What are the reasons for black spots seen in x-ray films of chest?

xray: On chest xrays, we typically look for white spots and possible indicators of disease. Black spots are typically air/fat.

On xray,: blacker areas are areas where there is less absorption of the xray beam as it passes through the body. Generally these are areas of lesser density, such as air and fat. Whiter areas(e.g. bone) are areas of greater density, which absorb more of the xray.