今天工作上遇到一個需求，需要掃描原圖與加水印之後的圖片做對比，從而拿到加水印圖片的原始圖片，想到的是把檔案轉換為二進位制流或者用圖片的畫素點做對比，巧合之下在網上發現了下面一段程式碼，稍作修改之後就能滿足我的需求，給作者點贊。

原文：http://www.open-open.com/code/view/1448334323079。

程式碼如下：

import java.awt.image.BufferedImage;
import java.io.File;
import javax.imageio.ImageIO;

/**
 * 比較兩張圖片的相似度
 * @author Guihua
 *
 */
public class BMPLoader {
    // 改變成二進位制碼
    public static String[][] getPX(String args) {
        int[] rgb = new int[3];

        File file = new File(args);
        BufferedImage bi = null;
        try {
            bi = ImageIO.read(file);
        } catch (Exception e) {
            e.printStackTrace();
        }

        int width = bi.getWidth();
        int height = bi.getHeight();
        int minx = bi.getMinX();
        int miny = bi.getMinY();
        String[][] list = new String[width][height];
        for (int i = minx; i < width; i++) {
            for (int j = miny; j < height; j++) {
                int pixel = bi.getRGB(i, j);
                rgb[0] = (pixel & 0xff0000) >> 16;
                rgb[1] = (pixel & 0xff00) >> 8;
                rgb[2] = (pixel & 0xff);
                list[i][j] = rgb[0] + "," + rgb[1] + "," + rgb[2];

            }
        }
        return list;

    }
    
    public static void compareImage(String imgPath1, String imgPath2){
        String[] images = {imgPath1, imgPath2};
        if (images.length == 0) {
            System.out.println("Usage >java BMPLoader ImageFile.bmp");
            System.exit(0);
        }

        // 分析圖片相似度 begin
        String[][] list1 = getPX(images[0]);
        String[][] list2 = getPX(images[1]);
        int xiangsi = 0;
        int busi = 0;
        int i = 0, j = 0;
        for (String[] strings : list1) {
            if ((i + 1) == list1.length) {
                continue;
            }
            for (int m=0; m<strings.length; m++) {
                try {
                    String[] value1 = list1[i][j].toString().split(",");
                    String[] value2 = list2[i][j].toString().split(",");
                    int k = 0;
                    for (int n=0; n<value2.length; n++) {
                        if (Math.abs(Integer.parseInt(value1[k]) - Integer.parseInt(value2[k])) < 5) {
                            xiangsi++;
                        } else {
                            busi++;
                        }
                    }
                } catch (RuntimeException e) {
                    continue;
                }
                j++;
            }
            i++;
        }

        list1 = getPX(images[1]);
        list2 = getPX(images[0]);
        i = 0;
        j = 0;
        for (String[] strings : list1) {
            if ((i + 1) == list1.length) {
                continue;
            }
            for (int m=0; m<strings.length; m++) {
                try {
                    String[] value1 = list1[i][j].toString().split(",");
                    String[] value2 = list2[i][j].toString().split(",");
                    int k = 0;
                    for (int n=0; n<value2.length; n++) {
                        if (Math.abs(Integer.parseInt(value1[k]) - Integer.parseInt(value2[k])) < 5) {
                            xiangsi++;
                        } else {
                            busi++;
                        }
                    }
                } catch (RuntimeException e) {
                    continue;
                }
                j++;
            }
            i++;
        }
        String baifen = "";
        try {
            baifen = ((Double.parseDouble(xiangsi + "") / Double.parseDouble((busi + xiangsi) + "")) + "");
            baifen = baifen.substring(baifen.indexOf(".") + 1, baifen.indexOf(".") + 3);
        } catch (Exception e) {
            baifen = "0";
        }
        if (baifen.length() <= 0) {
            baifen = "0";
        }
        if(busi == 0){
            baifen="100";
        }

        System.out.println("相似畫素數量：" + xiangsi + " 不相似畫素數量：" + busi + " 相似率：" + Integer.parseInt(baifen) + "%");

    }

    public static void main(String[] args){
        BMPLoader.compareImage("E:\\12.bmp", "E:\\1.bmp");
    }
}