With above training set, face detection works well; it can
detect faces in images with low false alarm rate. But, it can not
detect faces in low light condition and dark skin faces. To solve
this problem, there are two approaches; one is image
preprocessing and another is enhancing training set. Lizuo Jin
and Shin’ich Satoh introduced a good method to estimate an
illumination condition of image and enhance its quality [14].
But their method is computationally, it is not feasible on mobile
product