A method, apparatus, and computer program product for estimating face
direction using a single gray-level image (110, 150) of a face are
described. Given the single image (110, 150), a face direction can be
determined by computing a nose axis (140, 180) maximising a correlation
measure between left and right sides (120, 130; 160, 170) of the face.
The correlation measure is computed by comparing one of the two sides (A)
with another synthetic side (C) derived from the other side (B) using
symmetry and perspective transforms. Optionally, this process can be
accelerated using a contrast enhancement algorithm taking advantage of
the circumstances that the nose is the part of a face reflecting the most
light and that this reflected light is represented as a line-like region
close to the real nose axis. The computation result is a word describing
the spatial position of the face and combining height ("up", "normal",
"down") and neck-rotation ("left", "frontal", "right").