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Text Digital Watermarking Of A Malayalam Text Document Based On Fragments Regrouping Strategy
Problem Definition
Embedding a digital watermark into a digital text document that carries information unique to the copyright owner or the creator of the document.
Introduction
Digital Watermarking
Text Digital Watermarking
Process of embedding a digital watermark into a digital text document.
Proposed in 1995 by Brassil and Low.
Classification
Based on the format
Based on Expand space
Based on semantics
Format based Text Watermarking
Three methods
Line shift coding
Word shift coding
Feature coding
Watermark capacity and robustness of most algorithms unsatisfactory.
Enhancing robustness using Fragments regrouping strategy.
Literature Survey
Existing works
Brassil and Maxemchunk[1] proposed coding methods that is applied either to a bitmap image or to a format file.
Line shift coding
Word shift coding
Feature coding : altering features (eg: alter upward the vertical endlines – letters b,d,h etc.)
Merits and demerits:
Line shift coding has stronger robust but low watermarking capacity.
Word shift coding has better watermarking imperceptibility.
Feature coding is hard to implement for all kind of formats.
R.Davarsani and K.Yaghmei[2] proposed a method to embed watermark data in Farsi letters by readjusting the amount of their slopes.
Merits: Better watermarking capacity and blindness
Demerits: Can only be used with special scripts.
Thein vui khen and A.Makur[3] introduced a word based self embedding watermarking scheme for document images coded in binary format.
Merits: Better coding of self embedding watermark.
Demerits: Extraneous detection and restoration failure.
Qing-Cheng Li and Zhen-Hua Dong[4] Proposed a novel watermarking algorithm based on Chinese character structure.
Merits : Stronger watermarking robustness , greater watermarking capacity and better watermarking imperceptibility.
Demerits: Applicable only to Chinese language. Watermark may be attacked.
Xinmin Zhou et al.[5] proposed a semi-fragile watermarking scheme for content authentication of Chinese text documents.
Merits: More secure and reliable
Demerits :No copyright protection.
Liu Jin’ An et al.[6] proposed a text digital watermarking for Chinese word document where inter character spaces are modified for coding.
Merits: Better capacity and efficient extraction of watermark.
Wengang Cheng et al.[7] proposed a text digital watermarking algorithm based on fragments regrouping strategy.
Merits : Stronger watermarking robustness,greater watermarking capacity and better watermarking invisibility.
Problem Description
In [7] an efficient text digital watermarking algorithm is proposed based on fragments regrouping strategy.
Hash function is used for mapping watermark into document.
Format based watermarking – color feature used for embedding watermarking.
This algorithm can only be used with document in RGB color format.
Study
Approach
Input : A Malayalam text document ,a watermark.
Fragment the watermark.
Find the characters with loops in the text document.
Embed the fragment using hash function into document characters redundantly.
Expected output.
A watermarked Malayalam document which is more robust ,have better capacity and better invisibility.