Measuring pulse rate (PR) and blood oxygenation (also peripheral oxygen saturation, SpO2) is a common monitoring procedure in veterinary medicine which gives important information about the patient's cardiovascular and respiratory systems. It can be performed as a part of physical examination (ASAVA 2013), surgical procedure (Bednarski et al 2011) or intensive care treatment (Humm and Kellett-Gregory 2016). In addition to veterinary professionals, pet owners are also becoming interested in painless and stress-free monitoring of their animals. This trend is reflected in the pet market, where gadget devices for monitoring the canine or feline location and activity are on the rise (Weiss et al 2013).Measuring PR and SpO2 can be done by the same optical probe, which is based on a pulse oximetry sensor comprising continuously emitting light sources. The probe first emits and then, by the form of design, receives either the transmitted (e.g. on finger, tongue) or the reflected (e.g. on tail) red and infrared (IR) light (Allen 2007). If the acquired data is evaluated in time from a single spectral band, the technique is generally called photoplethysmography (PPG). In this way, pulse oximetry is based on comparing red and IR PPG signal baselines. The acquired PPG signal consists of non-pulsatile (DC) and pulsatile (AC) components. A baseline of PPG signal (i.e. non-pulsatile DC) reflects the collective light absorption due to blood and other tissues while the pulsatile PPG component (AC) is a consequence of local blood volume changes in accordance with the cardiac cycle.In humans, PPG is one of the most popular monitoring tools (Orphanidou 2018) since the device is small, reliable and low cost. In addition to PR and SpO2, PPG is also used to monitor blood pressure, cardiac output, and respiration rate, to detect various vascular diseases (Erts et al 2005, Karlen et al 2012, Bartels and Thiele 2015 and to assess regional anesthesia efficiency (Nijboer and Dorlas 1985, Rubins et al 2010). PPG probes are normally placed on the fingertip for direct bedside monitoring. Recently, imaging PPG (iPPG) has become increasingly valuable since the PPG signals can be obtained from a camera or a mobile phone video (Huelsbusch and Blazek 2002, Jonathan and Leahy 2010, Remer and Bilenca 2015. It was shown that the PPG pulse varies significantly among measurement sites such as fingertips, toes, and ears (Spigulis 2005, Allen 2007). This phenomenon probably occurs due to differences in the cutaneous blood supply of the different anatomic regions (Maeda et al