Most of the existing distortion functions for digital images steganography allot a same embedding cost for ±1 embedding change, which should be different intuitively. This paper proposes a general method to distinguish the embedding cost for different polarity of embedding change for spatial images. The fluctuation after pixels are +1 or -1 modified respectively, and the texture of cover image are employed to adjust a given distortion function. After steganography with the adjusted distortion function, the fluctuation around stego pixels become more similar to the fluctuation around their neighbourhoods. This similarity performs less detectable artifacts. Experiment results show that the statistical undetectability of current popular steganographic methods is increased after incorporated the proposed method.
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