The shortage of the existing image digital watermarking algorithms that imbed watermarks into the largest singular values of sub blocks of the original image is analyzed and discussed.Then two novel image digital watermarking algorithms are proposed.The two algorithms imbed watermarks into the singular values of sub blocks of original image excluding the largest ones.Using the quantization scheme,the two new algorithms can extract watermarks without original information.Experimental results show that the proposed two new algorithms have good transparency of the embedded watermark image and are robust against attacks,such as brightness adjustment,contrast adjustment,slight rotation,slight translation and noise adding.