Book Image

Advanced Deep Learning with TensorFlow 2 and Keras - Second Edition

By : Rowel Atienza
Book Image

Advanced Deep Learning with TensorFlow 2 and Keras - Second Edition

By: Rowel Atienza

Overview of this book

Advanced Deep Learning with TensorFlow 2 and Keras, Second Edition is a completely updated edition of the bestselling guide to the advanced deep learning techniques available today. Revised for TensorFlow 2.x, this edition introduces you to the practical side of deep learning with new chapters on unsupervised learning using mutual information, object detection (SSD), and semantic segmentation (FCN and PSPNet), further allowing you to create your own cutting-edge AI projects. Using Keras as an open-source deep learning library, the book features hands-on projects that show you how to create more effective AI with the most up-to-date techniques. Starting with an overview of multi-layer perceptrons (MLPs), convolutional neural networks (CNNs), and recurrent neural networks (RNNs), the book then introduces more cutting-edge techniques as you explore deep neural network architectures, including ResNet and DenseNet, and how to create autoencoders. You will then learn about GANs, and how they can unlock new levels of AI performance. Next, you’ll discover how a variational autoencoder (VAE) is implemented, and how GANs and VAEs have the generative power to synthesize data that can be extremely convincing to humans. You'll also learn to implement DRL such as Deep Q-Learning and Policy Gradient Methods, which are critical to many modern results in AI.
Table of Contents (16 chapters)
14
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15
Index

4. Loss functions

In SSD, there are thousands of anchor boxes. As discussed earlier in this chapter, the goal of object detection is to predict both the category and offsets of each anchor box. We can use the following loss functions for each prediction:

  • - Categorical cross-entropy loss for ycls
  • - L1 or L2 for yoff. Note that only positive anchor boxes contribute to L1 is also known as mean absolute error (MAE) loss, while L2 is also known as mean squared error (MSE) loss.

The total loss function is:

(Equation 11.4.1)

For each anchor box, the network predicts the following:

  • ycls or the category or class in the form of a one-hot vector
  • yoff = ((xomin,yomin),(xomax,yomax)) or the offsets in the form of pixel coordinates relative to anchor box.

For computational convenience, the offsets are better expressed in the form:

yoff = ((xomin,yomin),(xomax,yomax)) (Equation 11.4.2)

SSD is a supervised object detection algorithm...