Improved image watermarking scheme based on DWT coefficients modification in LL sub-band

This paper proposes a new color image watermarking scheme based on coefficients modification in LL sub-band. Basically, the blue component of original color image is decomposed by the Discrete Wavelet Transform (DWT) to obtain the coefficients in LL sub-band in order for embedding a single watermark bit with a tuned constant value to achieve the optimum watermark strength. To extract this embedded bit, the original DWT coefficients in LL sub-band are predicted using the DWT, and then subtracted from the watermarked coefficient to obtain the extracted watermark bit. The same proposed concept is also extended to embed several bits into the whole image frame in order to improve capacity and robustness of embedded information. The efficiency of the watermarking scheme is evaluated by the Bit Error Rate (BER) from the extracted bits, and compared to the two previous schemes at equivalent image quality. The experiments show promising results in both accuracy and robustness of the extracted watermark.