Demosaicing
Definition
The interpolation step that reconstructs all three colour channels at every pixel from the single-channel Bayer mosaic. The algorithm used is camera-specific and leaves a spatial correlation pattern that can be used to detect local regions of tampering.
- What it does
- Reconstructs all three color channels (red, green, blue) at every pixel from the single-channel Bayer mosaic.
- Forensic clue
- Leaves a spatial correlation pattern that varies by algorithm, useful for detecting local tampering and verifying camera authenticity.
- Common algorithms
- Bilinear, AHD, VNG, and deep-learning methods each produce distinct interpolation fingerprints.
Common questions
What is demosaicing and why does it matter in forensics?+
Demosaicing reconstructs the full color image from a Bayer mosaic, which is how digital camera sensors capture light. The reconstruction algorithm leaves a detectable spatial fingerprint, allowing forensic analysts to spot tampering by finding inconsistencies in the expected pattern.
Do different cameras produce different demosaicing fingerprints?+
Yes. The specific algorithm a camera uses to demosaice (bilinear, AHD, VNG, or deep-learning methods) creates a unique pattern. This means comparing an image's fingerprint against known camera signatures can reveal inconsistencies that point to splicing or other editing.
Can demosaicing artifacts help detect forgery?+
Definitely. When an image is edited or tampered with, the patched region typically does not match the camera's original demosaicing fingerprint. Analysts look for breaks in these correlation patterns to isolate suspicious areas.
Related terms
- Bayer CFA
- A colour filter array arranged in a repeating 2×2 mosaic of red, green (×2), and blue filters over the sensor. Each photosite...
- Camera noise model
- 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...
- 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...
- Colour space
- A defined mapping between numerical RGB values and real-world colours. sRGB is the web default with a smaller gamut; Adobe RGB covers...
- Fixed-pattern noise (FPN)
- Any repeatable, spatially correlated noise in an image sensor, as opposed to random shot noise. PRNU and DCNU are both forms of...
- JPEG compression
- A lossy codec that divides an image into 8×8 pixel blocks, applies the discrete cosine transform, quantises the coefficients, and entropy-codes the...
- Noise residual
- The high-frequency component of an image obtained by subtracting a denoised version from the original. The residual retains camera-model fingerprint noise and...
- RAW format
- A camera capture format that records unprocessed sensor data, preserving all original exposure and colour information. RAW files are preferred over JPEG...
- Steganography
- Concealing one file inside another in a way that hides the existence of the hidden file. LSB image manipulation, JPEG DCT coefficient...
Explained in these topics
- Digital Image Fundamentals: Pixels, Sensors, and FormatsThe interpolation step that reconstructs all three colour channels at every pixel from the single-channel Bayer mosaic. The algorithm used is camera-specific a...
- Noise and CFA Inconsistency DetectionThe interpolation process that reconstructs missing colour channels at each pixel from adjacent CFA samples. Different algorithms (bilinear, AHD, VNG, deep-lea...