The depth of bit refers to the number of signal bits available that camera provides.
In a 8-bit camera, each pixel integrates 256 gray level colors from black to white. A 10-bit camera has 1,000 gray level colors and a 12-bit camera has 4,000 grey level colors.
Even though a camera has been designed as a 12-bit analogue -digital converter, this camera can not really provide 4,000 grey level colors. Many things vary, in accordance with the quality and layout of sensor, the quality of electronic components, the quality and layout of camera, signal transmittance speed, temperature and external intervention.