Java绘制PNG图片时的黑色背景问题

 

1. 生成png图片

 

int width = 400;

 

int height = 300;

 

// 创建BufferedImage对象

 

BufferedImage image = new BufferedImage(width, height,     BufferedImage.TYPE_INT_RGB);

 

// 获取Graphics2D

 

Graphics2D g2d = image.createGraphics();

 

// 画图

 

g2d.setColor(new Color(255,0,0));

 

g2d.setStroke(new BasicStroke(1));

 

g2d.draw

 

//释放对象

 

g2d.dispose();

 

// 保存文件   

 

ImageIO.write(image, "png", new File("c:/test.png"));

 

int width = 400;

 

int height = 300;

 

// 创建BufferedImage对象

 

BufferedImage image = new BufferedImage(width, height,     BufferedImage.TYPE_INT_RGB);

 

// 获取Graphics2D

 

Graphics2D g2d = image.createGraphics();

 

// 画图

 

g2d.setColor(new Color(255,0,0));

 

g2d.setStroke(new BasicStroke(1));

 

g2d.draw

 

//释放对象

 

g2d.dispose();

 

// 保存文件   

 

ImageIO.write(image, "png", new File("c:/test.png"));

 

这只是绘制图形的代码，其背景是黑色的，如何才能背景透明呢？继续搜索，没有得到结果，不过搜出以下代码，它只是把自己绘制的图形设置为透明或半透明，背景并不透明，如下：

 

2. 绘制半透明图形

 

int width = 400;

 

int height = 300;

 

// 创建BufferedImage对象

 

BufferedImage image = new BufferedImage(width, height,     BufferedImage.TYPE_INT_RGB);

 

// 获取Graphics2D

 

Graphics2D g2d = image.createGraphics();

 

// 设置透明度

 

g2d.setComposite(AlphaComposite.getInstance(AlphaComposite.SRC_ATOP, 1.0f)); // 1.0f为透明度 ，值从0-1.0，依次变得不透明

 

// 画图

 

g2d.setColor(new Color(255,0,0));

 

g2d.setStroke(new BasicStroke(1));

 

g2d.draw

 

//释放对象

 

//透明度设置 结束

 

g2d.setComposite(AlphaComposite.getInstance(AlphaComposite.SRC_OVER));

 

g2d.dispose();

 

// 保存文件   

 

ImageIO.write(image, "png", new File("c:/test.png"));

 

这样绘制的图形应该说是前景透明的，背景依然是黑色，:(

 

网上没有看到有益的代码，在csdn上一位说自己实现了，但却没有说怎么实现的，没办法只能自己摸索了，耗了半个多小时，几乎查看了BufferedImage 和Graphics2D 所有方法和属性，终于找到了解决方案，只不过是增加两行代码而已，如下：

 

int width = 400;

 

int height = 300;

 

// 创建BufferedImage对象

 

BufferedImage image = new BufferedImage(width, height,     BufferedImage.TYPE_INT_RGB);

 

// 获取Graphics2D

 

Graphics2D g2d = image.createGraphics();

 

// ---------- 增加下面的代码使得背景透明 -----------------

 

image = g2d.getDeviceConfiguration().createCompatibleImage(width, height, Transparency.TRANSLUCENT);

 

g2d.dispose();

 

g2d = image.createGraphics();

 

// ---------- 背景透明代码结束 -----------------

 

// 画图

 

g2d.setColor(new Color(255,0,0));

 

g2d.setStroke(new BasicStroke(1));

 

g2d.draw

 

//释放对象

 

g2d.dispose();

 

// 保存文件   

 

ImageIO.write(image, "png", new File("c:/test.png"));

 

================================================

 

白背景变透明

 

package com.goldgrid.socket.client;

 

import java.awt.Graphics2D;

import java.awt.Image;

import java.awt.image.BufferedImage;

import java.io.ByteArrayOutputStream;

import java.io.File;

 

import javax.imageio.ImageIO;

import javax.swing.ImageIcon;

 

import org.apache.log4j.Logger;

 

public class Alpha {

 

    protected static Logger logger = Logger.getLogger(ClientSocket.class);

 

public byte[] transferAlpha(Image image) {

 

   ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();

 

   try {

    ImageIcon imageIcon = new ImageIcon(image);

    BufferedImage bufferedImage = new BufferedImage(imageIcon

      .getIconWidth(), imageIcon.getIconHeight(),

      BufferedImage.TYPE_4BYTE_ABGR);

    Graphics2D g2D = (Graphics2D) bufferedImage.getGraphics();

    g2D.drawImage(imageIcon.getImage(), 0, 0, imageIcon

      .getImageObserver());

    int alpha = 0;

    for (int j1 = bufferedImage.getMinY(); j1 < bufferedImage

      .getHeight(); j1++) {

     for (int j2 = bufferedImage.getMinX(); j2 < bufferedImage

       .getWidth(); j2++) {

      int rgb = bufferedImage.getRGB(j2, j1);

    

      int R =(rgb & 0xff0000 ) >> 16 ;

      int G= (rgb & 0xff00 ) >> 8 ;

      int B= (rgb & 0xff );

      if(((255-R)<30) && ((255-G)<30) && ((255-B)<30)){

       rgb = ((alpha + 1) << 24) | (rgb & 0x00ffffff);

      }

 

      bufferedImage.setRGB(j2, j1, rgb);

 

     }

    }

 

    g2D.drawImage(bufferedImage, 0, 0, imageIcon.getImageObserver());

    //ImageIO.write(bufferedImage, "png", new File("d:/test.png.png"));

 

    ImageIO.write(bufferedImage, "png", byteArrayOutputStream);

   } catch (Exception e) {

    logger.error(e.toString());

   }finally{

   

   }

 

   return byteArrayOutputStream.toByteArray();

 

}

}