
43Image Transforms
These values of step size are arrived at by the heuristic approach through
experimentation for the given values of PSNR. These values of step size will
be used in watermark embedding and extraction as described in the next
section.
3.5.2.2 Watermark Embedding
• Divide the source image into nonoverlapping blocks of 8 × 8.
• Compute the forward DCT for each of these blocks.
• Scan the coefcients in a zigzag fashion.
• The DC coefcient and the rst AC coefcient are used for water-
mark embedding in the block. These locations are shared between
the encoder and decoder. The other coefcients in the block are left
unaltered. ...