## 1 Introduction  
Oxygen saturation is an indicator of how much of the hemoglobin in the blood is bound to oxygen. Oxygen saturation is generally expressed as a percentage and refers to the ratio of hemoglobin combined with oxygen. It is used as an important indicator in evaluating the amount of oxygen supplied to cells and tissues. Oxygen saturation plays a key role in maintaining a healthy state. A sufficient oxygen supply is essential for maintaining cell metabolism and function, and oxygen deficiency can lead to serious physiological problems. Therefore, measuring oxygen saturation helps to evaluate the oxygen supply status of the body and identify abnormalities in blood circulation and respiratory function [1, 2]. In particular, the importance of oxygen saturation has become more prominent in infectious disease situations such as COVID-19. Even before symptomsdevelop due to COVID-19 infection, there is a decrease in the oxygen saturation in the blood, which is helpful for the early detection and diagnosis of symptoms. Therefore, measuring oxygen saturation plays an important role in the early diagnosis and treatment of respiratory diseases [3]. One of the main ways to measure oxygen saturation is to use a finger pulseoximeter. A pulseoximeter measures the oxygen saturation in the blood in a non-invasive manner, allowing it to monitor the patient's current condition in real-time situations [4]. However, pulseoximeters may not provide accurate measurements in some environments. For example, cold hands can cause vasoconstriction, which can reduce blood flow and potentially affect the accuracy of the reading. In addition, for fingers with nail polish, the nail polish present may affect the amount of light transmission, resulting in inaccurate measurements [5]. Especially in infectious disease situations such as COVID-19, it can increase the risk of infectious diseases, as you have to use a device within someone else's use. As these problems and the risk of infection have become more prominent, non-contact oxygen saturation measurement methods have been actively studied in response [6; 7]. In general, non-contact oxygen saturation studies are based on the operating principle of a pulseoximeter. A pulseoximeter is based on the principles of the different absorptions of different light wavelengths by hemoglobin species. A pulseoximeter transmits infrared and red light to the finger. As shown in Figure 1, hemoglobin without oxygen and hemoglobin with oxygen absorb infrared and red light differently. At this time, hemoglobin that is not bound to oxygen absorbs more infrared light, and hemoglobin that is bound to oxygen absorbs more red light. The pulseoximeter measures and analyzes the amount of light absorbed by the sensor. It determines the oxygen saturation in the blood by calculating the difference in absorption for infrared and red light [9]. In measuring oxygen saturation, the alternating current (AC) and direct current (DC) components form an important part of the principle of measurement. By measuring the transmitted light hundreds of times per second, the pulseoximeter can distinguish between the AC component, which is a variable pulsating component of arterial blood, and the DC component, which is an unchanging static component of a signal consisting of tissue, venous blood, and non-pulse arterial blood. The static component  
Figure 1: The wavelength of oxygenated hemoglobin and the deoxygenated hemoglobin absorption coefficient [8]. can then be removed from the signal so that the pulsating component, which is typically composed of 1% to 5% of the total signal, can be separated. As shown in Equation (1), dividing the AC level by the DC level at each wavelength also compensates for the change in the incident light intensity, which can remove other complex variables from the equation. Doing this at each wavelength reduces the main source of absorption in the arterial blood and separates the relative absorbance of oxygenated Hb.