Bit depth is defined as the:

• A. total number of brightness levels that can be produced by the digital system
• B. total lp/mm that can be resolved by the digital system
• C. smallest exposure difference that can be detected by the digital system
• D. total number of x-ray photons striking the digital receptor

Answer: (A)

Bit depth determines how many brightness (gray) levels each pixel can display. It’s set by the number of bits used to represent a pixel, and each additional bit doubles the number of possible gray values. So the total brightness levels = 2^n, where n is the bit depth. This is why higher bit depth gives finer grayscale detail and better contrast resolution.

The other aspects aren’t about grayscale depth: lp/mm reflects spatial resolution (sharpness of detail), the smallest detectable exposure difference relates to noise and contrast sensitivity, and the total number of x-ray photons relates to exposure and detector efficiency, not the number of gray shades a pixel can show.