3) {
             this.colors[i][0] = (float).1 ; this.colors[i][1] = (float).8 ; this.colors[i][2] = (float).1 ;
             this.colors[i][3] = (float).8 ;      }
          //*make every 3rd rect
          for(int i = 2 ; i< colors.length ; i+= 3) {
             this.colors[i][0] = (float).1 ; this.colors[i][1] = (float).1 ; this.colors[i][2] = (float).8 ;
             this.colors[i][3] = (float).8 ;      }
       }




       public static void main (String[]args) throws IOException {
          HGrapher hg = new HGrapher("saved", 14) ;
       }

    }

推荐答案

setBackground（）仅设置用于清除图像的Color，它实际上不会清除图像。在 setBackground（）之后调用 Graphics.clearRect（int，int，int，int）。像这样：

setBackground() only set the Color that is used to clear the image, it does not actually clear the image. Call Graphics.clearRect(int,int,int,int) after setBackground(). Like so:

//*create the image
this.img = new BufferedImage( (int)availWidth, (int)availHeight, BufferedImage.TYPE_INT_ARGB);
Graphics2D drawer = img.createGraphics() ;
drawer.setBackground(Color.WHITE);
drawer.clearRect(0,0,(int)availWidth,(int)availHeight);

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