Recent advances in the design of high dynamic range (HDR) monitors enable the display of images having a large dynamic range, close to that encountered in the real world. As their usage will increase, we will be confronted with the problem of re-rendering images that have been mapped to standard dynamic range (SDR) displays so that they look natural on HDR monitors. We address this issue for SDR images representing original HDR scenes. We propose a tone scale function that takes advantage of the increase in dynamic range of HDR monitors to recreate the brightness of specular highlights, which were clipped or compressed by the capturing and rendering process to SDR. We validate the use of such functions with a psychovisual experiment conducted on an HDR display, where the observers' task was to judge pairs of tone-scaled images. The result of the experiment shows that using part of the extension of dynamic range provided by HDR displays to enhance the brightness of specular highlights leads to more natural looking images.