Experimental Substantiation of a Number of Requirements for Hardware and Methodology of Non-Contact Photoplethysmography Based on Video Image Analysis

Experimental assessment of the possibility of using a scientific video camera for realization of non-contact photoplethysmography is carried out. In view of the wide spread of digital cameras in endoscopic units photoplethysmography based on video-image analysis is an inexpensive and promising method for solving problems of medical diagnostics. A number of requirements to the camera parameters ensuring the specified level of the registered signals coded by RGB values, to the external illumination and video image postprocessing algorithms was substantiated. It was found that at signal levels on the green channel of not less than 130 and not more than 220 a. u. (for a camera with 8-bit color coding depth), the highest level of useful pulse signal is provided. It was shown that any source of light of equivalent color temperature in the range of 3500--6500 K as well as green LEDs can be used as a light source to obtain a high-quality signal of non-contact photoplethysmography. It is demonstrated that the signal has higher signal/noise ratio when the averaging area is larger than 40 × 40 pixels than when averaging over a smaller group of pixels. The obtained results can be used for the implementation of non-contact photoplethysmography to study local blood flow based on video image analysis This work was supported by the Foundation for Assistance to Small InnovativeEnterprises in Science and Technology (contract no. 13938GU/2019)

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