“…Interestingly, the top scoring system in the 2013 FER Challenge is a deep convolutional neural network [31], while the best handcrafted model ranked only in the fourth place [14]. With only a few exceptions [1,29,30], most of the recent works on facial expression recognition are based on deep learning [2,[6][7][8]11,13,16,[18][19][20][21]23,25,[34][35][36]. Some of these recent works [13,16,18,34,35] proposed to train an ensemble of convolutional neural networks for improved performance, while others [4,15] combined deep features with handcrafted features such as SIFT [22] or Histograms of Oriented Gradients (HOG) [5].…”