Antiblooming

Antiblooming refers to techniques used in light-sensing devices such as charge-coupled device (CCD) and complementary metal-oxide-semiconductor (CMOS) image sensors to prevent blooming, the unwanted spreading of charge from a saturated pixel into neighboring pixels when capturing very bright light. The goal is to preserve image quality in high-contrast scenes by limiting charge spillover.

In CCDs, anti-blooming gates (ABG) and drain structures divert excess charge away from the photosensitive node when the pixel potential exceeds a threshold. In CMOS sensors, antiblooming can be implemented with clamping diodes, overflow drains, or transistor arrangements that remove excess charge, or by pixel architectures that limit charge diffusion between neighboring pixels.

Antiblooming has been important in astronomy and high-contrast imaging, where bright stars can saturate detectors, as well as in consumer cameras and smartphone sensors, which must render scenes with bright highlights without veiling or streaks.

Limitations and trade-offs include potential reductions in effective full-well capacity or dynamic range near saturation, added circuit complexity, and possible noise implications. Modern sensor designs have reduced these drawbacks, balancing sensitivity with antiblooming performance.

Related topics include blooming, full-well capacity, CCD sensors, and CMOS sensors.