如何在压缩照片时设置背景透明

Question

我正在压缩一张照片，但有个问题阻止了我。它调用drawImage of Graphics2D，但最终输出显示源照片的透明区域作为黑色背景复制到最后一张照片。

为什么？?当源照片区域有透明背景时，如何设置背景透明?？

这是我的代码：

        Image image = ImageIO.read(new File(path + fileName));
        int imageWidth = image.getWidth(null);
        int imageHeight = image.getHeight(null);
        float scale = getRatio(imageWidth, imageHeight, 274, 392);
        imageWidth = (int) (scale * imageWidth);
        imageHeight = (int) (scale * imageHeight);

        image = image.getScaledInstance(imageWidth, imageHeight,
                Image.SCALE_SMOOTH);
        BufferedImage mBufferedImage = new BufferedImage(imageWidth,
                imageHeight, BufferedImage.TYPE_INT_RGB);
        Graphics2D g2 = mBufferedImage.createGraphics();

        g2.drawImage(image, 0, 0, imageWidth, imageHeight, null);
        g2.dispose();

        FileOutputStream out = new FileOutputStream(path + toFileName);
        ImageIO.write(mBufferedImage, "png", out);
        out.close();

Answer 1

package com.hb.util;


import java.awt.AlphaComposite;
import java.awt.Color;
import java.awt.Graphics2D;
import java.awt.Image;
import java.awt.Toolkit;
import java.awt.image.BufferedImage;
import java.awt.image.FilteredImageSource;
import java.awt.image.ImageFilter;
import java.awt.image.ImageProducer;
import java.awt.image.RGBImageFilter;
import java.io.ByteArrayOutputStream;
import java.io.File;
import java.io.IOException;

import javax.imageio.ImageIO;

import org.apache.commons.io.FileUtils;
import org.fusesource.hawtbuf.ByteArrayInputStream;

public class ImageCompressingUtils {

public static void main(String[] args) {
    String path = "F:/2huazhuangpin990x395.jpg";
    long c = System.currentTimeMillis();
    ImageCompressingUtils.compress(path, "F:/1.png", "png", 0.8);
    System.out.println("elapse time:"
            + (System.currentTimeMillis() - c) / 1000.0f + "s");
}

public static BufferedImage getTransparentScaledImage(BufferedImage originalImage, int finalWidth, int finalHeight) {
    int originalWidth = originalImage.getWidth();
    int originalHeight = originalImage.getHeight();

    if (originalWidth == 0 || originalHeight == 0
            || (originalWidth == finalWidth && originalHeight == finalHeight)) {
        return originalImage;
    }

    BufferedImage intermediateImage = new BufferedImage(finalWidth, finalHeight, BufferedImage.TYPE_INT_ARGB);
    Graphics2D gi = intermediateImage.createGraphics();
    gi.setComposite(AlphaComposite.SrcOver);
    gi.setColor(new Color(0, 0, 0, 0));
    gi.fillRect(0, 0, finalWidth, finalHeight);
    gi.drawImage(originalImage.getScaledInstance(finalWidth, finalHeight, Image.SCALE_SMOOTH), 0, 0, null);
    gi.dispose();

    return intermediateImage;
}

public static Image makeColorTransparent(Image im, final Color color) {
    ImageFilter filter = new RGBImageFilter() {
        public int markerRGB = color.getRGB() | 0xFF000000;

        public final int filterRGB(int x, int y, int rgb) {
            if ((rgb | 0xFF000000) == markerRGB) {
                return 0x00FFFFFF & rgb;
            } else {
                return rgb;
            }
        }
    };

    ImageProducer ip = new FilteredImageSource(im.getSource(), filter);
    return Toolkit.getDefaultToolkit().createImage(ip);
}

/**
 * 压缩
 * @param datas 数据
 * @param rate 压缩比率
 * @return
 */
public static byte[] compress(byte[] datas, String format, double rate) {
    try {
        BufferedImage srcImage = ImageIO.read(new ByteArrayInputStream(datas));
        int width = srcImage.getWidth();
        int height = srcImage.getHeight();
        BufferedImage descImage = getTransparentScaledImage(srcImage, ((Double)(width * rate)).intValue(), ((Double) (height * rate)).intValue());
        ByteArrayOutputStream out = new ByteArrayOutputStream();
        ImageIO.write(descImage, format == null ? "jpg" : format, out);
        return out.toByteArray();
    } catch (IOException e) {
        throw new RuntimeException(e);
    }
}

public static void compress(String srcPath, String descPath, String format, double rate) {
    try {
        byte[] datas = FileUtils.readFileToByteArray(new File(srcPath));
        byte[] finalDatas = compress(datas, format, rate);
        FileUtils.writeByteArrayToFile(new File(descPath), finalDatas);
    } catch(IOException e) {
        throw new RuntimeException(e);
    }
}
}

它起作用了。