Input: Colored Secret Image (Image) of size N × M a Private Key K1

Output: Key share of size N × M

Steps:

1. Halftone the colored secret image (Image) using a dithering technique (Img).

2. Split (Img) into three layers R,G, and B, where:

3. Generate one layer Random share (mask share) with the same size as the secret image (see Figure 1 and Figure 2).

, do the following:

According to the private key K1, generate randomly a value either 0 or 1 and store it in the first pixel in the mask block (Mask_ij). The other pixel (Mask_i+1j) is filled with the complement value of the first pixel (Mask_ij). This step will make the mask a half black- and-white block.

The values for each block will be:

4. Generate a key share (share 2) according to the following steps:

For all halftone image layers of the secret image (ImgR, ImgG, ImgB) do the following:

a), do the following:

According to the value of first pixel in each block (ImgR_ij):

i) If ImgR_ij = 0, set the complement of the corresponding mask block values to the corresponding position of Share 2R block (Share 2R_ij, Share 2R_i+1j)

ii) If ImgR_ij = 1, set the same values of the corresponding mask block to the corresponding position of Share 2R block (Share 2R_ij, Share 2R_i+1j)

b) Repeat step (a) for ImgG and ImgB, then store the outcomes in Share 2G and Share 2B respectively.