A Neural Image Caption Generator

1. Introduction
2. Architecture

Introduction

• This is a neural image caption generator based on the paper Show and Tell: A Neural Image Caption Generator by Vinyals et al.
• The model is trained on the Flickr8k dataset.

Architecture

• The pytorch implementation can be found in encoder_decoder.py.

Encoder

• The encoder is an EfficientNet with weights pretrained on ImageNet.
• The final layer of the EfficientNet is removed all prior layers are frozen for the duration of the training process.
• The image embedding is passed through a linear layer to reduce the dimensionality of the feature vector to the dimensionality of the joint embedding space.
• This final layer is jointly trained along with the decoder in order to learn the joint embedding space.

Decoder

• The decoder is an LSTM which generates a caption for the image.
• At the start of the decoding process, the feature vector from the encoder is passed through the LSTM to allow the hidden state to view the embedded representation of the image.
• A linear layer is added in order to map the hidden state outputs to the vocabulary space, in order to generate a probability distribution over the next word in the caption.