Fixed-pattern noise (FPN)
Definition
Any repeatable, spatially correlated noise in an image sensor, as opposed to random shot noise. PRNU and DCNU are both forms of FPN, but only PRNU scales with incoming light and is therefore the dominant forensic signal.
- Noise type
- Spatially consistent, repeatable across exposures
- Sensor property
- Unique to each individual camera
- Primary forensic use
- PRNU-based camera fingerprinting
Common questions
What is fixed-pattern noise and why does it matter in digital forensics?+
Fixed-pattern noise is spatially consistent noise that arises from tiny variations in how a camera's photosites are manufactured. Because FPN is stable across repeated exposures and unique to each sensor, it becomes the fingerprint of that camera. This makes it the foundation for PRNU camera fingerprinting, which is used to determine which camera took a particular image.
How is FPN different from random noise?+
FPN is repeatable and spatially correlated noise that stays the same across multiple exposures from the same sensor. Random shot noise, by contrast, changes each time you take a picture. PRNU is the type of FPN that scales with incoming light and creates the strongest forensic signal for camera identification.
What are PRNU and DCNU, and how do they relate to FPN?+
Both PRNU (photo response non-uniformity) and DCNU (dark current non-uniformity) are specific forms of fixed-pattern noise. PRNU is the forensically dominant form because it scales with the amount of light hitting the sensor, making it a reliable fingerprint for camera identification.
Related terms
- Bayer CFA
- A colour filter array arranged in a repeating 2×2 mosaic of red, green (×2), and blue filters over the sensor. Each photosite...
- Colour space
- A defined mapping between numerical RGB values and real-world colours. sRGB is the web default with a smaller gamut; Adobe RGB covers...
- 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...
- Demosaicing
- The interpolation step that reconstructs all three colour channels at every pixel from the single-channel Bayer mosaic. The algorithm used is camera-specific...
- JPEG compression
- A lossy codec that divides an image into 8×8 pixel blocks, applies the discrete cosine transform, quantises the coefficients, and entropy-codes the...
- 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...
- RAW format
- A camera capture format that records unprocessed sensor data, preserving all original exposure and colour information. RAW files are preferred over JPEG...
- 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...
Explained in these topics
- Digital Image Fundamentals: Pixels, Sensors, and FormatsSpatially consistent noise arising from photosite manufacturing variations. FPN is unique to each sensor and stable across exposures, making it the basis for p...
- PRNU: Physics and the Camera FingerprintAny repeatable, spatially correlated noise in an image sensor, as opposed to random shot noise. PRNU and DCNU are both forms of FPN, but only PRNU scales with...