I. Introduction
Emotions are strongly related to the activation of particular brain regions and the release of specific hormones and neurotransmitters into the bloodstream. For instance, the amygdala, a little almond-shaped structure in the brain, initiates the release of adrenaline and other stress chemicals that prepare the body to respond to a perceived threat when we experience fear. Research on emotion analysis has grown significantly in the past two decades. Previous attempts to solve this challenge used handcrafted methods based on psychological ideas [1] and image perception. Color, edges, lines, texture, composition and picture descriptors like Histogram of Oriented Gradients (HOG) were handcrafted. Balance, emphasis and harmony were linked to the emotions elicited from an image. Lu et al. [2] attempted to retrieve shape features and classify the emotions of an image. Yanulevskaya et al. [3] retrieved Gabor and Wiccest surface texture features from images and mapped them to emotions. The type of line influences the emotional response as well. In the image, oblique, horizontal and vertical lines had distinct effects on the emotional response. Chang et al. [4] extracted edges, ridges and lines to classify images. Zhao et al. [5] extracted features using image descriptors (such as Histogram of Oriented Gradients) and combined them with other handcrafted features. Both Mehrabian and Valdez [6] attempted to map color primitives to emotions and classify images.