Shadle, C.H., Carter, J.N., Monks, T.P. and Field, J.
Depth Measurement of Face and Palate by Structured Light.
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In order to model speech production for purposes such as articulatory synthesis, articulatory data must be acquired, preferably in a way that does not impede the speaker's ability to speak. A variety of techniques has been used, many of them, such as ultrasound, X-rays, or MRI, adapted from medical imaging. For externally accessible articulators such techniques are not appropriate, but the task of measuring the shape of a complex three-dimensional object is still difficult. For a static object such as a dental impression manual methods such as slicing a mold of the impression and measuring the slices with calipers can be quite accurate, though time-consuming. For a dynamic object such as the face shape during speech such manual methods cannot be used. A workable alternative has been developed at Grenoble that instead uses simultaneous video pictures of front and profile face. Blue lipstick is used on the subject's lips to provide a definite outline and provide maximum contrast with the teeth and tongue. The images must then be post-processed before parameters such as mouth area are extracted. In this paper we present a structured light system which uses a slide projector and a single video camera to acquire depth coordinates of a static or moving object. We discuss pilot experiments aimed at optimising its output and establishing its accuracy, and make some preliminary comparisons with the Grenoble double-video system. In the next section the structured light technique is summarised, focusing on the experimental constraints it imposes. The technique is described in more detail elsewhere. In `Static measurements' its use on the static object of an EPG palate is described. In `Dynamic measurements' its use in acquiring dynamic face shape data is described, focusing on methodology issues that arose in an extended recording session with a human speaker. In the discussion we describe the calibration procedure and the related tradeoffs, and finally we make some initial comparisons to the double-video system.
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