Spread Transform Dither Modulation(STDM) is a watermarking algorithm having good performance.In this algorithm

the Project-vector used for spread transform is an important factor that affects its performance.This paper studies on the project-vector of STDM.Random project vector

uniform project vector

parallel project vector

project vector chosen according frequency and project vector chosen according HVS are introduced

the robustness under different project vectors is compared and analyzed

the way of choosing project-vectors that makes the robustness of STDM best under different attacks is obtained.Further

in order to make full use of the HVS's characteristics

choosing project-vector combined with HVS is introduced

and the experiment results show that by using this method

the visual quality and robustness of the STDM algorithm can be improved further.