A Steganographic Method for Images by PixelValue Differencing

1
A Steganographic Method for Images by Pixel-Value
Differencing

• Source Pattern Recognition Letters, vol. 24, pp.
  1613-1626, 2003
• Authors Da-Chun Wu and Wen-Hsiang Tsai
• Present by ???

2
The LSB Methods Problem

• Less imperceptible
• The dual statistics methods can be employed to
  detect the existence of LSB steganography in
  images

3
Pixel-Value Differencing Method

• Principle
• Changes of the gray values of pixels in smooth
  areas in images are more easily noticed by human
  eyes
• Concept
• Embed more data in edged areas than in the smooth
  areas

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Smooth Area V.S. Edge Area
Better
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Algorithm
6
Algorithm (Cont.)
7
Difference Table
Difference range -255255 Absolute range
0255
3-bits
6-bits
255
0
8
16
32
64
128
8
8
16
32
64
128
100
-1


-
-
100
200
100
99
8
Scan Order
120
20, -23, -31, 5
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Embedding Process
Difference table
255
0
8
16
32
64
128
8
8
16
32
64
128
Secret bits11000011
How to embed?
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Embedding Process (Cont.)
11
Embedding Process (Cont.)
161228
secret bits1100212
20
28
20

-
100
120
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Example 2
secret bits000020
16
20
20

-
100
120
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Example 3 (falling-off-boundary)
161228
secret bits1100212
20
28
20

-
0
20
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Falling-Off-Boundary

• If either or falls off the boundary of 0
  or 255, we regard the block to have the
  possibility of falling-off, and abandon the block
  for embedding data.

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Example
secret bits1100212
20
20

-
0
20
16
Experiments
17
Experiments (Cont.)
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Discussions
19
Discussions (Cont.)