How is interstitial lung disease seen on a chest x-ray?

Guesstimate: Healthy lung x-rays are rather uniform, with darker areas representing air within & light areas denser areas/tissue or bone. If areas that are supposed to be darker appear lighter the assumption is made that there is thickening of tissue. Interstitial ling disease is thus branded by x-ray appearance. A more specific labeling would require a lung biopsy/looking at tissue under the microscope.