Detecting Hand-Head Occlusions in Sign Language Video

A large body of current linguistic research on sign language is based on analyzing large corpora of video recordings. This requires either manual or automatic annotation of the videos. In this paper we introduce methods for automatically detecting and classifying hand-head occlusions in sign language videos. Linguistically, hand-head occlusions are an important and interesting subject of study as the head is a structural place of articulation in many signs. Our method combines easily calculable local video properties with more global hand tracking. The experiments carried out with videos of the Suvi on-line dictionary of Finnish Sign Language show that the sensitivity of the proposed local method in detecting occlusion events is 92.6%. When global hand tracking is combined in the method, the specificity can reach the level of 93.7% while still maintaining the detection sensitivity above 90%.