Blind image data hiding based on self reference Source : Pattern Recognition Letters, Vol. 25, Aug. 2004, pp Authors: Yulin Wang and Alan Pearmain Speaker: Nan-I Wu ( 吳男益 ) Date: 2004/11/25( 四 )

Introduction Blind watermark technique: recover the watermark without using original host data. The proposed method base on relative modulation of the pixel value/DCT coefficient value by referring to its estimated one. One is based on the estimation of pixel luminance in spatial domain Another based on the estimation of block DCT AC coefficients.

The proposed scheme 1 (Spatial Domain) For a nature image, the luminance value of one pixel normally has a relation with its neighbor L Real The mean luminance value: Lmean

The embedding algorithm Embed an one-bit watermark into 3 x 3 sub-block Embedded bit is ‘1’ L Real ≥ L mean + ∆ 1 Embedded bit is ‘0’ L Real < L mean - ∆ 2 As experienced values, ∆ 1 and ∆ 2 are selected as 5- 10% of L Real

The extracting algorithm If L Real ≥ L mean extract bit ‘1’ If L Real < L mean extract bit ‘0’

The proposed scheme 2 (Frequency Domain) RGB to Y C b C r Y = R G B R=100 G=80 B= = 0.299* * *120

DCT The proposed scheme 2 (Frequency Domain)

The embedding algorithm Block1 DC1 Block2 DC2 Block3 DC3 Block4 DC4 Block5 DC5 Block6 DC6 Block7 DC7 Block8 DC8 Block9 DC AC(0,1)= x (DC 4 -DC 6 )/8 Select every nine 8 x 8 blocks as one group, in which 5 watermark bits can be embedded

The embedding algorithm Block1 DC1 Block2 DC2 Block3 DC3 Block4 DC4 Block5 DC5 Block6 DC6 Block7 DC7 Block8 DC8 Block9 DC AC(0,1)= x (DC 4 -DC 6 )/8 Set AC i ≥ AC’ i + ∆ to embed bit ‘1’ Set AC i ≤ AC’ i - ∆ to embed bit ‘0’ ∆ can be chosen as 5-15% of the original AC i value

The embedding algorithm Block1 DC1 Block2 DC2 Block3 DC3 Block4 DC4 Block5 DC5 Block6 DC6 Block7 DC7 Block8 DC8 Block9 DC AC(1,0)= x (DC 2 -DC 8 )/8 Set AC i ≥ AC’ i + ∆ to embed bit ‘1’ Set AC i ≤ AC’ i - ∆ to embed bit ‘0’

The embedding algorithm Block1 DC1 Block2 DC2 Block3 DC3 Block4 DC4 Block5 DC5 Block6 DC6 Block7 DC7 Block8 DC8 Block9 DC AC(0,2)= x (DC 4 +DC 6 – 2 x DC 5 )/8 Set AC i ≥ AC’ i + ∆ to embed bit ‘1’ Set AC i ≤ AC’ i - ∆ to embed bit ‘0’

The embedding algorithm Block1 DC1 Block2 DC2 Block3 DC3 Block4 DC4 Block5 DC5 Block6 DC6 Block7 DC7 Block8 DC8 Block9 DC AC(2,0)= x (DC 2 +DC 8 – 2 x DC 5 )/8 Set AC i ≥ AC’ i + ∆ to embed bit ‘1’ Set AC i ≤ AC’ i - ∆ to embed bit ‘0’

The embedding algorithm Block1 DC1 Block2 DC2 Block3 DC3 Block4 DC4 Block5 DC5 Block6 DC6 Block7 DC7 Block8 DC8 Block9 DC AC(1,1)= x (DC 1 +DC 9 – DC 3 - DC 7 )/8 Set AC i ≥ AC’ i + ∆ to embed bit ‘1’ Set AC i ≤ AC’ i - ∆ to embed bit ‘0’

The extracting algorithm The original image is not require for the watermark bit detection, only the comparison of the relative value between AC i and its estimated value AC’ i is needed. If AC i > AC’ i, then the extracted bit is ‘1’, If AC i < AC’ i, then the extracted bit is ‘0’. Of course, if AC i =AC’ i, there is uncertainly about whether the watermark bit is a ‘1’ or ‘0’.

Experimental Results

Conclusion This paper presents a kind of estimation based blind image watermarking technique. Our DCT technique achieves the optimal trade-off among imperceptibility capacity and robustness.