Transfer Learning
Transfer learning refers to the concept that knowledge gained for solving one problem can be applied to a different but related problem. Although computing resources for deep learning become more and more accessible and affordable, training a CNN on a large dataset, such as ImageNet, can still be a daunting task. Knowing many images share similar features at certain levels, features learned from large image datasets can be leveraged and used for various computer vision tasks or applications. For example, the convolutional layers in a pretrained network can be used as a feature extractor for a new image classification problem. However, the final FC layer needs to be customized to match the number of classes required by the new problem. In this case, the weights and biases of the pretrained convolutional layers will be frozen (i.e., they are not allowed to change during training) and only the weights and biases of the new FC layers will be adjusted. As such, transfer learning significantly reduces the number of trainable parameters and the amount of data required for training.
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