Deep learning (deep machine learning, or deep structured learning, or hierarchical learning, or sometimes DL) is a branch of machine learning based on a set of machine learning methods based on learning representations of data. An observation (e.g., an image) can be represented in many ways such as avector of intensity values per pixel, or in a more abstract way as a set of edges, regions of particular shape, etc.. Some representations make it easier to learn tasks (e.g., face recognition or facial expression recognition[6]) from examples. One of the promises of deep learning is replacing handcraftedfeatures with efficient algorithms for unsupervised or semi-supervised feature learning and hierarchicalfeature extraction.[7]