Multi-Plane Phase Detection Autofocus for 8K Three-Chip Color Imaging Cameras

A phase detection (PD) autofocus (AF) method for three-chip color imaging cameras is proposed. The method detects the focus state of a lens by calculating the disparity between a half-shielded PD pixel and other normal pixels corresponding to the same incident position among three sensors, which can perform accurate AF without employing state-of-the-art dual-photodiode technology. By using a prototype 8K sensor with half-shielded PD pixels (PD sensor), we demonstrated that installing the PD sensor into a blue channel of the three-chip system can achieve an excellent phase separation ratio and robust disparity calculation with less image quality degradation due to defects of PD pixels.

I. Introduction

Autofocus (AF) is becoming an essential feature as cameras get higher and higher resolution (e.g., 4K and 8K), which makes manual focusing with small view-finders more difficult. Sensor-based phase detection (PD) AF methods are commonly-used for quick and accurate focusing in single-chip imaging cameras [1, 2]. Meanwhile, cameras with three-chip color imaging have been used to acquire high-quality images with high color reproducibility in broadcasting and even in consumer applications. However, investigations into PDAF in such optics have been insufficient. In this paper, we discuss a PDAF method appropriate for the three-chip cameras and evaluate PD performance using a prototype 8K image sensor with PD pixels.