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Chapter 5 — technique
Image Processing and ISP: Bayer Matrix and Demosaicing
How your device transforms raw sensor data into a visible image. Bayer matrix, demosaicing, and the role of the ISP processor.
The Bayer Matrix: A Color Filter Per Pixel
Each photosite on the sensor only sees one color through a filter (red, green, or blue). The standard arrangement assigns 50% of the filters to green, 25% to red, and 25% to blue.
Demosaicing is the algorithm that reconstructs the two missing colors for each pixel by interpolating the values of neighboring pixels. The quality of this algorithm directly impacts the sharpness and color accuracy.
Key Concept: Each pixel captures only one color component. Demosaicing reconstructs the complete color image through interpolation. This is why a RAW file cannot be viewed directly without processing.
The ISP: The Image Processing Maestro
The Image Signal Processor (ISP) executes a series of processes in milliseconds: dead pixel correction, demosaicing, automatic white balance, tonal mapping, noise reduction, sharpening, aberration correction, and final compression.
Underwater Photography
Underwater, automatic white balance is often affected by the blue/green dominance. The ISP interprets this dominance as an incorrect white balance and attempts to correct it, often with unnatural results. Shooting in RAW allows you to precisely control the white balance in post-production.
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Frequently asked questions
Pourquoi la matrice de Bayer contient-elle 50% de vert ?
L'oeil humain est plus sensible au vert. 50% de filtres verts reproduit mieux la perception humaine de la luminosite et des details.
Le dematricage affecte-t-il la nettete sous l'eau ?
Oui. Les logiciels RAW pro extraient plus de details qu'un traitement basique. Raison supplementaire de photographier en RAW.
Qu'est-ce que l'ISP fait exactement ?
Correction defauts capteur, dematricage, balance des blancs, reduction bruit, accentuation nettete, correction aberrations, compression finale.