In this paper, we reveal the impact of the fixed synchronization pattern on the halftone image under DBS processing; and an improved watermarking method is proposed to avoid this impact, which is extended from a previously developed DBS based watermarking method. The watermark and synchronization pattern is to be embedded into the appropriate region of the host image adaptively; and excellent image quality and decent watermark capacity is provided. The method has good resistance to a printing and scanning attack while only size of the watermark and host image is required additionally in the watermark detection. Experimental results are presented for some special host images, including a sketch and a round logo to prove the flexibility of the method.