ECG-derived value; NICU; O2; adhesive electrodes; adhesive sensors; adult healthy human volunteers; ambient light; biochemistry; biomedical equipment; biomedical optical imaging; blood vessels; bradycardia identification; breathing rate estimation; camera-derived estimates; cardiac cycle; cardiology; clinical letter; continuous heart rate estimation; continuous noncontact vital sign monitoring; continuous oxygen saturation estimation; continuous pre-term infant monitoring; continuous respiratory rate estimation; continuous vital sign monitoring technologies; digital video camera; direct patient contact; electrocardiogram; estimation theory; feature extraction; high-dependency care area; hospital; incubators; infant nursing; infant pain; infant skin damage; infant stress; major desaturation; mean absolute error; medical image processing; minimal infant motion; neonatal intensive care unit; oximetry; oxygen; paediatrics; patient care; patient monitoring; pneumodynamics; pulse oximeter; reference heart rate value; stable sections; superficial blood vessel colour change measurement; superficial blood vessel volume change measurement; time 4 day; video cameras; video recording; video signal processing algorithms; video-based noncontact monitoring methods