We consider two crucial problems in continuous sign language recognition from unaided video sequences. At the sentence level, we consider the movement epenthesis (me) problem and at the feature level, we consider the problem of hand segmentation and grouping. We construct a framework that can handle both of these problems based on an enhanced, nested version of the dynamic programming approach. To address movement epenthesis, a dynamic programming (DP) process employs a virtual me option that does not need explicit models. We call this the enhanced level building (eLB) algorithm. This formulation also allows the incorporation of grammar models. Nested within this eLB is another DP that handles the problem of selecting among multiple hand candidates. We demonstrate our ideas on four American Sign Language data sets with simple background, with the signer wearing short sleeves, with complex background, and across signers. We compared the performance with Conditional Random Fields (CRF) and Latent Dynamic-CRF-based approaches. The experiments show more than 40 percent improvement over CRF or LDCRF approaches in terms of the frame labeling rate. We show the flexibility of our approach when handling a changing context. We also find a 70 percent improvement in sign recognition rate over the unenhanced DP matching algorithm that does not accommodate the me effect.

One of the hard problems in automated sign language recognition is the movement epenthesis (me) problem. Movement epenthesis is the gesture movement that bridges two consecutive signs. This effect can be over a long duration and involve variations in hand shape, position, and movement, making it hard to explicitly model these intervening segments. This creates a problem when trying to match individual signs to full sign sentences since for many chunks of the sentence, corresponding to these mes, we do not have models. We present an approach based on version of a dynamic programming framework, called Level Building, to simultaneously segment and match signs to continuous sign language sentences in the presence of movement epenthesis (me). We enhance the classical Level Building framework so that it can accommodate me labels for which we do not have explicit models. This enhanced Level Building algorithm is then coupled with a trigram grammar model to optimally segment and label sign language sentences. We demonstrate the efficiency of the algorithm using a single view video dataset of continuous sign language sentences. We obtain 83% word level recognition rate with the enhanced Level Building approach, as opposed to a 20% recognition rate using a classical Level Building framework on the same dataset. The proposed approach is novel since it does not need explicit models for movement epenthesis.

We consider the problem of computing the likelihood of a gesture from regular, unaided video sequences, without relying on perfect segmentation of the scene. Instead of requiring that low-and mid-level processes produce near-perfect segmentation of relevant body parts such as hands, we take into account that such processes can only produce uncertain information. The hands can only be detected as fragmented regions along with clutter. To address this problem, we propose an extension of the HMM formalism, which we call the frag-HMM, to allow for reasoning based on fragmented observations, via the use of an intermediate grouping process. In this formulation, we do not match the frag- HMMto one observation sequence, but rather to a sequence of observation sets, where each observation set is a collection of groups of fragmented observations. Based on the developed model, we show how to perform three kinds of computations. The first one is to decide on the best observation group for each frame, given a sequence of observation groups for the past frames. This allows us to incrementally compute the best segmentation of the hand for each frame, given the model. The second one involves the computation of likelihood of a sequence, averaged over all possible states sequences and possible groupings. The third is the computation of the likelihood of a sequence, maximized over all possible state sequences and group sequences. This can give us the best possible groupings for each frame, as well. We demonstrate our ideas using a publicly available hand gesture dataset that spans different subjects, is against complex background, and involves hand occlusions. The recognition performance is within 2% of that obtained with manually segmented hands and about 10% better than that obtained with segmentations that use the prior knowledge of the hand color.