The type of surface that a depth belongs to is used to
determine if it is a nose or eye. For this purpose, the two
previously found curvature measures need to be thresholded.
Following [3] a point will be considered to be a nose if
K > TKnose and H > THnose where TKnose = 0.0325 and
THnose = 0.0925. Similarly a point will be considered to
be a mouth if K > TKeye and H > THeye where TKeye =
0.000275 and THeye = −0.018. Examination of the depth
image using these thresholded measures reveals the possible
points for nose and mouth on the depth image. It should
be mentioned that a 4×4 neighborhood relationship will be
used to connect pixels which belong to the same type of
element: eye or mouth and at the end blocks representing
possible eyes and mouths will be considered (Figure 3(c)).