Computer lipreading via hybrid deep neural network hidden Markov models

Constructing a viable lipreading system is a challenge because it is claimed that only 30% of information of speech production is visible on the lips. Nevertheless, in small vocabulary tasks, there have been several reports of high accuracies. However, investigation of larger vocabulary tasks is rare. This work examines constructing a large vocabulary lipreading system using an approach based-on Deep Neural Network Hidden Markov Models (DNN-HMMs). We present the historical development of computer lipreading technology and the state-ofthe-art results in small and large vocabulary tasks. In preliminary experiments, we evaluate the performance of lipreading and audiovisual speech recognition in small vocabulary data sets. We then concentrate on the improvement of lipreading systems in a more substantial vocabulary size with a multi-speaker data set. We tackle the problem of lipreading an unseen speaker. We investigate the effect of employing several stepstopre-processvisualfeatures. Moreover, weexaminethecontributionoflanguage modelling in a lipreading system where we use longer n-grams to recognise visual speech. Our lipreading system is constructed on the 6000-word vocabulary TCDTIMIT audiovisual speech corpus. The results show that visual-only speech recognition can definitely reach about 60% word accuracy on large vocabularies. We actually achieved a mean of 59.42% measured via three-fold cross-validation on the speaker independent setting of the TCD-TIMIT corpus using Deep autoencoder features and DNN-HMM models. This is the best word accuracy of a lipreading system in a large vocabulary task reported on the TCD-TIMIT corpus. In the final part of the thesis, we examine how the DNN-HMM model improves lipreading performance. We also give an insight into lipreading by providing a feature visualisation. Finally, we present an analysis of lipreading results and suggestions for future development

A novel lip geometry approach for audio-visual speech recognition

By identifying lip movements and characterizing their associations with speech sounds, the performance of speech recognition systems can be improved, particularly when operating in noisy environments. Various method have been studied by research group around the world to incorporate lip movements into speech recognition in recent years, however exactly how best to incorporate the additional visual information is still not known. This study aims to extend the knowledge of relationships between visual and speech information specifically using lip geometry information due to its robustness to head rotation and the fewer number of features required to represent movement. A new method has been developed to extract lip geometry information, to perform classification and to integrate visual and speech modalities. This thesis makes several contributions. First, this work presents a new method to extract lip geometry features using the combination of a skin colour filter, a border following algorithm and a convex hull approach. The proposed method was found to improve lip shape extraction performance compared to existing approaches. Lip geometry features including height, width, ratio, area, perimeter and various combinations of these features were evaluated to determine which performs best when representing speech in the visual domain. Second, a novel template matching technique able to adapt dynamic differences in the way words are uttered by speakers has been developed, which determines the best fit of an unseen feature signal to those stored in a database template. Third, following on evaluation of integration strategies, a novel method has been developed based on alternative decision fusion strategy, in which the outcome from the visual and speech modality is chosen by measuring the quality of audio based on kurtosis and skewness analysis and driven by white noise confusion. Finally, the performance of the new methods introduced in this work are evaluated using the CUAVE and LUNA-V data corpora under a range of different signal to noise ratio conditions using the NOISEX-92 dataset

Visual speech recognition:from traditional to deep learning frameworks

Speech is the most natural means of communication for humans. Therefore, since the beginning of computers it has been a goal to interact with machines via speech. While there have been gradual improvements in this field over the decades, and with recent drastic progress more and more commercial software is available that allow voice commands, there are still many ways in which it can be improved. One way to do this is with visual speech information, more specifically, the visible articulations of the mouth. Based on the information contained in these articulations, visual speech recognition (VSR) transcribes an utterance from a video sequence. It thus helps extend speech recognition from audio-only to other scenarios such as silent or whispered speech (e.g.\ in cybersecurity), mouthings in sign language, as an additional modality in noisy audio scenarios for audio-visual automatic speech recognition, to better understand speech production and disorders, or by itself for human machine interaction and as a transcription method. In this thesis, we present and compare different ways to build systems for VSR: We start with the traditional hidden Markov models that have been used in the field for decades, especially in combination with handcrafted features. These are compared to models taking into account recent developments in the fields of computer vision and speech recognition through deep learning. While their superior performance is confirmed, certain limitations with respect to computing power for these systems are also discussed. This thesis also addresses multi-view processing and fusion, which is an important topic for many current applications. This is due to the fact that a single camera view often cannot provide enough flexibility with speakers moving in front of the camera. Technology companies are willing to integrate more cameras into their products, such as cars and mobile devices, due to lower hardware cost for both cameras and processing units, as well as the availability of higher processing power and high performance algorithms. Multi-camera and multi-view solutions are thus becoming more common, which means that algorithms can benefit from taking these into account. In this work we propose several methods of fusing the views of multiple cameras to improve the overall results. We can show that both, relying on deep learning-based approaches for feature extraction and sequence modelling, as well as taking into account the complementary information contained in several views, improves performance considerably. To further improve the results, it would be necessary to move from data recorded in a lab environment, to multi-view data in realistic scenarios. Furthermore, the findings and models could be transferred to other domains such as audio-visual speech recognition or the study of speech production and disorders