High-speed cameras make it possible to detect luminance variations in images of a scene under AC illuminations. This paper proposes a method for estimating an image when AC illumination components are eliminated. If the eliminated illumination component is the source of specular reflection, the image produced only contains the diffuse reflection components of other illuminations. Removal of the specular reflection enhances the adaptability of a robot vision system to real environments. Experimental results show the advantage of the proposed method over using previous methods. The results also show that the method is applicable to moving objects while some errors are generated depending on the illumination frequency and the speed of the objects.