An Intro

Transform is applied on 2×2 masks of the source image in row major order to transform original sub image (cover image) block to its corresponding frequency domain.

What Does It Do?

So it looks like we can mask an image using Z-Transform and embed an message or even an image….Along with the hidden image , the dimensional values are also embedded into the real part of the host image mask on fourth LSB bit of the transformed coefficient within 2×2 mask

How does Z-transform work?

The Formula For Z-Transform is:

limit is taken 0 to α as pixel value m=0cannot be negative for an image) In the present implementation the value of r is taken as 1 and ω varies between 0<= ω <=2π.

The Schematic Diagram of FDSZT is as follows :

Algorithm For Insertion

• Step 1: Obtain the size of the hidden image m×n
• Step 2: For each hidden message/image, read source image mask of size 2×2 in row major order. Apply Z-Transform onto the selected cover image mask(2 x 2) to obtain coefficients in transformed domain.
• Step 3:Obtain Median of the four frequency coefficients obtained in step 2 to choose the byte for embedding.
• Step 4:Embed 1 secret bit onto the fourth LSB position towards left of the byte.
• Step 5:Apply adjustmet if necessary so that the coefficient will be the median of the mask after embedding
• Step 5: Apply IZ-Transform to back the mask from Z domain to spatial domain.
• Step 6: Repeat step 2 to 6 for the whole cover image image.
• Step 7: Stop

Formulas Used :

Algorithm For Extraction

The hidden image is received in spatial domain. The embedded image is taken as the input and the hidden message/ image size, content are extracted from it in transform domain.

Input: Embedded image of size p×q. Output: Host image of size p×q, hidden image of size m×n.

Method: Extract bits of hidden image from embedded image

• Step 1: Read embedded image mask( of size 2×2) in row major order. Apply Z-Transform onto the embedded image mask to transform the embedded sub image from spatial to frequency domain so that four frequency components are regenerated.
• Step 2:Obtain Median of four frequency components to choose the embedded byte from 2×2 mask.
• Step 3: Extract the secret bit from the byte embedded in fourth LSB position. Replace hidden message/ image bit position in the block by ‘1’. For each eight extracted bits construct one image pixel of authenticating image.
• Step 4: Repeat step 1 to 3 to regenerate hidden image as per size of the hidden image.
• Step 5: Stop