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Transcript of 1 A Combined Approach to Integrity Protection and Verification of Palette Images Using Fragile...
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A Combined Approach to Integrity Protection and Verification of Palette Images Using
Fragile Watermarks and Digital Signatures
Source: IEICE TRANS. On FUNDAMENTALS, vol.
E87-A, no. 6, pp. 1612- 1619, Jun. 2004
Author: Chih-Hsuan Tzeng and Wen-Hsiang Tsai
Speaker: Na-I Wu ( 吳男益 )
Data: 2004/09/16
2
Outline
• Introduction
• The proposed method
(1) Fragile watermarking embedding
(2) Generate “digital signatures”
• Experimental results
3
Introduction An indexed image consists of data matrix, X, and a colormap matrix, map.
Size: 129 x 126
Ex: 256 色Indices:
form 1 to 256
File Size: Color map: 129 x 126 x 8 Indices: 256 x 3 x 8
6.19k bytes
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Introduction
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The proposed method Fragile watermarking embedding
To classify pixels into embeddable and non-embeddable
ones.
Embed
authentication
signals
Generate
Digital
signature
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Fragile watermarking embedding
• Raster Scanning Manner : to find “embeddable”, and “non-embeddable”
256 256 256 200 154 123 200 154
256 256 256 200 155 132 200 155
256 256 256 200 156 133 200 156
200 200 200 200 163 50 200 163
256 256 256 200 154 123 200 154
256 256 256 200 155 132 200 155
256 256 256 200 156 133 200 156
200 200 200 200 163 50 200 163
8x8
• Raster Scanning Manner : to find “embeddable”, and “non-embeddable”
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• Raster Scanning Manner : to find “embeddable”, and “non-embeddable”
P1(i-1, j-1) P2(i, j-1) P3(I+1, j-1)
P4(i-1, j) X(i,j)
Raster Scanning
Fragile watermarking embedding
α: the number of distinct colors of pixels in Prec(X)
β: The maximum color distance dmax(X, Prec(X))
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• How to compute α, β values
12 12 12
12 60 α = 1
12 12 16
10 10 α = 3
Fragile watermarking embedding
12(50, 60, 70) 轉成 L, a, b 顏色模式 (69, 10, 5)10(90, 10, 60) 轉成 L, a, b 顏色模式 (10, 7, 6)兩者的距離 =[(69-10)2+(10-7)2+(5-6)2]1/2
L: luminancea: green to red B: blue to yellow
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Fragile watermarking embedding
The values of Tc and Td be set by user
EX1: Tc =2, Td =10
12 12 12
12 12α = 0, β = 0
12 12 12
12 60α = 1, β = 48
“non-embeddable”
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The values of Tc and Td be selected by user
EX2: Tc =2, Td =10
“embeddable”
12 12 16
10 10α = 3, β = 6
12 16 17
10 18α = 4, β = 8
Fragile watermarking embedding
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Palette Mapping Function M
Fragile watermarking embedding
1 (120,50,30)
2 (111,51,21)
3 (112,52,32)
4 (123,13,33)
5 (134,4,34)
6 (25,55,35)
Color palette
重排列
f(u)=216xr +28xg +b
換算權重值 1 7877150
2 7287573
3 7353376
4 8064289
5 8782882
6 1652515
5 8782882
4 8064289
1 7877150
3 7353376
2 7287573
6 1652515
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Palette Mapping Function M
Fragile watermarking embedding
58782882
48064289
17877150
37353376
27287573
6 1652515
K: secret key
Generate a random bit stream
1 1 0 0 1 1 若為 n 色,則產生 n bits.
51
41
10
30
21
6 1
13
Fragile watermarking embedding
Palette Mapping Function M
1 (120,50,30)1
2 (111,51,21)1
3 (112,52,32)0
4 (123,13,33)0
5 (134,4,34)1
6 (25,55,35)1
attack
1 (120,50,30)1
3 (112,52,32)1
2 (111,51,21)0
4 (123,13,33)0
5 (134,4,34)1
6 (25,55,35)1
將 pixel 值 2 變 3 , 3 變2
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EX2: Tc =2, Td =10 , and want to hide “0”
12 12 16
10 10α = 3, β = 6
Fragile watermarking embedding
1 2 3 4 5 6 7 8
9 10 11 12 13 14 15 16
1 0 1 1 0 1 0 1
0 0 1 0 1 0 1 1
K: secret key
No modify
Authentication Data: 010101011
K: secret key
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EX2: Tc =2, Td =10 , and want to hide “1”
12 12 16
10 10α = 3, β = 6
Fragile watermarking embedding
1 2 3 4 5 6 7 8
9 10 11 12 13 14 15 16
1 0 1 1 0 1 0 1
0 0 1 0 1 0 1 1
K: secret key
(1) 去找週遭 4 個的 Lab 顏色 模式,其差最小的那一個and (2) M(i)==secret data修改完之必需符合
“Embeddable pixels” 的規定 α > Tc and Td < β
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16
The proposed method Generate “digital signatures”
1 2 3 4 5 6 7 8
9 10 11 12 13 14 15 16
1 0 1 1 0 1 0 1
0 0 1 0 1 0 1 1
EX1: Tc =2, Td =10
12 12 12
12 12α = 0, β = 0
“non-embeddable”
0
Authentication Data: 010101011
K: secret key
XOR operator
0Generate “digital signatures”
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The proposed method
每個 8x8 區塊的 “ digital signatures ” 的長度不一樣, 故每個 簽章的前面先放 ceil(nxn) bits ,用來 記錄每個 小區塊的 簽章的長度。
將每個小區塊的簽章的長度,合併起來來, 最後放在檔頭。
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The Authentication ProcessThe Authentication ProcessEX2: Tc =2, Td =10
12 12 16
10 10α = 3, β = 416
1 2 3 4 5 6 7 8
9 10 11 12 13 14 15 16
1 0 1 1 0 1 0 1
0 0 1 0 1 0 1 1
K: secret key
K: Authentication Data
secret data “1”
temper
12 12 16
10 10α = 3, β = 412
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The Authentication ProcessThe Authentication ProcessEX1: Tc =2, Td =10
12 12 12
12 12α = 0, β = 0
“non-embeddable”
1 2 3 4 5 6 7 8
9 10 11 12 13 14 15 16
K: secret key
K: Authentication Data
010101011
“digital signatures” 0
1 0 1 1 0 1 0 1
0 0 1 0 1 0 1 1
XOR operator
temper
12 12 12
10 13α = 1, β = 1
1
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Experimental Results
1
1( , ' )
N
i ii
ADEPB d c cN
Block size = 8 × 8 Tc= 2, Td= 15
Size: 560 × 504
256 palette colors
Digital signatures:
7938bytes
The degrees of average distortion in the embeddable pixels of a block:
1
1( , ' )
N
i ii
ADEPB d c cN
ADEPB(max):8.25
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Experimental Results
Size: 488 × 672
64 palette colores
Digital signatures: 11907bytes
ADEPB(max):9.76