The problem of sign recognition is posed everywhere because one should not neglect this important number of these deaf-mute people in the whole world because we have more than 450M of deaf-mute people in the world according to statistics of the world health organization (2021), that's why a lot of researches have been done in this theme in order to find the solution for the communication between deaf-mute and normal people, also several hardware and software solutions have been proposed for the automatic sign recognition. A review and analysis of recent advances in this field can be found in (Machine learning methods for sign language recognition)
Most of the proposed solutions are based on connected gloves. For example, there are a multitude of smart gloves using sensors to recognize hand and finger gestures and movements. These embedded solutions do not facilitate the exchange between deaf mutes and normal people and do not recognize the signs made by full body gestures. Other solutions have been proposed that are based on image processing, sensors and artificial intelligence. Thus, image processing is used to capture and identify gestures while artificial intelligence is used for sign recognition and transcription into written language.
American researchers have developed connected gloves that can recognize signs and make automatic transcriptions (“The Language of Glove: Wireless gesture decoder with low-power and stretchable hybrid electronics”.). The solution proposed in the form of a leather sports glove on which nine movement sensors have been placed at the level of the joints, its various electrodes allow to translate the gestures made by the fingers and the wrist to designate the 26 letters of the American alphabet. To date, this innovation can only spell words. Unfortunately and due to lack of funding, this solution remains expensive and unreliable. Boon Giin Lee et al. in ("Smart Wearable Hand Device for Sign Language Interpretation System With Sensors Fusion,", Feb.1, 2018) proposed a wearable smart device for sign language recognition. This proposed system uses 10 sensors: five flexible sensors, two pressure sensors, and a three-axis inertial motion sensor. The system can recognize sign language with an accuracy rate of 65.7%. In ("A new data glove approach for Malaysian sign language detection", Decembre 2015), Shukor et al. proposed a glove for Malay sign language recognition. The proposed system is based on 10 click sensors, an accelerometer, a microcontroller, and a Bluetooth module. The proposed system has not been tested extensively to approve its effectiveness but over four uses, they were able to achieve a sign recognition accuracy equal to 89%.
Solutions based on gloves and sensors are very limited in their use and do not manage all the gestures that deaf and dumb people can make. On the other hand, the use of image processing and artificial intelligence remains an effective solution for the recognition of signs and gestures of deaf and dumb people. In sign language recognition approaches that rely on image processing and artificial intelligence, image processing is used to capture and identify gestures while artificial intelligence is used for sign recognition and transcription into written language. Hand detection is the first step in such a system. In addition, it is essential to detect it correctly in order to be able to effectively recognize the sign made. This step is considered a challenge. In (Hand landmarks detection and localization in color images., 2016), the authors proposed an approach for the detection and localization of hand landmarks using color images. The proposed approach is based on the use of a mask for skin identification and the use of a distance to detect hand landmarks. Ravikiran et al. in (Finger detection for sign language recognition, March 2009) proposed an approach for finger detection. Fingers are detected based on boundary tracing for tip detection. For sign recognition, we use machine-learning methods for their classification. Thus, the objective is to design a classification model using supervised classification algorithms able to recognize the sign of a gesture image. In this step, a database of labeled images is used to train a classification model.
In paper (CNN based feature extraction and classification for sign language., 2021), the authors used two deep learning architectures, AlexNet and VGG16 for feature extraction. Classification is performed using the SVM algorithm. The authors obtained a very good classification rate, but using only the training data. Deriche et al. in ( "An Intelligent Arabic Sign Language Recognition System Using a Pair of LMCs With GMM Based Classification,", Sept.15, 2019) proposed to use a classification based on a combination of a Bayesian approach and a mixture of Gaussian models (GMM) with the use of linear discriminant analysis (LDA) for dimensionality reduction. The simulation results showed that the proposed approach performs moderately well with a classification rate equal to 92%.
There are many works in the literature for American Sign Language, Indian, and Indonesian...
However, for Moroccan Sign Language (MSL), there are not yet enough research works except for those shown below which are based on an approach to classify Moroccan signs using different machine learning techniques by a group of researchers(Moroccan sign language recognition based on machine learning, 2022) who tried to create a new approach to have the alphabet suitable for the captured signs following a set of procedures shown in the figure below:
Moreover, they found that the system with a fully recurrent architecture performed best with 98.33% accuracy for static sign recognition.
The gesture recognition techniques proposed in the literature are not always adequate for RLS. As a result, the field of RLS has developed its own literature over the years. (RLSAr) systems, in particular, have not received much attention only in recent years. In (Automatic recognition of Arabic sign Language finger spelling ), the authors used colored gloves to collect alphabet data (RLSAr) from multiple users, where an adaptive neuro-fuzzy inference system was the recognition approach.
Below is the proposed architecture of the RLSAr system
Fasihuddin et al. (Smart Tutoring System for Arabic Sign Language Using Leap Motion Controler, 2018) proposed an interactive system that allows able-bodied learners who wish to learn Arabic sign language to practice (RLSAr) at different levels and to self-assess. This system uses the K-nearest neighbor algorithm for sign classification.
In (Automatic translation of Arabic text-to-Arabic sign language, 2018), the authors proposed an automatic visual system that translates isolated Arabic word signs into text. This system has four main steps: segmentation and tracking of the hand by a skin detector, feature extraction and finally classification are done by Euclidean distance since the data is not large enough.
Luqman et al. (Automatic translation of Arabic text-to-Arabic sign language, 2018) have gone further by proposing an automatic system that simultaneously performs morphological, syntactic and semantic analysis on an Arabic sentence to translate it into a sentence with the grammar and structure of (LSAr).
Maraqa et al. (Recognition of Arabic Sign Language (ArSL) using recurrent neural network, 2008) Compared two neural network-based systems: feedforward (Svozil, 1997) and recurrent (Recurrent neural network based language model, 2010)and found that the system with a fully recurrent architecture provided the best performance with 95% accuracy for static sign recognition.
In this next section we will talk about sign language and especially Moroccan sign language