Device for determining arterial blood oxygen saturation of a subject comprising: - an interface for receiving a data stream derived from detected electromagnetic radiation emitted or reflected from one or more skin portions of the subject, said data stream comprising a data signal per skin pixel for a plurality of skin pixels of said one or more skin portions, a data signal representing the detected electromagnetic radiation emitted or reflected from the respective skin pixel over time and having a DC portion and an AC portion, - an analyzer for determining the AC portions of the data signals of said plurality of skin pixels and determining the change in arterial blood oxygen saturation of said plurality of skin pixels from said AC portions of the data signals, - a selector for selecting a group of skin pixels comprising either i) the skin pixels showing the fastest change in arterial blood oxygen saturation at which the arterial blood oxygen saturation changes earliest or ii) said plurality of skin pixels except for skin pixels showing the slowest change in arterial blood oxygen saturation at which the arterial blood oxygen saturation changes last, wherein said selector is configured to select said group of skin pixels by use of an upper or lower threshold for the arterial blood oxygen saturation or by use of a threshold for the percentage of skin pixels of said plurality of skin pixels to be selected as said group, and - a processor for determining a total blood oxygen saturation value of the subject's arterial blood oxygen saturation based on the data signals of the selected group of skin pixels by use of photoplethysmography, by i) averaging blood oxygen saturation values determined per skin pixel of the selected group of skin pixels from the AC portions of the data signals of said skin pixels, or ii) averaging the data signals of the skin pixels of the selected group of skin pixels to obtain an averaged data signal and determining the total blood oxygen saturation value of the subject from the averaged data signal. - an interface for receiving a data stream derived from detected electromagnetic radiation emitted or reflected from one or more skin portions of the subject, said data stream comprising a data signal per skin pixel for a plurality of skin pixels of said one or more skin portions, a data signal representing the detected electromagnetic radiation emitted or reflected from the respective skin pixel over time and having a DC portion and an AC portion, - an analyzer for determining the AC portions of the data signals of said plurality of skin pixels and determining the change in arterial blood oxygen saturation of said plurality of skin pixels from said AC portions of the data signals, - a selector for selecting a group of skin pixels comprising either i) the skin pixels showing the fastest change in arterial blood oxygen saturation at which the arterial blood oxygen saturation changes earliest or ii) said plurality of skin pixels except for skin pixels showing the slowest change in arterial blood oxygen saturation at which the arterial blood oxygen saturation changes last, wherein said selector is configured to select said group of skin pixels by use of an upper or lower threshold for the arterial blood oxygen saturation or by use of a threshold for the percentage of skin pixels of said plurality of skin pixels to be selected as said group, and - a processor for determining a total blood oxygen saturation value of the subject's arterial blood oxygen saturation based on the data signals of the selected group of skin pixels by use of photoplethysmography, by i) averaging blood oxygen saturation values determined per skin pixel of the selected group of skin pixels from the AC portions of the data signals of said skin pixels, or ii) averaging the data signals of the skin pixels of the selected group of skin pixels to obtain an averaged data signal and determining the total blood oxygen saturation value of the subject from the averaged data signal. i) averaging blood oxygen saturation values determined per skin pixel of the selected group of skin pixels from the AC portions of the data signals of said skin pixels, or ii) averaging the data signals of the skin pixels of the selected group of skin pixels to obtain an averaged data signal and determining the total blood oxygen saturation value of the subject from the averaged data signal.