Synthetic Sub-Aperture Phase Augmentation for Demosaicing 2×2 Shared Microlens Sensors

Modern high-resolution mobile sensors often adopt clusteredcolor filter array (CFA) layouts such as Quad and Hexadeca Bayer,while some premium sensors use quad-pixel phase-detection or 2 × 2 on-chip-lens (OCL) architectures with shared microlenses for dense phase-detection autofocus (PDAF). While effective for PDAF, this structurecan introduce grid-aligned phase artifacts during demosaicing, which aredifficult to model without calibrated sub-aperture streams, PSF super-vision, or sensor-specific optical calibration. We propose Synthetic Sub-Aperture Phase Augmentation (SPA), a physics-inspired data genera-tion framework for artifact-aware demosaicing. SPA uses compact phasekernels to approximate focus-dependent sub-aperture shifts in syntheticRAW, requiring no measured point spread functions (PSFs) or sensor-specific calibration. Experiments on synthetic and real RAW data fromHexadeca and Quad Bayer sensors show consistent suppression of zipper-ing, color bleeding, and grid-aligned artifacts. We also introduce spatiallattice imbalance (SLI) and Nyquist energy ratio (NER) for 2× 2 artifactanalysis and validate robustness to spatial phase variations.