Visual attention retargeting

This thesis explores attention retargeting---a concept related to visual saliency where the content or composition of an image is altered in an effort to guide the viewer's attention. Attention retargeting is currently in its infancy with numerous unexplored possibilities, no common methodology for evaluating performance, and no unified framework. The difficulty of attention retargeting as a saliency inversion problem lies in the lack of one-to-one mapping between saliency and the image domain, in addition to the possible negative impact of saliency alterations on image naturalness. Several approaches from recent literature to solve this challenging problem are reviewed in this context. Two novel attention retargeting methods are proposed to efficiently compute a region's propensity for drawing attention after it has been modified. The first method manipulates the orientation of a selected region, while the second modifies its hue. Both methods are applied to maximize the saliency of selected regions in various images. The likelihood of drawing attention towards the modified regions is evaluated through eye-tracking. Subjective experiments, in which participants are told to decide which image looks better between two alternatives, are used to measure the relative naturalness of the modification. An experiment was conducted to determine whether subliminal flicker is capable of drawing attention in natural images without the viewer's knowledge. Flicker was introduced to selected regions in a set of images by alternating the contrast in these regions from high to low at a frequency of 50 Hz. A comparison of eye-tracking data between participants who viewed the flickering images against those who viewed the original images suggests that subliminal flicker may, on average, repel attention rather than attract it.