如何根据我的信息更改每个像素的LSB

Question

I am trying to implement a simple encoding program where I can hide a message in the LSB of the pixels of an image. So far I've got the byte array from the message

    private static byte[] ConvertMessageToByte(String message,
        byte[] messageBytes) {
    // takes in the message and stores them into bytes
    // returns message byte array
    byte[] messageByteArray = message.getBytes();

    return messageByteArray;

}

I have also got the byte array for the corresponding image that i want to encode onto

    private static byte[] getPixelByteArray(BufferedImage bufferedImage) {

    WritableRaster raster = bufferedImage.getRaster();

    DataBufferByte buffer = (DataBufferByte) raster.getDataBuffer();

    return buffer.getData();

}

Till this point I don't quite understand my following steps after. Do I iterate through the image byte array and store each ARGB values in another byte array? Also how would I apply the message bit values to the pixels?

Answer 1

private static byte[] ConvertMessageToByte(String message, byte[] messageBytes) {
    byte[] messageByteArray = message.getBytes();
    return messageByteArray;
}

Regarding this method: convertMessageToBytes is a better name as a lowercase first letter is more conventional as well as the fact that you are producing an array of multiple bytes and not just one. This method does not require the second byte[] parameter as it can be simplified to return message.getBytes(); and produce the same effect. Furthermore, String.getBytes() is typically called in the parent function of this as it is not widely considered worthy of wrapping given that is one line. In conclusion: remove this method and use byte[] ba = s.getBytes(); in your main code instead.

Personally, I process images as 3_BYTE_RGB as that is how they are most commonly thought of and, indeed, represented on a physical monitor or printer and stored in the case of many image formats. HSL (LSB) is typically a user-end representation of colour. You should be thinking in RGB not HSL.

Instead of dealing with the image as a byte[] , use int BufferedImage.getRGB(int x, int y) as it's easier to do and easier to access. The following function may be of use. I'll let you write the reverse.

private static int[] getColourAt(BufferedImage image, int x, int, y) {
  int rgb = image.getRGB(x, y);
  int r = rgb >> 16;
  int g = (rgb >> 8) % 256;
  int b = rgb % 256;
  return new int[] {r, g, b};
}

From there, you should loop through each pixel and adjust as you like.