Watermarking Text Document Images Using Edge Direction Histograms

Young-Won Kim and Il-Seok OhPattern Recognition Letters, Vol. 25, 2004, pp. 1243–1251Reporter: Jen-Bang Feng

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Outline

Data Hiding vs. Watermark vs. Authentication

Related Works The Proposed Scheme Experimental Results Comments

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Watermark

Purpose: Copyright protection for digital media

Considerations: Embed watermark into media Retrieve watermark against attacks

(capacity is not important relatively)WM+

Original image

Protected image

Embed

tested image

RetrieveWM’

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Data Hiding vs. Watermark vs. Authentication

Data Hiding (Steganographic) Hide data in media Request high capacity

Watermark Copyright protection for media Request high robust

Authentication Check the correctness of media Request high sensitive

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Related Works Character-level methods

Brassil et al. (1999) moves a line (word) upward or downward (left or right) depending on the bin

ary signal Huang and Yan (2001)

modifes the inter-word spaces Feature-level methods

Amano and Misaki (1999) modifying features such as stroke (筆觸 ) width or serif (截線 ) shape

Brassil et al. (1994) adjusts the height of the vertical strokes of characters such as b, d, and h

Pixel-level methods Bhattacharjya and Ancin, (1999)

an image is partitioned into a set of 3x3 sites and one bit is inserted per two sites

upward

downward

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The Proposed Scheme

For grayscale text document images Modify the distribution of edges

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The Proposed Scheme1. Edge detection

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The Proposed Scheme2. Change the distribution of edges

0 is embedded 1 is embedded

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The Decoding Process

Δ > 0: 0 is embeddedΔ < 0: 1 is embedded

Hm: ratio of mother histogramHc: ratio of child histogram

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Experimental Results

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Experimental Results

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Experimental Results

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Comments

Should not need the original image Can be modified and used for

authentication Filled ratio?