## 1 Introduction  
Automatic recording of vital parameters (VP) as a surrogate for health is part of clinical standard procedures, e.g., heartbeat by electrocardiography (ECG), pulse rate and oxygenation of the blood by pulse-oxymetry and blood pressure by intermittent sphygmomanometry. These procedures serve many purposes, e.g., diagnostics, risk stratification and monitoring, and finally lead to better clinical outcomes in various settings [1; 2; 3]. In case of primary admission, gathering data on VP may help in identifying patients at risk and in arriving at the diagnosis and its differential diagnoses from a very early stage, e.g., through determination of the affected organs [4]. Beyond momentary assessment, repeated recording of VP may serve to adapt treatment of the patient. Detecting changes of VP may help in risk stratification and consecutively lead to tailored degrees of medical surveillance according to individual needs [5] and timely treatment in case of deterioration [6; 7; 8]. Complications and sudden deteriorations are most often unexpected in hospitals. In retrospective analyses of in-hospital deaths, less than 30% were anticipated and countered by intensive care treatment and over 70% occurred unexpectedly [9]. Continuous monitoring may help to avoid unexpected deaths and to achieve a better outcome by timely intervention. Long-term automated recording of VP yields additional great health benefits [10; 11]. Various changes in VP that hint to potentially severe diseases occur only intermittently and thereby escape momentary diagnostics [12; 13]. Automatically recording and evaluating VP based on predetermined limits allows continuous monitoring of health with affordable resources and early diagnosis of intermittent diseases [14]. Up to now, established VP recording is based on touch-dependent sensor technology. This kind of sensor technology has its disadvantages and limitations. Mobility and autonomy are reduced significantly for those in need of care. Additionally, skin irritations may occur when using adhesive electrodes and the constant unfamiliar sensation caused by sensors and cables may lead to discomfort and manipulation of the sensors, false alarms and an increased workload for clinical staff. Compliance of patients to use touch-dependent monitoring is further limited as the obvious presence of a medical device means emphasizing their illness and has an impact on social participation [15; 16]. In cases of patients suffering from dementia or delirium, fixation measures may have to be ordered to ensure monitoring although external fixation itself promotes confusion and reduces quality of life [17]. Monitoring methods in hospitals and at home have to be chosen based on their benefits and disadvantages. For some patients the setting of an intensive or intermediate care unit with various degrees of invasive monitoring is favorable in terms of their personal outcome and in view of societal challenges regarding limited resources [18]. A large collective of patients would profit from an adaptable and non-invasive form of monitoring [19], especially if this kind of monitoring could bridge the gap between hospital and home care. To address this challenge adequately, the monitoring device should be touch-less, allow easy set-up and intuitive operation and has to capture basic VP, which are valid surrogate parameters for overall health, e.g., heartbeat and breathing. To address the need of contactless VP monitoring, engineers have developed and investigated various novel concepts in the past years [20]. Using a high-resolution thermal camera, for instance, the heart rate of a person under test (PUT) can be extracted by sensing the temperature modulation of the skin in vicinity to blood vessels [21]. However, direct line-of-sight (LOS) between camera and PUT is required. While the results are very promising regarding respiration rate, the accuracy of the heart rate is limited to a root mean square error (RMSE) of several beats per minute [22].