Discrete Cosine Transform Watermarking
In DCT the image is divided into different frequency band, and then embedding watermarking
into the middle frequency bands of an image. DCT represents data in terms of frequency space
rather than an amplitude space. DCT based watermarking techniques are robust compared to
spatial domain techniques.
Steps in DCT Watermarking Algorithm (Block Based).
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Divide the image into non-overlapping blocks of 8×8
Apply forward DCT to each of these blocks
Apply some block selection criteria (e.g. HVS)
Apply coefficient selection criteria
Embed watermark
Apply inverse DCT transform on each block