In this paper, we propose a so-called bipolar split scheme to promote watermarking robustness while not at the expense of imperceptibility which is desired to be resolved in the research area. The watermark is split up into bipolar parts such that we can enhance the watermarked image quality by 3dB without loss of the watermark robustness. The experimental study shows our method can gain about 3dB benefit in PSNR beyond the single watermark with double strength method. And, our method can even compete in the extracted watermark quality with the latter.