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In this paper, we suggest an adaptive watermarking method to improve both transparence and robustness of quantization index modulation (QIM) scheme. Instead of a fixed quantization step size, we apply a step size adapted to image content in each 8times8 block to make a balance of the robustness extraction and the transparence of embedding. The modified steps are determined by the contrast masking thresholds of Watson's perceptual model. From normalized cross correlation between the original watermark and the detected watermark, we observe that it is robust to attacks of additive white Gaussian noise, salt & pepper noise, JPEG compression than the original QIM.