nice one

 Steganography

Original Images

This is the image that will be used to hide the second image!
And this is the image that will be hidden in the first image!
Sources for the images:
https://www.hdwallpapers.net/abstract/colorful-diamond-wallpaper-674.htm
https://www.hdwallpapers.net/abstract/dark-wood-texture-wallpaper-383.htm

After the Hiding

This is what the image looks like with the hidden value:
And this is what the hidden image looks like after it is extracted:

Algorithm

The algorithm used to hide an image inside another using 2 bits is quite similar to the 4 bits, but has some distinctive differences. Instead of using 2^4, or 16, as the number used for dividing, we will be using 2^2, or 4.

The first two bits of the image to be hidden are selected using the shift function. Since it's a 2 bit hidden message, we take the two most significant bits of the image we are hiding, i.e., "Diamond.jpg", by dividing the pixel values by 64.

The first six bits of the image, "Dark Wood.jpg", are obtained using the chop2hide function.

Finally, the combined image is formed by adding the bits of the modified images together.

To get the hidden value back, we simply reverse what we have done to modify the image. This is implemented using the extract function.

Code

var start = new SimpleImage("Dark Wood.jpg");
var hide = new SimpleImage("Diamond.jpg");

function pixchange(pixval)
{
    //Since it's only two bits, instead of 2^4, we use 2^2
    var x = Math.floor(pixval/4) * 4;
    return x;
}

//Function to alter the image to be hidden
function chop2hide(image)
{
    for(var p of image.values())
    {
        p.setRed(pixchange(p.getRed()));
        p.setGreen(pixchange(p.getGreen()));
        p.setBlue(pixchange(p.getBlue()));
    }
    return image;
}

//Function to shift the bits of the main image
function shift(im)
{
  var nim = new SimpleImage(im.getWidth(), im.getHeight());
  for(var p of im.values())
  {
    var x = p.getX();
    var y = p.getY();
    var np = nim.getPixel(x,y);
    np.setRed(Math.floor(p.getRed()/64));
    np.setGreen(Math.floor(p.getGreen()/64));
    np.setBlue(Math.floor(p.getBlue()/64));
  }
  return nim;
}

start_mod = chop2hide(start);
hide_mod = shift(hide);
print(starts); //Prints the first image modified
print(hides); // Prints the second image modified

//Function to add the two numbers 
function add(a, b)
{
    var ans = a + b;
    return ans;
}

//Function to combine both images
function combine(st,hi)
{
    var fin = new SimpleImage (st.getWidth(),st.getHeight());
    for (var pixel_st of st.values())
    {
        var x = pixel_st.getX();
        var y = pixel_st.getY();
        var pixel_hi = hi.getPixel(x,y);
        var pixel_fin = fin.getPixel(x,y);
        pixel_fin.setRed(add(pixel_st.getRed(),pixel_hi.getRed()));
        pixel_fin.setGreen(add(pixel_st.getGreen(),pixel_hi.getGreen()));
        pixel_fin.setBlue(add(pixel_st.getBlue(),pixel_hi.getBlue()));
    }
    return fin;
}

combinedimage=combine(start_mod,hide_mod);
print(combinedimage); //Prints combined image

//Function to get the hidden value back
function pchange(pixval)
{
    var x = (pixval-Math.floor(pixval/4)*4)*64;
    return x;
}

//Function to extract the hidden image
function extract(image)
{
    for(var pixel of image.values())
    {
        pixel.setRed(pchange(pixel.getRed()));
        pixel.setGreen(pchange(pixel.getGreen()));
        pixel.setBlue(pchange(pixel.getBlue()));
    }
    return image;
}

hiddenimage = extract(combinedimage);
print(hiddenimage); //Prints hidden image

Hidden Message in Given Picture

The following picture was given with a hidden message to extract:
After extraction, this is what the hidden message was!

Algorithm

The algorithm used for the extraction is similar to the one used for extraction in the first part.

Code

function pchange(pixval)
{
    var x = (pixval-Math.floor(pixval/4)*4)*64;
    return x;
}

function extract(image)
{
    for(var pixel of image.values())
    {
        pixel.setRed(pchange(pixel.getRed()));
        pixel.setGreen(pchange(pixel.getGreen()));
        pixel.setBlue(pchange(pixel.getBlue()));
    }
    return image;
}

var combinedimage = new SimpleImage("hiltonHiding2bitMessage.png");
hiddenimage = extract(combinedimage);

print(hiddenimage);