DCNU (Dark Current Non-Uniformity)
Definition
Additive noise generated by thermal activity in pixels even without light. Unlike PRNU, DCNU varies with temperature and camera gain settings, so it is not a reliable fingerprint.
- Cause
- Thermal electron generation in sensor pixels, independent of incident light
- Contrast with
- PRNU, which is a stable multiplicative pattern
- Key variable
- Rises with sensor temperature and ISO/gain setting
- Forensic use
- Not used as a camera fingerprint because it is unstable
- Mitigation
- Dark-frame subtraction during camera calibration
Common questions
Why can't DCNU be used to identify a camera like PRNU can?+
PRNU works as a fingerprint because it is a fixed multiplicative pattern baked into the pixel structure at manufacture. DCNU changes with temperature and gain, so the same sensor produces a different DCNU pattern from one shot to the next, making it useless as a stable identifier.
Does DCNU interfere with PRNU-based source attribution?+
Yes, it adds additive noise on top of the multiplicative PRNU signal. Examiners typically average many flat-field frames or apply denoising filters to suppress DCNU and other additive noise before extracting the PRNU pattern.
Related terms
- 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...
- Lens Vignetting
- The radial darkening toward the corners of an image caused by the optical path. It creates a low-frequency spatially correlated pattern in...
- 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...