The localization procedure thus yields an output similar to the one found in
Figure . Note that the horizontal (i.e., parallel with
intra-ocular axis) position of the nose is uncertain. This is represented by
a white line across the vertical position of the nose from the left eye to the
right eye. The nose tip is a point on this line segment and its exact locus is
found by the techniques described in Chapter 4. Furthermore, it is possible
that the face detection computation will be triggered by a non-face which
happens to have a blob-like structure with eye blobs and a mouth-limb. These
'false alarms' by the face detector will be rejected using
techniques described in Chapter 4.
Thus, we have given a procedure for localizing the face and facial features in
an image. We begin by finding the face-blob and then estimating a facial
contour. From there, we can define the eye-band, a region where the eyes might
be present. Eye-blob detection is then performed and the blobs are tested
geometrically to see if an adequate pair can be found. If two blobs are
``eye-like'' geometrically, we search for a mouth between them and then,
finally, a nose-line. At this stage, however, the localization is not
complete and requires further development in Chapter 4. Consequently, we shall
defer localization testing to Chapter 5. Several examples of the complete
localization are given there. It is also important to note that the exact
location of the facial features in Figure (and other faces
that are processed) is not critical. This is because this localization is to
undergo further processing before face recognition is performed. This
post-processing will desensitize the recognition to small localization errors.