Camera Noise Model
Definition
A mathematical description of a sensor's noise as a function of signal level, combining signal-dependent shot noise and signal-independent readout noise. The model is specific to the sensor, ISO, and exposure conditions.
- Two noise sources
- Signal-dependent shot noise, signal-independent readout noise
- Depends on
- Sensor model, ISO setting, exposure conditions
- Forensic use
- Detecting inconsistent noise levels across a spliced image
- Related check
- Colour filter array (CFA) interpolation consistency
Common questions
How is a noise model used to detect image tampering?+
A region pasted from a different camera, ISO setting, or a resaved/recompressed source usually carries a noise signature that does not match its surroundings. Estimating local noise level across the image and flagging regions that deviate from the expected model can reveal the splice.
Can heavy JPEG compression defeat noise-based detection?+
Yes, aggressive compression suppresses fine noise and can mask inconsistencies, which is why examiners pair noise analysis with other cues such as CFA interpolation patterns, lighting, and shadow geometry rather than relying on noise alone.
Does denoising software in a phone camera complicate this analysis?+
Yes. Modern computational photography pipelines apply aggressive in-camera denoising that departs from simple sensor noise models, so an examiner must know the source device's processing pipeline before drawing conclusions from noise inconsistency.
Related terms
- CFA (Colour Filter Array)
- The mosaic of colour filters placed over a sensor so that each photosite captures one colour channel. The Bayer pattern (RGGB arrangement)...
- CFA Phase
- The spatial offset of the CFA mosaic pattern in an image. Pasting a region from a different image or after a non-CFA-aligned...
- Demosaicing
- The algorithm used to interpolate full-colour pixel values from the single-channel raw sensor data. Common methods include bilinear interpolation, gradient-based algorithms (AHD,...
- Noise Residual
- The signal remaining after a denoising filter removes the scene component from an image. For PRNU estimation, the residual approximates the sum...
- Steganography
- Concealing one file inside another in a way that hides the existence of the hidden file. LSB image manipulation, JPEG DCT coefficient...