一种曝光时间自适应宽动态行车记录仪设计

Design for Vehicle Recorder with Wide Dynamic Range Based on Self-adjusting Exposure Time Technology

针对夜间行车环境中,行车记录仪后路摄像头处于逆光、强光或明暗反差大等复杂光线情况下不能清晰获取汽车后方影像的问题,提出一种像素单元曝光时间自适应技术来拓宽CMOS图像传感器的动态范围。在有源像素传感器像素单元电路基础上增加积分电容、电压比较器和时间-电压编码信号读入电路。其功能是当积分电容电压低于曝光时间阈值电压时,光电二极管停止积分,像素单元曝光时间短;当积分电容电压高于曝光时间阈值电压时,光电二极管曝光至固定时间,以此实现像素单元曝光时间自适应。在受到后方车辆远光灯照射情况下对两种行车记录仪摄像头进行测试,试验结果表明:与采用传统有源像素传感器的行车记录仪相比,安装有宽动态CMOS图像传感器的行车记录仪所拍摄的图像明亮区域图像不刺眼、阴暗区域图像不失真,降低了眩光、反射光、阴影对画面清晰度的影响,能够清晰、真实地还原拍摄环境图像信息。

Sometimes rear camera of vehicle recorder can＇ t capture images clearly behind the car when driving at night due to the com-plex light conditions which are backlight, bright light and high contrast light. In order to solve the problems mentioned above, a pixel unit withself-adjusting exposure time technology was proposed to broaden the dynamic range of CMOS image sensor. Based on the active pixel sensor（APS） pixel unit circuit, the integral capacitor, the voltage comparator and the time-voltage coding signal read-in circuit were added to thenew pixel unit. The photodiode would stop integral if the integral capacitor voltage was lower than the exposure time threshold voltage, so thepixel unit exposure time was short; and the photodiode exposure time was fixed if the integral capacitor voltage was higher than the exposuretime threshold voltage, thus adaptive exposure time could be achieved by the methods mentioned above. Two kinds of vehicle recorder camerawere tested under high beam irradiation from rear vehicles, the experimental results show that compared with conventional active pixel sensorvehicle recorder, the images which are photographed by the vehicle recorder equipped with wide-dynamic range CMOS image sensor have thesefeatures： bright areas are not dazzling, dark areas are not distortion. The influences of glare, reflecting and shadow on the resolution arereduced. In one word, this novel vehicle recorder can restore the shooting environmental image-information truly and clearly.