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Overcurrent-driven LEDs for consistent image colour and brightness in agricultural machine vision applications
Computers and Electronics in Agriculture ( IF 8.3 ) Pub Date : 2021-06-23 , DOI: 10.1016/j.compag.2021.106266
Omeed Mirbod , Daeun Choi , Roderick Thomas , Long He

Machine vision systems are being utilized extensively in agriculture applications. Daytime imaging in outdoor field conditions presents challenges such as variable lighting and colour inconsistencies due to sunlight. Motion blur can occur due to vehicle movement and vibrations from ground terrain. A camera system with active lighting can be a solution to overcome these challenges. In this study, the usage of over-current driven LEDs to produce a powerful flash was investigated as a viable light source for daytime imaging. The current drawn by an LED was increased by a factor of six times its normal rating resulting in increased illuminance. A circuit was designed for storing and releasing energy to the LEDs for a strobe-like effect and a controller was used for synchronizing the strobe with a camera to acquire images. The system was deployed in an apple orchard on three days in summer of 2020. Images were taken throughout the day in both sunny and cloudy conditions of different canopy structures. There was substantial improvement in image brightness and colour consistency by using the LED flashes. Images captured by the prototype system during an 11-hour period showed an average decrease of 85% in standard deviation for the Hue-Saturation-Value (HSV) channels compared to that of the auto-exposure setting. Additionally, the prototype system was able to fix motion blur in images averaging 7 mm in error for a stereo vision application with the camera moving at 7 km/hr. These results show that the designed LED flash system can reduce the undesirable effects of lighting variability and motion blur in images stemming from outdoor field conditions.



中文翻译:

过电流驱动 LED 可在农业机器视觉应用中实现一致的图像颜色和亮度

机器视觉系统被广泛用于农业应用。室外野外条件下的白天成像会带来各种挑战,例如由于阳光导致的光照变化和颜色不一致。由于车辆移动和地面振动,可能会发生运动模糊。具有主动照明功能的相机系统可以成为克服这些挑战的解决方案。在这项研究中,研究了使用过电流驱动的 LED 来产生强大的闪光灯作为白天成像的可行光源。LED 消耗的电流增加了其正常额定值的六倍,从而导致照度增加。设计了一个电路来为 LED 存储和释放能量,以产生类似频闪的效果,并使用控制器将频闪与相机同步以获取图像。该系统在 2020 年夏季的三天内部署在一个苹果园中。 全天在晴天和多云条件下拍摄不同树冠结构的图像。通过使用 LED 闪光灯,图像亮度和色彩一致性得到了显着改善。原型系统在 11 小时内捕获的图像显示,与自动曝光设置相比,色相饱和度值 (HSV) 通道的标准偏差平均降低了 85%。此外,原型系统能够修复图像中平均 7 毫米误差的运动模糊,用于相机以 7 公里/小时移动的立体视觉应用。这些结果表明,所设计的 LED 闪光灯系统可以减少室外场地条件下图像中照明可变性和运动模糊的不良影响。

更新日期:2021-06-23
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