ALT is “sensitive” to changes in the ambient illumination
(the changes, I guess, might be present in an art installation).
If you are using using a Kinect for Xbox 360 or an Occipital Structure Sensor (https://structure.io/
) as a light source element and a Pi NoIR camera as a camera element for an ALT setup and if there are substantial and rapid ambient light variations which can be picked up by the Pi NoIR camera (e.g. incandescent light), you can put an optical filter in front of the camera to reduce the effect of the light variations
(the filter which lets into the camera mostly the wavelengths around those on which the Kinect’s or the Sensor’s light emitter operates).
Alternatively, you can capture the IR video stream directly
from the Kinect or the Sensor and process the frames in that stream to get the ALT data. Both Kinect and Sensor already have built-in IR filter optics.
Respiration and body movements might also be an interesting source of “biofeedback” (for an art installation or otherwise).