A radiologist needs to see the full range of densities, that is, shades of gray from white to black, to make a proper diagnosis. Some X-rays can have black areas that are over 500 times darker than the brightest areas, although the typical range in the tissues of interest is much smaller than this, about 32 to 1. X-rays are transparent like photographic slides rather than prints. Radiologists read X-rays on a lighted view box. This way of displaying the image presents a much greater contrast and tonal range than a photographic print.
Movies look much more vivid than photos for the same reason.
Even a good quality photograph of an X-ray will not have a contrast ratio higher than about 63 to 1. A reproduction in a book will be even lower. These ratios are significantly less the than full range of gray levels contained in the original X-rays. This means that an X-ray reproduced to show good detail in the brighter areas, such as bones, will render darker areas, such as tissues, as all black. And if the publisher adjusts the gray levels so that both the brightest and the darkest areas reproduce, then detail will be lost in the middle gray levels.