Table 5.

Comparison table of nonwearable-type heartbeat measuring methods in this review (continued). NA means that no description of accuracy can be found.

Measuring Methods	Developers/ Authors	Year	Technology	Accuracy Compared to EEG
Camera- type	Sakamaki and Fujita [78]	2020	Signal processing of person’s skin image	BPM difference is less than 3 bpm
	Okada et al. [79]	2018	Change in the average pixel value of the hemoglobin component images obtained using the skin pigment separation on the RGB pixel values of facial images	NA (only the accuracy of facial expression classification was evaluated)
	Kwon et al. [80]	2012	Facial color change took by a smartphone’s camera	NA
	Sun et al. [81]	2018	Facial color change took by RGB camera	$r=0.96$
	Google [85]	2014	Pulsewave detected by smartphone’s camera	NA
	HRV4Training [86,87,88]	2015		MAPE, median and IQR of rMSSD is 4.10, 2.76 and 3.74, respectively
	Huang [90]	2016	Facial color change took by smartphone’s camera	The mean of absolute errors of HRV metrics is 3.53 ms