Liquid crystal displays (LCD) are replacing analog film in radiology and permit to reduce diagnosis times. Their typical dynamic range, however, can be too low for some applications, and their poor ability to reproduce low luminance areas represents a critical drawback. The black level of an LCD can be drastically improved by stacking two liquid crystal panels in series. In this way the global transmittance is the pointwise product of the transmittances of the two panels and the theoretical dynamic range is squared. Such a high dynamic range (HDR) display also permits the reproduction of a larger number of gray levels, increasing the bit depth of the device. The two panels, however, are placed at a small distance one from each other due to mechanical constraints, and this introduces a parallax error when the display is observed off-axis. A complex, spatially-adaptive algorithm is therefore necessary to generate the images used to drive the two panels. In this paper, we describe the characteristics of a prototype dual-layer HDR display and discuss the issues involved in the image splitting algorithms. We propose some solutions and analyze their performance, giving a measure of the capabilities and limitations of the device.
