This paper proposes a blind reversible watermarking approach for medical images based on histogram shifting in wavelet domain. An integer wavelet transform is applied to map the integer host image components to integer wavelet coefficients. The watermark information is inserted into the high frequency subband regions of the transformed image. According to the capacity required for the watermark, two thresholds, T1 and T2, are selected, one in the begging part and the other in the end part of the histogram of the high frequency subbands of the transformed image. Two zero-points, Z1 and Z2 are also created by properly shifting the beginning and the end parts of the histogram. The part of the histogram located between the two thresholds remains unchanged. The binary watermark data are inserted in the thresholds and zero-points locations. The high PSNR (above 53 dB) obtained for several watermarked medical images, indicates imperceptibility of the approach. Experimental results also show superiority of the proposed approach in compare to some other methods that are based on histogram shifting in spatial as well as integer wavelet domains. Enabling lossless reconstruction of both watermark and host image, beside providing the high quality for the watermarked image, make the proposed approach attractive for medical image watermarking applications.
