Sommeling, Generalizing Exposure Time to Dwell Time in Scanning Systems (Section 16.2) #32
Description
While the text centers on the camera pipeline, it emphasizes broader principles like Photon Shot Noise. Currently, this is framed strictly through “Exposure Time.” Adding a note on “Dwell Time” (used in scanning systems like LIDAR and SEM) would help students apply this principle to broader imaging systems without changing the book's core scope.
Usefulness: Understanding Photon Shot Noise is critical for scanning systems like LIDAR, which are essential for the autonomous driving applications mentioned in Chapter 18. Unlike cameras that integrate light over a full frame, LIDAR raster-scans point-by-point, meaning “Integration Time” effectively becomes “Pixel Dwell Time.” If the dwell time is too short, the photon count drops, and the signal becomes shot-noise limited. Recognizing that the Signal-to-Noise Ratio scales with the square root of the count (SNR ∝ √N) in both cases allows engineers to apply the same fundamental physics to optimize LIDAR scan patterns.
Improvement: Currently, this section illustrates sensitivity using a standard camera example (Section 16.2). This phrasing implicitly assumes a global shutter model. I propose appending a brief generalization to this paragraph:
“Note: In scanning instruments (such as LIDAR, Scanning Electron Microscopes, or Confocal Microscopes), this 'exposure' is determined by the Dwell Time—the brief moment the beam pauses on a single point. A dwell time of 1 microsecond results in the same photon shot noise limit as a 1-microsecond shutter opening on a standard camera pixel.”
This connects the noise analysis from Chapter 14 to the computer vision applications mentioned in Chapter 18, showing students the universality of the physics for both technologies.