Low level Resources regarding Convolutional Neural Networks

Hi guys, could someone point me to a book resource, or similar, regarding the implementation of CNNs for identification of features in images, such as letters, and then more complex features, like animals? I would like to understand the underlying theory, and then do a CUDA implementation. Yes, I know there are libraries out there that already do this quite efficiently, but I would like to do this from scratch for academic, and then internal company reasons. Thanks everyone and anyone for any help on this.


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