Most DSLR's use 12 or 14 bits to represent the voltage each pixel generated when it was exposed to light. By the way, no digital camera has a digital image sensor. They all have analog image sensors and the voltages the pixels record have to be converted to digital numbers, which is done in an analog-to-digital converter on the image sensor chip after the analog voltages are amplified (also on the image sensor chip).
Luminosity data is the
only information an image sensor is capable of recording. Yep, the image sensor doesn't record color. All digital images start as a grayscale image.
111111111111 (4096) is the largest number (bit depth) 12 bits can represent, and allows for 4096 potentila levels of luminosity at each pixel.
11111111111111 (16,384) is the largest number (bit depth) that 14 bits can represent.
A JPEG also starts as a 12 or 14 bit image data file. But JPEG is a lossy, compressed file type.
A JPEG retains most of the luminosity data an image sensor records. The lossy part of JPEG is the result of 2 changes; 1. The
color bit depth is reduced from 12 or 14 bits to just 8 bits - 11111111 (256). 2. The pixels in the image are converted into 8x8, 8x16, or 16x16 pixels units (Minimum Coded Units - MCU's).
JPEG - Wikipedia, the free encyclopedia