All image formats use multiples of 8 bits, so 8, 16, 24, 32. When using a 12 bit ADC and 16 bit output, all image info essentially is 12 bit bit stored in 16 bit. There are several ways of doing this and it depends on the driver which one is used. When you use 8 bit output, the data get compressed to fit within the 8 bits and you essentially loose intensity information.
