Noise Residual (W_hat)
Definition
The per-image estimate of PRNU, computed by subtracting a denoised version of the image from the original. It contains PRNU plus random noise. Averaging many residuals produces a cleaner reference pattern.
- Symbol
- W-hat
- Computed as
- Original image minus its denoised version
- Contains
- PRNU plus random noise
- Refinement
- Averaging many residuals isolates PRNU
Common questions
Why isn't a single noise residual used directly for camera identification?+
One residual from a single image is dominated by random sensor and scene noise that swamps the weak, consistent PRNU pattern. Averaging residuals from many images of the same camera cancels the random component and leaves the fixed pattern noise.
What denoising step produces the residual?+
The image is passed through a denoising filter, commonly a wavelet-based filter, and the residual is the difference between the original pixel values and that filtered output.
Related terms
- BM3D (Block-Matching 3D)
- A state-of-the-art denoising algorithm that groups similar image patches across the image, transforms them jointly, thresholds in the transform domain, and inverts....
- Hypothesis Testing in Camera Attribution
- The framework in which H0 is 'the query image was not taken by this camera' and H1 is 'it was'. The PCE...
- NCC (Normalised Cross-Correlation)
- The standard measure of similarity between a query noise residual and a reference PRNU pattern. It produces a value between -1 and...
- PCE (Peak-to-Correlation Energy)
- A refined statistic that divides the peak of the cross-correlation surface by the energy of the non-peak region. PCE is more sensitive...
- Wavelet Denoiser
- A denoising filter that works in the wavelet transform domain, thresholding coefficients at each scale and direction to remove random noise while...