What is VGGNet

Understanding VGGNet: A Comprehensive Guide to the Convolutional Neural Network

Convolutional Neural Network (CNN) is undoubtedly one of the most powerful and widely-used machine learning models in the computer vision field. Among numerous CNN models, VGGNet stands out as one of the most accurate and popular models for image classification. In this article, we will dive deeply into VGGNet, its architecture, principles, and applications.

Introduction to VGGNet

VGGNet, also known as the OxfordNet, is a convolutional neural network designed by the Visual Geometry Group at the University of Oxford. The network was developed to compete in the ImageNet Large Scale Visual Recognition Challenge (ILSVRC) in 2014, where it achieved significant success and gained widespread popularity.

The VGGNet architecture consists of 16 or 19 layers, depending on the version of the network. It follows a simple philosophy of stacking convolutional layers of 3x3 filters with a stride of 1, following by a max-pooling layer of 2x2 filters with a stride of 2. The network also uses only small-size filters, which helps in learning more complex features in the input image. The architecture also uses fully-connected layers at the end for classification purposes. The simplicity and effectiveness of this architecture make it an ideal choice for image classification tasks.

Architecture of VGGNet

The architecture of VGGNet can be divided into two parts: convolutional layers and fully-connected layers. The convolutional part consists of 16 or 19 layers of convolution and pooling operations, while the fully-connected part performs the final classification of the input image. Let's examine each part separately:

Convolutional Layers

The convolutional layers of VGGNet follow a similar pattern of using 3x3 filters with a stride of 1. Each convolutional layer is named according to its depth, where 'convX' represents a convolutional layer with X number of filters. The output of each convolution layer is passed through a Rectified Linear Unit (ReLU) activation layer, which applies an element-wise activation function that sets negative values to zero, helping to speed up the training process and improving model performance.

Additionally, the architecture uses max-pooling layers following each convolutional layer to reduce the spatial dimensions of the input, allowing the model to learn more abstract features in the input image. The max-pooling layers have a kernel size of 2x2 with a stride of 2, resulting in a downsampling of the input volume. This process is repeated several times, resulting in the reduction of the input size by a factor of 16 or 32, depending on the depth of the network.

The table below shows the architecture of the convolutional layers in the VGGNet-16 model:

Layer Filter Size / Stride Number of Filters Output Size
Input - - 224x224x3
Conv1_1 3x3 / 1 64 224x224x64
Conv1_2 3x3 / 1 64 224x224x64
Pool1 2x2 / 2 - 112x112x64
Conv2_1 3x3 / 1 128 112x112x128
Conv2_2 3x3 / 1 128 112x112x128
Pool2 2x2 / 2 - 56x56x128
Conv3_1 3x3 / 1 256 56x56x256
Conv3_2 3x3 / 1 256 56x56x256
Conv3_3 3x3 / 1 256 56x56x256
Pool3 2x2 / 2 - 28x28x256
Conv4_1 3x3 / 1 512 28x28x512
Conv4_2 3x3 / 1 512 28x28x512
Conv4_3 3x3 / 1 512 28x28x512
Pool4 2x2 / 2 - 14x14x512
Conv5_1 3x3 / 1 512 14x14x512
Conv5_2 3x3 / 1 512 14x14x512
Conv5_3 3x3 / 1 512 14x14x512
Pool5 2x2 / 2 - 7x7x512
Fully-Connected Layers

The fully-connected layers of the VGGNet architecture are made up of 3 fully-connected layers, each followed by a ReLU activation layer. The output of the final fully-connected layer is passed through a Softmax activation layer, which normalizes the output probability of each class. The final output of the network is a probability distribution of the predicted classes.

The table below shows the architecture of the fully-connected layers in the VGGNet-16 model:

Layer Number of Neurons Output Size
FC6 4096 1x1x4096
FC7 4096 1x1x4096
FC8 1000 1x1x1000
Benefits of VGGNet

There are several benefits to using VGGNet in image classification tasks:

  • Accuracy: VGGNet achieves higher accuracy on several benchmark datasets related to image classification tasks.
  • Flexibility: VGGNet can be used for a wide range of image classification tasks and produces accurate results.
  • Transfer learning: It is possible to use transfer learning with VGGNet by training the network on a similar dataset and reusing the learned features on a new dataset.
  • Readable architecture: The VGGNet architecture is easy to understand and visualize due to its simplicity, making it easier to implement and optimize.
Applications of VGGNet

VGGNet has been used for a wide range of applications, including but not limited to:

  • Art classification: VGGNet has been used to classify artwork based on its style, period, and author.
  • Automated medical diagnosis: VGGNet has been used to diagnose ailments from medical imagery, such as identifying breast cancer in mammograms.
  • Object detection: VGGNet has been applied for object detection tasks, such as identifying and localizing objects within an image.
  • Image segmentation: VGGNet has been used to segment images into different regions, such as separating a cancerous tumor from the surrounding healthy tissue.

VGGNet is an accurate and flexible CNN model that has established itself as a reliable option for image classification tasks. Its architecture is simple and effective, allowing it to learn high-level features from input images and produce accurate predictions. VGGNet has been widely used in various applications and continues to play a critical role in computer vision research, making it an essential model to stay familiar with, for anyone working with image classification tasks.