Which term describes image noise due to insufficient photons reaching the detector?

• A. Capture efficiency
• B. Spatial resolution
• C. Quantum mottle
• D. Quantization

Answer: (C)

When too few photons reach the detector, the image shows a grainy, mottled appearance caused by the random nature of photon arrival. This is described as quantum mottle. Photon counts per pixel follow a Poisson distribution, so low exposure leads to larger relative fluctuations and more noticeable noise across the image. This concept is different from capture efficiency (how many photons the detector can convert into signal), spatial resolution (how well small details are resolved), and quantization (the discrete digital levels used to represent signal). Therefore, the term that fits best is quantum mottle.