Holz Christian, Ofek Eyal
Annu Int Conf IEEE Eng Med Biol Soc. 2018 Jul;2018:1-4. doi: 10.1109/EMBC.2018.8513286.
Recent smartphones have the potential to bring camera oximetry to everyone using their powerful sensors and the capability to process measurements in real-time, potentially augmenting people's lives through always-available oximetry monitoring everywhere. The challenge of camera oximetry on smartphones is the low contrast between reflections from oxyhemoglobin and deoxyhemoglobin. In this paper, we show that this is the result of using the camera flash for illumination, which illuminates evenly across bands than thus leads to the diminished contrast in reflections. Instead, we propose capturing pulse using the front-facing camera and illuminating with the phone's display, a selective illuminant in the red, green, and blue band. We evaluate the spectral characteristics of the phone display using a spectroradiometer in a controlled experiment, convolve them with the sensitivity curves of the phone's camera, and show that the screen's narrow-band display illumination increases the contrast between the reflections in the desired bands by a factor of two compared to flash illumination. Our preliminary evaluation showed further support for our approach and findings.
近期的智能手机凭借其强大的传感器以及实时处理测量数据的能力，有潜力将摄像头血氧测定技术普及到每一个用户，通过随时随地进行血氧测定监测，有可能改善人们的生活。智能手机上摄像头血氧测定的挑战在于氧合血红蛋白和脱氧血红蛋白反射光之间的对比度较低。在本文中，我们表明这是使用相机闪光灯进行照明的结果，闪光灯在各个波段均匀照明，从而导致反射光中的对比度降低。相反，我们建议使用前置摄像头捕捉脉搏，并利用手机显示屏进行照明，手机显示屏是红、绿、蓝波段的选择性光源。我们在控制实验中使用光谱辐射计评估手机显示屏的光谱特性，将它们与手机相机的灵敏度曲线进行卷积，并表明与闪光灯照明相比，屏幕的窄带显示照明使所需波段反射光之间的对比度提高了两倍。我们的初步评估进一步支持了我们的方法和研究结果。
