Flat-Field Image
Definition
A photograph of a uniformly illuminated surface, typically a white wall or diffuser, taken at moderate brightness to avoid saturation. Used to estimate the PRNU reference pattern because the scene contribution is constant across the frame.
- Subject
- Uniformly illuminated surface, e.g. white wall or diffuser
- Exposure
- Moderate brightness, avoiding saturation
- Purpose
- Estimating the PRNU reference pattern
- Why it works
- Scene content is constant across the frame
Common questions
Why must a flat-field image avoid sensor saturation?+
A saturated pixel clips at its maximum value regardless of the underlying sensor response, which erases the subtle multiplicative noise pattern PRNU analysis depends on, so the exposure is deliberately kept moderate to preserve that signal across the frame.
How many flat-field images does a reliable PRNU reference typically require?+
A single image is rarely enough because random shot noise would dominate the estimate; examiners average many flat-field frames from the same device to suppress that random noise and isolate the fixed pattern unique to the sensor.
Related terms
- Noise Residual
- The signal remaining after a denoising filter removes the scene component from an image. For PRNU estimation, the residual approximates the sum...
- 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...
- Peak-to-Correlation Energy (PCE)
- An extension of NCC that computes the ratio of the squared correlation peak to the energy of the surrounding correlation map. PCE...
- Photo Response Non-Uniformity (PRNU)
- A fixed-pattern noise component caused by microscopic sensitivity differences between individual sensor pixels. PRNU is deterministic and camera-specific, making it a sensor...
- 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...