FluentSigners-50: A signer independent benchmark dataset for sign language processing

This paper presents a new large-scale signer independent dataset for Kazakh-Russian Sign Language (KRSL) for the purposes of Sign Language Processing. We envision it to serve as a new benchmark dataset for performance evaluations of Continuous Sign Language Recognition (CSLR) and Translation (CSLT) tasks. The proposed FluentSigners-50 dataset consists of 173 sentences performed by 50 KRSL signers resulting in 43,250 video samples. Dataset contributors recorded videos in real-life settings on a wide variety of backgrounds using various devices such as smartphones and web cameras. Therefore, distance to the camera, camera angles and aspect ratio, video quality, and frame rates varied for each dataset contributor. Additionally, the proposed dataset contains a high degree of linguistic and inter-signer variability and thus is a better training set for recognizing a real-life sign language. FluentSigners-50 baseline is established using two state-of-the-art methods, Stochastic CSLR and TSPNet. To this end, we carefully prepared three benchmark train-test splits for models’ evaluations in terms of: signer independence, age independence, and unseen sentences. FluentSigners-50 is publicly available at https://krslproject.github.io/FluentSigners-50/publishedVersio

Improving Continuous Sign Language Recognition with Consistency Constraints and Signer Removal

Most deep-learning-based continuous sign language recognition (CSLR) models share a similar backbone consisting of a visual module, a sequential module, and an alignment module. However, due to limited training samples, a connectionist temporal classification loss may not train such CSLR backbones sufficiently. In this work, we propose three auxiliary tasks to enhance the CSLR backbones. The first task enhances the visual module, which is sensitive to the insufficient training problem, from the perspective of consistency. Specifically, since the information of sign languages is mainly included in signers' facial expressions and hand movements, a keypoint-guided spatial attention module is developed to enforce the visual module to focus on informative regions, i.e., spatial attention consistency. Second, noticing that both the output features of the visual and sequential modules represent the same sentence, to better exploit the backbone's power, a sentence embedding consistency constraint is imposed between the visual and sequential modules to enhance the representation power of both features. We name the CSLR model trained with the above auxiliary tasks as consistency-enhanced CSLR, which performs well on signer-dependent datasets in which all signers appear during both training and testing. To make it more robust for the signer-independent setting, a signer removal module based on feature disentanglement is further proposed to remove signer information from the backbone. Extensive ablation studies are conducted to validate the effectiveness of these auxiliary tasks. More remarkably, with a transformer-based backbone, our model achieves state-of-the-art or competitive performance on five benchmarks, PHOENIX-2014, PHOENIX-2014-T, PHOENIX-2014-SI, CSL, and CSL-Daily

Data mining and modelling for sign language

Sign languages have received significantly less attention than spoken languages in the research areas of corpus analysis, machine translation, recognition, synthesis and social signal processing, amongst others. This is mainly due to signers being in a clear minority and there being a strong prior belief that sign languages are simply arbitrary gestures. To date, this manifests in the insufficiency of sign language resources available for computational modelling and analysis, with no agreed standards and relatively stagnated advancements compared to spoken language interaction research. Fortunately, the machine learning community has developed methods, such as transfer learning, for dealing with sparse resources, while data mining techniques, such as clustering can provide insights into the data. The work described here utilises such transfer learning techniques to apply neural language model to signed utterances and to compare sign language phonemes, which allows for clustering of similar signs, leading to automated annotation of sign language resources. This thesis promotes the idea that sign language research in computing should rely less on hand-annotated data thus opening up the prospect of using readily available online data (e.g. signed song videos) through the computational modelling and automated annotation techniques presented in this thesis

Sign Language Transformers: Joint End-to-end Sign Language Recognition and Translation

Prior work on Sign Language Translation has shown that having a mid-level sign gloss representation (effectively recognizing the individual signs) improves the translation performance drastically. In fact, the current state-of-the-art in translation requires gloss level tokenization in order to work. We introduce a novel transformer based architecture that jointly learns Continuous Sign Language Recognition and Translation while being trainable in an end-to-end manner. This is achieved by using a Connectionist Temporal Classification (CTC) loss to bind the recognition and translation problems into a single unified architecture. This joint approach does not require any ground-truth timing information, simultaneously solving two co-dependant sequence-to-sequence learning problems and leads to significant performance gains. We evaluate the recognition and translation performances of our approaches on the challenging RWTH-PHOENIX-Weather-2014T (PHOENIX14T) dataset. We report state-of-the-art sign language recognition and translation results achieved by our Sign Language Transformers. Our translation networks outperform both sign video to spoken language and gloss to spoken language translation models, in some cases more than doubling the performance (9.58 vs. 21.80 BLEU-4 Score). We also share new baseline translation results using transformer networks for several other text-to-text sign language translation tasks

Automatic Sign Language Recognition from Image Data

Tato práce se zabývá problematikou automatického rozpoznávání znakového jazyka z obrazových dat. Práce představuje pět hlavních přínosů v oblasti tvorby systému pro rozpoznávání, tvorby korpusů, extrakci příznaků z rukou a obličeje s využitím metod pro sledování pozice a pohybu rukou (tracking) a modelování znaků s využitím menších fonetických jednotek (sub-units). Metody využité v rozpoznávacím systému byly využity i k tvorbě vyhledávacího nástroje "search by example", který dokáže vyhledávat ve videozáznamech podle obrázku ruky. Navržený systém pro automatické rozpoznávání znakového jazyka je založen na statistickém přístupu s využitím skrytých Markovových modelů, obsahuje moduly pro analýzu video dat, modelování znaků a dekódování. Systém je schopen rozpoznávat jak izolované, tak spojité promluvy. Veškeré experimenty a vyhodnocení byly provedeny s vlastními korpusy UWB-06-SLR-A a UWB-07-SLR-P, první z nich obsahuje 25 znaků, druhý 378. Základní extrakce příznaků z video dat byla provedena na nízkoúrovňových popisech obrazu. Lepších výsledků bylo dosaženo s příznaky získaných z popisů vyšší úrovně porozumění obsahu v obraze, které využívají sledování pozice rukou a metodu pro segmentaci rukou v době překryvu s obličejem. Navíc, využitá metoda dokáže interpolovat obrazy s obličejem v době překryvu a umožňuje tak využít metody pro extrakci příznaků z obličeje, které by během překryvu nefungovaly, jako např. metoda active appearance models (AAM). Bylo porovnáno několik různých metod pro extrakci příznaků z rukou, jako např. local binary patterns (LBP), histogram of oriented gradients (HOG), vysokoúrovnové lingvistické příznaky a nové navržená metoda hand shape radial distance function (hRDF). Bylo také zkoumáno využití menších fonetických jednotek, než jsou celé znaky, tzv. sub-units. Pro první krok tvorby těchto jednotek byl navržen iterativní algoritmus, který tyto jednotky automaticky vytváří analýzou existujících dat. Bylo ukázáno, že tento koncept je vhodný pro modelování a rozpoznávání znaků. Kromě systému pro rozpoznávání je v práci navržen a představen systém "search by example", který funguje jako vyhledávací systém pro videa se záznamy znakového jazyka a může být využit například v online slovnících znakového jazyka, kde je v současné době složité či nemožné v takovýchto datech vyhledávat. Tento nástroj využívá metody, které byly použity v rozpoznávacím systému. Výstupem tohoto vyhledávacího nástroje je seřazený seznam videí, které obsahují stejný nebo podobný tvar ruky, které zadal uživatel, např. přes webkameru.Katedra kybernetikyObhájenoThis thesis addresses several issues of automatic sign language recognition, namely the creation of vision based sign language recognition framework, sign language corpora creation, feature extraction, making use of novel hand tracking with face occlusion handling, data-driven creation of sub-units and "search by example" tool for searching in sign language corpora using hand images as a search query. The proposed sign language recognition framework, based on statistical approach incorporating hidden Markov models (HMM), consists of video analysis, sign modeling and decoding modules. The framework is able to recognize both isolated signs and continuous utterances from video data. All experiments and evaluations were performed on two own corpora, UWB-06-SLR-A and UWB-07-SLR-P, the first containing 25 signs and second 378. As a baseline feature descriptors, low level image features are used. It is shown that better performance is gained by higher level features that employ hand tracking, which resolve occlusions of hands and face. As a side effect, the occlusion handling method interpolates face area in the frames during the occlusion and allows to use face feature descriptors that fail in such a case, for instance features extracted from active appearance models (AAM) tracker. Several state-of-the-art appearance-based feature descriptors were compared for tracked hands, such as local binary patterns (LBP), histogram of oriented gradients (HOG), high-level linguistic features or newly proposed hand shape radial distance function (denoted as hRDF) that enhances the feature description of hand-shape like concave regions. The concept of sub-units, that uses HMM models based on linguistic units smaller than whole sign and covers inner structures of the signs, was investigated in the proposed iterative method that is a first required step for data-driven construction of sub-units, and shows that such a concept is suitable for sign modeling and recognition tasks. Except of experiments in the sign language recognition, additional tool \textit{search by example} was created and evaluated. This tool is a search engine for sign language videos. Such a system can be incorporated into an online sign language dictionary where it is difficult to search in the sign language data. This proposed tool employs several methods which were examined in the sign language recognition task and allows to search in the video corpora based on an user-given query that consists of one or multiple images of hands. As a result, an ordered list of videos that contain the same or similar hand configurations is returned