ResNet

Evolution in Computer Vision: The ResNet Revolution

The domain of computer vision has made substantial advancements in the past few years. Tasks like image recognition and classification have been significantly optimized due to the implementation of deep Convolutional neural networks, which deliver quite impressive outcomes.

The Challenge of Deepening Neural Networks

To maximize recognition precision, scientists have added numerous layers to these neural networks, enabling them to learn more complex features gradually. However, the difficulty of training them escalates with the addition of layers, resulting in a decline in accuracy. Various strategies, like introducing auxiliary loss for additional supervision, have been attempted to mitigate this vanishing gradient issue, but none resulted in a perfect resolution.

So, what is ResNet? Initially proposed in the study “Deep Residual Learning for Image Recognition," ResNet, or Residual Network, is designed to incorporate an “identity shortcut link” that bypasses one or more layers. This innovative feature made training highly evolved networks feasible. These evolved networks consist of unique structures called Residual Blocks.

The most striking feature of these blocks is a bypass or 'skip connection,' which overrides some intermediate layers, thereby modifying the output of the layer. Without this skip connection, the input ‘x’ undergoes a series of transformations, rendering the output as H(x). However, with the skip connection, this output gets changed.

Challenges, such as the possibility of varied dimensions of the input and output, do arise. But they can be addressed either by padding extra zero entries or by using a projection method for dimension matching.

ResNet’s Unique Proposition

The unique feature of ResNet, as per its creators, is the idea that adding layers should not degrade the network's performance. In essence, it’s easier for the added layers to fit a residual mapping rather than the actual desired mapping. Residual blocks are crafted specifically for this purpose.

Later, an upgraded version of the residual block was introduced, which featured a pre-activation variant allowing for even better gradient flow.

ResNet's Impact on Deep Learning

ResNet's significance lies in its skip connections, which counteract the disappearing gradient problem in deep neural networks. These connections also enable the model to learn identity functions, ensuring the upper layer's performance meets or exceeds that of the lower layer.

Comparative Performance: Shallow vs. Deep Networks

Consider a shallow network and a deep network. The ideal expectation is that the deep network should perform at least as well as the shallow one. By using ResNet's approach, the additional layers in the deep network can merely learn the identity function, guaranteeing performance stability with the addition of layers. The hope is that ResNet would perform comparably or even surpass regular deep neural networks.

Owing to its remarkable outcomes, ResNet soon became a go-to solution for various computer vision challenges.