Effective atomic numbers associated with pixels in a region are received. An effective atomic number is associated with each pixel in the region. X-ray data for the region is received, and an item within the region is identified from the x-ray data. Some of the pixels in the region are correlated with the item such that the item is associated with an effective atomic number. An image of the region is rendered. The pixels of the item have a display style based on the effective atomic number of the item.