Lens Vignetting
Definition
The radial darkening toward the corners of an image caused by the optical path. It creates a low-frequency spatially correlated pattern in images that overlaps with the PRNU signal but can be averaged out across images taken under varied conditions.
- Cause
- Optical light falloff toward image corners
- Pattern type
- Low-frequency, spatially correlated
- Overlaps with
- PRNU sensor fingerprint signal
- Mitigation
- Averaging across images with varied framing
Common questions
Why does vignetting complicate PRNU camera-source analysis?+
Vignetting adds its own low-frequency darkening pattern to every image, and that pattern can correlate with parts of the PRNU noise pattern the examiner is trying to isolate, inflating a correlation score if not accounted for.
How do examiners separate vignetting from PRNU?+
Because vignetting is tied to lens and aperture rather than sensor defects, averaging reference images shot at varied focal lengths, apertures, or scene content suppresses the fixed vignetting component while the sensor-specific PRNU pattern remains.
Related terms
- DCNU (Dark Current Non-Uniformity)
- Additive noise generated by thermal activity in pixels even without light. Unlike PRNU, DCNU varies with temperature and camera gain settings, so...
- Fixed-Pattern Noise (FPN)
- Any repeatable, spatially correlated noise in an image sensor, as opposed to random shot noise. PRNU and DCNU are both forms of...
- Multiplicative Noise Model
- The mathematical description of PRNU: each pixel's output is approximately the product of the true light signal and the pixel's gain factor...
- PRNU (Photo Response Non-Uniformity)
- The unique pattern of pixel-level sensitivity variations in a camera sensor, used as a device fingerprint. A genuine camera-original image carries the...
- Sensor Pattern Noise (SPN)
- The composite fixed-pattern component in an image that includes PRNU plus lower-level contributions from optics and pixel defects. The PRNU component dominates...