hide_subimage.py

from PIL import Image

def int_to_string(rgb):
    r, g, b = rgb
    return ('{0:08b}'.format(r),
            '{0:08b}'.format(g),
            '{0:08b}'.format(b))

def string_to_int(rgb):
    r, g, b = rgb
    return (int(r, 2),
            int(g, 2),
            int(b, 2))

def merge_rgb(rgb1, rgb2):
    r1, g1, b1 = rgb1
    r2, g2, b2 = rgb2
    rgb = (r1[:4] + r2[:4],
           g1[:4] + g2[:4],
           b1[:4] + b2[:4])
    return rgb

def merge_images(img1, img2):
    if img2.size[0] > img1.size[0] or img2.size[1] > img1.size[1]:
        raise ValueError('Image 2 should not be larger than Image 1!')

    # Get the pixel map of the two images
    pixel_map1 = img1.load()
    pixel_map2 = img2.load()

    # Create a new image that will be outputted
    new_image = Image.new(img1.mode, img1.size)
    pixels_new = new_image.load()

    for i in range(img1.size[0]):
        for j in range(img1.size[1]):
            rgb1 = int_to_string(pixel_map1[i, j])
            # Use a black pixel as default
            rgb2 = int_to_string((0, 0, 0))

            # Check if the pixel map position is valid for the second image
            if i < img2.size[0] and j < img2.size[1]:
                rgb2 = int_to_string(pixel_map2[i, j])

            # Merge the two pixels and convert it to a integer tuple
            rgb = merge_rgb(rgb1, rgb2)

            pixels_new[i, j] = string_to_int(rgb)

    return new_image

def unmerge(img):

    # Load the pixel map
    pixel_map = img.load()

    # Create the new image and load the pixel map
    new_image = Image.new(img.mode, img.size)
    pixels_new = new_image.load()

    # Tuple used to store the image original size
    original_size = img.size

    for i in range(img.size[0]):
        for j in range(img.size[1]):
            # Get the RGB (as a string tuple) from the current pixel
            r, g, b = int_to_string(pixel_map[i, j])

            # Extract the last 4 bits (corresponding to the hidden image)
            # Concatenate 4 zero bits because we are working with 8 bit
            rgb = (r[4:] + '0000',
                   g[4:] + '0000',
                   b[4:] + '0000')

            # Convert it to an integer tuple
            pixels_new[i, j] = string_to_int(rgb)

            # If this is a 'valid' position, store it
            # as the last valid position
            if pixels_new[i, j] != (0, 0, 0):
                original_size = (i + 1, j + 1)

    # Crop the image based on the 'valid' pixels
    new_image = new_image.crop((0, 0, original_size[0], original_size[1]))

    return new_image