Recently, Nikolova and Steidl have proposed a hue and range preserving histogram specification method which outputs a weighted average of two images generated by additive (shifting) and multiplicative (scaling) algorithms, where the weights are fixed for all pixels in an image. In this paper, we propose a method for selecting the one of the two algorithms at each pixel adaptively. Therefore, there is no need to prepare the weights for combining additive and multiplicative algorithms in the proposed method. Experimental results show that the proposed method can improve the saturation better than the convex combination method by Nikolova and Steidl. We also verify the property of saturation improvement in the proposed method theoretically.