有什么方法可以将getRGB和setRGB与隐写术一起使用？

Question

Im writing a program with simple steganography implementation.

I have a problem becouse if I use setRGB and then getRGB for one pixel i got different values. I read that setRGB and getRGB are not the best idea for byte and bits operation but maybe there is a way? i would like to work with LSB of alpha red green and blue of every pixel and I have no idea how to do it with rasters and to be honest i spend a lot of time with writing some code to generate proper TYPE_INT_ARGB value... I would like to use every 2 LSB from ARGB so I have 8 bits for pixel - that gives one char for pixel.

System.out.println("ARGB in int befor edit: " + obraz.getRGB(0, 0));
    int RGB = obraz.getRGB(0, 0);
    int alpha = (RGB >> 24) & 0xFF;
    int red = (RGB >> 16) & 0xFF;
    int green = (RGB >> 8) & 0xFF;
    int blue = (RGB) & 0xFF;

   System.out.println("RGB: " + RGB);
   System.out.println("alpha: " + alpha);
   System.out.println("red: " + red); 
   System.out.println("green: " + green); 
   System.out.println("blue: " + blue);

   System.out.println("After:");
   int newARGB = addLetter(RGB, 'b'); //this change every two bits of ARGB
   int alpha2 = (newARGB >> 24) & 0xFF;
   int red2 = (newARGB >> 16) & 0xFF;
   int green2 = (newARGB >> 8) & 0xFF;
   int blue2 = (newARGB) & 0xFF;


obraz.setRGB(0,0,newRGB);

 System.out.println("ARGB in int after edition: " + obraz.getRGB(0, 0));
    int RGB3 = obraz.getRGB(0, 0);
    int alpha3 = (RGB3 >> 24) & 0xFF;
    int red3 = (RGB3 >> 16) & 0xFF;
    int green3 = (RGB3 >> 8) & 0xFF;
    int blue3 = (RGB3) & 0xFF;

   System.out.println("RGB: " + RGB3);
   System.out.println("alpha: " + alpha3);
   System.out.println("red: " + red3); 
   System.out.println("green: " + green3); 
   System.out.println("blue: " + blue3);

and the results are different so stegenography does not work...

this is the addLetter function

    public static int addLetter(int i, char letter)
{
    byte tym, tc;
    tc = (byte) letter;
    int ARGB;


    byte byte3 = (byte) ((i & 0xFF000000) >> 24);
    byte3 = (byte) (byte3 & (~0x00000003));
    tym = (byte) ((tc & 0xC0) >> 6);
    byte3 = (byte) (byte3 | tym);


    byte byte2 = (byte) ((i & 0x00FF0000) >> 16);
    byte2 = (byte) (byte2 & (~0x00000003));
    tym = (byte) ((tc & 0x30) >> 4);
    byte2 = (byte) (byte2 | tym);

    byte byte1 = (byte) ((i & 0x0000FF00) >> 8);
    byte1 = (byte) (byte1 & (~0x00000003));
    tym = (byte) ((tc & 0x0C) >> 2);
    byte1 = (byte) (byte1 | tym);

    byte byte0 = (byte) ((i & 0x000000FF));
    byte0 = (byte) (byte0 & (~0x00000003));
    tym = (byte) ((tc & 0x03));
    byte0 = (byte) (byte0 | tym);

    byte[] wynik = (new byte[]{byte3, byte2, byte1, byte0});
    return ByteBuffer.wrap(wynik).getInt();   

I will be greatefull for any help and understanding. Im still a beginer in Java

EDITED:

I will try to explain my problem one more time: Im using function //int i - im passing result of getRGB for pixel //char letter - that is a letter that im adding to 2 LSB of A,R,G and B value public static int addLetter(int i, char letter) { byte tym, tc; tc = (byte) letter; int ARGB;

    byte byte3 = (byte) ((i & 0xFF000000) >> 24);
    byte3 = (byte) (byte3 & (~0x00000003));
    tym = (byte) ((tc & 0xC0) >> 6);
    byte3 = (byte) (byte3 | tym);


    byte byte2 = (byte) ((i & 0x00FF0000) >> 16);
    byte2 = (byte) (byte2 & (~0x00000003));
    tym = (byte) ((tc & 0x30) >> 4);
    byte2 = (byte) (byte2 | tym);

    byte byte1 = (byte) ((i & 0x0000FF00) >> 8);
    byte1 = (byte) (byte1 & (~0x00000003));
    tym = (byte) ((tc & 0x0C) >> 2);
    byte1 = (byte) (byte1 | tym);

    byte byte0 = (byte) ((i & 0x000000FF));
    byte0 = (byte) (byte0 & (~0x00000003));
    tym = (byte) ((tc & 0x03));
    byte0 = (byte) (byte0 | tym);

    byte[] result = (new byte[]{byte3, byte2, byte1, byte0});
    return ByteBuffer.wrap(result).getInt();   
}

The problem is that after i pass it to BufferedImage using setRGB it change the values different than I want it to. Im checking it by another getRGB and the values are slighty different so I can't read my hidden letter.

Answer 1

You may have a problem here:

tym = (byte) ((tc & 0xC0) >> 6);

If tc (which is a byte ) is 1100 0100 , the mask will give 1100 0000 and right shifting by 6 using the >> operator will give... 1111 1111 !

Not sure whether this is what you really mean. If what you wanted is 0000 0011 then you must use >>> . The >> operator carries the sign bit.

Answer 2

I will take a guess and assume that your BufferedImage is of type RGB, even if you think you've set it to ARGB. The RGB type doesn't support an alpha channel and by setting your pixel value, it defaults to 255. If you need the information in the alpha channel to be stored properly, loading your image in a manner similar to below should work.

Example case set with a url, but you can ignore that and load any image you want.

You will notice that if you change BufferedImage.TYPE_INT_ARGB to BufferedImage.TYPE_INT_RGB , the alpha channel defaults to 255 when you fetch the pixel value.

import java.awt.Graphics2D;
import java.awt.image.BufferedImage;
import javax.imageio.ImageIO;
import java.io.*;
import java.net.URL;

class Blah {
    public static BufferedImage loadImage(String fname) {
        BufferedImage img = null;
        try {
            //File file = new File(fname);
            URL file = new URL("http://cdn.sstatic.net/stackexchange/img/logos/so/so-logo-med.png");
            BufferedImage in = ImageIO.read(file);
            img = new BufferedImage(in.getWidth(), in.getHeight(), BufferedImage.TYPE_INT_ARGB);
            Graphics2D g = img.createGraphics();
            g.drawImage(in, 0, 0, null);
            g.dispose();
        } catch (IOException e) { 
            e.printStackTrace();
        }
        return img;
    }

    public static int addLetter(int i, char letter) {
        byte byteChar = (byte)letter;
        int embeddingBits = (((byteChar >> 6) & 3) << 24) +
                            (((byteChar >> 4) & 3) << 16) +
                            (((byteChar >> 2) & 3) << 8) + 
                            (byteChar & 3);
        return (i & 0xfcfcfcfc) + embeddingBits;
    }

    public static char extractLetter(int i) {
        int intChar = (((i >> 24) & 3) << 6) +
                      (((i >> 16) & 3) << 4) +
                      (((i >> 8) & 3) << 2) +
                      (i & 3);
        return (char)intChar;
    }

    public static void main(String[] args) {
        BufferedImage img = loadImage("secret.png");

        int pixel = img.getRGB(0, 0);
        int modifiedPixel = addLetter(pixel, 'b');
        img.setRGB(0, 0, modifiedPixel);

        int checkPixel = img.getRGB(0, 0);
        char newLetter = extractLetter(checkPixel);

        System.out.println(modifiedPixel + " " + checkPixel);
        System.out.println("Extracted letter: " + newLetter);
    }
}