Geometric features
no vote
Before building a face detection system, it is very useful if we know how eyes function. In general, eyes can detect a wide variety of objects under various environment. However, if an object appears at a particular pose, e.g., upside down, we may not recognize it at once. The reason is the orientation of this object is different from that of its counterpart in memory. Therefore, when one wants to check what exists in an image, usually the whole geometrical configuration is checked instead of checking object's details. Besides, since a face contains four main organs, i.e., eyebrows, eyes, nose, and mouth, it is very important to detect these facial features so that the whole geometrical configuration of the face can be identified. In general, eyebrows, eyes, nostrils and mouth always look darker than the rest of a face due to illumination. Among them, the darkness of eyebrows also depends on their density and color, and the nostrils may not always be seen.