Video acquisition unit consists of a high resolution camera. Even though the video acquired seems to be static, subtle changes in the blood flow beneath
the human skin creates change in colour and undetectable motions on the skin surface. These changes are recovered by processing the video.
We can simply use our smartphones for this purpose. The simplicity and utility of the project comes here. A finger is kept pressed to the camera while taking the video.
This is what we see on the screen when a finger is pressed against the camera sensor. Actually, this video has enough details for estimation of pulse rate. But those changes cannot be detected with naked eyes.
Sampling of the input signals plays a key role in the accurate detection of the pulse rate from the raw video. In order to compute the sampling frequency, first the heart beat ratethat can be detected accurately by the unit is fixed between the range of 40bpmto 230bpm. This range is included to ensure accurate measurement across allage groups, physical activity involved in while measuring and the level of fitnesslevel of a person. The sampling frequency for this range would lie in the rangeof 0.67Hz to 3.83Hz. Considering the Nyquist condition for avoiding aliasingeffects, the sampling frequency is set to 2 × 3.83Hz = 7.67Hz.