3. Embed the watermark into the LL

3. Embed the watermark into the LL sub-band of the transformed host image, and adjust the signal strength until the PSNR value of watermarked image reaches 30±0.1dB. Note that the PSNR measurement must be performed on the watermarked image in spatial domain, i.e. the embedded watermarked coefficients in the LL sub-band together with the intact coefficients in the remaining three sub-bands must be invert transformed to reconstruct the practical watermarked image.