Photo Response Non-Uniformity (PRNU)
Definition
A fixed-pattern noise component caused by microscopic sensitivity differences between individual sensor pixels. PRNU is deterministic and camera-specific, making it a sensor fingerprint. It is estimated by averaging many flat-field images to cancel random noise.
- Cause
- Pixel-level sensitivity variation from sensor manufacturing
- Nature
- Deterministic, camera-specific fixed pattern
- Extraction
- Averaging many flat-field images to cancel random noise
- Main use
- Matching an image to the specific camera that took it
- Comparison metric
- Normalised cross-correlation between image noise and reference pattern
Common questions
Can PRNU distinguish between two identical camera models?+
Yes, that is its forensic value. Two units of the same model share design and lens characteristics, but the microscopic pixel sensitivity variation is unique to each individual sensor, so PRNU can separate camera A from camera B even when both are the same make and model.
What weakens a PRNU match?+
Heavy JPEG compression, image resizing, cropping, and social media re-uploading all degrade or shift the noise pattern, lowering correlation scores. Strong scene content and lighting variation across the reference images used to build the fingerprint can also introduce noise.
How many reference images are needed to build a reliable camera fingerprint?+
Practitioners typically average tens of flat-field or plain-content images from the suspect camera to suppress random noise and isolate the fixed pattern. Fewer images leave more residual random noise, weakening confidence in the resulting fingerprint.
Related terms
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- Noise Residual
- The signal remaining after a denoising filter removes the scene component from an image. For PRNU estimation, the residual approximates the sum...
- Noise Variance Map
- A per-pixel or per-block estimate of local noise variance across an image, computed by filtering out image content with a high-pass or...
- Normalised Cross-Correlation (NCC)
- A scalar statistic in the range -1 to 1 that measures how closely the noise residual of a query image matches a...
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- PRNU Fingerprint
- Photo Response Non-Uniformity: the unique pattern of pixel-level sensitivity variations in a camera sensor, which acts as a device fingerprint. Used to...
- Shot Noise
- Random noise proportional to the square root of the number of photons captured. Shot noise is scene-dependent and cannot be predicted from...
Explained in these topics
- Media Authentication FundamentalsA unique, stable noise pattern produced by manufacturing variations in a camera sensor's individual pixels. Because the pattern is consistent across all images...
- Noise Inconsistency and Lighting Analysis for Image Forgery
- Photo Response Non-Uniformity and Sensor FingerprintingA multiplicative fixed-pattern noise component caused by pixel-level sensitivity variation in an imaging sensor. PRNU is stable, unique per device, and present...