Research On Imaging Technology Of High-resolution Back-illuminated CMOS Sensor

Low-illuminance CMOS and Electronic Bombardment CMOS(EBCMOS)are two popular directions for the development of digital low-light night vision technology.Back-illuminated CMOS image sensor is an important technical approach to achieve low-illuminance CMOS and EBCMOS.Based on the back-illuminated CMOS image sensor,this paper develops low-light CMOS imaging system and EBCMOS imaging system,designs and implements the image processing algorithms suitable for low-light CMOS imaging and EBCMOS imaging respectively.This article first briefly introduces the development of low-light night vision technology.Then,a hardware system that can be shared by low-luminance CMOS imaging and EBCMOS imaging is designed according to specific needs.After the hardware circuit debugging is completed,the imaging logic and image processing algorithms of low-illuminance CMOS and EBCMOS are studied.Among them,the imaging logic and automatic exposure algorithm are common parts.The low-light algorithm is designed separately for the low-light environment use requirements of low-light CMOS and EBCMOS.The imaging logic mainly includes clock management module,system master control module,I² C general module,CMOS driver module,image training module,cache module and OLED display module,the resolution is up to2048×2048 full-frame;in order to improve the adaptability of low-light CMOS imaging system and EBCMOS imaging system to bright and dark scenes,to avoid overexposure or underexposure,after studying the principle of the automatic exposure algorithm,combining the characteristics of the imaging system,this paper designs an automatic exposure control algorithm based on gray average and brightness histogram;in order to meet the requirements of low illumination environment,a dynamic adaptive platform histogram equalization algorithm is designed in low-light CMOS imaging system and implemented in hardware,a piecewise linear stretching based on histogram is designed in EBCMOS imaging system and implemented in hardware.Finally,a low-light CMOS and EBCMOS low-light imaging comparison experiment was performed,under the same operating mode,PGA gain and exposure time,low-illumination CMOS can recognize objects under1×10^-2lxillumination,and EBCMOS can recognize objects under2×10^-4lxillumination.The results show that the low-illumination detection capability of EBCMOS developed with back-illuminated CMOS is significantly improved compared with back-illuminated CMOS itself.