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.