Description
1. Transfer Learning for Image Classification1
It is highly recommended that you complete this project using Keras2 and Python.
(a) In this problem, we are trying to build a classifier that distinguishes images of 20
bird species. You are provided with text data in twenty folders.
(b) Data Exploration and Pre-processing
i. Images in each class are given in separate folders. The file Classes.xlsx provides the classes assigned to the bird species images in each folder. Therefore,
you encode your classes using one-hot encoding and Classes.xlsx.
ii. Randomly select d0.7nie images from each folder as your training set, d0.15nie
as validation set, and the rest as your test set, where ni
is the number of
images in folder i and dxe is the ceiling of x.
iii. In order for all the images to have the same size, zero-pad or resize the images
in your dataset. This can be done using various tools, including OpenCV.
(c) Transfer Learning3
i. When dealing with classification of relatively small image datasets, deep networks may not perform very well because of not having enough data to train
them. In such cases, one usually uses transfer learning, which uses deep
learning models that are trained on very large datasets such as ImageNet
as feature extractors.
The idea is that such deep networks have learned to
extract meaningful features from an image using their layers, and those features can be used in learning other tasks. In order to do that, usually the
last layer or the last few layers of the pre-trained network are removed, and
the response of the layer before the removed layers to the images in the new
dataset is used as a feature vector to train one more multiple replacement layers.
The dataset in this task has only around 50-60 images per class. Given
that we have 20 classes, training a deep network with such a small dataset
may not yield desirable results. In this project, you will use pre-trained models EfficientNetB0 and VGG16. For both pre-trained networks, you will only
train the last fully connected layer, and will freeze all layers before them (i.e.
we do not change their parameters during training) and use the outputs of the
penultimate layer in the original pre-trained model as the features extracted
from each image.
ii. To perform empirical regularization, crop, randomly zoo, rotate, flip, contrast,
and translate images in your training set for image augmentation. You can
use various tools to do this, including OpenCV.
iii. Use ReLU activation functions in the last layer and a softmax layer, along
with batch normalization 4 and a dropout rate of 20% as well as ADAM
1
I acknowledge the contribution of my assistants Jerry Alan Akshay and Sunit Ashish Vaidya to preparing
this project.
2https://keras.io
3https://builtin.com/data-science/transfer-learning
4https://en.wikipedia.org/wiki/Batch_normalization
optimizer. Use multinomial cross entropy loss. You can try any batch size,
but a batch size of 5 seems reasonable.
iv. Train the networks (EfficientNetB0 and VGG16) for at least 50 epochs
(preferably 100 epochs) and perform early stopping using the validation set.
Keep the network parameters that have the lowest validation error. Plot the
training and validation errors vs. epochs.
v. Report Precision, Recall, and F1 score for your model. Remember that this
is a multi-class classification problem.
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