Foreground Enlargement of Omnidirectional Images by Spherical Trigonometry

Omnidirectional images with a 360-degree field of view have much smaller foreground regions compared to background regions and thus are difficult to visually recognize, especially when displaying on a small size display. In this paper, we propose a method for enhancing visibility of omnidirectional images by enlarging the user specified foreground regions while compressing the other background regions without the sense of visual incompatibility. The proposed method first transforms the omnidirectional image into a 3D spherical image, and then relocates the spherical nodes, which are assigned pixel values, from their initial position to a preferable position based on point correspondence between spherical polygons. The experiments demonstrate that our approach produces satisfactory omnidirectional images in which the foreground regions are enlarged analogously.