Deep Learning for Sign Language Recognition: A Comparative Review

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Related works’ Classifiers employed in SLR using DL_

Author	year	Input modality	Classifier	result
[129]	2018	Static	DCNN	92.4%
[131]	2018	Static	DCNN	99.85%
[133]	2018	Static	DCNN	85.3 %
[134]	2018	Static	restricted Boltzmann machine	98.13 %
[135]	2018	Isolated	LRCNs and 3D CNNs	99 %
[136]	2018	Static	DAN	73.4%
[137]	2018	Static	(CNNs) of variant depth sizes and stacked denoising autoencoders	92.83%
[139]	2018	Static	DCNN	82.5%
[142]	2018	Static	DCNN	90.3 %
[145]	2018	Isolated	DCNN	88.59%
[146]	2018	Continues	CNN-HMM hybrid	7.4 error
[147]	2018	Static	DCNN	98.05 %
[151]	2018	Isolated	3DCNN, and enhanced fully connected (FCRNN)	69.2 %
[155]	2019	Continues	Deep Capsule networks and game theory	92.50%
[156]	2019	Continues	Hierarchical Attention Network (HAN) and Latent Space	82.7 %
[157]	2019	Static	DCNN	93.667%
[160]	2019	Static	DCNN	97 %
[161]	2019	Continues	DCNN	2.80 WER
[162]	2019	Continues Isolated	Modified LSTM	72.3%89%
[167]	2019	Isolated	DCNN based Dense NET	90.3 %
[168]	2019	Static	DCNN	97.71%
[176]	2020	Static	DCNN	90%
[181]	2020	Static	DCNN	97.6%
[184]	2020	Static	Eight CNN layers+ stochastic pooling, batch normalization and dropout	89.32 %
[185]	2020	Isolated	Cascaded model (SSD, CNN, LSTM)	98.42 %
[187]	2020	Static	Deep Elman recurrent neural network	98.89 %
[188]	2020	Static	DCNN	93%
[190]	2020	Static	Enhanced Alex Net	89.48%
[198]	2020	Static	Multimodality fine-tuned VGG16 CNN+ Leap Motion network	82.55%
[199]	2020	Continues	Multi-channel CNN	10.8 WER
[200]	2020	Static	Hybrid model based on the Inception v3+ SVM	99.90%
[201]	2020	Static	11 Layer CNN	95%
[205]	2021	Static	Three-layered CNN model	90.8%
[206]	2021	Isolated	Hybrid deep learning with convolutional (LSTM)+ and BiLSTM.	76.21%
[209]	2021	Isolated	DCNN+ Sentiment analysis	99.63%
[211]	2021	Continues	GRU+LSTM	19.56error
[214]	2021	Isolated	Generic temporal convolutional network	77.42%
[215]	2021	Static	DCNN	96.65%
[216]	2021	Static	DCNN	99.7%
[220]	2021	Static	Pretrained InceptionV3+ Mini-batch gradient descent optimizer	85%
[221]	2021	Static	Apply the PSO algorithm to find the optimal parameters of the convolutional neural networks	99.58%
[223]	2021	Continues	Visual hierarchy to lexical sequence alignment network H2SNet	91.72%
[227]	2021	Static	Novel lightweight deep learning model based on bottleneck motivated from deep residual learning	99.52%
[228]	2021	Continues	Novel hyperparameter based optimized Generative Adversarial Networks (H-GANs)	97%
[229]	2021	Isolated	3DCNN	88.24%
[232]	2021	Continues	Bidirectional encoder representations from transformers (BERT) + ResNet	23.30 WER
[234]	2021	Continues	Generative Adversarial Network (SLRGAN)	23.4 WER
[238]	2021	Static	DCNN	97%
[239]	2022	Static	Optimized DCNN hybridization of Electric Fish Optimization (EFO), and Whale Optimization Algorithm (WOA) called Electric Fish based Whale Optimization Algorithm (E-WOA).	98.7%
[241]	2022	Isolated	CNN+ RNN	98.8%
[242]	2022	Static	Modified CapsNet architecture, (SLR-CapsNet)	99.60%
[245]	2022	Static	DCNN	99.52%
[247]	2022	Static	DCNN+ diffGrad optimizer	88.01%
[250]	2022	Static	DCNN	92%
[251]	2022	Static	DCNN	99.38%
[252]	2022	Static	Lightweight CNN	94.30%
[254]	2022	Isolated	Hybrid model based on VGG16-BiLSTM	83.36%

Related works on SLR using DL that address overfitting problem_

Author(s)	Year	dataset	Model	technique	result
[129]	2018	NTU	DCNN	Augmentation	92.4%
[130]	2018	Collected	Modified VGG net	Dropout	84.68%
[132]	2018	Ishara-Lipi	DCNN	Dropout	94.88%
[133]	2018	Collected	DCNN	small convolutional filter sizes, Dropout, and learning strategy	85.3%
[136]	2018	HUST	Deep Attention Network (DAN)	data augmentation	73.4%
[142]	2018	ASL Finger Spelling A	DNN	Dense Net	90.3%
[143]	2018	Collected	3DCNN	SGD	88.7%
[146]	2018	SIGNUM	CNN-HMM hybrid	Augmentation	7.4 error
[157]	2019	Collected	DCNN	Augmentation	93.667%
[79]	2019	Collected	ResNet-152	batch size, Augmentation	55.28%
[163]	2019	Collected	VGG-16	Dropout	95%
[166]	2019	Collected	DCNN	Augmentation	95.83%
[167]	2019	Collected	DCNN	Dense Net	90.3%
[171]	2019	Collected	LSTM	Increase hidden state number	94.7%
[172]	2019	NVIDIA	Squeeze-net	Augmentation	83.29%
[173]	2019	G3D	Four stream CNN	Sharing of multi modal features with RGB spatial features during training and drop out	86.87%
[175]	2019	Collected	DCNN	Augmentation	98.9%.
[176]	2020	Collected	DCNN	Pooling Layer	90%
[181]	2020	Collected	DCNN	Reduce epochs to 30, and dropout added after each maxpooling	97.6%
[184]	2020	Collected	CNN with 8 layers	Augmentation	89.32 %
[188]	2020	MNIST	CNN	Dropout	93%
[190]	2020	Collected	Enhanced Alex Net	Augmentation	89.48%
[191]	2020	Collected	SVM	Augmentation, and k-fold cross validation	99.9%
[193]	2020	KETI	CNN+LSTM	New data augmentation	96.2%
[194]	2020	Collected	VGG16, and ResNet152 with enhanced softmax layer	Augmentation	99%
[196]	2020	Collected	RNN-LSTM	dropout layer (DR)	99.81%
[201]	2020	Collected	CNN	dropout layer, and augmentation	95%
[203]	2020	NTU	2 stream CNN	randomness in the features interlocking fusion with dropout	93.01%
[207]	2021	Jochen-Triesch’s	DCNN	two dropouts	99.96%
[214]	2021	Collected	Generic temporal convolutional network (TCN)	Dropout	77.42%
[215]	2021	Collected	DCNN	Dropout	96.65%
[216]	2021	Collected	DCNN	Cyclical learning rate method	99.7%
[217]	2021	MU	Modified AlexNet and VGG16	Augmentation	99.82%
[222]	2021	Collected	CNN	Dropout	97.62%
[229]	2021	Collected	3DCNN	Dropout & Regularization	88.24%
[236]	2021	Collected	ResNet-18	Zero-patience stopping criteria	93.4%
[238]	2021	Collected	DCNN	Synthetic Minority Oversampling Technique (SMOTE)	97%
[240]	2022	Collected	DCNN	Augmentation	99.67%
[253]	2022	Collected	ResNet50-BiLSTM	Augmentation	99%
[256]	2022	Collected	LSTM, and GRU	Dropout	97%
[263]	2022	BdSL	CNN	Augmentation	99.91%

Public sign language datasets

Dataset	Language	Equipment	Modalities	Signers	Samples
ASL alphabets [45]	American	Webcam	RGB images	-	87,000
MNIST [46]	American	Webcam	Grey images	-	27,455
ASL Fingerspelling A [47]	American	Microsoft Kinect	RGB and depth images	5	48,000
NYU [48]	American	Kinect	RGB and depth images	36	81,009
ASL by Surrey [49	American	Kinect	RGB and depth images	23	130,000
Jochen-Triesch [50]	American	Cam	Grey images with different background	24	720
MKLM [51]	American	Leap Motion device and a Kinect sensor	RGB and depth images	14	1400
NTU-HD [52]	American	Kinect sensor	RGB and depth images	10	1000
HUST [53]	American	Microsoft Kinect	RGB and depth images	10	10880
RVL-SLLL [54]	American	Cam	RGB video	14
ChicagoFSWild [55]	American	Collected online from YouTube	RGB video	160	7,304
ASLG-PC12 [56]	American	Cam	RGB video	-	880
American Sign Language Lexicon Video (ASLLVD) [57]	American	Cam	RGB videos of different angles	6	3,300
MU [58]	American	Cam	RGB images with illumination variations in five different angles	5	2515
ASLID [59]	American	Web cam	RGB images	6	809
KSU-SSL [60]	Arabic	Cam and Kinect	RGB Videos with uncontrolled environment	40	16000
KArSL [61]	Arabic	Kinect V2	RGB video	3	75,300
ArSL by University of Sharjah [62]	Arabic	Analog camcorder	RGB images	3	3450
JTD [63]	Indian	Webcam	RGB images with 3 different backgrounds	24	720
IISL2020 [64]	Indian	Webcam	RGB video with uncontrolled environment	16	12100
RWTH-PHOENIX-Weather 2014 [65]	German	Webcam	RGB Video	9	8,257
SIGNUM [66]	German	Cam	RGB Video	25	33210
DEVISIGN-D [67]	Chinese	Cam	RGB videos	8	6000
DEVISIGN-L [67]	Chinese	Cam	RGB videos	8	24000
CSL-500 [68]	Chinese	Cam	RGB, depth and skeleton videos	50	25,000
Chinese Sign Language [69]	Chinese	Kinect	RGB, depth and skeleton videos	50	125000
38 BdSL [70]	Bengali	Cam	RGB images	320	12,160
Ishara-Lipi [71]	Bengali	Cam	Greyscale images	-	1800
ChaLearn14 [72]	Italian	Kinect	RGB and depth video	940	940
Montalbano II [73]	Italian	Kinect	RGB and depth video	20	940
UFOP–LIBRAS [74]	Brazilian	Kinect	RGB, depth and skeleton videos	5	2800
AUTSL [75]	Turkish	Kinect v2	RGB, depth and skeleton videos	43	38,336
RKS-PERSIANSIGN [76] in	Persian	Cam	RGB video	10	10,000
LSA64 [77]	Argentine	Cam	RGB video	10	3200
Polytropon (PGSL) [78]	Greek	Cam	RGB video	6	840
kETI [79]	Korean	Cam	RGB video	40	14,672

Gesture public datasets

Name	Modality	device	signers	samples
LMDHG [82]	RGB, and depth videos	Kinect and	21	608
SHREC Shape Retrieval Contest (SHREC) [83]	RGB, and depth videos	Intel RealSense short range depth camera	28	2800
UTD–MHAD [84]	RGB, depth and skeleton videos	Kinect and wearable inertial sensor	8	861
The Multicamera Human Action Video Data (MuHAVi) [85]	RGB video	8 camera views	14	1904
NUMA [86]	RGB, depth and skeleton videos	10 Kinect with three different views	10	1493
WEIZMANN [87]	Low resolution RGB video	Camera with 10 different viewpoints	9	90
NTU RGB [88]	RGB, depth and skeleton videos	Kinect	40	56 880
Cambridge hand gesture [89]	RGB video captured under five different illuminations	Cam	9	900
VIVA [90]	RGB, and depth videos	Kinect	8	885
MSR [91]	RGB, and depth videos	Kinect	10	320
CAD-60 [92]	RGB and depth video in different environments, such as a kitchen, a living room, and office	Kinect	4	48
HDM05MoCap (motion capture) [93]	RGB video	Cam	5	2337
CMU [94]	RGB images	CAM	25	204
isoGD [95]	RGB and depth videos	Kinect	21	47,933
NVIDIA [96]	RGB and depth video	Kinect	8	885
G3D [97]	RGB and depth video	Kinect	16	1280
UT Kinect [98]	RGB and depth video	Kinect	10	200
First-Person [99]	RGB and depth video	RealSense SR300 cam	6	1,175
Jester [100]	RGB	Cam	25	148,092
Ego Guster [101]	RGB and depth video	Kinect	50	2,081
NUS II [102]	RGB images with complex backgrounds, and various hand shapes and sizes	Cam	40	2000

Related works on SLR using DL that address movement orientation, trajectory, occlusion problems_

Author(s)	Year	Type of variation	language	Signing mode	Model	Accuracy	Error Rate
[129]	2018	similarities, and occlusion	American	Static	DCNN	92.4%
[135]	2018	Movement	Brazilian	Isolated	Long-term Recurrent Convolutional Networks	99%	-
[138]	2018	size, shape, and position of the fingers or hands	American	Static	CNN	82%	-
[140]	2018	Hand movement	American	Isolated	VGG 16	99%	-
[144]	2018	Movement	American	Isolated	Leap Motion Controller	88.79%	-
[145]	2018	3D motion	Indian	Isolated	Joint Angular Displacement Maps (JADMs)	92.14%
[150]	2018	head and hand movements	Indian	Continues	CNN	92.88 %	-
[155]	2019	Hand movement	Indian	Continues	Wearable systems to measure muscle intensity, hand orientation, motion, and position	92.50%	-
[156]	2019	Variant hand orientations	Chines	Continues	Hierarchical Attention Network (HAN) and Latent Space	82.7%	-
[165]	2019	Similarity and trajectory	Chines	Isolated	Deep 3-d Residual ConvNet + BiLSTM	89.8%	-
[166]	2019	orientation of camera, hand position and movement, inter hand relation	Vietnam	Isolated	DCNN	95.83%
[173]	2019	Movement, self-occlusions, orientation, and angles	Indian	Continues	Four stream CNN	86.87%
[174]	2019	Movement in different distance from the camera	American	Static	Novel DNN	97.29%	-
[176]	2020	Angles, distance, object size, and rotations	Arabic	Static	Image Augmentation	90%	0.53
[180]	2020	fingers' configuration, hand's orientation, and its position to the body	Arabic	Isolated	Multilayer perceptron+ Autoencoder	87.69%
[185]	2020	Hand Movement	Persian	Isolated	Single Shot Detector (SSD) +CNN+LSTM	98.42%
[186]	2020	shape, orientation, and trajectory	Greek	Isolated	Fully convolutional attention-based encoder-decoder	95.31%	-
[192]	2020	Trajectory	Greek	Isolated	incorporate the depth dimension in the coordinates of the hand joints	93.56%	-
[195]	2020	finger angles and Multi finger movements	Taiwan	Continues	Wristband with ten modified barometric sensors+ dual DCNN	97.5%
[196]	2020	movement of fingers and hands	Chinese	Isolated	Motion data from IMU sensors	99.81%	-
[197]	2020	finger movement	Chinese	Isolated	Trigno Wireless sEMG acquisition system used to collect multichannel sEMG signals of forearm muscles	93.33%
[199]	2020	finger and arm motions, two-handed signs, and hand rotation	Chinees	Continues	Two armbands embedded with an IMU sensor and multi-channel sEMG sensors are attached on the forearms to capture both arm, and finger movements	-	10.8%
[76]	2020	Hand occlusion	Persian	Isolated	Skeleton detection	99.8%
[204]	2020	Trajectory	Brazilian	Isolated	Convert the trajectory information into spherical coordinates	64.33%
[210]	2021	Trajectory	Arabic	Isolated	Multi-Sign Language Ontology (MSLO)	94.5%
[213]	2021	Movement	Korean	Isolated	3DCNN	91%
[214]	2021	finger movement	Chines	Isolated	Design a low-cost data glove with simple hardware structure to capture finger movement and bending simultaneously	77.42%
[218]	2021	Skewing, and angle rotation	Bengali	Static	DCNN	99.57	0.56
[219]	2021	Hand motion	American	Continues	Sensing Gloves	86.67%
[223]	2021	spatial appearance and temporal motion	Chines	Continues	Lexical prediction network	91.72%	6.10
[226]	2021	finger self-occlusions, view invariance	Indian	Continues	Motion modelled deep attention network (M2DA-Net)	84.95%
[228]	2021	Occlusions of hand/hand, hands/face, or hands/upper body postures.	American	Continues	Novel hyperparameter based optimized Generative Adversarial Networks (H-GANs) Deep Long Short-Term Memory (LSTM) as generator and LSTM with 3D Convolutional Neural Network (3D-CNN) as a discriminator	97%	1.4
[230]	2021	Variant view	American	Isolated	3-D CNN’s cascaded	96%
[233]	2021	Hand occlusion,	Italian	Isolated	LSTM+CNN	99.08%
[237]	2021	Finger occlusion, motion blurring, variant signing styles.	Chines	Continues	Dual Network up on a Graph Convolutional Network (GCN).	98.08%
[239]	2022	self-structural characteristics, and occlusion	Indian	Continues	Dynamic Time Warping (DTW)	98.7%
[240]	2022	High similarity and complexity	American	Static	DCNN	99.67%	0.0016
[241]	2022	Movement	Arabic	Isolated	The difference function	98.8%
[259]	2022	Hand Occlusion	American	Static	Re-formation layer in the CNN	91.40%
[260]	2022	Trajectory, hand shapes, and orientation	American	Isolated	Media Pipe’s Landmarks with GRU	99%
[261]	2022	ambiguous and 3D double-hand motion trajectories	American	Isolated	3D extended Kalman filter (EKF) tracking, and approximation of a probability density function over a time frame.	97.98%
[262]	2022	Movement	Turkish	Continues	Motion History Images (MHI) generated from RGB video frames	94.83%
[264]	2022	Movement	Argentina	Continues	Propose an accumulative video motion (AVM) technique	91.8%
[269]	2022	orientation angle, prosodic, and similarity	American	continues	Develop robust fast fisher vector (FFV) in in Deep Bi-LSTM	98.33%
[270]	2022	variant length, sequential patterns,	English	Isolated	Novel Residual-Multi Head model	95.03%

Related works on SLR using DL that aim to achieve generalization_

Author(s)	Year	Datasets	Technique	Result
[129]	2018	ASL finger spelling ANTU	DCNN	92.4%99.7%
[134]	2018	NYUMUASL Fingerspelling AASL Surrey	Restricted Boltzmann Machine (RBM)	90.01%99.31%98.13%97.56%
[136]	2018	NTUHUST	DAN	98.5%73.4%
[143]	2018	Collected CSLChaLearn14	3D-CNN	88.7%95.3%
[145]	2018	Collected MD05CMU	JADM+CNN	88.59%87.92%87.27%
[146]	2018	RWTH 2012RWTH 2014SIGNUM	CNN-HMM hybrid	30.0 WER32.57.4
[156]	2019	CollectedRWTH-2014	Hierarchical Attention Network (HAN) + Latent Space LS-HAN	82.7%61.6%
[161]	2019	RWTH-2014SIGNUM	DCNN	22.86 WER2.80
[164]	2019	CSLIsoGD	Proposed multimodal two-stream CNN	96.7%63.78%
[165]	2019	DEVISIGN-DCollected	Deep 3-d Residual ConvNet + BiLSTM	89.8%86.9%
[170]	2019	KSU-SSLArSLRVL-SLLL	3D-CNN	77.32%34.90%70%
[173]	2019	Collected RGB-DMSRUT KinectG3D	Four stream CNN	86.87%86.98%85.23%88.68%
[174]	2019	Jochen-TrieschMKLMNovel SI-PSL	Novel DNN	97.29%96.8%51.88%
[182]	2020	KSU-SSLArSL by University of SharjahRVL-SLLL	3DCNN	84.38%34.9%70%
[186]	2020	PGSLChicagoFSWildRWTH 2014T	DCNN	95.31%92.63%76.30%
[187]	2020	ASLMU	Deep Elman recurrent neural network	98.89%97.5%
[192]	2020	GSLChicagoFSWild	CNN	93.56%91.38%
[76]	2020	NYUFirst-Person, RKS-PERSIANSIGN	CNN	4.64 error91.12%99.8%
[202]	2020	NUSAmerican fingerspelling A	DCNN	94.7%99.96%
[203]	2020	HDM05CMUNTUCollected	2 stream CNN	93.42%92.67%94.42%93.01%
[204]	2020	UTD–MHADIsoGDCollected	linear SVM classifier	94.81%67.36%64.33%
[207]	2021	Collected RGB images.Jochen-Triesch’s	DCNN	99.96%100%
[210]	2021	LSA64LSACollected	3DCNN	98.5%99.2 %94.5%
[211]	2021	ASLG-PC12RWTH-2014	GRU and LSTM Bahdanau and Luong’s attention mechanisms	66.59%19.56% BLEU
[221]	2021	ASL alphabet, ASL MNIST MSL	Optimized CNN based on PSO	99.58%99.58%99.10%
[225]	2021	KSU-ArSLJesterNVIDIA	Inception-BiLSTM	84.2%95.8%86.6%
[226]	2021	CollectedNTUMuHAVi,WEIZMANNNUMA	Motion modelled deep attention network (M2DA-Net)	84.95%89.98%85.12%82.25%88.25%
[228]	2021	RWTH-2014ASLLVD	Novel hyperparameter based optimized Generative.Adversarial Networks (H-GANs)	73.9%97%
[232]	2021	RWTH-2014Collected	Bidirectional encoder representations from transformers (BERT) + ResNet	20.123.30 WER
[233]	2021	Montalbano IIisoGDMSRCAD-60	LSTM+CNN	99.08%86.10%98.40%95.50%
[234]	2021	RWTH2014(CSL)(GSL)	GAN	23.42.12.26
[237]	2021	CSL-500DEVISIGN-L	Dual Network up on a Graph Convolutional Network (GCN).	98.08%64.57%
[242]	2022	SLDDMNIST	Modified Caps Net architecture (SLR-Caps Net)	99.52%99.60%
[243]	2022	RKS-PERSIANSIGNFirst-PersonASVIDisoGD	Single shot detector, 2D convolutional neural network, singular value decomposition (SVD), and LSTM	99.5%91%93%86.1%
[247]	2022	CollectedCollectedASL finger spelling	DCNN+ diffGrad optimizer	92.43%88.01%99.52%
[248]	2022	38 BdSLCollectedIshara-Lipi	BenSignNet	94.00%99.60%99.60%
[251]	2022	CollectedCollectedCollected	DCNN	99.41%99.48%99.38%
[254]	2022	CollectedCambridge hand gesture	Hybrid model based on VGG16-BiLSTM	83.36%97%
[255]	2022	CollectedMNIST,JTDNUS	Hybrid Fist CNN	97.89%,95.68%94.90%95.87%
[256]	2022	ASLGSLAUTSLIISL2020	LSTM+GRU	95.3%94%95.1%97.1%
[261]	2022	CollectedSHRECLMDHG	DLSTM	97.98%96.99%97.99%
[262]	2022	AUTSLCollected	3D-CNN	93.53%94.83%
[265]	2022	CSL-500JesterEgo Gesture	deep R (2+1) D	97.45%97.05%94%
[266]	2022	MUHUST-ASL	end-to-end fine-tuning method of a pre-trained CNN model with score-level fusion technique	98.14%64.55%
[269]	2022	SHRECCollectedLMDHG	FFV-Bi-LSTM	92.99%98.33%93.08%

Related works on SLR using DL that address the various environmental conditions problem_

Author (s)	Year	Language	Modality	Type of condition	Deal with technique	results
[130]	2018	Bengali	RGB images	Variant background and skin colors	Modified VGG net	84.68%
[134]	2018	American	RGB images	noise and missing data	Augmentation	98.13%
[150]	2018	Indian	RGB video	Different viewing angles, background lighting, and distance	Novel CNN	92.88%
[158]	2019	American	Binary images	Noise	Erosion, closing, contour generation, and polygonal approximation,	96.83%
[159]	2019	American	Depth image	Variant illumination, and background	Attain depth images	88.7%
[164]	2019	chines	RGB, and depth video	Variant illumination, and background	Two-stream spatiotemporal network	96.7%
[173]	2019	Indian	RGB, and depth video	Variant illumination, background, and camera distance	Four stream CNN	86.87%
[178]	2020	Arabic	RGB images	Variant illumination, and skin color	DCNN	94.31%
[179]	2020	Arabic	RGB videos	Variant illumination, background, pose, scale, shape, position, and clothes	Bi-directional Long Short-Term Memory (BiLSTM)	89.59%
[180]	2020	Arabic	RGB Videos	Variant illumination, clothes, position, scale, and speed	3DCNN and SoftMax function	87.69%
[182]	2020	Arabic	RGB Videos	Variations in heights and distances from camera	Normalization	84.3%
[194]	2020	Arabic	RGB images	variant illumination, and background	VGG16 and the ResNet152 with enhanced softmax layer	99%
[201]	2020	American	Grayscale images	illumination, and skin color	Set the hand histogram	95%
[202]	2020	American	RGB images	Variant illumination, background	DCNN	99.96%
[206]	2021	Indian	RGB video	Variant illuminations, camera positions, and orientations	Google net+ BiLSTM	76.21%
[207]	2021	Indian	RGB images	Light and dark backgrounds	DCNN with few numbers of parameters	99.96%
[209]	2021	American	RGB video	Noise	Gaussian Blur	99.63%
[213]	2021	Korean	Depth Videos	Low resolution	Augmentation	91%
[224]	2021	Bengali	RGB images	Variant backgrounds, camera angle, light contrast, and skin tone	Conventional deep learning + Zero-shot learning ZSL	93.68%
[225]	2021	Arabic	RGB video	Variant illumination, background, and clothes	Inception-BiLSTM	84.2%
[227]	2021	American	Thermal images	Varying illumination	Adopt live images taken by a low-resolution thermal camera	99.52%
[229]	2021	Indian	RGB video	Varying illumination	3DCNN	88.24%
[230]	2021	American	RGB video	Noise, varying illumination	Median filtering + histogram equalization	96%
[236]	2021	Arabic	RGB images	Variant illumination, and background	Region-based Convolutional Neural Network (R-CNN)	93.4%
[239]	2022	Indian	RGB video	Variant illumination, and views	Grey scale conversion and histogram equalization	98.7%
[241]	2022	Arabic	RGB video	Variant illumination, and background	CNN+ RNN	98.8%
[249]	2022	Arabic	Greyscale images	Variant illumination, and background	Sobel filter	97%
[253]	2022	Arabic	RGB, and depth video	Variant Background	ResNet50-BiLSTM	99%
[259]	2022	American	RGB, and depth images	Noise and illumination variation	Median filtering and histogram equalization	91.4%
[261]	2022	American	Skeleton video	Noise in video frames	An innovative weighted least square (WLS) algorithm	97.98%
[270]	2022	English	Wi-Fi signal	Noise and uncleaned Wi-Fi signals.	Principal Component Analysis (PCA)	95.03%

Related works on SLR using DL that address feature extraction problem_

Author(s)	Year	Dataset	Technique	Signing mode	Feature(s)	Result
[130]	2018	Collected	DCNN	static	Hand shape	84.6%
[135]	2018	Collected	3D CNN	Isolated	spatiotemporal	99%
[138]	2018	ASL Finger Spelling	CNN	Static	depth and intensity	82%
[141]	2018	RWTH-2014	3D Residual Convolutional Network (3D-ResNet)	Continues	Spatial information, and temporal connections across frames	37.3WER
[143]	2018	Collected	3D-CNNs	Isolated	spatiotemporal	88.7%
[144]	2018	Collected	DCNN	Isolated	hand palm sphere radius, and position of hand palm and fingertip	88.79%
[149]	2018	ASL Finger Spelling	Histograms of oriented gradients, and Zernike moments	Static	Hand shape	94.37%
[150]	2018	Collected	CNN	Continues	Hand shape	92.88 %
[151]	2018	Collected	3DRCNN	Continues/Isolated	motion, depth, and temporal	69.2%
[152]	2018	SHREC	Leap Motion Controller (LMC) sensor	Isolated, static	finger bones of hands.	96.4%
[153]	2018	Collected	Hybrid Discrete Wavelet Transform, Gabor filter, and histogram of distances from Centre of Mass	Static	Hand shape	76.25%
[154]	2018	Collected	DCNN	Static	Facial expressions	89%
[156]	2019	Collected	Two-stream 3-D CNN	Continues	Spatiotemporal	82.7%
[158]	2019	Collected	CNN	Static	Hand shape	96.83%
[79]	2019	Collected	Open Pose library	Continues	human key points (hand, face, body)	55.2%
[159]	2019	ASL fingerspelling	PCA Net	Static	hand shape (corners, edges, blobs, or ridges)	88.7%
[161]	2019	SIGNUM	Stacked temporal fusion layers in DCNN	Continues	spatiotemporal	2.80WER
[162]	2019	Collected	Leap motion device	Continues Isolated	3D positions of the fingertips	72.3%89%
[163]	2019	Collected	CNN	Static	Hand shape	95%
[164]	2019	CSL	D-shift Net	Continues	spatial features time features, and temporal.	96.7%
[165]	2019	DEVISIGN_D	B3D Res-Net	Isolated	spatiotemporal	89.8%
[166]	2019	Collected	Local and GIST Descriptor	Isolated	Spatial and scene-based features	95.83%
[169]	2019	Collected	Restricted Boltzmann Machine (RBM)	Isolated	Handshape, and network generated features	88.2%
[170]	2019	KSU-SSL	3D-CNN	Isolated	hand shape, position, orientation, and temporal dependence in consecutive frames	77.32%
[171]	2019	Collected	C3D, and Kinect device	Continues	Temporal, and Skeleton	94.7%
[175]	2019	Collected	Open Pose library with Kinect V2	Static	3D skeleton	98.9%.
[177]	2020	Ishara-Lipi	Mobile Net V1	Isolated	Two hands shape	95.71%
[178]	2020	Collected	DCNN	Static	Hand shape	94.31%.
[179]	2020	Collected	Single layer Convolutional Self-Organizing Map (CSOM)	Isolated	Hand shape	89.59%
[180]	2020	KSU-SSL	Enhanced C3D architecture	Isolated	Spatiotemporal of hand and body	87.69 %
[182]	2020	KSU-SSL	3DCNN	Isolated	Spatiotemporal	84.3%
[185]	2020	Collected	ResNet50 model	Isolated	Hand shape, Extra Spatial hand Relation (ESHR) features, and Hand Pose (HP), temporal.	98.42%
[186]	2020	Polytropon (PGSL)	ResNet-18	Isolated	Optical flow of skeletal, handshapes, and mouthing	95.31%
[187]	2020	Collected	Discrete cosines transform, Zernike moment, scale-invariant feature transform, and social ski driver optimization algorithm	Static	Hand shape	98.89%
[189]	2020	RWTH-2014	Temporal convolution unit and dynamic hierarchical bidirectional GRU unit	Continues	spatiotemporal	10.73% BLEU
[191]	2020	Collected	Standard score’ normalization on the raw Channel State Information (CSI) acquired from the Wi-Fi device, and MIFS algorithm	Static, and continues	The cross-cumulant features (unbiased estimates of covariance, normalized skewness, normalized kurtosis)	99.9%
[192]	2020	GSL	Open Pose human joint detector	Isolated	3D hand skeletal, and region of hand, and mouth	93.56%
[197]	2020	Collected	Four channel surface electromyography (sEMG) signals	Isolated	time-frequency joint features	93.33%
[199]	2020	Collected	Euler angle, Quaternion from IMU signal	Continues	Hand Rotation	10.8% WER
[76]	2020	RKS-PERSIANSIGN	3DCNNs	Isolated	Spatiotemporal	99.8%
[202]	2020	ASL fingerspelling A	DCNN	Static	Hand Shape	99.96%
[203]	2020	Collected	Construct a color-coded topographical descriptor from joint distances and angles, to be used in 2 streams (CNN)	Isolated	distance and angular	93.01%
[204]	2020	Collected	Two CNN models and a descriptor based on Histogram of cumulative magnitudes	Isolated	Two hands, skeleton, and body	64.33%
[208]	2021	RWTH-2014T	Semantic Focus of Interest Network with Face Highlight Module (SFoI-Net-FHM)	Isolated	Body and facial expression	10.89Bleu
[210]	2021	Collected	(ConvLSTM)	Isolated	Spatiotemporal	94.5%
[212]	2021	Collected	ResNet50	Static	hand area, the length of axis of first eigenvector, and hand position changes.	96.42%.
[214]	2021	Collected	f-CNN (fusion of 1-D CNN and 2-D CNN	Isolated	Time and spatial-domain features of finger resistance movement	77.42%
[217]	2021	MU	Modified Alex Net and VGG16	Static	Hand edges and shape	99.82%
[222]	2021	Collected	VGG net of six convolutional layers	Static	Hand shape	97.62%
[224]	2021	38 BdSL	DenseNet201, and Linear Discriminant Analysis	Static	Hand shape	93.68%
[225]	2021	KSU-ArSL	Bi-LSTM	Isolated	spatiotemporal	84.2%
[226]	2021	Collected	Paired pooling network in view pair pooling net (VPPN)	Isolated	spatiotemporal	84.95%
[228]	2021	ASLLVD	Bayesian Parallel Hidden Markov Model (BPaHMM) + stacked denoising variational autoencoders (SD-VAE) + PCA	Continues	Shape of hand, palm, and face, along with their position, speed, and distance between them	97%
[230]	2021	ASLLVD	3-D CNN’s cascaded	Isolated	spatiotemporal	96.0%
[231]	2021	Collected	leap motion controller	Static, and Isolated	sphere radius, angles between fingers their distance	91.82%
[232]	2021	RWTH-2014	(3 C 2 C 1) D ResNet	Continues	height, motion of hand, and frame blurriness levels	23.30WER
[233]	2021	Montalbano II	AlexNet + Optical Flow (OF) + Scene Flow (SF) methods	Isolated	Pixel level, and hand pose	99.08%
[234]	2021	RWTH-2014	GAN	Continues	spatiotemporal	23.4WER
[235]	2021	MNIST	DCNN	Static	Hand shape	98.58%
[236]	2021	Collected	R-CNN	Static	Hand shape	93%
[237]	2021	CSL-500	Multi-scale spatiotemporal attention network (MSSTA)	Isolated	Spatiotemporal	98.08%
[242]	2022	MNIST	modified CapsNet	Static	Spatial, and orientations	99.60%
[243]	2022	RKS-PERSIANSIGN	Singular value decomposition SVD	Isolated	3D hand key points between the segments of each finger, and their angles.	99.5%
[244]	2022	Collected	2DCRNN + 3DCRNN	Continues	Spatiotemporal out of small patches	99%
[246]	2022	Collected	Atrous convolution mechanism, and semantic spatial multi-cue model	Static Isolated	pose, face, and hand, and Spatial, full frame,	99.85%
[253]	2022	Collected	4 DNN models using 2D and 3D CNN	Isolated	Spatiotemporal	99%
[255]	2022	Collected	Scale-Invariant Feature Transformation (SIFT)	Static	Corner, edges, rotation, blurring, and illumination.	97.89%
[256]	2022	Collected	InceptionResNetV2	Isolated	Hand shape	97%
[257]	2022	Collected	Alex net	Static	Hand shape	94.81%
[258]	2022	Collected	Sensor + mathematical equations+ CNN	Continues	Mean, Magnitude of Mean, Variance, correlation, Covariance, and frequency domain features+ spatiotemporal	0.088WER
[260]	2022	Collected	Media Pipe framework	Isolated	hands, body, and face	99%
[261]	2022	Collected	Bi-RNN network, maximal information correlation, and leap motion controller	Isolated	hand shape, orientation, position, and motion of 3D skeletal videos.	97.98%
[264]	2022	LSA64	dynamic motion network (DMN)+ Accumulative motion network (AMN)	Isolated	spatiotemporal	91.8%
[265]	2022	CSL-500	Spatial–temporal–channel attention (STCA) is proposed	isolated	spatiotemporal	97.45%
[268]	2022	Collected	SURF (Speeded Up Robust Features)	Isolated	distribution of the intensity material within the neighborhood of the interest point	99%
[269]	2022	Collected	Thresholding and Fast Fisher Vector Encoding (FFV)	Isolated	Hand, palm, finger shape, and position and 3D skeletal hand characteristics	98.33%

Related works on SLR using DL that address segmentation problem_

Author(s)	Year	Input Modality	Segmentation method	Results
[131]	2018	RGB image	HSV color model	99.85%
[148]	2018	RGB image	Skin segmentation algorithm based on color information	94.7%
[149]	2018	RGB images	k-means-based algorithm	94.37%
[158]	2019	RGB images	Color segmentation by MLP network	96.83%
[159]	2019	Depth image	Wrist line localization by algorithm-based thresholding	88.7%
[164]	2019	RGB, and depth video	Aligned Random Sampling in Segments (ARSS)	96.7%
[168]	2019	RGB, and depth images	Depth based segmentation using data of Kinect RGB-D camera	97.71%
[171]	2019	RGB video	Design an adaptive temporal encoder to capture crucial RGB visemes and skeleton signees	94.7%
[179]	2020	RGB videos	Hand semantic Segmentation named as DeepLabv3+	89.59 %
[180]	2020	RGB Videos	Novel method based on open pose	87.69 %
[182]	2020	RGB Videos	Viola and Jones, and human body part ratios	84.3%
[183]	2020	RGB images	Robert edge detection method	99.3 %
[185]	2020	RGB video	SSD is a feed-forward convolutional network A Non-Maximum Suppression (NMS) step is used in the final step to estimate the final detection	98.42%
[187]	2020	RGB images	Sobel edge detector, and skin color by thresholding	98.89%
[188]	2020	RGB images	Open-CV with a Region of Interest (ROI) box in the driver program	93%
[189]	2020	RGB Videos	Frame stream density compression (FSDC) algorithm	10.73 error
[199]	2020	RGB Videos	Design an attention-based encoder-decoder model to realize end-to-end continuous SLR without segmentation	10.8% WER
[200]	2020	RGB images	Single Shot Multi Box Detection (SSD)	99.90%
[209]	2021	RGB Video	Canny	99.63%
[216]	2021	RGB images	Erosion, Dilation, and Watershed Segmentation	99.7 %
[219]	2021	RGB Video	Data sliding window	86.67%
[236]	2021	RGB images	R-CNN	93%
[239]	2022	RGB videos	Novel Adaptive Hough Transform (AHT)	98.7%
[246]	2022	RGB images, and video	Grad Cam and Cam shift algorithm	99.85%
[248]	2022	Grey images	YCbCr, HSV and watershed algorithm	99.60%,
[249]	2022	RGB images	Sobel operator method	97 %
[263]	2022	RGB images	Semantic	99.91%
[267]	2022	RGB images	R-CNN	99.7%
[268]	2022	RGB video	Mask is created by extracting the maximum connected region in the foreground assuming it to be the hand+ Canny method	99%