This paper presents an empirical audit of the widely used RWTH-PHOENIX-2014T corpus, examining its suitability as a benchmark for sign language recognition and translation. Through human annotation of the training set and extensive sign-to-text back translation of the test set, we provide detailed statistics that indicate substantial quality issues, including information loss and lexical errors. Automatic scores comparing human sign-to-text back translations to the original speech transcribed references are remarkably low, suggesting strong translationese effects and substantial paraphrasing, revealing limitations of lexical metrics in adequately scoring translation quality. Replacing the original speech-transcribed references with human sign-to-text back translations while scoring existing sign language translation systems reveals the lack of robustness of system evaluation with lexical metrics against this test set. Our findings highlight risks associated with relying on this corpus for model evaluation and call for more rigorous, linguistically grounded evaluation practices in sign language technology research. The back-translated test set and error annotations are made publicly available.

In this article, we describe DGS-BIGEKO, a sign language dataset containing a conversation in a crisis scenario signed by a professional interpreter in German Sign Language (DGS). The dataset comprises 14 sentences with common questions and answers from protocols occurring in emergency call scenarios translated into DGS. Additionally, the dataset contains signs for an additional 108 concepts that are relevant to emergency call scenarios. The dataset is intended to support research in sign language linguistics and sign language machine translation by providing resources in a very specific domain, where no previous resources are available in DGS. The dataset is freely available for research purposes at the following address: https://doi.org/10.5281/zenodo.18458557

Emotion Recognition research in Sign Languages is still in its infancy. Still today, there exists a lack of knowledge about appropriate annotation guidelines and the impact that facial expressions, body postures and head positions have in recognizing emotions while signing, considering that sign language encompasses manual and non-manual cues with linguistic purposes. In this article, we present an acquisition protocol to record acted emotions in German Sign Language under four scenarios (High-Valence and High-Arousal, High-Valence and Low Arousal, Low-Valence and High-Arousal, and Low-Valence and Low-Arousal). The goal is to provide a reference dataset to explore the use of machine learning techniques for an automated classification of emotions in sign language utterances. As a baseline reference, we trained static models with features extracted from the facial muscle activations. The best model achieved an accuracy of 68.84% and a F1 of 67.96% with a random forest trained on the statistics extracted from Action Units. These results highlight the importance of facial expression in sign language, not only for carrying linguistic information but also for transmitting emotions. Results also indicate challenges in detecting emotions in the High-Valence and Low Arousal scenario, which suggests future investigation lines to explore.

We present a dataset and a model for sentiment analysis of German sign language (DGS) fairy tales. First, we perform sentiment analysis for three levels of valence (negative, neutral, positive) on German fairy tales text segments using four large language models (LLMs) and majority voting, reaching an inter-annotator agreement of 0.781 Krippendorff’s alpha. Second, we extract face and body motion features from each corresponding DGS video segment using MediaPipe. Finally, we train an explainable model (based on XGBoost) to predict negative, neutral or positive sentiment from video features. Results show an average balanced accuracy of 0.631. A thorough analysis of the most important features reveal that, in addition to eyebrows and mouth motion on the face, also the motion of hips, elbows, and shoulders considerably contribute in the discrimination of the conveyed sentiment, indicating an equal importance of face and body for sentiment communication in sign language.

We present the acquisition process and the data of DGS-Fabeln-1, a parallel corpus of German text and videos containing German fairy tales interpreted into the German Sign Language (DGS) by a native DGS signer. The corpus contains 573 segments of videos with a total duration of 1 hour and 32 minutes, corresponding with 1428 written sentences. It is the first corpus of semi-naturally expressed DGS that has been filmed from 7 angles, and one of the few sign language (SL) corpora globally which have been filmed from more than 3 angles and where the listener has been simultaneously filmed. The corpus aims at aiding research at SL linguistics, SL machine translation and affective computing, and is freely available for research purposes at the following address: https://doi.org/10.5281/zenodo.10822097.

In this paper, we investigate the capability of convolutional neural networks to recognize in sign language video frames the six basic Ekman facial expressions for ‘fear’, ‘disgust’, ‘surprise’, ‘sadness’, ‘happiness’, ‘anger’ along with the ‘neutral’ class. Given the limited amount of annotated facial expression data for the sign language domain, we started from a model pre-trained on general-purpose facial expression datasets and we applied various machine learning techniques such as fine-tuning, data augmentation, class balancing, as well as image preprocessing to reach a better accuracy. The models were evaluated using K-fold cross-validation to get more accurate conclusions. It is experimentally demonstrated that fine-tuning a pre-trained model along with data augmentation by horizontally flipping images and image normalization, helps in providing the best accuracy on the sign language dataset. The best setting achieves satisfactory classification accuracy, comparable to state-of-the-art systems in generic facial expression recognition. Experiments were performed using different combinations of the above-mentioned techniques based on two different architectures, namely MobileNet and EfficientNet, and is deemed that both architectures seem equally suitable for the purpose of fine-tuning, whereas class balancing is discouraged.

We present the requirements, design guidelines, and the software architecture of an open-source toolkit dedicated to the pre-processing of sign language video material. The toolkit is a collection of functions and command-line tools designed to be integrated with build automation systems. Every pre-processing tool is dedicated to standard pre-processing operations (e.g., trimming, cropping, resizing) or feature extraction (e.g., identification of areas of interest, landmark detection) and can be used also as a standalone Python module. The UML diagrams of its architecture are presented together with a few working examples of its usage. The software is freely available with an open-source license on a public repository.

This paper presents an overview of AVASAG; an ongoing applied-research project developing a text-to-sign-language translation system for public services. We describe the scientific innovation points (geometry-based SL-description, 3D animation and video corpus, simplified annotation scheme, motion capture strategy) and the overall translation pipeline.