Java核心: 为图片生成水印

今天干了一件特别不务正业的事，做了一个小程序用来给图片添加水印。事情的起因是需要将自己的身份证照片分享给别人，手边并没有一个趁手的工具来生成图片水印。很多APP提供了水印的功能，但会把我的图片上传到他们的服务器，身份证太敏感了，显然我并不想让别人有机会保留照片。

我把图片处理做了一个抽象，入参是BufferedImage，对图片添加水印、盲印、隐式写入后返回新的BufferedImage作为结果。

package org.keyniu.watermark.image;

import java.awt.image.BufferedImage;

public interface ImageProcess {

    /**

     * @param org
     * @return
     */
    public BufferedImage process(BufferedImage org) throws Exception;

}

1. 基本实现

我们先给出一版基本的实现

package org.keyniu.watermark.image;


...
/**
 * 基于JDK的Graphics2D实现
 */
public class Graphics2DWatermark implements ImageProcess {
    ...     
    public BufferedImage process(BufferedImage org) throws UnsupportedEncodingException, NoSuchAlgorithmException {
        BufferedImage marked = new BufferedImage(org.getWidth(), org.getHeight(), BufferedImage.TYPE_INT_RGB);
        Graphics2D g2d = marked.createGraphics();
        g2d.drawImage(org, 0, 0, null); // 创建结果图片，并绘制原图

        // 设置字体，计算每个水印文字的块大小
        FontRenderContext context = g2d.getFontRenderContext();
        Font font = new Font(fontName, Font.BOLD, fontSize);
        g2d.setFont(font);
        TextMetadata textMeta = getTextMetadata(font, context, text);

        // 设置水印透明度，默认选择45°
        g2d.setComposite(AlphaComposite.getInstance(AlphaComposite.SRC_OVER, alpha)); // 设置透明度，0.0~1.0
        g2d.rotate(Math.PI * rotateArch / 180, org.getWidth() / 2, org.getHeight() / 2);

        // 计算图片中每行能放几个水印，要放多少行
        ImageMetadata imageMeta = new ImageMetadata(org.getWidth(), org.getHeight());
        int columnCount = imageMeta.getColumnCount(textMeta.getWidth());
        int rowCount = imageMeta.getRowCount(textMeta.getHeight() + textMeta.getCrcHeight());

        AffineTransform transform = g2d.getTransform();
        for (int rIdx = 0; rIdx < rowCount; rIdx++) {
            for (int cIdx = 0; cIdx < columnCount; cIdx++) {
                g2d.setTransform(transform);
                randomRotate(g2d, imageMeta);
                randomTransform(g2d);
                watermark(g2d, imageMeta, textMeta, rIdx, cIdx);
            }
        }
        g2d.setTransform(transform);
        // 结束绘制，释放资源
        g2d.dispose();
        return marked;
    }

    private void watermark(Graphics2D g2d, ImageMetadata imageMeta, TextMetadata textMeta, int rIdx, int cIdx) {
        Point offset = imageMeta.getOffset();
        Point textLoc = textMeta.textLocation(rIdx, cIdx);
        Point crcLoc = textMeta.crcLocation(rIdx, cIdx);
        randomGradient(g2d, offset.x + textLoc.x, offset.y + textLoc.y, textMeta.totalTextWidth(), textMeta.totalTextHeight());
        g2d.drawString(textMeta.getText(), offset.x + textLoc.x, offset.y + textLoc.y);
        randomGradient(g2d, offset.x + crcLoc.x, offset.y + crcLoc.y, textMeta.totalCrcWidth(), textMeta.totalCrcHeight());
        g2d.drawString(textMeta.getCrc(), offset.x + crcLoc.x, offset.y + crcLoc.y);
    }

    protected void randomRotate(Graphics2D g2d, ImageMetadata imageMeta) { // 供子类覆盖，自定义旋转的逻辑
    }


    protected void randomTransform(Graphics2D g2d) { // 供子类覆盖，自定义AffineTransform的逻辑
    }


    protected void randomGradient(Graphics2D g2d, int x, int y, int dx, int dy) { // 供子类覆盖，实现渐变色的逻辑
    }

    ... 
}

本地main方法测试，测试代码是这样的的。

public static void main(String[] args) throws Exception {
    Graphics2DWatermark watermark = new Graphics2DWatermark("仅用于车险办理");
    BufferedImage image = ImageIO.read(new File("D:\\blog\\linux.png"));
    BufferedImage certified = watermark.process(image);
    ImageIO.write(certified, "jpg", new File("D:\\blog\\linux_mark.png"));
}

左边是原始图片，右边是加了水印后的图片

2. 旋转变换

太有规律的水印很容易就被擦除水印，上面的实现中我们预留了3个接口，用来扩展实现，分别是:

randomRotate，输出一行水印之前，有机会做旋转
randomTransform，输出一行水印前，有机会执行AffineTransfrom
randomGradient，输出水印文字和CRC之前，有机会设置渐变色

我们提供了一个增强实现

public class EnhancedGraphics2DWatermark extends Graphics2DWatermark {

    public EnhancedGraphics2DWatermark(String text) {
        super(text);
    }

    protected void randomRotate(Graphics2D g2d, ImageMetadata imageMeta) {
        g2d.rotate(Math.PI * (Math.random() * 45 - 45) / 180, imageMeta.getSourceX(), imageMeta.getSourceY());
    }

    @Override
    protected void randomTransform(Graphics2D g2d) {
        if (Math.random() < 0.5) {
            g2d.shear(Math.random() * 0.2, 0);
        } else {
            g2d.shear(0, Math.random() * 0.2);
        }
    }

    protected void randomGradient(Graphics2D g2d, int fx, int fy, int tx, int ty) {
        Color from = generateColor();
        Color to = reverse(from);
        GradientPaint gp = new GradientPaint(fx, fy, from, tx, ty, to);
        g2d.setPaint(gp);
    }

    private Color generateColor() {
        int r = (int) (256 * Math.random() + fontColor.getRed()) & 0xFF;
        int g = (int) (256 * Math.random() + fontColor.getGreen()) & 0xFF;
        int b = (int) (256 * Math.random() + fontColor.getBlue()) & 0xFF;
        return new Color(r, g, b);
    }

    private Color reverse(Color c) {
        return new Color((256 - c.getRed()) & 0xFF, (256 - c.getGreen()) & 0xFF, (256 - c.getBlue()) & 0XFF, c.getAlpha());
    }

}

修改测试的main方法，改用这个实现

public static void main(String[] args) throws Exception {
    Graphics2DWatermark watermark = new EnhancedGraphics2DWatermark("仅用于车险办理");
    BufferedImage image = ImageIO.read(new File("D:\\blog\\linux.png"));
    BufferedImage certified = watermark.process(image);
    ImageIO.write(certified, "jpg", new File("D:\\blog\\linux_mark.png"));
}

这是新的水印效果