In a radiograph, contrast is directly affected by altering:

Radiographic contrast is a general term that describes the range of densities on a radiograph. It is defined as the difference in densities between light and dark regions on a radiograph. An image that shows both light areas and dark areas has high contrast; Alternatively, a radiographic image composed only of light gray and dark gray zones has low contrast. The energy of the x-ray beam, selected by the kVp, influences image contrast. As the kVp of the x-ray beam increases, subject contrast decreases. Similarly, when relatively low kVp energies are used, subject contrast increases.