Phase-detect Pixel
A photosite masked on one side, or split in two, so it sees the scene through only part of the lens and can contribute to focus measurement.
Measured in
count
In depth
Embedding these among the imaging photosites is what brought phase detection onto the sensor itself, removing the calibration errors of separate modules. Masked designs sacrifice the affected photosites, which must be interpolated and can leave faint striping in extreme shadow lifts; split-pixel designs avoid that by summing both halves.
Examples in practice
Heavily lifting the shadows of a file from a masked phase-detect sensor can reveal a faint regular pattern of lighter points.