11 Remote Space- and Time-Resolved Skin Perfusion Detection …
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Fig. 11.8 Raw PPGI signal recorded using environmental light. The small oscillations best visible
in the first half of the signal correlate to the subject’s heartbeat. Starting 15 s after recording, a
second person is walking closely around the measurement location but outside the field of view
of to the camera. Nevertheless, artefacts are visible in the measurement caused by shading of the
test subject or additional reflections from the light clothing of the person walking by respectively
(modified from [10]
Fig. 11.9 PPGI LED illumination panels: (left) single wavelength panels, (right) PPGI camera (1)
with multi- wavelength illumination panel (2) (green wavelength activated); the illumination can
be synchronized with the frame grabbing of the camera by the illumination control box (3)
The dimensions and positioning of LED panels can be easily adapted according
to the individual measurement task. To achieve a sufficiently bright and homogenous
illumination, the correct choice may be made from either a large area single panel,
customized arranged multi-LED panels or ring lights around the camera objective.
As mentioned earlier, the readout process of the camera can be synchronized
with a color change of the illumination unit (see Fig. 11.10). This step would result
187
Fig. 11.8 Raw PPGI signal recorded using environmental light. The small oscillations best visible
in the first half of the signal correlate to the subject’s heartbeat. Starting 15 s after recording, a
second person is walking closely around the measurement location but outside the field of view
of to the camera. Nevertheless, artefacts are visible in the measurement caused by shading of the
test subject or additional reflections from the light clothing of the person walking by respectively
(modified from [10]
Fig. 11.9 PPGI LED illumination panels: (left) single wavelength panels, (right) PPGI camera (1)
with multi- wavelength illumination panel (2) (green wavelength activated); the illumination can
be synchronized with the frame grabbing of the camera by the illumination control box (3)
The dimensions and positioning of LED panels can be easily adapted according
to the individual measurement task. To achieve a sufficiently bright and homogenous
illumination, the correct choice may be made from either a large area single panel,
customized arranged multi-LED panels or ring lights around the camera objective.
As mentioned earlier, the readout process of the camera can be synchronized
with a color change of the illumination unit (see Fig. 11.10). This step would result