为不同大小的图片添加纯色背景

 调用代码：

 File file = new File("需要加背景的图片的全路径");  //比如"D:\Download\test.png"
InputStream in = new FileInputStream(file);
BufferedImage bufferedImage = ImageUtil.reSquareAddBackground(in, 背景图宽, 背景图高, 背景颜色);
//比如 ImageUtil.reSquareAddBackground(in, 1024, 1024, Color.PINK(粉色)/Color.WHITE(白色))
File newFile = new File("生成的新图片的全路径");  //比如"D:\Download\test-pink.png"
ImageIO.write(bufferedImage, "生成图片格式/后缀", newFile);  //比如 "png"

处理前：

处理后：

白色背景不太明显，换个粉色的~

    
    public static BufferedImage reSquareAddBackground(InputStream downloadImage, Integer backWidth, Integer backHeight, Color color) throws IOException {
        // 先创建一个纯色背景图
        BufferedImage biNew = new BufferedImage(backWidth, backHeight, BufferedImage.TYPE_INT_RGB);
        Graphics g = biNew.getGraphics();
        g.setColor(color);  //g.setColor(Color.white);
        g.fillRect(0, 0, backWidth, backHeight);   // 矩形填充
        g.dispose();

        BufferedImage bi = ImageIO.read(downloadImage);
        int width = bi.getWidth();
        int height = bi.getHeight();
        int stepH = 0; //上下间隙
        int stepW = 0; //左右间隙
        double ratioW = width * 1.0 / backWidth;
        double ratioH = height * 1.0 / backHeight;
        if (ratioH > ratioW) {
            //按高缩放
            height = backHeight;
            width = (int) (width / ratioH);
            stepW = (backWidth - width) / 2;
            //获取缩放后的Image对象
            bi = getZoomScaleBufferedImage(bi, width, height);
        } else {
            //按宽缩放
            //获取缩放后的长和宽
            width = backWidth;
            height = (int) (height / ratioW);
            stepH = (backHeight - height) / 2;
            //获取缩放后的Image对象
            bi = getZoomScaleBufferedImage(bi, width, height);
        }

        int minX = bi.getMinX();
        int minY = bi.getMinY();
        //遍历长和宽上的每个像素
        for (int i = minX; i < width; i++) {
            for (int j = minY; j < height; j++) {
                //得到指定像素（i,j)上的RGB值，
                int pixel = bi.getRGB(i, j);
                //判断改像素是否有值（也可以通过位运算分别求得RGB值再进行判断）
                if (pixel == -16777216) {
                    continue;
                }
                biNew.setRGB(i + stepW, j + stepH, pixel);
            }
        }
        System.out.println("完成^ ^");
        return biNew;
    }