Implementing Multiple Deep Learning Architectures on the zArASL_Database_54K Dataset

This is a submission of Second Assignment for the CIS735 course.

It contains the code necessary to implement multiple deep learning architectures for the zArASL_Database_54K multiclass image classification problem.

The dataset from the zArASL_Database_54K has been used.

Getting Started

Clone the project from GitHub

$ git clone https://github.com/tariqshaban/arabic-sign-language-image-classification.git

No further configuration is required.

Usage

Navigate to the bottom of the notebook and specify the following hyperparameters:

• Seed
• Neural network type:
  • Fully connected neural network (FCNN)
  • Convolutional neural network (CNN)
  • Convolutional neural network (CNN) using a pretrained model (transfer learning on the EfficientNetB0 architecture)
• Generic network size:
  • Nano
  • Micro
  • Small
• Activation function type:
  • Sigmoid
  • Tanh
  • ReLU
  • Leaky ReLU
• Optimizer
  • Stochastic gradient descent (SGD)
  • Root Mean Squared Propagation (RMSProp)
  • Adam
• Number of epochs [1, 100]
• Early stopping value

Warning: Even though specifying the seed should ensure reproducible results, the kernel must be reset after finishing a single model

Warning: The seed is ineffective if the running machine is different, or if the runtime was switched between CPU and GPU

Note: The learning rate field was discarded since the optimizer's default value usually yields better results

Invoke the following methods:

# Ready the dataset and partition it into training, validation, and testing folders
prime_dataset()

# Conducts preliminary exploration methods
# :param bool show_dataframe: Specify whether to show the classes dataframe or not
# :param bool show_image_sample: Specify whether to display a sample image from each class or not
# :param bool show_class_distribution: Specify whether to plot the distribution of each class with respect to its train/valid/test partitioning
explore_dataset(show_dataframe: bool = True, show_image_sample: bool = True, show_class_distribution: bool = True)

# Builds the model, and returns the fitted object
# :param bool plot_network: Specify whether to visually plot the neural network or not
# :param bool measure_performance: Specify whether to carry out the evaluation metrics on the created model (shows loss/accuracy trend across epochs and displays a confusion matrix on the test set)
build_model(plot_network: bool = True, measure_performance: bool = True)

Methodology

Dataset Exploration

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The following is a table denotes the classes of the dataset (sorted alphabetically based on the ClassAr column).

Note that a total of 32 classes can be observed from the table.

ClassId	Class	ClassAr
29	ya	ئ
1	al	ال
2	aleff	الف
3	bb	باء
27	toot	ة
24	taa	تاء
25	thaa	ثاء
12	jeem	جيم
11	haa	حاء
14	khaa	خاء
4	dal	دال
26	thal	ذال
19	ra	راء
31	zay	زاي
21	seen	سين
22	sheen	شين
20	saad	صاد
6	dhad	ضاد
23	ta	طاء
5	dha	ظاء
0	ain	عين
9	ghain	غين
7	fa	فاء
8	gaaf	قاف
13	kaaf	كاف
15	la	لا
16	laam	لام
17	meem	ميم
18	nun	نون
10	ha	هاء
28	waw	واو
30	yaa	ياء

The figure below displays an image from each class:

The image displays how well the classes are balanced, note that (ain) عين has approximately 700 more images than (yaa) ياء.

Dataset Preprocessing

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• No significant image processing techniques have been carried out
• All images have the same size (64x64x3)
• Image rescaling technique has been used (pixel normalization)

Note: In transfer learning architectures, image rescaling was omitted since the EfficientNetB0 network already contains a normalization layer

Note: In transfer learning architectures, image resolution is upscaled to (256, 256); in order to comply with the EfficientNetB0 input specifications

Models Construction

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As previously stated, below are the generic network sizes that are enforced on all neural networks in this repository:

• Nano
• Micro
• Small

The leveraged neural networks:

• Fully connected neural network (FCNN)
• Convolutional neural network (CNN)
• Convolutional neural network (CNN) using a pretrained model

The following images display the affect of each network size on the architecture of each neural network:

Fully Connected Neural Network (FCNN)
Nano
Micro
Small

Convolutional Neural Network (CNN)
Nano
Micro
Small

Convolutional Neural Network (CNN) w/ Transfer Learning
Nano
Micro
Small

Findings

FCNN

		Nano		Micro		Small
Activation	Optimizer	Accuracy	Loss	Accuracy	Loss	Accuracy	Loss
Sigmoid	SGD	%29.00	2.6779	%5.170	3.4457	%3.92	3.4597
	RMSProp	%36.90	2.1605	%39.33	1.9779	%27.71	2.3854
	Adam	%18.75	2.8965	%20.55	2.8522	%3.92	3.4603
Tanh	SGD	%49.32	1.8810	%66.83	1.2045	%73.47	0.8914
	RMSProp	%26.22	2.5885	%30.38	2.3663	%7.32	3.2007
	Adam	%3.40	3.4650	%14.46	3.0153	%3.49	3.4675
ReLU	SGD	%54.92	1.5363	%70.84	0.9636	%50.19	1.7976
	RMSProp	%3.92	3.4597	%3.92	3.4597	%3.92	3.4597
	Adam	%3.92	3.4597	%83.26	0.6132	%3.92	3.4597
Leaky Relu	SGD	%53.35	1.6143	%67.84	1.0764	%74.21	0.8452
	RMSProp	%51.77	1.5967	%55.16	1.8461	%76.97	0.7628
	Adam	%67.73	1.1280	✅%84.50	✅0.5878	%84.22	0.5939

CNN

		Nano		Micro		Small
Activation	Optimizer	Accuracy	Loss	Accuracy	Loss	Accuracy	Loss
Sigmoid	SGD	%3.92	3.4587	%3.92	3.4527	%4.58	3.4398
	RMSProp	%2.90	8.5300	%5.48	4.8434	%12.00	7.3554
	Adam	%6.29	4.902	%6.53	9.1905	%18.18	5.5146
Tanh	SGD	%4.58	4.6877	%14.13	3.1408	%88.84	0.4504
	RMSProp	%7.65	6.9120	%19.38	6.1763	%87.74	0.4868
	Adam	%7.45	7.2570	%31.41	4.4689	%76.34	0.9064
ReLU	SGD	%10.23	3.6544	%59.78	1.1868	%96.77	0.1303
	RMSProp	%15.16	7.1755	%38.74	4.7649	%88.93	0.4513
	Adam	%15.51	9.1730	%87.02	0.4670	%95.12	0.2065
Leaky Relu	SGD	%10.08	4.4987	%38.68	2.5518	%96.35	0.1434
	RMSProp	%9.51	14.118	%84.24	0.6299	%94.49	0.2322
	Adam	%11.31	8.1749	%52.73	2.8816	✅%98.03	✅0.1078

CNN w/ Transfer Learning

		Nano		Micro		Small
Activation	Optimizer	Accuracy	Loss	Accuracy	Loss	Accuracy	Loss
Sigmoid	SGD	%56.83	1.8929	%3.92	3.4471	%3.92	3.4597
	RMSProp	%93.52	0.2538	%94.77	0.2047	%95.71	0.1624
	Adam	%93.55	0.2537	%95.01	0.1874	%96.28	0.1377
Tanh	SGD	%76.05	0.8074	%83.94	0.6029	%86.61	0.5011
	RMSProp	%94.11	0.2150	%96.46	0.1321	%96.42	0.1200
	Adam	%94.14	0.2163	%96.15	0.1356	%96.39	0.1182
ReLU	SGD	%83.98	0.5926	%85.64	0.4804	%89.76	0.3596
	RMSProp	%94.62	0.1921	%96.53	0.1130	✅%97.29	0.0907
	Adam	%94.60	0.1956	%96.63	0.1154	%97.14	✅0.0883
Leaky Relu	SGD	%84.41	0.5792	%87.04	0.4233	%90.44	0.3406
	RMSProp	%94.68	0.1906	%96.57	0.1184	%97.18	0.0922
	Adam	%94.58	0.1974	%96.20	0.1280	%97.01	0.1045

Model Performance

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The following images are the result of using the following hyperparameters (one of the hyperparameters that yielded the highest results):

• Seed: 42
• Network Type: CNN w/ transfer learning (EfficientNetB0)
• Network Size: small, see Models Construction section for exact architecture
• Activation function: ReLU (used in dense layers appended to the base model)
• Optimizer: Adam
• Epochs: 30
• Early stopping: upon 10 epochs

Notice that the accuracy converged rapidly, and stabilized at approximately the 20ᵗʰ epoch, this indicates that the number of epochs is sufficient for this given model.

Similarly, the model was able to converge quickly when inspecting the loss plot

Based on the confusion matrix, the model was effective in discriminating between Arabic letters represented by sign language, almost all the test set entries reside on the diagonal.

Assignment Related Questions

Note: Each activation function has its own case, generally assuming an activation function to be poor might not be a good practice

Note: It appears that different combinations of hyperparameters yield different results (e.g. Adam optimizer performed well on most networks, but it returns suboptimal results when paired with Sigmoid and Tanh for the FCNN architecture)

Note: These observations are strictly bounded to the dataset and should not be generalized. Such observations can be easily contradicted when altering a hyperparameter

Assess the impact of the activation function (Sigmoid, Tanh, ReLU, Leaky ReLU) on the accuracy, loss

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The impact of each activation function cannot be easily determined, several variables can affect the behaviour of the activation function.

• Sigmoid:
  • Computationally expensive
  • Complex derivative calculations due to the exponent
  • Flattened ends on both sides cause saturation, saturation causes vanishing gradients
  • Converges slowly
  • Commonly used in binary classification
• Tanh:
  • Similar characteristics to the sigmoid
  • Less computationally expensive than sigmoid (but still noticeable)
  • Commonly used in NLP domains
• ReLU:
  • Well known
  • Converges quickly
  • Does not saturate easily
  • Very simple formula, expedites the computation of the derivative
  • Commonly used in the hidden layers of the FCNN
• Leaky ReLU
  • Similar characteristics to the sigmoid
  • Further reduce the risk of saturation

Observations:

• ReLU and Leaky ReLU Relu almost always had better results than Sigmoid and Tanh (sometimes by a large margin)
• Sigmoid and Tanh often saturate; causing the training to stop early
• If Sigmoid and Tanh were provided with more epochs, they might achieve results that compete with ReLU and Leaky ReLU

Assess the impact of the optimizer (SGD+ Momentum, Adam, RMSProp) on the accuracy, loss

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Similarly to the previous question, the impact cannot be generalized, since the parameters of the optimizer can affect its behaviour.

Observations:

• RMSProp and Adam obtained higher results than SGD in many cases
• SGD takes longer time to converge, note that the learning rate default value for the SGD is ten higher than RMSProp and Adam

Assess the impact of the neural network depth on the accuracy, loss

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While it seems from intuition that deeper neural networks should yield better results, it can cause, in some cases, the exact opposite effect. It may result in overfitting; making the test accuracy high but low on unseen data (such as validation and test sets). In addition, it may unnecessarily increase the number of parameters, which subsequently, increases the computational requirement.

Observations:

• Deeper networks provide better results, but they can have a negative effect in some cases
• Deeper networks can exhaust resources exponentially, especially the memory
• Deeper networks should not be used to solve simple problems, this will cause the model to overfit

Identify the factor which contributes to the model's overfitting

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• Data has noise (outliers/errors); prevents the model from generalizing well
• Data is not standardized (no regularization)
• Model is too deep/complex
• No dropout layers (for CNN architectures)
• Training data is biased (the sample does not represent the population, or represents only a specific stratum)
• No implementation of early stopping (prematurely stop the training when validation loss does not decrease for a predefined number of epochs)
• Usage of SGD rather than RMSProp or Adam

Notes

• Surprisingly, some fully connected networks achieved relatively acceptable results, this can be caused by the number of parameters for the image (64x64x3), FCNN is known to be a poor option when used solely on image problems; because unlike CNN, it lacks image feature extraction
• Transfer learning expedites the convergence, making it possible to achieve satisfactory results with only one digit epochs

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