paper：
本文把人脸区域分成7个部分，分析那部分区域与心率是高相关的。
摘要： We divided the face into seven regions and evaluated the quality of the signal of each region using the area ratio of high-SNR and high-correlation, and mean and standard deviation (SD) of SNR and correlation coefficient.
The results show that a forehead and both cheeks especially have a potential to be a good candidates for computationally efficient ROI. On the other hand, the signal quality from a mouth and a chin was relatively low. A nasion and a nose have a limitation to be efficient ROI.
结论是：forehead 和both check 比较好的候选区域。
I
对这个问题的理解：如果能用整个人脸，还是用整个人脸吧。额头区域和脸颊区域虽然相关度最高，但是还是不如整个人脸
论文中写为什么不用整个人脸？ 因为计算量大，都2020 年了，计算量大还是个事？