Transdermal optical imaging, also known as transdermal optical imagery[1] or TOI, is a method of detecting blood flow of the face by measuring hemoglobin concentration using a digital video camera.
[3] The re-emitted light from underneath the skin is affected by chromophores, mainly hemoglobin and melanin,[4] which differ in color.
[5] The color difference allows TOI machine learning software to separate the images into layers, which are known as bitplanes.
[6][7] Transdermal optical imaging has been proposed as an alternative to cuff-based methods of measuring blood pressure because it is able to measure heart rate accurately in a "contactless and non-invasive" way.
[8] Transdermal optical imaging may be able to detect hidden emotions using the patterns of blood flow in the face.