Frequency-Domain CFA Spectrum
Definition
When a demosaiced image is transformed into the frequency domain (using a 2D DFT), the CFA interpolation introduces periodic peaks at spatial frequencies corresponding to the CFA tile period. These peaks form a fingerprint that can be detected even in JPEG-compressed images.
- Transform
- 2D DFT of the demosaiced image
- Cause
- Periodic CFA interpolation pattern
- Peak location
- Spatial frequencies matching CFA tile period
- Survives
- JPEG compression
Common questions
What forensic question does the frequency-domain CFA spectrum help answer?+
It helps confirm whether an image region underwent the demosaicing process consistent with a genuine camera capture, or whether that region was spliced in, resaved, or resampled, since tampering disrupts the regular interpolation pattern and shifts or removes the expected periodic peaks.
Why does this technique still work on JPEG-compressed images?+
The CFA interpolation peaks occupy specific, well-separated spatial frequencies that survive typical JPEG quantization, which discards high-frequency detail more broadly but does not fully erase the structured, low-order periodicity the demosaicing filter imprints.
Related terms
- Brown-Conrady Model
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- Colour Filter Array (CFA)
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- 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,...
- Device-Class Identification
- Establishing that an image was captured by one of a set of cameras sharing the same sensor architecture and firmware, rather than...
- Radial Distortion
- A geometric lens aberration in which magnification changes with distance from the optical axis. Barrel distortion (negative radial coefficient k1) bows straight...