Contrast and Spatial Resolution Practice Test 2026 - Free Practice Questions and Study Guide

Quantum noise comes from the random, discrete nature of photon arrival. The number of photons detected at each location fluctuates, so the recorded signal has grainy, speckle-like variations around the true value. That graininess lowers the contrast-to-noise ratio and makes fine structures harder to distinguish, so the visibility of recorded detail is diminished. This effect is more pronounced at lower exposures, where fewer photons are detected, and it doesn’t inherently raise the average brightness or improve edge detection.