Factors affecting the appearance  
 

SHAPE

The shape of an object will affect its final appearance on radiography. The shape affects how much of the x-ray beam is attenuated by a structure, mostly because of differences in thickness. For example, if looking at a round structure of uniform composition, like a solid ball, the center will appear denser, or whiter on a radiograph than the edges because the center is thicker and attentuates more of the x-ray beam.

This radiograph shows a more complex structure; a green pepper. As you know, the inside of a pepper is comprised of air, and the walls are the "flesh". Area "B" appears more lucent (black) than area "A", despite the fact that the outer wall of the pepper is of uniform thickness. This is because the x-rays passing through area B had to go through the flesh of only the front and back wall, while those passing through area A had to pass through much more of the "flesh", as the beam traveled "down the barrell" where the wall of the pepper curves. As a result, more of the beam was attenuated and the lateral walls of the pepper appear whiter.